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Context: The evaluation of quadriceps muscle inhibition with the interpolated twitch technique is usually performed by stimulating the femoral nerve (FN). However, there are some problems related to the use of this stimulation site, which may be partially overcome by delivering the stimulation over the motor point (MP). This study sought to compare MP to FN stimulation at different joint angles for the evaluation of quadriceps muscle inhibition, resting peak torque, and discomfort in healthy women. Design: Cross-sectional study. Methods: Sixteen healthy women (age: 28 [4] y; body mass: 60 [5] kg; height: 162 [5] cm) participated in this study. Supramaximal paired stimuli were delivered to the FN and to the rectus femoris MP before and during maximal voluntary contractions at different knee angles (15°, 30°, 45°, 60°, and 90° of knee flexion) to assess muscle inhibition and resting peak torque. Discomfort was also recorded for each stimulation site and knee angle. Results: Muscle inhibition was similar between the 2 stimulation sites (P >.05) and was higher at 45° than at 90° (P =.03). MP stimulation evoked lower resting peak torque at 30° (P =.004), 60° (P =.006), and 90° (P =.006) and higher discomfort at 30° (P =.008) and 90° (P =.027) compared to FN stimulation. Conclusions: Despite lower resting peak torque and higher discomfort at some angles, MP stimulation provided similar muscle inhibition to FN stimulation at all knee angles and is therefore a valid method to evaluate quadriceps muscle inhibition in healthy women. MP stimulation can be used as an alternative to FN stimulation for the evaluation of quadriceps muscle inhibition with no added discomfort at the angles where muscle inhibition is the highest. [ABSTRACT FROM AUTHOR]

Context: The Y-Balance Test Lower Quarter (YBT-LQ) is a widely utilized tool for evaluating dynamic postural control, requiring a combination of mobility and strength. This study aimed to investigate the combined relationship between isometric thigh muscle strength and joint kinematics on YBT-LQ performance. Design: Cross-sectional laboratory study. Methods: Isometric quadriceps and hamstrings strength were measured before the YBT-LQ in 39 healthy participants (27 females and 12 males). The test was performed under 3-dimensional markerless motion capture, where joint kinematics were extracted from the maximum reach position from each direction. Three multivariable linear regression models were then used to determine the strongest combination of predictors for YBT-LQ performance. Results: Greater hamstrings strength and increased knee flexion, ankle dorsiflexion, and trunk ipsilateral-flexion joint angles explained 56.8% (P <.001) of the variance in anterior reach. Hip flexion, knee flexion, and ankle dorsiflexion angles were the strongest predictors for posteromedial reach distance, explaining 73.0% of the variance (P <.001). Last, 43.3% (P <.001) of the variance in posterolateral reach distance was predicted by hamstring strength and knee-flexion angle. Conclusions: These results emphasize the importance of hamstring strength in YBT-LQ performance across different reach directions. Additionally, the kinematics illustrate a potential movement strategy for maximizing reach distance on the YBT-LQ in healthy individuals. Clinicians can utilize this information to guide interventions aimed at improving dynamic postural control, particularly by focusing on increasing hamstring strength and testing for impairments in specific movement patterns. [ABSTRACT FROM AUTHOR]

Context: The quadriceps femoris is consistently ranked among the muscles most prone to sustain strain injuries in sports involving kicking and sprinting actions. Given the documented preventive effect of Nordic hamstring curl programs against hamstring strain injuries, incorporating exercises that induce eccentric overload on the quadriceps could potentially help mitigate strain injuries within this muscle group. The Reverse Nordic Curl (RNC) has emerged as a viable field-based exercise for eccentrically working the quadriceps. This study aimed to compare quadriceps muscle eccentric activation during the RNC with 3 bodyweight squat-based exercises: single-leg squat (SLS), Bulgarian squat, and forward lunge. Design: Cross-sectional study. Methods: Twenty-three healthy volunteers (15 men) were monitored for rectus femoris, vastus lateralis, and vastus medialis electromyographic signal, as well as knee range of motion, while performing 10 repetitions of each exercise. Electromyography data acquired during eccentric phases were normalized by maximum voluntary isometric contraction of the knee extensors. The exercises were compared based on the electromyography and knee range of motion values. Results: RNC generated a similar rectus femoris and vastus medialis eccentric activation compared with the squat-based exercises (P >.05 for all), and a lower vastus lateralis activation than SLS (P <.001). Among the bodyweight squat-based exercises, SLS generated greater eccentric activation than forward lunge and Bulgarian squat for the 3 muscles (P <.05 for all). RNC was performed with lower knee-flexion range of motion than bodyweight squat-based exercises (P <.001). Conclusions: RNC did not produce superior eccentric quadriceps activation compared to bodyweight squat-based exercises, even proving to be less demanding for the vastus lateralis compared to the SLS. These findings may assist practitioners in selecting exercises to elicit quadriceps eccentric stimulus, with a focus on preventing strain injuries. [ABSTRACT FROM AUTHOR]

Following anterior cruciate ligament reconstruction (ACLR), patients exhibit abnormal walking mechanics and quadriceps dysfunction. Quadriceps dysfunction has been largely attributed to muscle atrophy and weakness. While important, these factors do not capture intrinsic properties of muscle that govern its ability to generate force and withstand load. While fascicle abnormalities after ACLR have been documented in early stages of recovery (<12 mo), long-term effects of ACLR on fascicle mechanics remain unexplored. We evaluated quadriceps fascicle mechanics during walking 3 years post-ACLR and examined the relationship with knee mechanics. Participants included 24 individuals with ACLR and 24 Controls. Linear mixed models compared the ACLR, Contralateral, and Controls limbs for (1) quadriceps strength, (2) fascicle architecture and mechanics, and (3) knee mechanics. No difference in strength or overall fascicle length excursions was found between limbs. The ACLR limb exhibited longer fascicles at heel strike and peak knee extension moment (P <.001–.004), and smaller fascicle angles at heel strike, peak knee extension moment, and overall suppressed fascicle angle excursions (P <.001–.049) relative to the Contralateral and/or Control limb. This indicates an abnormality in fascicle architecture and mechanics following ACLR and suggests abnormalities in contractile function that cannot be explained by muscle weakness and may contribute to long-term gait irregularities. [ABSTRACT FROM AUTHOR]

Context: The hamstrings are the most commonly injured muscle in sports and are especially injury prone in lengthened positions. Measuring knee muscle strength in such positions could be relevant to establish injury risk. Handheld dynamometry has been shown to be a valid, reliable, and practical tool to measure isometric muscle strength clinically. The aim of this study was to assess the validity and reliability of the assessment of isometric knee muscle strength with a handheld dynamometer (HHD) at various muscle lengths, by modifying the hip and knee angles during testing. Design: Concurrent validity and test--retest reliability. Methods: Thirty young healthy participants were recruited. Hamstring and quadriceps isometric strength was measured with a HHD and with an isokinetic dynamometer, over 2 testing sessions, in a randomized order. Isometric strength was measured on the right lower limb in 6 different positions, with the hip at either 0° or 80° of flexion and the knee at either 30°, 60°, or 90° of flexion. Pearson and Spearman correlations were used to assess the validity, and intraclass correlation coefficients were calculated to establish the test--retest reliability of the HHD. Results: Good to excellent reliability and moderate to high validity were found in all the tested muscle length positions, except for the hamstrings in a seated position with the knee extended at 30°. Conclusions: The use of a HHD is supported in the clinical setting to measure knee muscle strength at varying muscle lengths in healthy adults, but not for the hamstrings in a lengthened position (hip flexed and knee extended). These results will have to be confirmed in sport-specific populations. [ABSTRACT FROM AUTHOR]

Purpose: We examined the effects of increasing hypoxia severity on oxygenation kinetics in the vastus lateralis muscle during repeated treadmill sprints, using statistical parametric mapping (SPM). Methods: Ten physically active males completed 8 sprints of 5 seconds each (recovery = 25 s) on a motorized sprint treadmill in normoxia (sea level; inspired oxygen fraction = 0.21), moderate hypoxia (inspired oxygen fraction = 0.17), and severe hypoxia (SH; inspired oxygen fraction = 0.13). Continuous assessment of tissue saturation index (TSI) in the vastus lateralis muscle was conducted using near-infrared spectroscopy. Subsequently, TSI data were averaged for the sprint–recovery cycle of all sprints and compared between conditions. Results: The SPM analysis revealed no discernible difference in TSI signal amplitude between conditions during the actual 5-second sprint phase. However, during the latter portion of the 25-second recovery phase, TSI values were lower in SH compared with both sea level (from 22 to 30 s; P =.003) and moderate hypoxia (from 16 to 30 s; P =.001). The mean distance covered at sea level (22.9 [1.0] m) was greater than for both moderate hypoxia (22.5 [1.2] m; P =.045) and SH (22.3 [1.4] m; P =.043). Conclusions: The application of SPM demonstrated that only SH reduced muscle oxygenation levels during the late portion of the passive (recovery) phase and not the active (sprint) phase during repeated treadmill sprints. These findings underscore the usefulness of SPM for assessing muscle oxygenation differences due to hypoxic exposure and the importance of the duration of the between-sprints recovery period. [ABSTRACT FROM AUTHOR]

Unloader braces are a treatment modality for medial compartment knee osteoarthritis. The functional mechanisms involved are not yet fully understood. Therefore, this two-part systematic review examines the following research questions: How is muscle activation altered by medial compartment knee osteoarthritis, and do medial tibiofemoral compartment unloader braces alter muscle activation? If so, could this alteration be part of the unloading mechanism by affecting the altered muscle activity in medial compartment knee osteoarthritis? A systematic literature search was conducted using PubMed, LIVIVO, Web of Science, Google Scholar, and CENTRAL for articles published until August 2023. The first systematic review, examining neuromuscular alterations, identified 703 articles, with a final inclusion of 20. The second systematic review, which evaluated the neuromuscular effects of unloader braces, identified 123 articles with the final inclusion of 3. Individuals with medial compartment knee osteoarthritis demonstrated increased activity and co-contraction of the periarticular knee muscles, whereas medial tibio-femoral compartment unloader braces seemed to reduce activity and co-contraction. In contrast to the belief that unloader braces result in muscle weakness as they decrease muscle activity and co-contraction, our limited insights indicate that they rather might reduce the pathological increase. This may result in joint load reduction due to lower compressive forces. However, further investigation is required. [ABSTRACT FROM AUTHOR]

Background: This study evaluates the clinical evidence for performing total knee arthroplasty (TKA) without a tourniquet, a shift from the near-universal use in 2009 to current trends towards tourniquet-less TKA in Norway and Sweden. This change is set against a backdrop of conflicting evidence regarding the positive and negative effects of tourniquet use. Questions/purposes: The aims were to determine if the tourniquet has an impact on [1] Forgotten Joint Score-12 (FJS-12) at 8 weeks after surgery; [2] postoperative strength and function; [3] postoperative pain and opioid analgesic use; and [4] operative time, bleeding, and length of stay (LOS). Methods: Eighty-one patients were randomised to TKA with or without a tourniquet. The outcome measures, FJS-12, muscle strength, functional test, pain, estimated blood loss, haemoglobin (Hb) loss, knee circumference, opioid consumption, and LOS were assessed preoperatively and at 1 day, 8 weeks, and 1 year after surgery. Results: No significant difference in FJS-12 scores was found between the two groups at postoperative 8 weeks. However, the tourniquet group showed statistically significant better knee extension strength at 8 weeks (p = 0.045). There were no differences in other outcomes, except for a greater decrease in haemoglobin levels (p = 0.02) and higher estimated perioperative blood loss (p < 0.001) in the no tourniquet group than the torniquet group. Conclusions: Our study indicates that tourniquet use during TKA causes no significant differences in FJS-12 at 8 weeks, significantly reduces bleeding and postoperative Hb loss, and improves quadriceps strength at 8 weeks. Trial registration: Clinicaltrails.gov. Registry Number: NCT03666598. Registered 30 August 2018. [ABSTRACT FROM AUTHOR]

Background: Previous studies have attempted to determine prognostic factors for predicting the occurrence of noncontact anterior cruciate ligament (ACL) injuries. However, studies on risk factors for noncontact ACL injuries in Asian female soccer players are limited. Purpose: To identify intrinsic risk factors for noncontact ACL injuries among young female Asian soccer players. Study Design: Cohort study; Level of evidence, 2. Methods: This study evaluated 145 female Japanese soccer players for potential risk factors for noncontact ACL injury during the preseason medical assessment. In total, 25 variables were examined—including anthropometric data, joint range of motion, muscle flexibility, muscle strength, and balance measurements. Participants were monitored throughout a single season for noncontact ACL injuries diagnosed by physicians. Results: Noncontact ACL injuries occurred in 13 knees of 13 players (9%). Lower hamstring-to-quadriceps ratio (0.44 ± 0.07 vs 0.50 ± 0.10; P =.04), greater knee extension muscle strength (3.2 ± 0.5 vs 2.7 ± 0.5 N·m/kg; P <.01), and longer playing experience (10.8 ± 3 vs 8.1 ± 4.2 years; P =.02) were significantly associated with new-onset noncontact ACL injuries in young female soccer players. No statistically significant between-group differences were found for any other variables. Conclusion: New-onset noncontact ACL injury in young female soccer players was significantly associated with lower hamstring-to-quadriceps ratio, greater knee extension muscle strength, and longer soccer experience. These findings will help develop strategies for preventing noncontact ACL injuries among female soccer players. [ABSTRACT FROM AUTHOR]

Background: The extensor apparatus of the knee is of paramount importance in generating the torque needed for a countermovement jump (CMJ), especially in jumping athletes. In anterior cruciate ligament reconstruction (ACLR) procedures, graft harvesting from the extensor apparatus may dramatically affect extensor strength and jumping performance. Hypothesis: The focused jump training of professional jumping athletes would increase the likelihood of restoring jumping performance after ACLR, despite the graft choice (autologous bone-patellar tendon-bone [BPTB] or hamstring [HS] tendon). Study Design: Cohort study; Level of evidence, 3. Methods: A retrospective evaluation of prospectively collected data was carried out. Only professional athletes were included, and all surgical procedures were performed by a single experienced surgeon. Data collection considered the type of surgery, sports activity, and functional evaluation at 3 months after surgery. From the functional evaluation, data on single-leg hop (SLH) test, triple hop (TH) test, and CMJ were extracted. Limb symmetry index (LSI) for maximal voluntary isometric contraction of the quadriceps and for each of the jumping tests was calculated. Multiple analysis of covariance (ANCOVA) models were used to assess mean differences among groups for the LSI in CMJ, SLH, and TH and estimate the effect of confounders. Results: From a subsequent series of 208 athletes, 44 professional athletes were included for data collection. Of these, 26 were male and 18 were female. A jumping sport (basketball, volleyball) was played by 17 athletes, while a running sport (soccer, judo, rugby, tennis, ski) was performed by 27 athletes. The mean time from injury to surgery was 17.8 ± 14.5 days. At 90 days from surgery, the overall mean LSI for CMJ was 85.3% ± 8.9%, for SLH was 92.2% ± 6.4%, and for TH was 90.8% ± 6.1%. When ANCOVA was fitted using the interaction term with BPTB autograft and jumping sport, a nonsignificant effect on LSI for CMJ (P =.56), SLH (P =.72), and TH (P =.98) was observed. Conclusion: The results of the present investigation on professional athletes showed that no difference occurred within the study cohort in overall jumping performance between jumping and running athletes undergoing ACLR either with BPTB or with HS tendon grafts. Although some evidence suggests that quadriceps strength may be dramatically affected by the harvesting of BPTB, the overall performance of the jump was not compromised. [ABSTRACT FROM AUTHOR]

BACKGROUND: Unilateral osteoarthritis (OA) affects single knees and presents a unique scenario where individuals experience varying degrees of symptoms between their affected and unaffected knees. OBJECTIVE: This study aims to investigate differences in muscle tightness between symptomatic and asymptomatic knees in individuals with unilateral knee OA while exploring the interplay among pain, functionality, and muscle tightness. METHODS: In this cross-sectional study, thirty knee OA patients underwent assessments for hamstring (Active Knee Extension, Straight Leg Raise), iliotibial band (Ober Test), and quadriceps tightness (Modified Thomas Test). Pain intensity was measured using the Visual Analog Scale (VAS), and functional limitations were evaluated via the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). RESULTS: A negative correlation was observed between participants' pain and AKE (p = 0.004, r = - 0.515), ASLR (p = 0.27, r = - 0.403), Ober (p = 0.010, r = - 0.461) values. However, no significant correlation was found with the Modified Thomas value (p = 0.204, r = - 0.239). There was also a negative correlation between participants' WOMAC scores and AKE (p = 0.019, r = - 0.427), OBER (p = 0.004, r = - 0.510), and Modified Thomas (p = 0.022, r = - 0.416) values, while ASLR (p = 0.286, r = - 0.202) values showed no significant correlation. Comparisons between AKE, Ober, and Modified Thomas values showed higher values in asymptomatic extremities (AKE: p = 0.025, Ober: p = 0.021, Modified Thomas: p = 0.030). CONCLUSION: This study emphasizes the significance of muscle tightness in the symptomatic extremities of individuals with unilateral knee OA. The results indicate that increased muscle tightness makes pain worse and limits movement. It's crucial for healthcare providers treating OA to focus on improving muscle flexibility, reducing pain, and enhancing overall function. [ABSTRACT FROM AUTHOR]

Individuals with anterior cruciate ligament reconstruction (ACLR) often fail to return to their previous level of sport performance. Although multifaceted, this inability to regain preinjury performance may be influenced by impaired plyometric ability attributable to chronic quadriceps dysfunction. Whole-body vibration (WBV) acutely improves quadriceps function and biomechanics after ACLR, but its effects on jumping performance outcomes such as jump height, the reactive strength index (RSI), and knee work and power are unknown. To evaluate the acute effects of WBV on measures of jumping performance in those with ACLR. Crossover study design. Research laboratory. Thirty-six individuals with primary, unilateral ACLR. Participants stood on a WBV platform in a mini-squat position while vibration or no vibration (control) was applied during six 60-second bouts with 2 minutes of rest between bouts. Double-leg jumping tasks were completed preintervention and postintervention (WBV or control) and consisted of jumping off a 30-cm box to 2 force plates half the participant's height away. The jumping task required participants to maximally jump vertically upon striking the force plates. Whole-body vibration did not produce significant improvements in any of the study outcomes (ie, jump height, RSI, and knee work and power) in either limb (P =.053–.839). These results suggest that a single bout of WBV is insufficient for improving jumping performance in individuals with ACLR. As such, using WBV to acutely improve jumping performance post-ACLR is likely not warranted. Future research should evaluate the effects of repeated exposure to WBV in combination with other plyometric interventions on jumping performance. [ABSTRACT FROM AUTHOR]

Foam rolling have gained popularity among elite athletes, but the effect of the speed parameter of foam rolling has not yet been determined. Our objective was to investigate the impact of different application speeds of foam roller on the mechanical properties of the quadriceps femoris muscle. Eighteen male professional basketball athletes (age 23 ± 4 years, body mass index 24.43 ± 1.59 kg/m²) participated in this study. We used a crossover design to randomize the order of the treatment speeds (30 beats per minute-FAST, 15 beats per minute-SLOW, and a self-determined speed-SELF) with a one-week washout period between each session. We measured dominant quadriceps femoris muscle tone, elasticity, and stiffness using the Myoton device before and after the interventions. We found that the average rate for SELF was 33±10 beats per minute, making SELF the fastest. All application speeds showed similar results in pre-intervention measurements of the mechanical properties of the tissues (P > 0.05). However, post hoc analysis revealed that a decrease was evident in SLOW compared to SELF in muscle tone in post-intervention measurements (P = 0.037). Also, we noted that comparison of pre- and post-intervention on FAST and SLOW showed a significant reduction in muscle tone (P = 0.002, P = 0.008). Slower foam rolling prior to training or competition may lead to a delay in the reaction time due to the reduction in tonus, that can increase the injury risks. Alternatively, the significant reduction in tonus may be useful in regulating the increased tonus after training and competition. [ABSTRACT FROM AUTHOR]

Whereas prolonged static stretching (SS: >60-seconds per muscle) can increase range of motion (ROM) for up to 2-hours, it can also decrease maximal voluntary isometric contraction (MVIC) forces, countermovement (CMJ) and drop jump (DJ) heights, and muscle activation immediately after the stretching exercise. When an appropriate SS duration (<60-seconds per muscle) is incorporated into a dynamic warm-up, performance decrements are often trivial. However, there is a lack of studies that observed the effects of extensive SS (180-seconds) 2-hours prior to a dynamic warm-up. The objective was to investigate ROM and performance effects of prolonged SS, 2-hours prior to a traditional warm-up. This study investigated 9 female and 8 male healthy recreationally active, young adult participants on the effects of prolonged SS (180-seconds per muscle) of the quadriceps and hamstrings, 2-hours before a traditional warm-up compared to an active control condition on hip flexion ROM, knee extension and flexion MVIC forces, CMJ, DJ, and quadriceps and hamstrings electromyography (EMG). There were no significant changes in knee flexion/extension MVIC forces, EMG, CMJ, or DJ height. However, there was significant, small magnitude (p = 0.002) greater post-warm-up left hip flexion ROM (115.4° ± 17.2) than pre-SS (108.9° ± 17.13, Effect size [ES]: 0.28) and control post-warm-up (p = 0.05, ES: 0.31, 109.5° ± 20.55). Similarly, right hip flexion ROM (117.2° ± 16.5) also demonstrated significant small magnitude (p = 0.003) greater than the pre-SS (112.4° ± 18.4, ES: 0.22) and control post-warm-up (p = 0.046, ES: 0.33, 110.8° ± 20.5). Additionally, significant, large magnitude greater hip flexion ROM was observed with the women vs. men (ES: 1.29 -- 1.34). Significant hip flexion ROM increases were not accompanied by significant changes in knee flexion/extension MVIC forces, EMG, or jump heights, suggesting that extensive SS can positively impact ROM without performance deficits when followed by a traditional warm-up, 2-hours after SS. [ABSTRACT FROM AUTHOR]

Clinical Scenario: The high recurrence of lateral ankle sprains progresses to chronic ankle instability (CAI) and can affect many athletes in all sports. CAI is often associated with a decrease in muscle strength, an increase in pain, a decrease in the range of motion, and a decrease in balance or neuromuscular control. The use of blood flow restriction (BFR) with CAI can increase muscular outcomes and be used as a rehabilitation tool. Clinical Question: Is there evidence to suggest that BFR improves strength, muscle activation, and/or cross-sectional area of the lower leg musculature in those with CAI? Clinical Bottom Line: There is moderate evidence to support therapeutic exercise with low-intensity BFR in patients with CAI. The evidence concluded a significant improvement in BFR to increase muscle activation of the fibularis longus, anterior tibialis, vastus lateralis, and soleus. There is moderate evidence suggesting BFR can induce strength gains in the muscles of the lower extremity in patients with CAI. Strength of Recommendation: The comprehensive evidence is a Strength of Recommendation Taxonomy (SORT) Grade B, with a level of evidence of 2, according to the Centre for Evidence-Based Medicine (CEBM) for the studies included. [ABSTRACT FROM AUTHOR]

The measurement of skeletal muscle fatigue in response to cycling exercise is commonly done in isometric conditions, potentially limiting its ecological validity, and creating challenges in monitoring the time course of muscle fatigue across an exercise bout. This study aimed to determine if muscle fatigue could be reliably assessed by measuring quadriceps twitch force evoked while pedaling, using instrumented pedals. Nine participants completed three laboratory visits: a step incremental test to determine power output at lactate threshold, and on separate occasions, two constant‐intensity bouts at a power output 10% above lactate threshold. Femoral nerve electrical stimulation was applied to elicit quadriceps twitch force both while pedaling (dynamic) and at rest (isometric). The test–retest reliability of the dynamic twitch forces and the agreement between the dynamic and isometric twitch forces were evaluated. Dynamic twitch force was found to have excellent reliability in an unfatigued state (intraclass correlation coefficient (ICC) = 0.920 and mean coefficient of variation (CV) = 7.5%), and maintained good reliability at task failure (ICC = 0.846 and mean CV = 11.5%). When comparing dynamic to isometric twitch forces across the task, there was a greater relative decline in the dynamic condition (P = 0.001). However, when data were normalized to the 5 min timepoint when potentiation between conditions was presumed to be more similar, this difference disappeared (P = 0.207). The reliability of this method was shown to be commensurate with the gold standard method utilizing seated isometric dynamometers and offers a new avenue to monitor the kinetics of muscle fatigue during cycling in real time. Highlights: The measurement of skeletal muscle fatigue during cycling exercise typically requires stopping the exercise task, potentially confounding the measurement, and limiting the frequency at which measurements can be madeWe have developed a novel method of assessing skeletal muscle fatigue which can be done while allowing cycling exercise to continue uninterruptedThe reliability of this method was shown to be commensurate with the gold standard method utilizing seated isometric dynamometers [ABSTRACT FROM AUTHOR]

Purpose: We investigated the effects of low- and high-volume speed endurance training (SET), with a reduced training volume, on sprint ability, short- and long-term exercise capacity, muscle mitochondrial properties, ion transport proteins, and maximal enzyme activity in highly trained athletes. Methods: Highly trained male cyclists (maximal oxygen consumption (...): 68.3 ± 5.0 mL⋅min-1⋅kg-1, n = 24) completed 6 wk of either low (SET-L; 6 x 30-s intervals, n = 8) or high (SET-H; 12 x 30-s intervals, n = 8) volume SET twice per week with a 30% reduction in training volume. A control group (CON; n = 8) maintained their training. Exercise performance was evaluated by i) 6-s sprinting, ii) a 4-min time trial, and iii) a 60-min preload at 60% ... followed by a 20-min time trial. A biopsy of m. vastus lateralis was collected before and after the training intervention. Results: In SET-L, 4-min time trial performance was improved (P < 0.05) by 3.8%, with no change in SET-H and CON. Sprint ability, prolonged endurance exercise capacity, ..., muscle mitochondrial respiratory capacity, maximal citrate synthase activity, fiber type--specific mitochondrial proteins (complexes I-V), and phosphofructokinase (PFK) content did not change in any of the groups. In SET-H, maximal activity of muscle PFK and abundance of Na+-K+ pump-subunit α1, α2, β1, and phospholemman (FXYD1) were 20%, 50%, 19%, 24%, and 42% higher (P < 0.05), respectively after compared with before the intervention, with no changes in SET-L or CON. Conclusions: Low SET volume combined with a reduced aerobic low- and moderate-intensity training volume does improve short-duration intense exercise performance and maintain sprinting ability, ..., endurance exercise performance, and muscle oxidative capacity, whereas, high volume of SET seems necessary to upregulate muscle ion transporter content and maximal PFK activity in highly trained cyclists. [ABSTRACT FROM AUTHOR]

Purpose: To compare the development of fatigability during a moderate-intensity cycling exercise between women with fibromyalgia (FM) and control women (CON) after acute ingestion of caffeine and placebo. Methods: Ten FM and 10 CON women performed a 30-min moderate-intensity cycling exercise 1 h after the ingestion of a capsule containing either caffeine or a placebo. Fatigability and its central and peripheral determinants were determined via changes from pre- to post-15 and post-30 min of exercise in maximal voluntary isometric contractions, voluntary activation (VA), and quadriceps potentiated twitch torque (Qtw-pot), respectively. Heart rate, muscle oxygen saturation, perceptive responses, mood state, localized and widespread pain, and sleepiness were also monitored during and after exercise. Results: There was a time versus group interaction for maximal voluntary isometric contraction and VA (P < 0.001) but not for Qtw-pot (P = 0.363), indicating a greater rate of fatigability development, mainly caused by central mechanisms, in the FM than in the CON group. There was also a main effect of condition for VA (P = 0.011), indicating that caffeine attenuates central mechanisms of fatigability in both groups. Caffeine ingestion also increased muscle oxygenation, perceived vigor, and energy, and decreased leg muscle pain, sleepiness, and perceived fatigue in both groups. However, caffeine improved perceived pleasure/displeasure and exercise adherence likelihood only in the FM group. Conclusions: Compared with CON, women with FM present a greater rate of fatigability during exercise, mainly of central origin. Caffeine seems to be a promising bioactive to counteract the central mechanisms of fatigability and improve the exercise experience among FM women. [ABSTRACT FROM AUTHOR]

Multiple exercises included in strength training involve greater activation of the quadriceps compared to hamstring muscles, which may lead to knee joint imbalances. The aim of this study was to examine the ratio of surface electromyography (sEMG) activity hamstring and quadriceps muscle groups (hamstring-to-quadriceps activation ratio; H:Q EMG), as well as lateral to medial hamstring activation ratio (LH:MH) in parallel squat, Romanian deadlift, hip thrust, lying leg curl and seated knee extension. The H:Q EMG was greater during lying leg curl compared to other exercises during both the concentric and eccentric phase, however the Romanian deadlift and hip thrust also resulted in relatively high H:Q EMG. Pairwise comparisons revealed that LH:MH was greater in the parallel squat compared to the Romanian deadlift and hip thrust in the concentric phase, and compared to the Romanian deadlift and hip thrust during the eccentric phase. Our data suggests that the lying leg curl promotes the greatest hamstring activation and H:Q EMG, amongst the exercises investigated, while also providing relatively homogenous LH:MH. The lying leg curl should be considered as a primary exercise in rehabilitation and training programmes, aiming to proportionally activate LH:MH and increase H:Q EMG, which may improve knee muscle balance. [ABSTRACT FROM AUTHOR]

BACKGROUND: A potential relationship may exist between the vastus medialis (VM) and the contractile efficiency of the vastus intermedius (VI) due to their anatomical connection and common innervation by the same branches of the femoral nerve. However, this relationship has not been explored using physiological experiments. OBJECTIVE: This study aimed to use electromyography (EMG) to investigate the functional significance of the VI and VM muscles during isometric contraction. METHODS: Twenty-six healthy male volunteers underwent EMG recordings from the VI, VM, and vastus lateralis (VL) at 90∘ or 30∘ of knee flexion. The EMG pre-motor time (PMT) was measured during rapid knee extension in response to an auditory stimulus. Additionally, the M-wave latency was determined by femoral nerve stimulation and subtracted from the PMT to calculate the descending conduction time (DCT). RESULTS: DCT was shortest at VM, followed by VL and VI. The DCT difference of VI-VM was significantly greater than that of VI-VL during maximal effort at 90∘ of knee flexion. CONCLUSIONS: VM is neurally driven to act as a pre-activator that primes the VI muscle; this tendency is particularly pronounced when explosive high-moment knee extension is required. [ABSTRACT FROM AUTHOR]

BACKGROUND: Cryotherapy is widely utilized for therapeutic purposes, yet its specific effects on knee joint proprioception and quadriceps muscle performance in healthy individuals remain unclear. This study addresses this gap by examining the impact of a 20-minute cryotherapy session on knee joint proprioception and related muscle parameters in a cohort of healthy college students. OBJECTIVES: To investigate the effects of cryotherapy on knee joint proprioception and quadriceps muscle peak moment, work and power in healthy college male and female students. METHODS: Thirty-two healthy students, aged 19–23, underwent a 20-minute cryotherapy session using Cryogel packs applied to the anterior thigh and knee. An isokinetic dynamometer measured knee joint proprioception and quadriceps muscle parameters before, immediately after, 10-min, and 20-min post-cryotherapy. RESULTS: Proprioception values did not significantly differ between genders or post-tests (p > 0.05). However, the female group exhibited significantly lower moment, power, and work values compared to males (p < 0.05). No significant differences were observed within or between post-tests in moment, power, and work for both genders (p > 0.05). CONCLUSIONS: A 20-minute cryotherapy application demonstrated no adverse effects on knee joint proprioception or quadriceps muscle metrics in healthy college students, supporting the safety of cryotherapy in this context. [ABSTRACT FROM AUTHOR]

To explore how plyometric-based hydro-kinesiotherapy (Plyo-HKT) would affect pain, muscle strength, postural stability, and functional performance in a convenience sample of children with hemophilic knee arthropathy (HKA). Forty-eight children with HKA (age: 8–16 years) were randomly allocated to the Plyo-HKT group (n = 24; underwent the Plyo-HKT for 45 min, twice/week over 12 wk in succession) or the comparison group (n = 24; performed the standard exercise rehabilitation at an equivalent frequency and duration). Pain, peak concentric torque of quadriceps and hamstring (produced at two angular velocities: 120 and 180 o/sec), dynamic limits of postural stability (DLPS), and functional performance [Functional Independence Score in Hemophilia (FISH) and 6-Minute Walk Test (6-MWT)] were assessed pre- and post-intervention. In contrast with the comparison group, the Plyo-HKT group achieved more favorable pre-to-post changes in pain (p =.028, η2p = 0.10), peak torque of quadriceps [120°/sec (p =.007, η2P = 0.15); 180°/sec (p =.011, η2P = 0.13)] and hamstring [120°/sec (p =.024, η2P = 0.11); 180°/sec (p =.036, η2P = 0.09)], DLPSdirectional [forward (p =.007, η2P = 0.15); backward (p =.013, η2P = 0.12); affected side (p =.008, η2P = 0.14); non-affected side (p =.002, η2P = 0.20)], DLPSoverall (p <.001, η2P = 0.32), and functional performance [FISH (p <.001, η2p = 0.26); 6-MWT (p =.002, η2p = 0.19)]. Plyo-HKT is likely helpful for reducing pain, improving strength, enhancing postural stability, and boosting functional capabilities in children with HKA. Physical rehabilitation practitioners should, therefore, consider this intervention strategy. [ABSTRACT FROM AUTHOR]

Background: Readiness for return to sports involves both physical and psychological aspects of recovery; however, the relationship between psychological and physical variables after anterior cruciate ligament (ACL) reconstruction (ACLR) is poorly understood. Hypothesis: ACLR patients with a higher psychological readiness would demonstrate better functional testing results at 6 months. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Participants were evaluated at 6 months after ACLR with various patient-reported outcome metrics: Hospital for Special Surgery Pediatric Functional Activity Brief Scale, pediatric or adult International Knee Documentation Committee Questionnaire (IKDC), Patient-Reported Outcomes Measurement Information System (PROMIS) - Psychological Stress Experience and ACL - Return to Sport After Injury (ACL-RSI) scale. Functional testing included quadriceps, hamstrings, and gluteal strength testing; Y-balance test; single-leg single hop, crossover hop, and triple hop tests; and timed 6-m hop test. Pearson correlation coefficient and multivariable regression were used to determine associations between the limb symmetry index (LSI) on functional testing and patient-reported outcomes. Those with LSI deficits <20% (better performance) were compared with those with deficits >20% (worse performance). Results: A total of 229 participants (89 male, 140 female) with a median age of 17 years (range, 10.3-30.6 years) were enrolled. IKDC had a moderate negative correlation with PROMIS - Psychological Stress Experience (r = -0.39; 95% CI = -0.49, -0.27; P <.001) and a moderate positive correlation with ACL-RSI (r = 0.55; 95% CI = 0.46, 0.64; P <.001). A total of 151 patients completed functional testing. ACL-RSI demonstrated a positive correlation with single-hop LSI (r = 0.21; 95% CI = 0.05, 0.35; P =.01) and timed 6-m hop (r = 0.28; 95% CI, 0.42; P =.001). When adjusting for sex, age, and graft type, patients who had <20% deficit on the single-hop test scored 16.6 points higher on ACL-RSI (P =.001), and those with <20% deficit on crossover hop testing scored a mean 13.9 points higher on ACL-RSI (P =.04) Conclusion: Higher psychological readiness for return to sport was associated with better performance and greater symmetry on hop testing 6 months after ACLR, suggesting a potential link between physical and psychological recovery. [ABSTRACT FROM AUTHOR]

Context: Slideboards are commonly used in exercise programs, but there is limited information about how they affect muscle activities during exercise. We aim to compare the activation levels of quadriceps and hamstring muscles and hip- and knee-flexion angles during lunge and single-leg squat exercises between normal ground and slideboard in physically active individuals. Design: Cross-sectional study. Methods: Thirty healthy individuals (age: 23.83 [2.84] y, body mass index: 21.75 [1.72] kg/m2) were included in the study. Surface electromyography was used to measure vastus medialis, vastus lateralis, biceps femoris, and semitendinosus activation levels during reaching and returning phases of the forward, lateral, and back lunges and squats that were performed on the normal ground and slideboard. Exercises were performed at a slow pace (60 beats/min). Hip- and knee-flexion angles during the exercises were evaluated by using 2-dimensional motion analysis. Repeated measures of analysis of variance were used for statistical analysis. Results: Vastus medialis and vastus lateralis activation levels were greater during reaching and returning phases of the exercises on slideboard compared with normal ground (P <.05). However, semitendinosus and biceps femoris activity were greater only during the returning phase of the forward lunge (P <.001) and the returning phase of the back squat (P =.002, P =.009, respectively). Hip-to-knee flexion ratios were closer to 1 when the forward lunge (P <.001), back lunge (P =.004), and forward squat (P =.001) exercises were performed on a slideboard. Conclusion: In exercise programs that target the quadriceps and hamstring muscles, slideboards can be effectively used in exercise progressions as they can increase muscle activity. Moreover, squat and lunge exercises on slideboard with a slow pace may also be helpful for improving the balance between hip- and knee-flexion angles. [ABSTRACT FROM AUTHOR]

Context: Posterior shoulder tightness evaluated as limited glenohumeral internal rotation and horizontal adduction is a risk factor for throwing-related shoulder and elbow injuries. Given that the throwing motion uses the entire body kinematics, limited lower-limb flexibility might be associated with posterior shoulder tightness. Therefore, we aimed to investigate the relationships between posterior shoulder tightness and lower-limb flexibility in college baseball players. Design: Cross-sectional study. Setting: University laboratory. Participants: Twenty-two college baseball players (20 right-handed and 2 left-handed). Methods: To investigate the relationships between glenohumeral range of motion and lower-limb flexibility using simple linear regression analysis, we measured passive range of motion of glenohumeral internal rotation and horizontal adduction, hip internal/external rotation in the prone/sitting position, ankle dorsiflexion, and quadriceps and hamstrings flexibility from both shoulders and legs. Results: Our analysis indicated that decreases in the lead leg hip external rotation in the prone position were moderately associated with limitations in glenohumeral internal rotation (R2 =.250, β [95% confidence interval, CI] = 0.500 [0.149 to 1.392], P =.018) and horizontal adduction (R2 =.200, β [95% CI] = 0.447 [0.051 to 1.499], P =.019) on the throwing shoulder. Furthermore, there were significant moderate relationships between decreases in glenohumeral internal rotation and limited lead leg quadriceps flexibility (R2 =.189, β [95% CI] = 0.435 [0.019 to 1.137], P =.022), and between decreases in glenohumeral horizontal adduction and limited stance leg ankle dorsiflexion (R2 =.243, β [95% CI] = 0.493 [0.139 to 1.438], P =.010). Conclusion: College baseball players with limited lower-limb flexibilities including the lead leg hip external rotation in the prone position, the lead leg quadriceps flexibility, and the stance leg ankle dorsiflexion showed excessive posterior shoulder tightness. The current results support the hypothesis that lower-limb flexibility is associated with posterior shoulder tightness in college baseball players. [ABSTRACT FROM AUTHOR]

Context: Hip muscle strength and hop performance limb symmetries after anterior cruciate ligament reconstruction (ACLR) are not well studied. This study aimed to determine the differences in hip abductors' (ABD) and external rotators' (ER) muscle strength measures between limbs, and the relationship between hip ABD and ER muscle strengths and hop performance limb symmetry indices (LSIs) 2 years after ACLR. Design: Cross-sectional study. Methods: Forty (level I/II) men athletes 2 years after unilateral ACLR completed 4 single-legged hop tests and involved hip ABD and ER strength testing (maximum voluntary isometric contraction [MVIC]; isokinetic peak torque [PKTQ] at 60°, 180°, and 300°/s; and isotonic peak velocity at 75% of their MVICs). Muscle strength measures were normalized to body mass, and hop performances were reported as LSIs. Paired t test was used to determine strength differences between limbs, and the Pearson correlation coefficient was used to assess the relationship between involved hip muscle strength measures and hop performance LSIs. Results: Hip ER-MVIC (involved: 60.26 [12.01], uninvolved: 63.68 [13.17] N·m/kg) and ER eccentric PKTQ at 60°/s (involved: 32.59 [9.28]; uninvolved: 35.73 [10.50] N·m/kg) were significantly different between limbs (P ≤.018). Single-hop LSI correlated with hip ER-PKTQ at 180°/s (r =.354) and 300°/s (r =.324, P ≤.041), while triple-hop LSI correlated with hip ER-MVIC (r =.320), concentric ER-PKTQ at 180°/s (r =.355), eccentric ER-PKTQ at 60°/s (r =.314), and hip ABD-PKTQ at 60°/s (r =.364) and 300°/s (r =.336, P ≤.049). Conclusions: Men athletes demonstrated symmetrical hop performance and hip muscle strengths, except for ER hip's MVIC and isokinetic eccentric peak torque at 60°/s 2 years after ACLR. Hop performance LSIs had a few, yet positive moderate relationships with involved hip ABDs and ER strength measures. This may indicate that hip ABD and ER muscle strength measures contribute to athletes' hop performances 2 years after ACLR. Post-ACLR rehabilitation programs might incorporate hip muscle strengthening training to improve athletes' functional performances. [ABSTRACT FROM AUTHOR]

Objective: To compare the efficacy of interferential current (IFC) therapy combined with quadriceps strengthening exercise versus sham IFC plus exercise for pain relief and functional improvement in patients with knee osteoarthritis. Study Design: Double-blind randomised controlled trial. Setting: Outpatient rehabilitation clinic. Subjects: Knee osteoarthritis patients aged 50–85 years with a pain score ≥4/10. Methods: One hundred forty-four participants were randomly allocated into the study and control groups. The study group received 20 min of IFC therapy (carrier frequency: 4000 Hz, beat frequency: 100 Hz) five times per week for three weeks, while the control group received sham IFC following the same protocol, followed by 10 min of exercise in both groups. Outcome measures included Numeric Rating Scale for Pain, Western Ontario and McMaster Universities Index (WOMAC) score, gait speed, and EuroQol-Five Dimensions-Five Levels questionnaire assessed at baseline, Week 3, and Week 6. Adverse events and patient satisfaction were evaluated at Week 3. Results: At Week 3, the study group demonstrated statistical improvement compared to the control group for Numeric Rating Scale for Pain, WOMAC Total, WOMAC Pain, and WOMAC Stiffness. The mean difference (95% confidence interval) between groups was 0.76 (0.21–1.30), 0.49 (0.03–0.95), 0.63 (0.13–1.13), and 0.62 (0.04–1.20), respectively. However, the mean differences between groups were below the Minimally Clinically Important Difference values for each outcome. Additionally, there were no significant differences between groups at Week 6 for any outcome measure. Conclusion: IFC had no effect on pain reduction and functional improvement in patients with mild to moderate knee osteoarthritis. [ABSTRACT FROM AUTHOR]

BACKGROUND: Test selection during the return to sport evaluation is an important aspect of ensuring athletes are safe to return to competition. OBJECTIVE: To assess the test-retest and inter-rater reliability of two new single leg hamstring bridge tests (SLHBT) and the relationships between these new tests and isokinetic strength of the quadriceps and hamstrings. METHODS: Thirty healthy college students completed the study. Two testing sessions were held three to seven days apart. Session one, participants performed two SLHBT as well as concentric isokinetic strength tests for the hamstring and quadriceps at 60, 180 and 300∘/sec. The participants performed only the two SLHBT during the second session. The first SLHBT, participants performed as many repetitions as possible of the SLHBT in 30-sec, while the second test measured how quickly the participants could perform five repetitions. Intraclass Correlation Coefficients (ICC2,1) were used to assess test-retest reliability while ICC(3,1) were used to test inter-rater reliability. RESULTS: The test-retest reliability for the SLHBTs was moderate to good, with ICC(2,1) ranging from 0.68 to 0.75, while the inter-rater reliability were excellent with ICC(3,1) all above 0.98. There were significant correlations between the SLHBT and the isokinetic tests, but all correlations were low to moderate. CONCLUSION: This study found good to excellent reliability with the new SLHBT and poor to moderate correlations were noted Therefore, SLHBT may not be an alternative to test hamstring test during the RTS evaluation due to the multiple compensatory strategies athletes may have. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the qualitative and quantitative changes seen in quadriceps muscles [QM] following tibial plateau fracture and surgery. Methods: A consecutive series of patients with an isolated tibial plateau fracture presenting to a single academic center were enrolled and prospectively followed. Bilateral knee MRIs were performed preoperatively and 3 and 12 months postoperatively to assess quantity and quality of the quadriceps muscles. All patients underwent tibial plateau operative repair and were made non-weight-bearing for 10 weeks postoperatively then advanced to weight-bearing as tolerated. Functional status assessed via the short musculoskeletal functional assessment (SMFA); knee range of motion [ROM]; vastus medialis oblique [VMO] and vastus lateralis [VL] muscle quantity (axial width, cross sectional area [CSA] and volume) on injured and contralateral limb; VMO, sartorius, semi-membranous and biceps femoris [BF] muscle quality (fat and water content, and proton density fat fraction). All muscle quantitative and qualitative measurements were compared across all time points. Results: Ten patients were included in the final analysis, 6 males and 4 females, with average age of 43.62 ± 16.3 years. While the VMO and VL axial width and CSA were significantly decreased at 3 months preoperatively, this was not statistically significant. There was no significant difference between any QM quantitative measurements at any time points. There was no difference in fat content, water content or PDFF at any time point for the VMO, sartorius, semi-membranous and BF muscles. Regression analysis also showed no association between 12-month SMFA scores and knee ROM with VMO/VL CSA at 1 year. Conclusions: QM quantity and quality do not significantly change at 3 months and 1 year postoperatively following tibial plateau fracture surgery. Level of evidence: Prognostic Level II. [ABSTRACT FROM AUTHOR]

This study investigated the influences of explosive quadriceps strength and landing task on sagittal plane knee biomechanics. Forty female participants performed isometric knee extensions on a dynamometer and had lower extremity biomechanics assessed during double-leg jump-landings (DLJL) and single-leg jump-cuts (SLJC). Explosive quadriceps strength was quantified by calculating rate of torque development (RTD) between torque onset and 100 ms after onset on a dynamometer. Participants were stratified into high and low RTD groups. Landing biomechanics were compared using 2 (Group) × 2 (Task) mixed-model ANOVAs. The relationships between quadriceps RTD and landing biomechanics were also assessed using simple, bivariate correlations. Across RTD groups, greater knee flexion at initial contact (KFIC), peak vertical ground reaction force, peak anterior tibial shear force, and peak internal knee extension moment, and lesser peak knee flexion was observed during SLJC compared to DLJL. The high RTD group exhibited significantly greater KFIC than the low RTD group across landing tasks. Greater quadriceps RTD was significantly associated with greater KFIC during SLJC, but not during DLJL. As landing with lesser KFIC is a risk factor for ACL injury, greater explosive quadriceps strength capacity might be beneficial for facilitating the use of safer landing mechanics during athletic tasks. [ABSTRACT FROM AUTHOR]

Patellar tendinopathy is more prevalent in males versus female athletes and commonly presents in the medial region of the tendon. Separate measures of patellar tendon strain in the medial, central, and lateral regions of the tendon, however, have not been quantified. The purpose was to investigate the differences in tendon strain between the medial, lateral, and central regions of the patellar tendon in healthy men and women. Strain in the medial and lateral regions of the patellar tendon in healthy participants (10 males, 10 females) was evaluated using ultrasound during isometric quadriceps contractions at 20%, 40%, 60%, 80%, and 100% of maximum voluntary contraction (MVIC) in 60° and 90° of knee flexion. Central strain was also measured at 60% MVIC in 90° of knee flexion. Mixed models were used to determine strain between tendon regions and sex at 60% MVIC in 90° of knee flexion. Sequential modeling was used to fit region, sex, %MVIC, and angle to predict strain. The central region had less strain compared with both medial and lateral regions. The lateral region had higher strain compared with the medial region regardless of sex. Females had higher strain compared with males, regardless of region. Knee position did not influence tendon strain. Patellar tendon strain differs by region and sex. The varying prevalence between sex and in location of patellar tendinopathy may in part be explained by the unbalanced strains. Differential assessment of regional patellar tendon strain may be of importance for understanding injury risk and recovery with exercise. [ABSTRACT FROM AUTHOR]

We explored the impact of running in the severe intensity domain on running mechanics and muscle oxygenation in competitive runners by investigating the relationship between mechanical deviations from typical stride characteristics and muscle oxygen saturation (SmO2) in the quadriceps muscle. Sixteen youth competitive runners performed an 8‐min exhaustive running test on an outdoor track. Running mechanics were continuously monitored using inertial measurement units. Rectus femoris SmO2 and total hemoglobin (a measure of blood volume) were continuously monitored by near‐infrared spectroscopy. One‐class support vector machine (OCSVM) modeling was employed for subject‐specific analysis of the kinematic data. Statistical analysis included principal component analysis, ANOVA, and correlation analysis. Mechanical deviations from typical stride characteristics increased as the running test progressed. Specifically, the percentage of outliers in the OCSVM model rose gradually from 2.2 ± 0.8% at the start to 43.6 ± 28.2% at the end (p < 0.001, mean ± SD throughout). SmO2 dropped from 74.3 ± 8.4% at baseline to 10.1 ± 6.8% at the end (p < 0.001). A moderate negative correlation (r = −0.61, p = 0.013) was found between the average SmO2 and the percentage of outlier strides during the last 15% of the run. During high‐intensity running, alterations in running biomechanics may occur, linked to decreased quadriceps muscle oxygenation. These parameters highlight the potential of using running kinematics and muscle oxygenation in training to optimize performance and reduce injury risks. Our research contributes to understanding biomechanical and physiological responses to endurance running and emphasizes the importance of individualized monitoring. [ABSTRACT FROM AUTHOR]

Bouts of military load carriage are rarely completed in isolation; however, limited research has investigated the physiological responses to repeated load carriage tasks. Twelve civilian men (age, 28 ± 8 years; stature, 185.6 ± 5.8 cm; body mass 84.3 ± 11.1 kg and maximal oxygen uptake, 51.5 ± 6.4 mL·kg−1 min−1) attended the laboratory on two occasions to undertake a familiarisation and an experimental session. Following their familiarisation session, participants completed three bouts of a fast load carriage protocol (FLCP; ∼65 min), carrying 25 kg, interspersed with a 65‐min recovery period. Physiological strain (oxygen uptake [V̇O2] and heart rate [HR]) was assessed during the FLCP bouts, and physical performance assessments (weighted counter‐movement jump [wCMJ], maximal isometric voluntary contraction of the quadriceps [MIVC] and seated medicine ball throw [SMBT]) was measured pre and post each FLCP bout. A main effect for bout and measurement time was evident for V̇O2 and HR (both p < 0.001 and Ѡ2 = 0.103–0.816). There was no likely change in SMBT distance (p = 0.201 and Ѡ2 = 0.004), but MIVC peak force reduced by approximately 25% across measurement points (p < 0.001 and Ѡ2 = 0.133). A mean percentage change of approximately −12% from initial values was also evident for peak wCMJ height (p = 0.001 and Ѡ2 = 0.028). Collectively, these data demonstrate that repeated FLCP bouts result in an elevated physiological strain for each successive bout, along with a substantial reduction in lower body power (wCMJ and MIVC). Therefore, future research should investigate possible mitigation strategies to maintain role‐related capability. Highlights: Given the progressively greater internal work rate for each successive load carriage bout (of equal external work rate), individuals responsible for load carriage planning should factor this elevated work rate into their operational planning (e.g., estimated maximal work durations).Elevated work rate for successive bouts should also be considered in other domains such as physical employment standards and development of working patterns.Group level perceptual measures appear to provide a good indication of physiological strain and therefore may provide useful information to commanders regarding the physical strain experienced by their team. [ABSTRACT FROM AUTHOR]

We examine the impact of the acute manipulation of oxygen availability during discrete phases (active and passive) of a repeated‐sprint cycling protocol on performance, physiological, and perceptual responses. On separate days, twelve trained males completed four sets of five 5‐s 'all out' cycle sprints (25‐s inter‐sprint recovery and 5‐min interset rest) in four randomized conditions: normobaric hypoxia (inspired oxygen fraction of 12.9%) applied continuously (C‐HYP), intermittently during only the sets of sprints (I‐HYPSPRINT) or between‐sets recovery periods (I‐HYPRECOVERY), or not at all (C‐NOR). Peak and mean power output, peripheral oxygen saturation, heart rate, blood lactate concentration, exercise‐related sensations, and vastus lateralis muscle oxygenation using near‐infrared spectroscopy were assessed. Peak and mean power output was ∼4%–5% lower for C‐HYP compared to C‐NOR (P ≤ 0.050) and I‐HYPRECOVERY (P ≤ 0.027). Peripheral oxygen saturation was lower during C‐HYP and I‐HYPSPRINT compared with C‐NOR and I‐HYPRECOVERY during sets of sprints (∼83–85 vs. ∼95%–97%; P < 0.001), while lower values were obtained for C‐HYP and I‐HYPRECOVERY than C‐NOR and I‐HYPSPRINT during between‐sets rest period (∼84–85 vs. ∼96%; P < 0.001). Difficulty in breathing was ∼21% higher for C‐HYP than C‐NOR (P = 0.050). Ratings of perceived exertion (P = 0.435), limb discomfort (P = 0.416), heart rate (P = 0.605), blood lactate concentration (P = 0.976), and muscle oxygenation‐derived variables (P = 0.056 to 0.605) did not differ between conditions. In conclusion, the method of hypoxic exposure application (continuous vs. intermittent) affects mechanical performance, while internal demands remained essentially comparable during repeated cycle sprints. Highlights: Continuous hypoxic exposure resulted in reduced repeated sprint performance compared to both normoxia and intermittent hypoxia during recoveries.Cardiovascular solicitation and glycolytic contribution showed no significant differences between ambient air and hypoxic conditions regardless of the timing of hypoxic gas administration (entire session, sprints only, or recovery only).The method of applying hypoxic exposure significantly affected mechanical performance, while internal physiological demands remained essentially comparable between conditions during repeated cycle sprints. [ABSTRACT FROM AUTHOR]

Background: This systematic review aimed to discern the relationships between muscle morphology, architecture, and quality with sprint cycling performance while considering the multifaceted nature of these relationships across diverse studies. Methods: Employing the PRISMA guidelines, an exhaustive search was performed across four primary databases: MEDLINE/PubMed, Web of Science, CINAHL Complete, and SPORTDiscus. The Methodological Index For Non-Randomised Studies (MINORS) was used to assess the methodological quality of the included studies. Out of 3971 initially identified records, only 10 studies met the eligibility criteria. Results: These investigations underscored the robust relationship of quadriceps muscle volume with peak power output (R2 from 0.65 to 0.82), suggesting its pivotal role in force production. In muscle architecture, the pennation angle and fascicle length showed varied associations with performance. Furthermore, muscle quality, as denoted by echo intensity, showed preliminary evidence of a potential inverse relationship with performance. The methodological quality assessment revealed varied scores, with the most consistent reporting on the aim, endpoints, and inclusion of consecutive patients. However, limitations were observed in the prospective calculation of study size and unbiased assessment of study endpoints. Conclusion: Our findings indicate that muscle volume is a major determinant of sprint cycling performance. Muscle architecture and quality also impact performance, although in a more intricate way. The review calls for standardised methodologies in future research for a more comprehensive understanding and comparability of results. PROSPERO registration number: CRD42023432824 (https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=432824). Key Points: • Muscle size matters: greater muscle volume and cross-sectional area correlate strongly with peak power output, emphasising the importance of muscle size in sprint cycling. • Pennation angle positively correlates with peak power output, but varied associations indicate the existence of other influencing factors, highlighting the complexity of muscle architecture in sprint performance. • Preliminary evidence suggests lower echo intensity, indicating higher muscle quality, may be linked to better sprint performance, urging further exploration of this relationship in athletes. [ABSTRACT FROM AUTHOR]

Background. Anterior cruciate ligament (ACL) tear is the most frequent ligament injury in athletes and is often accompanied by a traumatic meniscus tear. When a patient is submitted to a concomitant ACL reconstruction and meniscal repair, early rehabilitation caution might slightly delay knee function progress, potentially affecting gains in range of motion, strength recovery and subsequent return to sports. Therefore, in this study, we investigated the evolution of isokinetic parameters in professional athletes who underwent ACL reconstruction, with and without concomitant meniscal repair. Methods. Isokinetic parameters of fifty-eight professional athletes were assessed at the pre-surgery stage, 3-6, 6-9, 9-12, and +12 months post-surgery. Employing linear mixed-effect models, the effects of time and meniscal repair on knee extensors and flexors peak torque, bilateral asymmetry index, and hamstrings-to-quadriceps ratio were analyzed. Results. There was a main effect of the time on the peak torque outcomes in the injured side and bilateral asymmetry index of the knee extensors and flexors. However, the main effect of meniscus repair was not significant for all outcomes. Concurrently, there was no main effect of any factor on the hamstrings-to-quadriceps strength ratio. Conclusions. Generally, our analysis revealed that associated meniscal repair did not influence the recovery of muscle strength in athletes. Additionally, athletes require a minimum of 9 months to exhibit significant enhancement in isokinetic parameters compared to their preoperative performance. [ABSTRACT FROM AUTHOR]

Using global surface electromyography (sEMG) and the sEMG threshold it has been suggested that children activate their type-II motor unit (MU) to a lesser extent compared with adults. However, when age-related differences in discrete MU activation are examined using sEMG decomposition this phenomenon is not observed. Furthermore, findings from these studies are inconsistent and conflicting. Therefore, the purpose of this study was to examine differences in discrete MU activation of the vastus lateralis (VL) between boys and men during moderate-intensity knee extensions. Seventeen boys and 20 men completed two laboratory sessions. Following a habituation session, maximal voluntary isometric knee extension (MVIC) torque was determined before completing trapezoidal contractions at 70% MVIC. sEMG of the VL was captured and mathematically decomposed into individual MU action potential trains. Motor unit action potential amplitude (MUAPamp), recruitment threshold (RT), and MU firing rates (MUFR) were calculated. We observed that MUAPamp–RT slope was steeper in men compared with boys (p < 0.05) even after accounting for fat thickness and quadriceps muscle depth. The mean MUFR and y-intercept of the MUFR–RT relationship were significantly (p < 0.001) lower in boys than in men. The slope of the MUFR–RT relationship tended to be steeper in men, but the differences did not reach statistical significance (p = 0.056). Overall, our results suggest that neural strategies used to produce torque are different among boys and men. Such differences may be related, in part, to boys' lower MUFR and lesser ability to activate their higher-threshold MUs. Although, other factors (e.g., muscle composition) likely also play a role. [ABSTRACT FROM AUTHOR]

Few studies have examined changes in skeletal muscle physiology post-stroke. This study examined changes in tissue oxygen saturation (StO2) of the vastus lateralis (VL) muscle of stroke survivors and age-matched control participants during maximal and submaximal isometric contractions of the knee extensor muscles. We hypothesized that tissue oxygen desaturation (ΔStO2) during knee extensor muscle contractions would be less in the VL in the paretic vs. the non-paretic and control legs. Ten chronic stroke survivors (>6 months post-stroke) with lower extremity muscle weakness and 10 age-matched controls completed this prospective cohort study. Maximum voluntary contractions (MVCs) of the knee extensor muscles were assessed with a Biodex dynamometer and StO2 of the VL was measured using near-infrared spectroscopy. In the paretic leg of the stroke survivors little change in StO2 of the VL was observed during an MVC (ΔStO2 = -1.7 ± 1.8%) compared to the non-paretic (ΔStO2 = -5.1 ± 6.1%; p < 0.05) and control legs (ΔStO2 = -14.4 ± 8.8%; p < 0.05 vs. paretic and non-paretic leg). These differences remained when normalizing for strength differences between the legs. Compared to controls, both the paretic and non-paretic VL showed pronounced reductions in ΔStO2 during ramp and hold contractions equal to 20%, 40%, or 60% of the MVC (p < 0.05 vs. controls at all load levels). These results indicate that oxygen desaturation in response to isometric muscle contractions is impaired in both the paretic and non-paretic leg muscle of stroke survivors compared to age-matched controls, and these differences are independent of differences in muscle strength. [ABSTRACT FROM AUTHOR]

Purpose: People with both pronated feet and anterior cruciate ligament repair may benefit from walking on sand as a therapeutic option. The consequences of walking on sand on the muscular activity and gait biomechanics of these people are not well understood. This study aims to determine how sand training affects gait... [ABSTRACT FROM AUTHOR]

(1) Objective: To examine the effects of blood flow restriction (BFR) training on muscle strength, cross-sectional area and knee-related function in patients selected for anterior cruciate ligament reconstruction (ACLR). (2) Methods: A literature search was conducted in PubMed, PEDro, Cochrane Library, Web of Science, SCOPUS, and ProQuest databases until 20 May 2024. Controlled clinical trials comparing the effects of BFR training with unrestricted training in patients before or after ACLR were selected. The GRADE approach was used to assess the degree of certainty for each meta-analysis. (3) Results: Ten studies were included (n = 287 participants). Standardized mean differences in favor of BFR training applied postoperatively were observed in knee extensor (SMD = 0.79; 95% CI = 0.06 to 1.52; I2: 68%) and flexor isokinetic strength (SMD = 0.53; 95% CI = 0.04 to 1.01; I2: 0%), and quadriceps cross-sectional area (SMD = 0.76; 95% CI = 0.27 to 1.26; I2: 0%). No changes were found in knee extensor isometric strength and knee-related function. The degree of certainty according to the GRADE was very low. (4) Conclusions: Very low degree of certainty suggests that BFR training provides additional benefits to unrestricted training on isokinetic strength and quadriceps cross-sectional area in patients undergoing ACLR. [ABSTRACT FROM AUTHOR]

The article focuses on assessing the impact of intramuscular temperature and fascicle angle on ultrasound echo intensity values (EI), highlighting the need for accurate measurement methods in estimating muscle quality. While Pinto et al. suggest a significant confounding effect of fascicle angle on EI, concerns arise regarding the experimental setup's ability to independently manipulate fascicle angle and properly account for factors like subcutaneous fat thickness.

Background: Neuromuscular function is considered as a determinant factor of endurance performance during adulthood. However, whether endurance training triggers further neuromuscular adaptations exceeding those of growth and maturation alone over the rapid adolescent growth period is yet to be determined. Objective: The present study investigated the concurrent role of growth, maturation, and endurance training on neuromuscular function through a 9‐month training period in adolescent triathletes. Methods: Thirty‐eight 13‐ to 15‐year‐old males (23 triathletes [~6 h/week endurance training] and 15 untrained [<2 h/week endurance activity]) were evaluated before and after a 9‐month triathlon training season. Maximal oxygen uptake (V̇O2max) and power at V̇O2max were assessed during incremental cycling. Knee extensor maximal voluntary isometric contraction torque (MVCISO) was measured and the voluntary activation level (VAL) was determined using the twitch interpolation technique. Knee extensor doublet peak torque (T100Hz) and normalized vastus lateralis (VL) electromyographic activity (EMG/M‐wave) were also determined. VL and rectus femoris (RF) muscle architecture was assessed using ultrasonography. Results: Absolute V̇O2max increased similarly in both groups but power at V̇O2max only significantly increased in triathletes (+13.8%). MVCISO (+14.4%), VL (+4.4%), and RF (+15.8%) muscle thicknesses and RF pennation angle (+22.1%) increased over the 9‐month period in both groups similarly (p < 0.01), although no changes were observed in T100Hz, VAL, or VL EMG/M‐wave. No changes were detected in any neuromuscular variables, except for coactivation. Conclusion: Endurance training did not induce detectible, additional neuromuscular adaptations. However, the training‐specific cycling power improvement in triathletes may reflect continued skill enhancement over the training period. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the relationship between muscle fiber type-specific properties of the vastus lateralis and quadriceps muscle performance in individuals after an anterior cruciate ligament (ACL) tear. 26 subjects (22.0 ± 5.4 years) were included in this cross-sectional study, and all data were collected before ACL reconstruction. Quadriceps peak torque (QPT) and early (0-100 ms) and late (100-200 ms) rate of torque development (RTD) were obtained from maximal voluntary isometric quadriceps strength testing. Muscle fiber cross-sectional area (fCSA) and percent fiber type distribution (FT%) were evaluated through immunohistochemical analysis of a muscle biopsy. Between-limb differences in fiber characteristics were assessed using paired t-tests (with α-level 0.05). Relationships between fiber-specific properties and quadriceps muscle performance were determined using separate multiple linear regression analyses for ACL-injured and noninjured limbs. There were significant differences in fCSA between ACL-injured and noninjured limbs across all fiber types, but no differences in FT%. Type 1 fCSA, type 2a fCSA, and their interaction effect were the explanatory variables with the strongest relationship to all performance outcomes for the ACL-injured limb. The explanatory variables in the ACL-injured limb had a significant relationship to QPT and late RTD, but not early RTD. These findings suggest that QPT and late RTD are more heavily influenced by fCSA than FT% in ACL-injured limbs. This work serves as a foundation for the development of more specific rehabilitation strategies aimed at improving quadriceps muscle function before ACL reconstruction or for individuals electing nonsurgical management. [ABSTRACT FROM AUTHOR]

This study examined neuromuscular performance using load-velocity (L-V) profiles in men and women before and after resistance exercise (RE) in hot (HOT; 40° C) and temperate (TEMP; 21° C) environments. Sixteen (f = 8, m = 8) resistance-trained individuals completed a single 70-minute whole-body high-volume load (6 exercises, 4 sets of 10 repetitions) RE bout in HOT and TEMP. Before and after RE, rectal temperature (TRE), muscle temperature ofthe vastus lateralis (TVL) and triceps brachii (TTB), and an L-V profile for the deadlift and bench press were recorded. Thermoregulatory and L-V data were analyzed using separate 2-way repeated measures analysis of variances (ANOVAs; condition [hot, temperate] and time [pre, post]) with significance level set at p ≤ 0.05. Deadlift peak velocity was reduced at 60% 1 repetition maximum (1RM) after RE in HOT but not TEMP. Peak velocity of 40% 1RM bench press was lower in TEMP vs. HOT pre-RE (p < 0.01). Peak velocity was decreased at all loads in the deadlift L-V profile after RE, regardless of condition. Despite elevated TRE (TEMP; 37.58 ± 0.35, HOT; 38.20 ± 0.39° C), TVL (TEMP; 35.24 ± 0.62, HOT; 37.92 ± 0.55° C), and TTB (TEMP; 35.05 ± 0.78, HOT; 38.00 ± 0.16° C) after RE in HOT vs. TEMP (p < 0.01), RE in HOT did not broadly affect L-V profiles. This indicates heated resistance exercise can be performed with high-volume load and high ambient temperature with minimal performance impairment. [ABSTRACT FROM AUTHOR]

Objective. The purpose of this study will be to determine the efficacy of low intensity lower extremity resistance training with and without blood flow restriction (BFR) on quadriceps muscle strength and thickness in veterans with advanced multiple sclerosis (MS). Methods. This will be an assessor-blinded, 2-group (1 to 1 allocation) randomized controlled trial targeting an enrollment of 58 participants with advanced MS as defined by Patient-Determined Disease Steps scale levels 4 to 7. Both groups will complete 10 weeks of twice weekly low-load resistance training (20%-30% of 1-repetition max) targeting knee and hip extension, knee flexion, and ankle plantarflexion. The intervention group will perform all training using BFR, with limb occlusion pressures between 60% and 80% of maximal limb occlusion pressure. Primary outcomes will be quadriceps muscle strength and thickness. Secondary outcomes will include knee flexion and ankle plantarflexion strength, functional mobility, physical activity, and patient-reported measures. All outcomes will be assessed at baseline before the intervention, immediately after the intervention, and at a 2-month follow-up assessment. The change between groups postintervention and after the 2-month follow-up will be reported for all outcomes. All analyses will assume a 2-sided test of hypothesis (α =.05). Impact. There is very little evidence for the efficacy of exercise interventions in people with MS who have advanced mobility disability. Resistance training with BFR may be an important approach for people with advanced MS who may not tolerate more conventional, moderate-to-high intensity resistance training. The results of this study will inform clinicians regarding exercise decisions for people with advanced MS and future investigations on the role of BFR in people with MS. [ABSTRACT FROM AUTHOR]

Purpose: To compare the acute performance and psychophysiological responses of repeated cycling sprints to exhaustion with a short exercise-to-rest ratio (1:6), between different effort durations and inspired oxygen fractions. Methods: On separate visits, 10 active participants completed 6 repeated cycling sprint exercises to exhaustion with 3 different effort durations (5, 10, and 20 s) and 2 conditions of inspired oxygen (20.9% and 13.6%). Exercise-to-rest ratio was 1:6 for all trials (ie, 5:30, 10:60, and 20:120). Vastus lateralis muscle oxygenation (near-infrared spectroscopy), blood lactate concentration, and lower-limb and breathing discomfort, using ratings of perceived exertion, were measured. Results: Number of sprints and peak power output decreased while blood lactate increased (all P <.001) during 5:30 compared with 10:60 or 20:120. No condition or interaction effects were reported for blood lactate and exercise-related sensation. Muscle deoxyhemoglobin increased (P <.001) and total hemoglobin decreased (P =.002) during sprint with increasing sprint duration (no condition or interaction). Conclusion: During repeated-sprint exercise to exhaustion with a short exercise-to-rest ratio, the psychophysiological responses did not differ between normoxia and moderate hypoxia, probably due to an extended recovery period. It means that hypoxia did not modify repeated-sprint exercise performance with a short exercise-to-rest ratio. The sprint duration was the primary underlying factor of the observed differences in performance and muscle oxygenation reported between the repeated-sprint exercise sessions. [ABSTRACT FROM AUTHOR]

Context: Quadriceps strength is considered a key contributor to performance in various athletic tasks. Yet, past research has reported conflicting results based on population, with little data available in highly trained female athletes. Design: Cross-sectional. Method: To examine how athletic performance relates to quadriceps strength and neural function, we measured the quadriceps maximum voluntary isometric contraction force (MVIC) and rate of force development over 0 to 50 ms (rate of force development [RFD]0−50ms), and various performance measures in 34 highly trained female athletes. Results: Stepwise multiple regression analysis revealed that the quadriceps variables explained 16 of 21 performance variables (R2 =.08–.36, P ≤.10). Squat performance related to RFD0−50ms alone (R2 =.17–.20, P <.05; βRFD = 0.41 to 0.45, P <.05) but only MVIC explained the variance in sprinting and vertical jump performance (R2 =.08–.34, P ≤.10; βMVIC = −0.51 to 0.58, P ≤.10). The broad jump model included both parameters and their interaction (R2 =.20, P =.08; βRFD = 0.06, P =.76; βMVIC = −0.39, P =.03; βRFD×MVIC = −0.24, P =.10). Conclusion: The contribution of the quadriceps MVIC or RFD0–50ms varies in size and nature depending on the task or leg dominance. While quadriceps are significant contributors to performance, because our models leave most of the variance in performance unexplained, rehabilitation and performance professionals should refrain from interpreting peak athletic performance as a reflection of knee-extensors function in highly trained female athletes. [ABSTRACT FROM AUTHOR]

Purpose: Contributions of neural and muscular factors to muscle strength change with growth, but such changes remain unclear in young populations. This study aimed to clarify the association between muscle strength and neural and muscular factors in youth athletes. Methods: Maximal voluntary contraction (MVC) during isometric knee extension, the motor unit firing rate (MUFR), and muscle thickness (MT) of the vastus lateralis were measured in 70 youth male soccer players (mean [SD]; chronological age = 16.3 [0.6] y, peak height velocity age = 13.1 [1.0] y). MUFR and MT were measured with high-density surface electromyography and ultrasonography, respectively. Results: For MUFR and MT, correlations with MVC were calculated and the values of different MVC groups were compared. A significant correlation between MVC and MT (r =.49, P <.01) was noted, but not MUFR (r =.03, P >.05). There was also no significant correlation between MT and MUFR (r = −.33, P >.05). In addition, comparison among groups (higher-/middle-/lower-strength groups) revealed that MT in the lower-strength group was significantly lower than in middle-and higher-strength groups (P <.01). Conclusion: In youth athletes, muscle strength is associated with muscular factors, rather than neural factors, and muscular and neural factors may independently contribute to muscle strength. [ABSTRACT FROM AUTHOR]

Purpose: To compare the difference in analgesic effect between femoral triangle block (FTB) and adductor canal block (ACB) during arthroscopic knee surgery. Methods: Patients who underwent arthroscopic knee surgery were randomized preoperatively to FTB group or ACB group. For each group, 20 mL of 0.1% ropivacaine was injected. Primary outcomes: The numeric rating score (NRS) at 12 h after surgery at rest and during movement. Secondary outcome: (1) The NRS at post anesthesia care unit (PACU) and 2, 24 h after surgery at rest and during movement; (2) The quadriceps muscle strength at PACU and 2, 12, 24 h after surgery; (3) Consumption of Rescue analgesia; (4) Incidence of adverse reactions. Results: The NRS at 12 h after surgery at rest and during movement of ACB group were higher than FTB group. Among secondary outcomes, the NRS at PACU at rest and during movement, 2 h after surgery during movement of FTB group lower than ACB group; the quadriceps muscle strength at 2 h after surgery of FTB group stronger than ACB group. After multiple linear regression model analysis, the data showed additional statistically significant reduction NRS at 24 h after surgery at rest (0.757, p = 0.037) in FTB group. Other outcomes were similar between two groups. Conclusions: The FTB appears to provide superior pain control after knee arthroscopy than ACB, the FTB is superior to the ACB in quadriceps muscle strength at 2 h after surgery. Trial registration: The trial was registered in the Chinese Clinical Trial Registry (ChiCTR2300068765). Registration date: 28/02/2023. [ABSTRACT FROM AUTHOR]

Introduction: A recent study showed that cadence modulation during short eccentric cycling exercise affects oxygen consumption (...O2), muscular activity (EMG), and perception of effort (PE). This study examined the effect of cadence on ...O2, EMG, and PE during prolonged eccentric cycling and exercise-induced neuromuscular alterations. Methods: Twenty-two participants completed three sessions 2-3 wk apart: 1) determination of the maximal concentric peak power output, familiarization with eccentric cycling at two cadences (30 and 60 rpm at 60% peak power output), and neuromuscular testing procedure; 2) and 3) 30 min of eccentric cycling exercise at a cadence of 30 or 60 rpm. PE, cardiorespiratory parameters, and vastus lateralis and rectus femoris EMG were collected during exercise. The knee extensors' maximal voluntary contraction torque, the torque evoked by double stimulations at 100 Hz (Dt100) and 10 Hz (Dt10), and the voluntary activation level were evaluated before and after exercise. Results: ...O2, EMG, and PE were greater at 30 than 60 rpm (all P <0.05). Maximal voluntary contraction torque, evoked torque, and Dt10/Dt100 ratio decreased (all P < 0.01) without cadence effect (all P > 0.28). Voluntary activation level remained constant after both eccentric cycling exercises (P = 0.87). Conclusions: When performed at the same power output, eccentric cycling exercise at 30 rpm elicited a greater PE, EMG, and cardiorespiratory demands than pedaling at 60 rpm. Exercise-induced fatigability was similar in both eccentric cycling conditions without neural impairments, suggesting that eccentric cycling seemed to alter more specifically muscular function, such as the excitation-contraction coupling process. In a rehabilitation context, eccentric cycling at 60 rpm seems more appropriate because it will induce lower PE for similar strength loss compared with 30 rpm. [ABSTRACT FROM AUTHOR]