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Background Loss of knee extensor strength in individuals with knee osteoarthritis (KOA) may induce inter-limb strength asymmetries and alter functionality. The aims were to analyse whether the condition of the uninvolved knee (advanced to severe KOA or no affection) may induce different degrees of knee extensor strength asymmetry in individuals with KOA and to study whether functionality may differ in cases of unilateral or bilateral KOA. Methods Sixty-eight subjects with advance-to-severe KOA were categorized into two groups (unilateral or bilateral KOA). The knee extensor strength ratio (KESR), and self-reported and performance-based functionality were analysed and compared. Sex and age were independent factors. One- and two-way analysis of variance assessed for significant between-group differences (95% confidence interval (CI)). Results Participants with unilateral KOA presented with 20% knee extensor strength asymmetry. The mean difference with the bilateral KOA group in terms of Knee Extensors Strength Ratio was 0.2 (95% CI 0–0.3; P = 0.021), of the Oxford Knee Scale score was 4.2 (95% CI 3.4–5.1; P = 0.037), and of the Timed Up and Go was 1.3 s (95% CI 0.5–2.2; P > 0.05). There were significant sex and age interactions (P Conclusions Individuals with unilateral or bilateral KOA present with different degrees of knee extensor strength asymmetry. The non-affected knee seems to help to better develop functional tasks in cases of unilateral condition. The findings may help the design of tailored strengthening interventions in which each knee condition in individuals with KOA should be considered.

Recently, we proposed the hypothesis that weekly running volume and preferred running pace may play a role in preserving ankle joint kinetics in middle-age runners as ankle joint kinetics were generally similar in young and middle-aged runners with similar running volume and preferred pace. To further address this hypothesis, we compared lower extremity joint kinetics between high and low training volume runners in both young and middle-aged groups. Joint kinetics calculated from 3D kinematic and ground reaction force data during over-ground running at 2.7 m·s-1 from young and middle-aged runners who ran low or high weekly volume were analyzed. A two-factor analysis of variance was used to compare joint kinetics between age and running volume groups. Positive hip work was greater in middle-aged compared to young runners (P = .005). Plantarflexor torque (P = .009) and positive ankle work (P = .042) were greater in young compared to middle-aged runners. Positive ankle work was also greater in the high compared to the low volume group (P = .021). Finally, age by volume interactions were found for knee extensor torque (P = .024), negative knee work (P = .018), and positive knee work (P = .019) but not for ankle and hip joint kinetics. These findings suggest less distal-to-proximal difference in positive joint work with high running volume in both young and middle-aged runners as a result of greater power generation at the ankle. Given the age main effects, our findings are also the first to suggest the age-related distal-to-proximal shift in joint kinetics appears in middle-aged runners.

Ultrasonography-derived cross-sectional area (CSA) and echo intensity (EI) are increasingly utilized by investigators to study muscle size and quality, respectively. We sought to examine age, sex, and region (proximal, middle, distal) differences in vastus lateralis and rectus femoris CSA and EI, and determine whether correction for subcutaneous fat thickness influences the magnitude of EI differences. Fifteen younger men (mean age = 23 years), 15 younger women (aged 21 years), 11 older men (aged 74 years), and 15 older women (aged 70 years) participated. Clear differences were observed among age, sex, and region for vastus lateralis CSA (p ≤ 0.013, d = 0.38–0.73), whereas rectus femoris CSA was only different between younger and older participants at the proximal region (p = 0.017, d = 0.65). Uncorrected EI was greatest at the distal region of both muscles (p < 0.001, d = 0.59–1.38), with only the younger men having significantly lower EI values than the other groups (p ≤ 0.043, d = 0.37–0.63). Subcutaneous fat correction resulted in a marked increase in the magnitude of sex-specific EI differences (p ≤ 0.032, d ≥ 0.42). Additionally, subcutaneous fat correction increased the uniformity of EI throughout the thigh. These findings highlight considerable region-specific differences in muscle size and quality among younger and older men and women and highlight the need to correct for subcutaneous fat thickness when examining EI. Novelty Rectus femoris CSA is similar between younger and older adults except at the most proximal site evaluated. Age- and sex-specific differences in uncorrected EI are nonuniform across the thigh. Correction for subcutaneous fat thickness substantially increased EI in women, resulting in greater sex differences.

The aim of the study was to evaluate the possibility to predict the muscle fiber-type proportion in men of different sports specialization by testing the maximal torque production by knee extensors at different velocities. For this reason the proportion of fast- and slow-twitch muscle fibers (MFs) in m. vastus lateralis of 23 athletes (11 endurance and 12 power athletes), as well the maximal torque production of knee extensors at various angular velocities in isokinetic mode were determined. The group of strength trained athletes significantly exceeded the group of endurance trained athletes in body mass, body mass index, volume of the m. quadriceps femoris, maximum torque production, and specific force at angular velocities 30, 180 and 300 degrees per second. In contrast to cross-sectional area (CSA) of slow-twitch MFs, the average CSA of fast-twitch MFs and the proportion of fast-twitch MFs in the group of power athletes significantly exceeded those in the group of endurance athletes. In the combined group of volunteers (n = 23), the proportion of fast-twitch MFs significantly correlated with the torque production at high angular velocities (r = 0.51 and p = 0.01 at 180 deg/s; r = 0.47 and p = 0.02 at 300 deg/s). We did not find any correlation between these parameters in the separate groups of power and endurance athletes. The results indicate a low accuracy in predicting the proportion of fast-twitch MF in m. vastus lateralis in athletes using the maximal torque production of knee extensors at different angular velocities. Significant correlation between the proportion of fast-twitch MF and maximal torque at high angular velocities in the general group (n = 23) was due to the presence of two significantly different subgroups.

Purpose: The purpose of this study was to investigate comparisons of vastus medialis (VMO) and vastus lateralis (VL) muscle activities according to different heights during drop landing in flatfooted adults. Methods: Fifteen subjects with a flat foot arch and 15 subjects with a normal feet arch were participated. Subjects performed a double limb drop landing task from 20, 40, and 60 cm heights. Surface electromyography was used to measure the muscle activities of the VMO and VL during drop landing. Results: There were significant differences of muscle activities in the VMO, VL, and the VMO and VL ratio between groups. The electro myography values of VMO, VL, and the VMO and VL ratio in the normal group were significantly greater than in the flat foot group, and muscle activities and the VMO and VL ratio significantly increased with landing heights in the both groups. Conclusion: Our results indicated that muscle activity patterns of VOM and VL in the flat foot group were lower at heights than in the normal group, so calf tightness was negative effects on balance and gait ability, so assessment of muscle activation patterns in the knee extensors should be considered during exercise and treatment of flat feet.

The relationship between muscle architectural properties and hind foot drumming of African mole-rats has yet to be determined using established methodology. Therefore, the internal structure of 32 hind limb muscles was evaluated in two drumming and one non-drumming species of Bathyergidae. The muscle mass (MM), fascicle length (Lf), and angle of pennation were measured to calculate the physiological cross-sectional area (PCSA) as well as estimate the maximum isometric force of contraction (Fmax). The most significant differences for the various muscle architecture parameters analyzed in synergistic muscle groups and individual muscles were observed between the rapid drumming Georychus capensis and the non-drumming Cryptomys hottentotus natalensis. The PCSA values of the hip extensors, hip adductors, knee extensors, and knee flexors of G. capensis were significantly larger than that of C. h. natalensis. Additionally, the hip extensors and knee flexors of both the drumming species (G. capensis and Bathyergus suillus) were shown to be capable of higher power output compared to the non-drumming species, and the hip adductors of G. capensis capable of faster contraction. M. gracilis anticus may play a key role in facilitating hind foot drumming as it was the only muscle to be significantly different in G. capensis and C. h. natalensis for all three muscle architecture parameters analyzed. Furthermore, it features in the high shortening capacity quadrant of the functional space plot of both G. capensis and B. suillus but not the non-drumming C. h. natalensis.

The biomechanical differences between cyclists with a high compared with a low blood lactate threshold (HLT; 80% VO2max vs LLT, 70% VO2max) have yet to be completely described. We hypothesize that HLT cyclists reduce the stress placed on the knee extensor muscles by increasing the relative contribution from the hip joint during high-intensity cycling. Sixteen well-trained endurance athletes, with equally high VO2max while cycling and running completed submaximal tests during incremental exercise to identify lactate threshold ( $${\text{LT}}_{{V{\text{O}}_{2} }}$$ ) while running and cycling. Subjects were separated into two groups based on % VO2max at LT during cycling (high; HLT: 80.2 ± 2.1% VO2max; n = 8) and (LLT: 70.3 ± 2.9% VO2max; n = 8; p 0.05) while running. While cycling in LLT, knee joint absolute power increased with work rate (p 0.05). The HLT generated significantly greater relative hip power compared with the LLT group at 90% VO2max (p

Introduction Fatigue-related group III/IV muscle afferent firing from agonist, antagonist or distal muscles impairs the ability to drive the elbow flexors maximally, that is, reduces voluntary activation. In the lower limb, the effect of feedback from distal muscles on the proximal knee extensors is unknown. Here, we test whether maintained group III/IV afferent feedback from the plantarflexor muscles reduces voluntary activation of the knee extensors. Methods On 2 d, voluntary activation of the knee extensors during maximal voluntary contractions (MVCs) was assessed in 12 participants before and after a 3-min fatiguing task of the plantarflexors. On 1 d, an inflatable cuff around the calf occluded blood flow for 2 min immediately postexercise (cuff day). The other day had no occlusion (no-cuff day). Supramaximal stimulation of the femoral nerve elicited superimposed twitches during MVC of the knee extensors and resting twitches 2 to 3 s after relaxation. Pain (0-10 point scale) was reported throughout. Results In the 2 min after the 3-min fatiguing plantarflexor task, voluntary activation was 5.3% (SD, 7%) lower on the cuff day than on the no-cuff day (P = 0.045), and MVC force was reduced by 13% (SD, 16%) (P = 0.021). The resting twitch was similar on both days (P = 0.98). Pain rated 4.9 points higher with the cuff inflated (P = 0.001). Conclusions Maintained group III/IV afferent feedback from the fatigued plantarflexor muscles reduced maximal force and voluntary activation of the unfatigued knee extensors, suggesting that afferents from the calf act centrally to inhibit the ability to drive the motoneurones of the knee extensors.

As the population ages, there is a growing burden owing to musculoskeletal diseases, such as knee osteoarthritis, and subsequent functional decline. In the absence of a cure, there is a need to identify factors amenable to intervention to prevent or slow this process. The Multicenter Osteoarthritis Study cohort was developed for this purpose. In this study, associations between variability in peak knee flexor and extensor torque at baseline and worsening of pain and physical function over the subsequent 60 mos were assessed in a cohort of 2680 participants. The highest quartile of baseline knee flexor torque variability was found to be associated longitudinally with worsening pain (fourth quartile s estimate, mean ± SE, 0.49 ± 0.19; P = 0.0115; with R2 = 0.28 and P for trend across quartiles = 0.0370) and physical function scores (fourth quartile s estimate, mean ± SE, 1.39 ± 0.64; P = 0.0296; with R2 = 0.25 and P for trend across quartiles = 0.0371), after adjusting for baseline knee osteoarthritis and maximum knee flexor torque. There were no associations between baseline knee extensor torque and worsening pain or physical function by 60 mos. The presence of greater variability in maximum knee flexor strength may identify patients who may benefit from therapies aimed at preventing worsening knee pain and physical function.

Transcutaneous electrical stimulation (TES) is used to activate muscles when volitional capacity is impaired but potential benefits are limited by rapid force loss (fatigue). Most TES fatigue protocols employ constant-frequency trains, with stimuli at a fixed interstimulus interval (ISI); however, a brief ISI between the first two pulses (variable-frequency train, VFT) to maximize the catchlike property of muscle can attenuate fatigue development. The purpose of this study was to investigate if a VFT that simulates intrinsic variability of voluntary motor unit discharge rates would also mitigate fatigue, owing to the sensitivity of muscle to acute activation history.On two visits, 24 healthy adults (25.3 ± 3.7 years; 12 females) received 3 min of intermittent TES to the quadriceps of the dominant leg. Trains of eight pulses at 10 Hz were delivered with a constant (100 ms) or variable ISI (80-120 ms). Contractile impulse, rate of force development (RFD), and rate of relaxation (RFR) were determined for each tetanus RESULTS: During fatigue and recovery, contractile impulse did not differ between protocols (p ≥ 0.796) and sexes (p ≥ 0.493), with values of 77 ± 17% control at task end and 125 ± 19% control 2 min later. RFD and RFR also showed no effect of the protocol (p ≥ 0.310) or participant sex (p ≥ 0.119). Both measures slowed (38 ± 23% and 33 ± 22%, respectively) but dissociated during recovery as RFD remained 16 ± 18% below control at 5 min, whereas RFR recovered to control by 30 s (101 ± 22%).Contrary to expectations, the VFT protocol did not attenuate fatigue development, which suggests no benefit to mimicking the inherent variability of motor unit discharge rates.

This study aimed to investigate the relationship between knee extensors maximum voluntary contraction (MVC) torque and rate of torque development (RTD) with jump performance and with echography intensity (EI) from the vastus lateralis muscle (VL). We assessed the MVC torque and RTD from knee extensors by a standard isokinetic device from 16 male professional soccer players (25.5 ± 3.9 years). Counter-movement jump (CMJ) and squat jump (SJ) height were calculated from their flight times. EI was determined from VL ultrasound images’ grayscale histogram acquired in the middle of the tight. Correlation between variables was investigated by the Pearson correlation coefficient. We observed a VL EI of 26.4 ± 7.8 a.u., and the SJ and CMJ heights were 36.0 ± 3.0 and 36.2 ± 4.1 cm, respectively. There was a significant correlation between the MVC torque and absolute late-phase RTD (r = 0.67 and 0.76—RTD200 and RTD250, respectively), between the CMJ height and absolute RTD50 (r = 0.50), and between the normalized early-phase RTD and SJ height (r = 0.53–0.60—RTD50 and RTD150). Additionally, normalized RTD200 (r = − 0.51) and RTD250 (r = − 0.56) were negatively correlated with EI. Such results suggest that athletes with the ability to produce torque explosively in the very beginning (between 50 and 150 ms) of knee extension can jump higher. Also, the muscle quality assessed by the VL IE seems to be more important to maximum strength and later periods of torque rise (> 200 ms).

Corso, M, Liang, L, Tran, S, Howitt, S, Srbely, J, and Mior, SA. The immediate effect of spinal manipulation on ball velocity and neuromuscular function during an instep kick in former Varsity soccer players: a feasibility study. J Strength Cond Res 36(9): 2558-2565, 2022-Spinal manipulation (SM) has been shown to increase ball velocity (BV) in soccer players. Evidence suggests that SM modulates responses at spinal or cortical levels to enhance force production in asymptomatic populations. No studies have explored the underlying neuromuscular mechanisms contributing to changes in BV post-SM in soccer players. We assessed the feasibility of measuring change in BV and neuromuscular function after SM in former Varsity level soccer players with a pre-post study design. Three to 5 maximal instep kicks were performed before and after SM at the L3-5 level. Ball velocity was measured using high-speed camera. Activation of lower limb and trunk musculature was recorded with electromyography. Outcomes included ease of recruitment, scheduling and data capture, as well as expectation and perception of SM effect and adverse events (AE). Fifteen potential subjects were recruited over 1.5 months. Eleven were scheduled (24-31 years; 8 females, 3 males). Two subjects reported mild AE after maximal voluntary isometric contraction testing. A significant increase in BV (mean change: 1.75 m·s -1 [95% confidence interval: 0.5-3.0]) and a trend to increased peak-activation of knee extensors (90.7%) were observed post-SM. Findings suggest that our recruitment strategy and methodology are feasible in a larger trial with some modifications. Our preliminary findings support previous research by suggesting that increased BV may be mediated through increased activation of knee extensors during the kick. Our findings may offer additional insight into the underlying neuromuscular mechanisms contributing to immediate change in BV post-SM.

OBJECTIVE Obesity is a major and functionally important problem in polio survivors. The aim of this study was to investigate the prevalence of obesity using body mass index and percentage body fat in polio survivors and to analyze the relationship between obesity and mobility. DESIGN Eighty-four polio survivors were included. Anthropometric parameters, knee extensor strength, and the Short Physical Performance Battery were evaluated. A questionnaire was used to explore the late effects of poliomyelitis. Obesity was determined using both body mass index and percentage body fat. RESULTS The prevalence of obesity in polio survivors was 39.3% and 81.5% using the body mass index and percentage body fat criteria, respectively. The Short Physical Performance Battery scores were significantly different between the obese and nonobese groups as determined by percentage body fat (P < 0.05). Only percentage body fat was significantly associated with mobility after controlling for the confounding variables in obese polio survivors (P < 0.05). CONCLUSIONS Obesity in polio survivors was underestimated when the body mass index criteria were used. Percentage body fat was a significantly associated factor for mobility in obese polio survivors. Obesity determined by percentage body fat criteria is useful to address obesity-related problems in polio survivors.

International audience; Purpose: Ultramarathon running includes two main types of events: single-stage race (SSR) and multistage races (MSR). Direct comparison of neuromuscular fatigue and recovery after SSR versus MSR race of comparable distance and elevation has never been performed. The aim of this study was to assess neuromuscular fatigue and recovery after two ultramarathons of equal distance performed either (i) in a single stage or (ii) in four successive days.Methods: Thirty-one runners participated in the study: 17 ran 169 km in a single-stage race and 14 performed around 40 km·d over 4 d. The two races were performed on the same course. Neuromuscular function was tested before (PRE), after (POST), and 2 (D + 2), 5 (D + 5) and 10 (D + 10) days after the races. Neuromuscular function was evaluated on both knee extensors (KE) and plantar flexors (PF) with voluntary and evoked contractions using electrical (femoral and tibial, respectively) nerve stimulation.Results: Reduction of voluntary activation measured in the KE was greater (i.e., central fatigue) for SSR than MSR directly after the race (-23% vs -7%), P < 0.01). Reductions in evoked mechanical KE and PF responses on relaxed muscle (i.e., peripheral fatigue) of both KE and PF took longer to recover in MSR than in SSR.Conclusions: Performing prolonged running exercise over several days, each separated by rest, elicits more prolonged impairments in contractile function compared with single-stage ultramarathon, whereas single-stage mountain ultramarathon ran on the same course is associated with greater central fatigue.

Abnormal tracking of the patella is a hallmark sign of patellar instability (PI). Gait deviations and strength deficits may exacerbate abnormal tracking. The identification of modifiable gait deviations and strength deficits can aid in developing more effective management strategies for individuals with PI. The purpose of this study was to identify modifiable gait and strength deficits in subjects with PI.32 subjects (16 PI, 16 controls, 3 males/13 females in each group, 21.1 years old, 23.5 BMI), performed an instrumented gait analysis while walking at 1.5 m per second. Subjects' peak hip adduction angles, external rotation angles, hip abduction moments, knee flexion angles, knee adduction angles, and knee extensor moments were measured during walking. Hip abduction, hip external rotation, and knee extension strength were assessed with a handheld dynamometer.Individuals with PI displayed significantly lower peak knee adduction angles (1.8 ± 2.8° PI, 5.5 ± 4.5° control, p .01) and peak hip abduction moments (0.2 ± 0.1 Nm/kg*m PI, 0.4 ± 0.1 Nm/kg*m control, p .01). Subjects with PI were weaker in knee extension strength (14.5 ± 4.1 kg/m PI, 23.8 ± 7.2 kg/m control, p .01), hip abduction strength (12.1 ± 2.0 kg/m PI, 17.8 ± 4.0 kg/m control, p .01), and hip external rotation strength (5.5 ± 1.9 kg/m PI, 7.1 ± 1.3 kg/m control, p = .01).Subjects with patellar instability have smaller joint moments and a more valgus knee position while walking. Coupled with deficits in muscle strength, this likely contributes to subjective reports of chronic patellar instability.III.

PURPOSE The purpose of this study was to concomitantly investigate the acute and delayed effects of a submaximal eccentric-induced muscle fatigue on the position sense and the neuromuscular function of the right knee extensor muscles. METHODS Thirteen young and physically active participants performed a unilateral isokinetic eccentric exercise of their right lower limb until a decrease in maximal voluntary isometric contraction (MVIC) of 20% was reached. Neuromuscular (i.e., MVIC, voluntary activation (VA) level, and evoked contractile properties [DB100 and DB10]) and psychophysical evaluations (i.e., bilateral position-matching task, perceived muscle soreness, and perceived fatigue) were performed at four time points: before (PRE), immediately after (POST), 24 (POST24), and 48 (POST48) the exercise. RESULTS The acute 20% MVIC reduction (P < 0.001) was associated with both central (i.e., -13% VA decrease, P < 0.01) and peripheral (i.e., -18% and -42% reduction of DB100 and DB10, respectively, P < 0.001) fatigue. In the following days (POST24 and POST48), VA levels had recovered despite the presence of a persisting peripheral fatigue and delayed-onset muscle soreness. Knee position sense, as revealed by position errors, was significantly altered only at POST (P < 0.05) with participants overestimating the length of their knee extensor. Position errors and VA deficits were significantly correlated at POST (r = -0.60, P = 0.03). Position errors returned to nonsignificant control values in the following days. CONCLUSION The acute central fatigue induced by the eccentric exercise contributes to the position sense disturbances. Central fatigue might lead to alterations in the sensory structures responsible for the integration and the processing of position-related sensory inputs.

This study investigated the acute effects of seated and supine knee extension exercise on muscle swelling, torque, and work output. Twelve resistance-trained men performed two isokinetic concentric-only knee-extension training protocols at different hip positions in a counter-balanced order. They completed the knee extension exercise in the seated (hip angle at 85°) and supine (hip angle at 180°) positions. The torque and work output were assessed during each set. Moreover, muscle thickness of the middle and proximal vastus lateralis and rectus femoris were evaluated before and after each protocol and used as an indicator of muscle swelling. Middle rectus femoris and proximal vastus lateralis thickness increased significantly (p=0.01) with no difference between exercise variations. However, the middle vastus lateralis thickness increased (p=0.01) only after the seated knee extension exercise (~7%). Knee extensors’ peak torque and work output were approximately 8% higher (p=0.04) in the seated when compared to the supine hip position. There was a similar decrease in torque and work output throughout both protocols (p=0.98). In conclusion, seated knee extension exercises produced greater torque, work output, and muscle swelling in the vastus lateralis when compared to the supine knee extension exercise.

Leg-extensor rate of power development (RPD) decreases during aging. This study aimed to identify the underlying mechanism of the age-related decline in RPD during a fast acceleration in terms of in vivo vastus lateralis (VL) fascicle shortening behavior. Thirty-nine men aged between 25 and 69 years performed three maximal isokinetic leg-extensor tests with a fixed initial acceleration of 45° knee extension in 150 ms until 340°/s knee angular velocity. RPD, VL activity, and ultrasound images were recorded to assess (relative) fascicle shortening and mean shortening velocity for the phases of electromechanical delay, pretension, and acceleration. Our findings show that fascicle shortening and mean shortening velocity during a fast action increase with aging (0.002 per year, P = .035 and 0.005 s-1 per year, P = .097, respectively), mainly due to a higher amount of shortening in the phase of electromechanical delay. The ratio of VL fascicle length over upper leg length at rest showed a negative correlation (r = -.46, P = .004) with RPD/body mass, while pennation angle at rest showed a trend toward a positive correlation (r = .28, P = .089). To conclude, our findings indicate that the ability to reach high VL fascicle shortening velocities in vivo is not reduced in older men while performing preprogrammed fast accelerations. The greater amount of fascicle shortening in old age is probably the result of age-related differences in the tendinous properties of the muscle-tendon complex, forcing the fascicles to shorten more in order to transmit the muscle force to the segment. ispartof: SCANDINAVIAN JOURNAL OF MEDICINE & SCIENCE IN SPORTS vol:30 issue:10 pages:1878-1887 ispartof: location:Denmark status: published

Purpose: The purpose of this study was to retrospectively investigate the effect of the severity of acute graft-versus-host disease (GVHD) on physical function after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Methods: 76 patients were included as subjects of this study. Severity of acute GVHD was classified according to the method defined by Grucksberg. To evaluate physical function, the knee extensor strength and six-minute walk distance (6MWD) were performed. Results: Among these patients, 54% developed acute GVHD; of these, 32%, 54%, and 15% of patients had grade I, grade II, and grades III–IV GVHD, respectively. In the grade I–II groups, mild acute GVHD following allo-HSCT resulted in a gradual decline in physical function, which improved at discharge. However, in cases of severe acute GVHD, physical function deteriorated, implementation of rehabilitation became difficult, and the decline in physical function persisted even at discharge. Conclusion: These results indicate that severe acute GVHD negatively affects physical function leading to longer hospital days because of inadequate rehabilitation interventions.

Sustained isometric maximal voluntary contractions (IMVCs) have blood flow occlusive effects on the microvasculature. However, it is unknown if this effect would be magnified with additional blood flow restriction via a cuff and what the influence on fatigue development would be. Twelve healthy male participants performed a 1-min IMVC of the knee extensors with and without additional blood flow occlusion induced by pneumatic cuff in counterbalanced order on separate days. Vastus lateralis muscle deoxygenation was estimated via near-infrared spectroscopy–derived tissue oxygen saturation (SmO2) throughout the fatiguing contraction. Central and peripheral measures of neuromuscular fatigue (NMF) were assessed via surface electromyography (EMG) and force responses to voluntary contractions and peripheral nerve/transcranial magnetic stimulations before, immediately after, and throughout an 8-min recovery period. SmO2, force, and EMG amplitude decreased during the 1-min IMVC, but there were no between-condition differences. Similarly, no significant (p > 0.05) between-condition differences were detected for any dependent variable immediately after the fatiguing contraction. Transcranial magnetic stimulation (TMS)-derived voluntary activation was lower (p < 0.05) in the no-cuff condition during the recovery period. Sustained IMVC results in a similar degree of muscle deoxygenation and NMF as IMVCs with additional occlusion, providing further evidence that a sustained IMVC induces full ischemia. Novelty NMF etiology, muscle oxygenation, and corticospinal factors during an IMVC are similar with or without an occlusion cuff. Contrary to all other measures, TMS-evaluated voluntary activation returned to baseline faster following the occluded condition.

This study aimed to evaluate the influence of hamstrings and quadriceps strength on the hamstrings-to-quadriceps conventional (H:Qcon) and functional (H:Qfun) ratios in male soccer players. Quadric...

West, JT, Miller, WM, Jeon, S, and Ye, X. The effects of a preconditioning rolling session on subsequent eccentric exercise-induced muscle damage. J Strength Cond Res 34(8): 2112-2119, 2020-The aim of this study was to examine the effects of a preexercise unilateral quadriceps muscle rolling intervention on subsequent ipsilateral (IPSI) or contralateral (CTRA) knee extension eccentric exercise-induced muscle damage. Twenty-seven healthy volunteers (14 men) underwent an eccentric exercise protocol (6 sets of 10 repetitions with 75% of the maximal isometric strength) with a single-leg knee extension machine. Before the eccentric exercise, the subjects were randomly assigned to either (a) IPSI group: rolling the ipsilateral knee extensor muscles, (b) CTRA: rolling the contralateral muscles, or (c) Control: sitting for 6 minutes (same duration as the rolling intervention protocol) relaxed. The muscle soreness, passive knee extension range of motion, and knee extension isometric strength were measured before, immediately, 24 hours, and 48 hours after exercise. The magnitudes of the range of motion decrement were attenuated in both the IPSI (p = 0.031) and CTRA (p = 0.014) groups 24 hours after the eccentric exercise, when compared with the control. Isometric strength (p = 0.783) and muscle soreness (p = 0.586) responses were not significantly different among the 3 groups (time points and sexes merged). Additionally, women displayed an overall faster recovery than men in isometric strength (p = 0.001) and muscle soreness (p = 0.024), evidenced by the measurements at 48 hours after exercise. Our study suggests that unilateral quadriceps rolling intervention before high-intensity muscle-damaging exercise has a beneficial effect on maintaining range of motion in both the ipsilateral and contralateral muscles.

Electrotherapy modalities are one of the increasing ways of muscle strength and endurance. However, it is not clear which electrotherapy modalities are more effective. The purpose of this study is to compare the effect of Russian current (RC) and high voltage pulsed current (HVPC) on the strength and endurance of the quadriceps muscle. The study was performed on 10 volleyball athletes. The participants’ extremities were divided into two groups as RC and HVPC. Muscle strength and endurance levels were assessed by an isokinetic device. Isokinetic training and 20-min electrotherapy were given in each treatment session. This training program consisted of a total of 12 sessions, scheduled twice a week for 6 weeks. After training, knee extensor peak torque values and endurance ratios have increased in both groups, but it was determined that this increase was only significant in terms of the endurance ratio (P0.05). RC or HVPC have no advantages over each other, and therefore it has been determined that both currents can be used in order to strengthen muscles and increase muscular endurance. Additional studies whose longer-term effects will investigate are needed.

Diabetes peripheral neuropathy (DPN) leads to balance impairment among diabetes mellitus (DM). The aims of this study were to (1) distinguish between DM patients who have/do not have DPN and to (2) compare quadriceps’ strength and balance performance of DM, DPN, and healthy groups. Fifteen healthy females and 33 females with type 2 diabetic patients participated. The electrodiagnostic method was used to classify diabetic patients into DM and DPN. A dynamometer was used to measure quadriceps’ strength. Single-leg standing on a force plate was also used to quantify participants’ balance. Smaller conduction velocity and amplitude and greater distal latency of all nerves were observed in the DPN compared with the DM in particular for sensory nerve. In DPN, conduction velocity was asymmetrical. The quadriceps’ strength of both legs in DPN and the right leg in DM was smaller than in the control group. The root mean square of the center of pressure was similar between DM and DPN. But it was larger in DPN than in the control group. DPN is associated with asymmetrical conduction velocity, smaller quadriceps’ strength, and weaker balance performance that is suggestive of higher risk of falling. Balance training is recommended for the DPN group during their rehabilitation to reduce their falling risk.

To assess if the alteration of neuromuscular properties of knee extensors muscles during heavy exercise co-vary with the SCV ($${\dot{{\rm{V}}}{\rm{O}}}_{2}$$V̇O2 slow component), eleven healthy male participants completed an incremental ramp test to exhaustion and five constant heavy intensity cycling bouts of 2, 6, 10, 20 and 30 minutes. Neuromuscular testing of the knee extensor muscles were completed before and after exercise. Results showed a significant decline in maximal voluntary contraction (MVC) torque only after 30 minutes of exercise (−17.01% ± 13.09%; p

The movement pattern during stair descent differs by gender, and this difference may be associated with gender differences in muscle strength or activation. The purpose of this study was to determine whether a gender difference in muscle activation exists by comparing the muscle activation amplitude and co-activation of lower extremity muscles during the stair-to-ground descent transition. Fifteen men and thirteen women descended stairs and the muscle activation was measured. Women showed a significantly lower peak normalized electromyography amplitude of the vastus lateralis (women: 171.7% peak EMG activation amplitude for level walking (PEALW), men: 297.0%PEALW, p

[Purpose] The mortality rate increases when peak oxygen uptake is less than 5 metabolic equivalents, and peak oxygen uptake correlates with knee extensor muscle strength. This study aimed to determine the knee extensor muscle strength at peak oxygen uptake corresponding to 5 metabolic equivalents. [Participants and Methods] We enrolled 45 consecutive patients (29 males and 16 females; average age, 63.6 ± 13.7 years) with heart disease receiving outpatient rehabilitation with us. We performed cardiopulmonary exercise testing with a bicycle ergometer to measure peak oxygen uptake. We investigated the relationship between peak oxygen uptake and isometric knee extensor muscle strength divided by the body weight (kgf/kg). The cutoff value for knee extensor muscle strength with peak oxygen uptake corresponding to 5 metabolic equivalents was calculated. [Results] Knee extensor muscle strength was significantly positively associated with peak oxygen uptake. The cutoff value for knee extensor muscle strength at peak oxygen uptake corresponding to 5 metabolic equivalents was 0.46 kgf/kg. [Conclusion] In this study, the cutoff value for knee extensor muscle strength for achieving peak oxygen uptake corresponding to 5 metabolic equivalents in patients with heart disease was 0.46kgf/kg.

Recovery stepping in response to forward slips has the potential to not only rebuild the base of support to prevent backward falling, but also provide extra limb support to prevent downward falling. Hence, recovery stepping is often necessary for fall prevention following an unexpected slip. However, less is known about whether recovery foot placement could affect the likelihood of recovery following a slip. The purpose of this study was to determine whether there is an optimal recovery landing zone within which older adults have a higher likelihood of recovery. 195 participants experienced a novel, unannounced forward slip while walking on a 7-m walkway. The center of mass (COM) stability (computed from its position and velocity), vertical limb support (computed from change in hip kinematics), and recovery limb joint moments (computed from joint kinematics and ground reaction force) in the sagittal plane were analyzed. The results showed that a longer distance between recovery foot landing position and the projected COM position at recovery foot touchdown (relative recovery step placement) was conducive to stability improvement but adverse to limb support enhancement, and vice versa for a shorter distance. Relative recovery step placement could predict the recovery likelihood with an accuracy of 67.3%, and the recovery rate was greater than 50% when the distance between recovery foot and COM is less than 0.3 × foot length. This study also found more posterior stepping could be attributed to insufficient ankle plantar flexor and hip flexor moments in the pre-swing phase, while more anterior stepping was induced by insufficient hip and knee extensor moments in the following swing phase.

AIM To assess effects of growth on lower limb maximal isometric muscle strength (MIMS) development in children with developmental coordination disorder (DCD). METHOD This observational study used hand-held dynamometry to evaluate MIMS (hip abductors, flexors, extensors; knee flexors and extensors; ankle dorsiflexors) in children with DCD (n=33, 12 females, 21 males, 6-12y, mean [SD] age 9y [2y]). Regression analysis compared changes in MIMS for similar changes in growth (height or body mass) for children with DCD and typically developing children (pre-existing database, n=183), controlling for age and sex. RESULTS For the same height gain, the gain in muscle strength was 37.3% to 69.2% less in children with DCD compared with typically developing children, with significantly lower slopes (p-value between

Graja, A, Kacem, M, Hammouda, O, Borji, R, Bouzid, MA, Souissi, N, and Rebai, H. Physical, biochemical, and neuromuscular responses to repeated sprint exercise in eumenorrheic female handball players: effect of menstrual cycle phases. J Strength Cond Res 36(8): 2268-2276, 2022-Very few studies have been interested in the relationship between ovarian hormones and physiological function in female athletes. The aim of this study was to assess the effect of menstrual phases (MP) on physical, neuromuscular, and biochemical responses after repeated sprint exercise (RSE) in female handball players. Ten eumenorrheic athletes (22.5 ± 1.5 years, 1.70 ± 0.04 m) participated in 3 study visits (follicular phase [FP], luteal phase [LP], and premenstrual phase [PMP]). During each MP, they performed 20 × 5-second cycle sprints interspersed with 25 seconds of rest. Maximal voluntary contraction (MVC) tests of the knee extensor muscles at 90° of knee flexion were performed before and after RSE. Peak force and electromyography (EMG) signals were measured during the MVC tests. Blood samples were collected before and 3 minutes after each session. The percentage of decrement in peak power output over the 20 × 5-second cycle test (i.e., fatigue index) calculated between sprints 1 and 20 decreased significantly during PMP (-43.3% ± 5.7%) but not in LP (-39.2% ± 7.7%) compared with FP (-32.44% ± 6.3%) ( p0.05). Moreover, no significant difference was found between MP in all frequency components of EMG before RSE ( p0.05). Maximal voluntary contraction, neuromuscular efficiency, and median frequency values of vastus lateralis and rectus femoris were significantly decreased in PMP compared with FP and LP ( p0.05). Creatine kinase (CK) levels were significantly higher in PMP compared with FP and LP after RSE ( p0.05). These findings suggest that RSE induces more peripheral fatigue associated with muscle damage in PMP. This might be attributable to hormonal variation across MP. Therefore, FP seems to be the right time for intense training to improve strength performance.

Purpose: To compare the effects of 2 different intensity distribution training programs (threshold [THR] and polarized [POL]) on fat metabolism and neuromuscular variables. Methods: Twenty ultrarunners were allocated to POL (n = 11; age 40.6 [9.7] y, weight 73.5 [10.8] kg, VO2max 55.8 [4.9] mL·kg−1·min−1) or THR group (n = 9; age 36.8 [9.2] y, weight 75.5 [10.4] kg, VO2max 57.1 [5.2] mL·kg−1·min−1) and performed a 12-week training program that consisted of 5 running sessions, 2 strength sessions, and 1 day of full rest per week. Both groups performed similar total training duration and load but with different intensity distribution during running sessions. Resting metabolic rate, fat metabolism, isometric rate of force development (RFD; N·s−1) and maximal voluntary contraction in the knee extensor, and electromyographic amplitude were measured before and after each program. Results: A significant decrease in RFD0–100 ms (Δ −13.4%; P ≤ .001; effect size [ES] = 1.00), RFD0–200 ms (Δ −11.7%; P ≤ .001; ES = 1.4), and RFDpeak (Δ −18%; P ≤ .001; ES = 1.4) were observed in the POL group. In THR group, a significant increase in mean electromyographic amplitude (Δ 24.4%; P = .02; ES = 1.4) was observed. There were no significant differences between groups in any of the variables. Conclusions: Similar adaptations in fat metabolism and neuromuscular performance can be achieved after 12 weeks of POL or THR intensity distribution. However, THR distribution appears to better maintain strength (RFD) and improve mean electromyographic amplitude. Nevertheless, the combination of both running and maximum strength training could influence on results because of the residual fatigue thus inducing suboptimal adaptations in the POL group.

To examine the effects of a rural community-based program integrating health education and self-directed home-based resistance training on the mobility function of older women with knee osteoarthritis (OA). Participants were assigned to the control (CON) or intervention (INT) group. Participants completed a mobility function assessment and questionnaire evaluation. The CON group received only the health education program and the INT group also participated in resistance training for 5 months. Primary outcomes were mobility function measured using a timed chair stand (TCS), timed up & go (TUG), gait speed (GS), and knee extensor strength (KES). We evaluated body composition and questionnaire results (WOMAC score, SARC-F scale, and SOF index) as secondary outcomes. There were significant differences in the interactions of group-by-time effects for TCS (p

The force-generating capacities of human skeletal muscles are interrelated, highlighting a common construct of limb strength. This study aimed to further determine whether there is an intermuscular relationship in maximal voluntary activation capacities and contractile kinetics of human muscles. Twenty-six young healthy individuals participated in this study. Isometric maximal voluntary contraction (MVC) torque, voluntary activation level (VAL), and doublet twitch contractile kinetics (contraction time and half-relaxation time) evoked by a paired supramaximal peripheral nerve stimulation at 100 Hz were obtained in elbow flexors, knee extensors, plantar flexors and dorsiflexors of the dominant limb. Peak MVC torque had significant positive correlations between all muscle group pairs (all P values

[Purpose] One-repetition maximum is an essential statistic for physical therapists and coaches in rehabilitation and athletic settings. In a previous study, we showed that one-repetition maximum of the knee extensor could be predicted more accurately with the combination of maximal voluntary isometric contraction strength, as measured by a handheld dynamometer, muscle thickness, and thigh circumference, in young adults. However, there has been no study in older adults investigating the relationship between one-repetition maximum and maximal voluntary isometric contraction strength, or muscle thickness, and thigh circumference. Therefore, the aim of this study was to investigate the relationship between one-repetition maximum and maximal voluntary isometric contraction strength, or muscle thickness, and thigh circumference in older adults. [Participants and Methods] Twenty-eight older community-dwelling adults (18 males and 10 females) participated in this study. Muscle strength of the knee extensor was measured using one-repetition maximum and maximal voluntary isometric contraction strength. In addition, muscle thicknesses of the refutes femoris and the vastus intermedius, and thigh circumference were measured using ultrasonography and measuring tape, respectively. [Results] Stepwise regression analysis revealed that body mass, gender, thigh circumference at 15 cm above the patella, and maximal voluntary isometric contraction strength were significant and independent determinants (R2=0.868). [Conclusion] One-repetition maximum could be predicted more accurately using a combination of maximal voluntary isometric contraction strength, as measured with a handheld dynamometer, and thigh circumference in older adults.

Background: Aging results in adaptations which may affect the control of motor units. Objective: We sought to determine if younger and older men recruit motor units at similar force levels. Design: Cross-sectional, between-subjects design. Setting: Controlled laboratory setting. Participants: Twelve younger (age = 25 ± 3 years) and twelve older (age = 75 ± 8 years) men. Measurements: Participants performed isometric contractions of the dominant knee extensors at a force level corresponding to 50% maximal voluntary contraction (MVC). Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis. A surface EMG signal decomposition algorithm was used to quantify the recruitment threshold of each motor unit, which was defined as the force level corresponding to the first firing. Recruitment thresholds were expressed in both relative (% MVC) and absolute (N) terms. To further understand age-related differences in motor unit control, we examined the mean firing rate versus recruitment threshold relationship at steady force. Results: MVC force was greater in younger men (p = 0.010, d = 1.15). Older men had lower median recruitment thresholds in both absolute (p = 0.005, d = 1.29) and relative (p = 0.001, d = 1.53) terms. The absolute recruitment threshold range was larger for younger men (p = 0.020; d = 1.02), though a smaller difference was noted in relative terms (p = 0.235, d = 0.50). These findings were complimented by a generally flatter slope (p = 0.070; d = 0.78) and lower y-intercept (p = 0.009; d = 1.17) of the mean firing rate versus recruitment threshold relationship in older men. Conclusion: Older men tend to recruit more motor units at lower force levels. We speculate that recruitment threshold compression may be a neural adaptation serving to compensate for lower motor unit firing rates and/or denervation and subsequent re-innervation in aged muscle.

International audience; Physiological signals present fluctuations that can be assessed from their temporal structure, also termed complexity. The complexity of a physiological signal is usually quantified using entropy estimators, such as Sample Entropy. Recent studies have shown a loss of force signal complexity with the development of neuromuscular fatigue. However, these studies did not consider the stationarity of the force signals which is an important prerequisite of Sample Entropy measurements. Here, we investigated the effect of the potential nonstationarity of force signals on the kinetics of neuromuscular fatigue-induced change in force signal's complexity. Eleven men performed submaximal intermittent isometric contractions of knee extensors until exhaustion. Neuromuscular fatigue was assessed from changes in voluntary and electrically evoked contractions. Sample Entropy values were computed from submaximal force signals throughout the fatiguing task. The Dickey-Fuller test was used to statistically investigate the stationarity of force signals and the Empirical Mode Decomposition was applied to detrend these signals. Maximal voluntary force, central voluntary activation and muscle twitch decreased throughout the task (all p < 0.05), indicating the development of global, central and peripheral fatigue, respectively. We found an increase in Sample Entropy with fatigue (p = 0.024) when not considering the nonstationarity of force signals (i.e. 43% of the signals). After applying the Empirical Mode Decomposition, we found a decrease in Sample Entropy with fatigue (p = 0.002). These findings confirm the presence of nonstationarity in force signals during submaximal isometric contractions which influences the kinetics of change in Sample Entropy with neuromuscular fatigue.