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Purpose: This study explored the effects of 4 bench-press (BP) training programs with different velocity-loss (VL) thresholds (0%, 15%, 25%, and 50%) on strength gains and neuromuscular adaptations. Methods: Forty-six resistance-trained men (22.8 [4.4] y) were randomly assigned into 4 groups that differed in the VL allowed within the set: 0% (VL0), 15% (VL15), 25% (VL25), and 50% (VL50). Training loads (40%–55% 1-repetition maximum), frequency (2 sessions/wk), number of sets (3), and interset recovery (4 min) were identical for all groups. Participants completed the following tests before and after an 8-week (16-session) BP training program: (1) maximal isometric test, (2) progressive loading test, and (3) fatigue test in the BP exercise. During all tests, triceps brachii muscle electromyography was assessed. Results: After completing the resistance-training program, no significant group × time interactions were noticed for isometric and dynamic BP strength variables. The dose–response relationship exhibited an inverted U-shaped relationship pattern, with VL25 showing the greatest effect sizes for almost all strength variables analyzed. The total number of repetitions performed during the training program increased as the VL magnitude increased. Conclusions: The group that trained with high VL threshold (50%), which performed a total of 876 repetitions, did not experience additional strength gains compared with those experienced by the 0%, 15%, and 25% of VL groups, which performed significantly fewer repetitions (48, 357, and 547, respectively). These findings suggest that when light loads (40%–55% 1-repetition maximum) are used, low and moderate VL thresholds (0%–25%) provide a higher training efficiency. [ABSTRACT FROM AUTHOR]

Different forearm postures can modulate corticospinal excitability. However, there is no consensus on whether handedness plays a role in such a mechanism. This study investigated the effects of 3 forearm postures (pronation, neutral, and supination) on the corticospinal excitability of muscles from the dominant and nondominant upper limbs. Surface electromyography was recorded from the abductor digiti minimi, flexor pollicis brevis, and flexor carpi radialis from both sides of 12 right-handed volunteers. Transcranial magnetic stimulation pulses were applied to each muscle's hotspot in both cerebral hemispheres. Motor-evoked potential peak-to-peak amplitude and latency and resting motor threshold were measured. The data were evaluated by analysis of variance. The level of significance was set at 5%. The resting motor threshold was similar for the 3 muscles and both sides. Motor-evoked potential peak-to-peak amplitude from flexor pollicis brevis was lower during supination, and the dominant upper limb latency was longer. The flexor carpi radialis presented lower motor-evoked potential peak-to-peak amplitudes for neutral and shorter latencies during supination. Abductor digiti minimi seemed not to be affected by posture or side. Different muscles from dominant and nondominant sides may undergo corticospinal modulation, even distally localized from a particular joint and under rest. [ABSTRACT FROM AUTHOR]

Musculoskeletal modeling, typically implemented using marker-based systems in laboratory environments, is commonly used for noninvasive estimations of loads. Inertial measurement units (IMUs) have become an alternative for the evaluation of kinematics. However, estimates of spine joint contact forces using IMUs have yet to be thoroughly evaluated. Dynamics tasks and static postures from activities of daily living were captured on 11 healthy subjects using both systems simultaneously. Spine kinematics obtained from IMU- and marker-based systems and L4–L5 joint contact forces were compared. Lateral bending resulted in a weak agreement with significant differences between the 2 systems (P =.02, average root mean-squared error = 4.81), whereas flexion–extension and axial rotation exhibited the highest agreement with no significant differences (P <.05, average root mean-squared error = 5.51 and P <.31, average root mean-squared error = 5.08, respectively). All tasks showed excellent correlations (R2 =.76–.99) in estimated loads between systems. Differences in predicted loads at the L4–L5 were only observed during flexion–extension (1041 N vs 947 N, P =.0004) and walking with weights (814 N vs 727 N, P =.004). Different joint reaction force outcomes were obtained in 2 of the 8 tasks between systems, suggesting that IMUs can be robust tools allowing for convenient and less expensive evaluations and for longitudinal assessments inside and outside the laboratory setting. [ABSTRACT FROM AUTHOR]

This study aimed to clarify the differences in muscular coordination during butterfly swimming between high- and low-performance swimmers using muscle synergy analysis. Eight female competitive swimmers and 8 female recreational swimmers participated in this study. The participants swam a 25-m butterfly stroke with maximum effort. Surface electromyography was measured from 12 muscles and muscle synergy analysis was performed from the data using nonnegative matrix factorization algorithms. From the results of the muscle synergy analysis, 4 synergies were extracted from both groups. Synergies 1 and 2 were characterized by coactivation of the upper and lower limb muscles in the recreational swimmers, whereas only synergy 1 was characterized by this in the competitive swimmers. Synergy 3 was involved in arm recovery in both groups. Synergy 4 was only involved in the downward kick in the competitive swimmers. From these results, it can be concluded that muscle synergies with combined coordination of upper and lower limb muscles were extracted more in the recreational swimmers and that the competitive swimmers controlled the downward kick with an independent synergy and that the adjustment of the timing of the downward kick may be an important factor for the efficient performance of butterfly swimming. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the influence of knee joint range of motion (RoM) on the torque–velocity relationship and fatigue in the knee extensor muscles of 7 young (median = 26 y) and 7 older (68 y) adults. Each leg was assigned a RoM (35° or 75°) over which to perform a torque–velocity protocol (maximal isokinetic contractions, 60–300°·s−1) and a fatigue protocol (120 maximal contractions at 120°·s−1, 0.5 Hz). Six older participants were unable to reach 300°·s−1 over 35°. Therefore, the velocity eliciting 75% of peak torque at 60°·s−1 (V75, °·s−1) was calculated for each RoM from a fit of individual torque–velocity curves (60–240°·s−1), and ΔV75 (35°–75°) was determined. Fatigue (final torque/initial torque) was used to calculate Δfatigue (35°–75°). ΔV75 was not different from 0 in young (−28.3°·s−1 [−158.6 to 55.7], median [range], P =.091) or older (−18.5°·s−1 [−95.0 to 23.9], P =.128), with no difference by age (P =.710). In contrast, fatigue was greater for 75° in young (Δfatigue = 25.9% [17.5–30.3], P =.018) and older (17.2% [11.9–52.9], P =.018), with no effect of age (P =.710). These data indicate that, regardless of age, RoM did not alter the torque–velocity relationship between 60 and 240°·s−1, and fatigue was greater with a larger RoM. [ABSTRACT FROM AUTHOR]

Background: Relative energy deficiency in sport (REDs) is a condition that is associated with negative health and performance outcomes in athletes. Insufficient energy intake relative to exercise energy expenditure, resulting in low energy availability, is the underlying cause, which triggers numerous adverse physiological consequences including several associated with musculoskeletal (MSK) health and neuromuscular performance. Purpose: This commentary aims to (1) discuss the health and performance implications of REDs on the skeletal and neuromuscular systems and (2) examine the role that MSK training (ie, strength and plyometric training) during treatment and return to performance following REDs might have on health and performance in athletes, with practical guidelines provided. Conclusions: REDs is associated with decreases in markers of bone health, lean body mass, maximal and explosive strength, and muscle work capacity. Restoration of optimal energy availability, mainly through an increase in energy intake, is the primary goal during the initial treatment of REDs with a return to performance managed by a multidisciplinary team of specialists. MSK training is an effective nonpharmacological component of treatment for REDs, which offers multiple long-term health and performance benefits, assuming the energy needs of athletes are met as part of their recovery. Supervised, prescribed, and gradually progressive MSK training should include a combination of resistance training and high-impact plyometric-based exercise to promote MSK adaptations, with an initial focus on achieving movement competency. Progressing MSK training exercises to higher intensities will have the greatest effects on bone health and strength performance in the long term. [ABSTRACT FROM AUTHOR]

The purposes of this study were to clarify the electromyography (EMG) of plantar flexors and to analyze the fascicle and tendon behaviors of the gastrocnemius medialis (GM) during running in the carbon-fiber plate embedded in thicker midsole racing shoes, such as the Nike ZoomX Vaporfly (VF) and traditional racing shoes (TRAD). We compared the fascicle and series elastic element behavior of the GM and EMG of the lower limb muscles during running (14 km/h, 45 s) in athletes wearing VF or TRAD. GM EMGs in the push-off phase were approximately 50% lower in athletes wearing VF than in TRAD. Although the series elastic element behavior and/or mean fascicle-shortening velocity during the entire stance phase were not significantly different between VF and TRAD, a significant difference was found in both the mean EMG and integral EMG of the GM during the push-off phase. EMG of the gastrocnemius lateralis (GL) during the first half of the push-off phase was significantly different between VF and TRAD. Present results suggest that VF facilitates running propulsion, resulting in a decrease in GM and GL EMGs at a given running velocity during the push-off phase, leading to a reduction in metabolic cost. [ABSTRACT FROM AUTHOR]

Background: Local high-frequency percussive (HFP) massage has recently found widespread application in physical therapy. Although HFP massage reportedly improves range of motion (ROM), the mechanism underlying its action has not yet been proven. This study aimed to clarify whether a 5-minute percussive massage regimen affects muscular or connective tissues, such as the deep fascia and deep intermuscular fascia and the change in joint ROM. Method: The study sample was calculated using G*Power analysis program, and this study enrolled 15 healthy men who underwent 5-minute HFP massage to the medial gastrocnemius muscle. Shear-wave elastography was used to measure tissue stiffness in the deep fascia, muscle, and deep intermuscular fascia through shear-wave velocity as well as the ROM of the volunteers' ankle joint dorsiflexion before and after the HFP massage. A value of P < .05 was used to declare statistical significance, and post hoc was used to calculate the effect size using G*Power. Results: Shear-wave velocity revealed a significant change in the deep fascia (P = .003; shear-wave velocity: -0.7 m/s) and significant increase in ROM of ankle dorsiflexion (P = .002; increase in ROM: 3.0°) after 5 minutes of HFP massage. However, the muscle and deep intermuscular fascia did not exhibit any significant changes. Conclusions: HFP massage for 5 minutes modified the stiffness of the deep fascia and concurrently improved the ankle joint-dorsiflexion ROM. This method can be used as an intervention to decrease stiffness of the deep fascia and increase the ROM efficiently. [ABSTRACT FROM AUTHOR]

Nitrate ( NO 3 − ) has properties that can improve muscle function, leading to improvements in metabolic cost of exercise as well as enhance force production. Gymnastics is a whole-body sport, involving events that demand a high level of strength and fatigue resistance. However, the effect of NO 3 − supplementation on both upper- and lower-body function in gymnasts is unknown. This study examined the effect of acute beetroot juice (BRJ) supplementation on isokinetic strength and endurance of the upper- and lower-body in highly trained international-level male gymnasts. In a double-blind, randomized crossover design, 10 international-level male gymnasts completed two acute supplementation periods, consuming either 2 × 70 ml NO 3 − -rich (∼12.8 mmol/L of NO 3 − ) or NO 3 − -depleted (PLA) BRJ. Maximal strength of the upper-leg and upper-arm at 60°/s, 120°/s, 180°/s, and 300°/s, and muscular endurance (50 repeated isokinetic contractions at 180°/s) were assessed. Plasma NO 3 − (BRJ: 663 ± 164 μM, PLA: 89 ± 48 μM) and nitrite ( NO 2 − ) concentrations (BRJ: 410 ± 137 nmol/L, PLA: 125 ± 36 nmol/L) were elevated following BRJ compared to PLA (both p <.001). Maximal strength of knee and elbow extensors and flexors did not differ between supplements (p >.05 for all velocities). Similarly, fatigue index of knee and elbow extension and flexion was not different between supplements (all p >.05). Acute BRJ supplementation, containing ∼12.8 mmol/L of NO 3 − , increased plasma NO 3 − and NO 2 − concentrations, but did not enhance isokinetic strength or fatigue resistance of either upper or lower extremities in international-level male gymnasts. [ABSTRACT FROM AUTHOR]

Purpose: Core strength is vital for athletic performance, and many more exercises that involve the kinetic chain have been designed for able-bodied athletes. Disabilities that impair the kinetic chain can reduce the effectiveness of strength training. However, the impact of amputation on core strength training of people with disabilities and its underlying mechanism remains unclear. This study aimed to evaluate the muscle activation patterns and levels in athletes with amputation during 4 basic and modified weight-bearing core strength-training exercises. Methods: Fifteen elite athletes with unilateral amputation (170.6 [7.3] cm; 63.9 [11.9] kg; 25.9 [5.3] y) volunteered for this study. Surface electromyography was used to measure the muscle activity mainly in the lumbopelvic–hip complex-stabilizing muscles during 4 kinetic chain trunk exercises with and without modifications. Results: The significance level was set at α =.05. The results showed a significant difference in muscle activation between different body sides (P <.05). Specifically, amputation on the support position resulted in a diagonal pattern of muscle activation, and amputation on the free distal segments resulted in a unilateral dominant pattern with higher activation in muscles on the nonamputated side (P <.05). Modifications led to significant decreases in muscle activation asymmetry index (P <.05). Conclusions: Amputation caused muscle activation asymmetry and 2 activation patterns. Modifications by enhancing proximal stability and adjusting distal loading effectively reduced the asymmetry of muscle activation. Coaches and clinicians can use these results to tailor exercises for athletes with disabilities in training and rehabilitation. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the relationship between items of the Short Recovery and Stress Scale (SRSS) related to physical stress and recovery and the biomarker creatine kinase (CK) in professional handball. Methods: CK and SRSS items (physical performance capability, overall recovery, muscular stress, and overall stress) were assessed in an observational study of 16 adult male professional handball players from a team in the highest German league during the 2019–20 preseason. Their preseason training schedule included several microcycles, each consisting of 3 consecutive days of intense training followed by a rest day. On 5 of these rest days, when players were classified as nonrested, and the 5 immediately following days, when players were classified as rested, players completed the SRSS between 8:00 and 9:00 AM, followed by blood sampling. Correlations between SRSS items were performed using Kendall τ. The relationship between each SRSS item and CK levels over time was examined using a mixed-effects model with a random intercept. Results: CK levels and SRSS stress items were significantly higher and SRSS recovery items were significantly lower in nonrested players. SRSS items were significantly positively or negatively correlated (all items: P <.001) and showed a significant effect indicating lower CK levels in rested players (all items: P ≤.001; η p 2 =.1 −.32). Conclusions: The investigated SRSS items may be a viable option for assessing muscle recovery in adult male professional handball players in a cost-effective and noninvasive manner. They can be used as a single monitoring tool or as part of a multimodal approach. [ABSTRACT FROM AUTHOR]

Purpose: An inspiratory muscle warm-up (IMW) improves inspiratory muscle function, but the effects of high-intensity exercise are inconsistent. We aimed to determine the effects of high-intensity IMW on high-intensity exercise performance and muscle oxygenation. Methods: Ten healthy men (maximal oxygen uptake [ V ˙ O 2 max ] 52.2 [5.0] mL·kg–1·min–1) performed constant-load exercise to exhaustion on a cycle ergometer at V ˙ O 2 max under 2 IMW conditions: a placebo condition (PLA) and a high-intensity IMW condition (HIGH). The inspiratory loads were set at 15% and 80% of maximal inspiratory pressure, respectively. Maximal inspiratory pressure was measured before and after IMW. Oxyhemoglobin was measured in the vastus lateralis by near-infrared spectroscopy during exercise. Rating of perceived exertion (RPE) for a leg was measured after 1 and 2 minutes of exercise. Results: Exercise tolerance was significantly higher under HIGH than PLA (228 [49] s vs 218 [49] s, P =.003). Maximal inspiratory pressure was significantly increased by IMW under HIGH (from 125 [20] to 136 [25] cm H2O, P =.031). Oxyhemoglobin was significantly higher under HIGH than PLA at 80% of the total duration of exercise (P =.048). RPE for the leg was significantly lower under HIGH than PLA after 2 minutes of exercise (P =.019). Conclusions: Given that oxyhemoglobin is an index of local oxygen supply, the results of this study suggest that high-intensity IMW increases the oxygen supply to active limbs. It may also reflect a reduction in RPE in the leg. In addition, high-intensity IMW may improve exercise performance. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the dose–response effect of a high-load, 6-repetition, maximum effort inertial flywheel (IFw) squat postactivation performance enhancement (PAPE) protocol on countermovement jump (CMJ) performance metrics. Thirteen subjects completed 5 squat testing sessions: 1 session to determine back-squat 6-repetition maximum, 1 session to determine 6-repetition maximum IFw load, and 3 sessions to investigate the dose–response effect of an IFw PAPE protocol set at the load determined in the second session. In the IFw PAPE sessions, subjects completed either 1, 2, or 3 sets of IFw squats, then performed 5 CMJs over 12 minutes (1, 3, 6, 9, and 12 min post-IFw). All CMJ tests were conducted on a force platform where CMJ performance outcomes and impulse variables were calculated. There was no main time or volume effect for jump height, contact time, reactive strength index, peak force, or any of the impulse variables. A main time effect was identified for flight time (P =.006, effect size = 0.24) and peak power (P =.001, effect size = 0.28). The lack of change in jump height may indicate that too much fatigue was generated following this near-maximal IFw squat protocol, thereby reducing the PAPE effect. [ABSTRACT FROM AUTHOR]

Context: Anterior cruciate ligament injuries are directly related to the control of dynamic knee valgus in the landing of a jump, and this is mainly due to the correct activation and neuromuscular function of the lower-extremity muscles. The aim of the study is to assess the relationship between lower limb muscle activity during a single-legged drop jump and knee frontal plane projection angle (FPPA). Design: A correlation study. Methods: Thirty healthy collegiate female athletes were included in the study. Main outcomes measures were peak knee FPPA and muscle activity (% of maximal voluntary isometric contraction). Peak knee FPPA during a single-legged drop jump test was identified using a 2-dimensional motion analysis system. Muscle activity was assessed using a surface electromyograph for gluteus maximus, gluteus medius, biceps femoris, semitendinosus, vastus medialis quadriceps, vastus lateralis quadriceps, medial gastrocnemius, and lateral gastrocnemius. All variables were assessed for both dominant and nondominant limbs. A correlation analysis between peak knee FPPA and muscle activity was performed. Statistical significance was set at P <.05. Results: A mean peak knee FPPA of 14.52° and 13.38° was identified for dominant and nondominant limb single-legged drop jump test, respectively. Muscle activity (% of maximal voluntary isometric contraction) for muscles assessed ranged from 43.97% to 195.71% during the single-legged drop jump test. The correlation analysis found no significant correlation between any of the muscles assessed and peak knee FPPA during the single-legged drop jump test (Pearson coefficient between −.3 and.1). Conclusions: There is no association between muscle activity from the lower limb muscles and the knee FPPA during a single-legged drop jump in female athletes. Thus, different muscle properties should be assessed in order to understand such an important movement as the knee FPPA during a jump. [ABSTRACT FROM AUTHOR]

Androgen deprivation therapy (ADT) forms the cornerstone in the treatment of advanced prostate cancer. However, by suppressing testosterone ADT results in a decrease of skeletal muscle mass. In this narrative review, we explore the magnitude and mechanisms of ADT-induced muscle mass loss and the consequences for muscle strength and physical performance. Subsequently, we elucidate the effectiveness of supervised resistance exercise training as a means to mitigate these adverse effects. Literature shows that resistance exercise training can effectively counteract ADT-induced loss of appendicular lean body mass and decline in muscle strength, while the effect on physical performances is inconclusive. As resistance exercise training is feasible and can be safely implemented during ADT (with special attention for patients with bone metastases), it should be incorporated in standard clinical care for prostate cancer patients (starting) with ADT. [ABSTRACT FROM AUTHOR]

Introduction: This case study aimed to describe potential changes in neuromuscular activation and synergies after an 8-day cross-country mountain-bike stage race. Methods: A peak power output test was performed 5 days before the race. Two days before the start and after 7 days of racing, the athlete performed a power-based Lamberts Submaximal Cycling Test, including surface electromyography, and completed a Daily Analysis of Life Demands of Athletes questionnaire. Neuromuscular activation, in terms of root mean square, timing (onset-offset) of muscle activation, and synergies, was obtained from electromyography recordings. Results: The athlete reported an increase in symptoms of experienced stress after the stage race on the Daily Analysis of Life Demands of Athletes questionnaire. Both biceps femoris and tibialis anterior muscles showed a reduction in normalized amplitude after the stage race. In addition, the number of synergies that was necessary to describe neuromuscular activation increased from 2 to 3. Conclusions: In this case study, the increase in synergies suggests that, after the stage race, the athlete showed a more complex muscle-recruitment pattern. This may indicate that muscle coordination can change when muscle fatigue occurs; however, further research is needed to confirm these results in a larger sample. [ABSTRACT FROM AUTHOR]

Context: Plantar intrinsic foot muscle strength training is difficult to master to a degree sufficient to elicit muscle hypertrophy in most individuals. It is possible that combining neuromuscular electrostimulation (NMES) and blood flow restriction (BFR) can elicit plantar intrinsic foot muscle hypertrophy regardless of the individual's technique. This study aimed to determine the effects of NMES training with BFR on acute muscle swelling in the abductor hallucis. Design: Randomized, controlled, single-blind trial design. Methods: Forty-eight participants were randomly allocated to the NMES + BFR, NMES, or Sham NMES + BFR groups. All participants received abductor hallucis NMES for 15 minutes. Participants in the NMES + BFR and Sham NMES + BFR groups received NMES with BFR. The intensity of NMES was the sensory threshold in the Sham NMES + BFR group. The cross-sectional area of the abductor hallucis was measured pretraining and posttraining using ultrasonography by a single investigator blinded to the participants' allocations. Results: After 15 minutes of training, the cross-sectional area of the abductor hallucis was significantly increased in the NMES + BFR (P<.001) and the Sham NMES + BFR (P = .004) groups. Moreover, the rate of increase was significantly higher in the NMES + BFR group than in the NMES or the Sham NMES + BFR groups (P<.001 and P = . 001, respectively). Conclusions: Since it is possible that the amount of muscle swelling immediately after training correlates with muscle hypertrophy when training is continued, the results of this study suggest that NMES training with BFR is a training method that can be expected to produce plantar intrinsic foot muscle hypertrophy. Further studies are needed to confirm the long-term effects of NMES training with BFR. [ABSTRACT FROM AUTHOR]

Context: Flossing is still a relatively new technique that has yielded varied results in the research literature; therefore, it requires further investigation. Previous research has shown that thigh tissue flossing might improve performance in countermovement jump, sprint time, maximum voluntary contraction, and rate of force development. Design. The present study aims to investigate the effect of the floss band on performance during the Wingate test (30-WAT), muscle oxygen saturation (SpO2), and total hemoglobin in vastus lateralis. Methods: Twenty-two students of physical education and sport (11 men and 11 women) were randomly selected to complete either the Wingate test with the application of a floss band in warm-up or the Wingate test without the use of a floss band, followed by the alternative 24 hours apart. Results: Throughout the testing, the floss band did not affect performance values during the Wingate test (relative peak power, relative average power, and fatigue index). However, there was a medium to large effect difference during 1 minute prior to 30-WAT (PRE), during the 30-WAT, and 10-minute recovery (REC) in values of SpO2 and total hemoglobin. Use of floss band displayed a higher SpO2 during PRE, 30-WAT, and REC by ~13.55%, d<2; ~19.06%, d = 0.89; and ~8.55%, d = 0.59, respectively. Conclusion: Collectively, these findings indicate that the application of thigh flossing during warm-up has no effect on 30-WAT performance; however, SpO2 was significantly increased in all stages of testing. This could lead to potential improvement in repeated anaerobic exercise due to increased blood flow. Increased muscle oxygen saturation can also lead to improved tissue healing as oxygen supply is essential for tissue repair, wound healing, and pain management. [ABSTRACT FROM AUTHOR]

Clinical Scenario: Exercise-associated muscle cramps (EAMC) are sudden, painful, and involuntary contractions of skeletal muscles during or after physical activity. The best treatment for EAMC is gentle static stretching until abatement. Stretching is theorized to relieve EAMC by normalizing alpha motor neuron control, specifically by increasing Golgi tendon organ activity, and physically separating contractile proteins. However, it is unclear if stretching or flexibility training prevents EAMC via the same mechanisms. Despite this, many clinicians believe prophylactic stretching prevents EAMC occurrence. Clinical Question: Do athletes who experience EAMC during athletic activities perform less prophylactic stretching or flexibility training than athletes who do not develop EAMC during competitions? Summary of Key Findings: In 3 cohort studies and 1 case-control study, greater preevent muscle flexibility, stretching, or flexibility training (ie, duration, frequency) was not predictive of who developed EAMC during competition. In one study, athletes who developed EAMC actually stretched more often and 9 times longer (9.8 [23.8] min/wk) than noncrampers (1.1 [2.5] min/wk). Clinical Bottom Line: There is minimal evidence that the frequency or duration of prophylactic stretching or flexibility training predicts which athletes developed EAMC during competition. To more effectively prevent EAMC, clinicians should identify athletes' unique intrinsic and extrinsic risk factors and target those risk factors with interventions. Strength of Recommendation: Minimal evidence from 3 prospective cohort studies and 1 case-control study (mostly level 3 studies) that suggests prophylactic stretching or flexibility training can predict which athletes develop EAMC during athletic competitions. [ABSTRACT FROM AUTHOR]

Context: Contusion and soft tissue injuries are common in sports. Photobiomodultion, light and laser therapy, is an effective aid to increase healing rates and improve function after various injury mechanisms. However, it is unclear how well photobiomodulation improves function after a contusion soft tissue injury. This study aimed to determine the effects of a pulsed red and blue photobiomodulation light patch on muscle function following a human thigh contusion injury. Design: Single-blinded randomized control trial design. Methods: We enrolled 46 healthy participants. Participants completed 5 visits on consecutive days. On the first visit, participants completed a baseline isokinetic quadriceps strength testing protocol at 60°/s and 180°/s. On the second visit, participants were struck in the rectus femoris of the anterior thigh with a tennis ball from a serving machine. Immediately following, participants were treated for 30 minutes with an active or placebo photobiomodulation patch (CareWear light patch system, CareWear Corp). Following the treatment, participants completed the same isokinetic quadriceps strength testing protocol. Participants completed the treatment and isokinetic quadriceps strength test during the following daily visits. We normalized the data by calculating the percent change from baseline. We used a mixed model analysis of covariance, with sex as a covariate, to determine the difference between treatment groups throughout the acute recovery process. Results: We found the active photobiomodulation treatment significantly increased over the placebo group, quadriceps peak torque during the 180°/s test (P =.030), and average power during both the 60°/s (P =.041) and 180°/s (P ≤.001) assessments. The mean peak torque and average power of 180°/s, at day 4, exceeded the baseline levels by 8.9% and 16.8%, respectively. Conclusions: The red and blue photobiomodulation light patch improved muscle strength and power during the acute healing phase of a human thigh contusion injury model. [ABSTRACT FROM AUTHOR]

Precise protein supplementation strategies for muscle improvement are still lacking. The timing or type of protein supplementation has been debated as a window of opportunity to improve muscle mass, strength, and physical performance. We conducted a network meta-analysis of randomized controlled trials with protein supplements and resistance training. PubMed, Web of Science, Cochrane Library, and SPORTDiscus databases were searched until May 1, 2023. We included 116 eligible trials with 4,711 participants that reported on 11 timing and 14 types of protein supplementation. Compared with placebo, protein supplementation after exercise (mean difference [MD]: 0.54 kg [95% confidence intervals 0.10, 0.99] for fat-free mass, MD: 0.34 kg [95% confidence intervals 0.10, 0.58] for skeletal muscle mass) and at night (MD: 2.85 kg [0.49, 5.22] for handgrip strength, MD: 12.12 kg [3.26, 20.99] for leg press strength) was most effective in improving muscle mass and strength, respectively (moderate certainty). Milk proteins (milk, whey protein, yogurt, casein, and bovine colostrum), red meat, and mixed protein were effective for gains in both muscle mass and strength (moderate certainty). No timing or type of protein showed a significant enhancement in physical performance (timed up-to-go test, 6-min walk test, and gait speed). Pre/postexercise and Night are key recommended times of protein intake to increase muscle mass and strength, respectively. Milk proteins are the preferred types of protein supplements for improving muscle mass and strength. Future randomized controlled trials that directly compare the effects of protein timing or types are needed. This trial was registered at International Prospective Register of Systematic Reviews as CRD42022358766. [ABSTRACT FROM AUTHOR]

Previous research has shown that there are differences in mechanical energy, kinematics, and muscle activation when comparing walking on level and incline surfaces, especially on inclines above 15%. Muscle activations are significantly different while walking on extreme inclines, suggesting a different coordination pattern. We utilized continuous relative phase to assess walking kinematic coordination with respect to increased incline angles. Twelve healthy, college-aged individuals walked for 7 inclines of 1 minute each on a motorized treadmill at 3 mph at 0%, 5%, 10%, 15%, 20%, 25%, and 30% inclines. Kinematic data were collected during the last 20 seconds of each stage (120 Hz). Segmental and joint angles and angular velocities in the sagittal plane were calculated, from which continuous relative phase was determined for 3 joint couples: hip–knee, hip–ankle, and knee–ankle. There were significant differences in the coordination patterns during the first part of the contact phase in the hip–knee and hip–ankle couplings between the 0% and 30% inclines, with all 3 joint couplings becoming more in-phase at inclines above 15%. Importantly, the hip–knee coupling changed significantly from more out-of-phase to more in-phase between 10% and 15% incline. Shifting lower-extremity joint coordination in response to extreme inclines identifies potential coordinative strategies to achieve steep walking. [ABSTRACT FROM AUTHOR]

Context: Individuals with chronic ankle instability (CAI) demonstrate reduced spinal reflex modulation and corticospinal excitability of the soleus, which may contribute to decreased balance performance. Objective: To determine the effects of a single session of balance training on Spinal-reflexive excitability modulation and corticospinal excitability in those with CAI. Design: Randomized controlled trials. Setting: Research laboratory. Participants: Thirty participants with CAI were randomly assigned to the balance training (BAL) or control (CON) group. Main Outcome Measures: Modulation of soleus spinal-reflexive excitability was measured by calculating relative change in normalized Hoffmann reflexes (ratio of the H-reflex to the M-wave) from prone to single-leg standing. Corticospinal excitability was assessed during single-leg stance using transcranial magnetic stimulation, outcomes of which included active motor threshold (AMT), motor evoked potential, and cortical silent period (CSP). Balance performance was measured with center of pressure velocity in anterior to posterior and medial to lateral directions. Separate 2x2 repeated-measures analyses of variance were employed to determine the effect of group (BAL and CON) and time (baseline and posttraining) on each dependent variable. Results: There were significant group by time interactions in the modulation of soleus spinal-reflexive excitability (F1.27 = 4.763, P=-04); CSP at 100% AMT (F F1.27 = 4.727, P = .04); and CSP at 120% AMT (F F1.27 16.057, f < .01). A large effect size suggests increased modulation of spinal-reflexive excitability (d = 0.81 [0.03 to 1.54]) of the soleus in BAL compared with CON at posttest, while CSP at 100% (d = 0.95 [0.17 to 1.70]) and 120% AMT (d = 1.10 [0.29 to 1.84]) was reduced in BAL when compared with CON at posttest. Conclusion: After a single session of balance training, individuals with CAI initiated increases in spinal reflex modulation and corticospinal excitability of the soleus. Thus, individuals with CAI who undergo balance training exhibit positive neural adaptations that are linked to improvements in balance performance. [ABSTRACT FROM AUTHOR]

Purpose: To compare the effects of graded hypoxia during exhaustive intermittent cycling on subsequent rapid and maximal torque-production capacity. Methods: Fifteen well-trained cyclists repeated intermittent cycling bouts (15 s at 30% of anaerobic power reserve; rest = 45 s) until exhaustion at sea level (FiO2 ∼0.21/end-exercise arterial oxygen saturation ∼96%), moderate hypoxia (FiO2 ∼0.16/∼90%), and severe hypoxia (FiO2 ∼0.12/∼79%). Rapid (rate of torque development [RTD]) and maximal isometric torque-production capacities of the knee extensors were assessed at baseline (visit 1) and exhaustion (visits 2–4). Results: Exercise capacity decreased with hypoxia severity (39 [30], 22 [13], and 13 [6] cycle efforts in sea level, moderate hypoxia, and severe hypoxia, respectively; P =.002). Changes in maximal-voluntary-contraction torque between baseline and postexercise in all conditions were not statistically significant (pooled values: −2.6% [5.7%]; P =.162). Peak RTD measured postexercise was reduced below baseline in all conditions (–21.5% [5.1%]; P ≤.015). Compared with baseline, absolute RTD values were lower at 0- to 30-millisecond (–35.1% [5.3%], P ≤.020), 0- to 50-millisecond (–40.0% [3.9%], P ≤.002), 0- to 100-millisecond (–30.7% [3.7%], P ≤.001), and 0- to 200-millisecond (–18.1% [2.4%], P ≤.004) time intervals in all conditions. Conclusions: Exhaustive intermittent cycling induces substantial yet comparable impairments in RTD of knee extensors between normoxia and moderate to severe hypoxia. [ABSTRACT FROM AUTHOR]

Purpose: After anterior cruciate ligament reconstruction (ACL-R), knee muscle strength symmetry is used as part of the return-to-sport criteria. However, little is known about the changes in the force–velocity (F–V) relationship, which could affect athletic performance. This study investigated the F–V relationship of knee muscles at 4 and 8 months after ACL-R, using the 2-point method tested by isokinetic dynamometry. Methods: A total of 103 physically trained individuals (24.6 [9.3] y, 59.2% male) who underwent primary ACL-R were included. Demographic information and surgery characteristics were collected at 6 weeks postoperatively. Isokinetic knee flexors' and extensors' peak torques were measured at 60° and 240° per second in the concentric mode at 4 and 8 months postoperative. Peak torques and angular velocities were converted to force and linear velocity for calculating maximum isometric force (F0) and the slope of the regression line (F–V slope). Results: At 4 and 8 months postoperative, F0 was significantly lower and F–V slope was significantly less steep (less negative) on the operated leg compared with the nonoperated leg for knee extensors (P <.001) and flexors (P <.001–.002). The limb symmetry index calculated using F0 was lower than the limb symmetry indexes assessed at 60° and 240° per second, especially for knee flexors (P <.001). The use of patellar tendon grafts was associated with lower F0 and a less steep F–V slope compared with hamstring tendon grafts (P <.010). Conclusion: The isokinetic 2-point model assessing the F–V relationship provides additional and relevant insight for evaluating knee muscle strength after ACL-R. [ABSTRACT FROM AUTHOR]

The "2-point method," originally referred to as the "2-load method," was proposed in 2016 by Prof Slobodan Jaric to characterize the maximal mechanical capacities of the muscles to produce force, velocity, and power. Two years later, in 2018, Prof Jaric and I summarized in a review article the scientific evidence showing that the 2-point method, compared with the multiple-point method, is capable of providing the outcomes of the force–velocity (F–V) and load–velocity (L–V) relationships with similar reliability and high concurrent validity. However, a major gap of our review was that, until 2018, the feasibility of the 2-point method had only been explored through testing procedures based on multiple (more than 2) loads. This is problematic because (1) it has misled users into thinking that implementing the 2-point method inevitably requires testing more than 2 conditions and (2) obtaining the data from the same test could have artificially inflated the concurrent validity of the 2-point method. To overcome these limitations, subsequent studies have implemented in separate sessions the 2-point method under field conditions (only 2 different loads applied in the testing protocol) and the standard multiple-point method. These studies consistently demonstrate that while the outcomes of the 2-point method exhibit comparable reliability, they tend to have slightly higher magnitudes compared with the standard multiple-point method. This review article emphasizes the practical aspects that should be considered when applying the 2-point method under field conditions to obtain the main outcomes of the F–V and L–V relationships. [ABSTRACT FROM AUTHOR]

The Executive Council of the International Society of Biomechanics has initiated and overseen the commemorations of the Society's 50th Anniversary in 2023. This included multiple series of lectures at the ninth World Congress of Biomechanics in 2022 and XXIXth Congress of the International Society of Biomechanics in 2023, all linked to special issues of International Society of Biomechanics' affiliated journals. This special issue of the Journal of Applied Biomechanics is dedicated to the biomechanics of the neuromusculoskeletal system. The reader is encouraged to explore this special issue which comprises 6 papers exploring the current state-of the-art, and future directions and roles for neuromusculoskeletal biomechanics. This editorial presents a very brief history of the science of the neuromusculoskeletal system's 4 main components: the central nervous system, musculotendon units, the musculoskeletal system, and joints, and how they biomechanically integrate to enable an understanding of the generation and control of human movement. This also entails a quick exploration of contemporary neuromusculoskeletal biomechanics and its future with new fields of application. [ABSTRACT FROM AUTHOR]

Clinical Scenario: Knee osteoarthritis (KOA) is a complex progressive synovial joint disease that results in impaired muscle function, including a considerable loss of maximal strength and power. Exercise therapies, such as sensorimotor or balance training and resistance training, are frequently used to improve muscle function, mobility, and quality of life, but their impact on maximal muscle strength in patients with KOA is not well understood. Focused Clinical Question: Does sensorimotor or balance training improve knee-extensor and knee-flexor maximal muscle strength compared with strength training or no intervention in patients with KOA? Summary of Key Findings: Results from 4 fair- to good-quality randomized controlled/clinical trials (level 1b) revealed inconsistent grade B evidence regarding the effect of sensorimotor or balance training to improve knee-extensor and knee-flexor maximal muscle strength in patients with KOA. Two studies, one good-quality study and one fair-quality study, showed significant strength improvements, and 2 good-quality studies demonstrated no significant strength enhancements. Clinical Bottom Line: Sensorimotor or balance training may be useful to improve maximal strength of quadriceps and hamstring muscle groups in patients with KOA; however, it seems that this depends on a training duration of at least 8 weeks and the use of unstable devices to induce destabilization of patients' balance, initiating neuromuscular adaptations. Strength of Recommendation: Due to inconsistent evidence (grade B), the true effect of sensorimotor or balance training to improve knee-extensor and knee-flexor maximal muscle strength in patients with KOA remains unclear and needs to be further investigated. [ABSTRACT FROM AUTHOR]

Purpose: This study examined the underlying mechanisms of postactivation potentiation and the time course of muscular- and neural-related variables. Methods: Fourteen trained males executed 4 sets of six 6-second maximum isometric conditioning plantar flexions, with 15 seconds and 2 minutes of interval between the contractions and sets, respectively. Peak twitch torque (TT), rate of torque development, time to peak torque, half relaxation time, and the neural-related variables of H-reflex and electromyogram, normalized to the maximum M-wave (H/M and RMS/M, respectively), were evaluated, as well as the level of the voluntary activation, assessed by the twitch interpolation technique. All neural-related variables were analyzed for the trial within each set when TT was maximal and for the trial within each set when the neural-related variable itself was maximal. Results: Compared with the baseline measures, TT and rate of torque development significantly increased in all sets (P <.001), whereas time to peak torque and half relaxation time significantly decreased in sets 1 to 4 and 2 to 4, respectively (P <.001). However, H/M and the RMS/M did not change for the repetition of each set for which the TT was maximal (P >.05). Interestingly, the within-set maximum H/M ratio of the lateral gastrocnemius muscle revealed a significant increase in all sets (P <.05), compared with the baseline measures. Conclusion: One set of 4 contractions with 6-second duration is sufficient to cause postactivation potentiation for most participants, whereas peak TT augmentation does not coincide with changes in the examined neural-related variables. Further experiments should consider the time lag on their maximal values and their inherent between-participants variability. [ABSTRACT FROM AUTHOR]

Recent research has highlighted the essential role of the microbiome in maintaining skeletal muscle physiology. The microbiota influences muscle health by regulating lipid metabolism, protein synthesis, and insulin sensitivity. However, metabolic disturbances such as obesity can lead to dysbiosis, impairing muscle function. Time‐restricted feeding (TRF) has been shown to mitigate obesity‐related muscle dysfunction, but its effects on restoring healthy microbiomes remain poorly understood. This study utilizes 16S microbiome analysis and bacterial supplementation to investigate the bacterial communities influenced by TRF that may benefit skeletal muscle physiology. In wild‐type and obese Drosophila models (axenic models devoid of natural microbial communities), the absence of microbiota influence muscle performance and metabolism differently. Specifically, axenic wild‐type Drosophila exhibited reduced muscle performance, higher glucose levels, insulin resistance, ectopic lipid accumulation, and decreased ATP levels. Interestingly, in obese Drosophila (induced by a high‐fat diet or predisposed obesity mutant Sk2), the absence of microbiota improved muscle performance, lowered glucose levels, reduced insulin resistance, and increased ATP levels. TRF was found to modulate microbiota composition, notably increasing Acetobacter pasteurianus (AP) and decreasing Staphylococcus aureus (SA) in both obesity models. Supplementation with AP improved muscle performance and reduced glucose and insulin resistance, while SA supplementation had the opposite effect. This study provides novel insights into the complex interactions between TRF, microbiota, and skeletal muscle physiology in different Drosophila models. [ABSTRACT FROM AUTHOR]

Background: Although several studies have suggested a potential positive association between serum vitamin D levels and muscle strength in older adults, it remains unclear whether this relationship is sex-dependent. Aim: To evaluate the association between serum 25 hydroxyvitamin D [25(OH)D] levels and muscle strength in older adults and to assess whether this association is dependent on sex. Methods: This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES) conducted between 2001 and 2002. A total of 1173 individuals aged 50–85 years (630 men and 543 women) were included in the analysis. The peak isokinetic force of the knee extensor was assessed using a kinetic communicator isokinetic dynamometer. Serum 25(OH)D levels were measured using the standardized liquid chromatography-tandem mass spectrometry method. Linear regression analyses were conducted to estimate coefficients and 95% confidence intervals for muscle strength across tertiles of serum vitamin D levels, adjusting for potential confounders. Results: Tertiles of serum vitamin D were positively associated with muscle strength in older men (p-trend = 0.007), whereas no association was observed in older women (p-trend = 0.140) or in the total sample (men and women together; p-trend = 0.139). Conclusion: Serum vitamin D levels were positively associated with muscle strength specifically in older men, whereas no association was observed in older women. These results suggest that the relationship between vitamin D and strength may be sex-dependent. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the relative muscular effort (RME) of the hip and knee extensor and ankle plantarflexor muscle groups during the back squat (BS) and split squat (SS) exercises across four external load conditions. Motion capture and force plate data were collected as participants performed the BS and SS at 0%, 25%, 50%, and 75% of their body-mass. These data were used to calculate net joint moments (NJM) at the hip, knee, and ankle of the front leg during the SS and the matched leg during the BS. A musculoskeletal model, which accounted for force-length-velocity properties of 52 muscles, was used to estimate the maximal possible NJM (NJMmax) of the hip and knee extensor and ankle plantarflexor muscle groups. RME was calculated as the ratio between NJM and NJMmax, and compared across exercises and loads. The results indicated that while hip extensor RME increased across all loads, the increases in hip extensor RME were disproportionately greater during the SS at loads of 50% and 75%. Knee extensor RME increased linearly across loads and did not differ between exercises. These results provide coaches and athletes with detailed information about how to optimise resistance training specificity. [ABSTRACT FROM AUTHOR]

Heightened stress during air pistol competitions may impair shooters' abilities to maintain gun stability, resulting in inferior performance. This study aimed to compare the pre-trigger muscle activation levels of upper muscles in 10-m air pistol shooters between training and simulated competition conditions. Seven sub-elite shooters from the Singapore National Youth Air Pistol Team shot 30 shots in a training versus simulated competition condition in randomised orders on separate days. Muscle activation for the forearm and shoulder muscles, namely extensor carpi radialis, flexor carpi ulnaris, anterior deltoid, and posterior deltoid, were recorded using electromyography (EMG). Shooting performance was evaluated by total shot scores. Stress level was monitored via heart rate and the Mental Readiness Form-3. No statistically significant differences were found in EMG, performance, or stress-related variables between conditions, although moderate-to-large effect sizes were observed in some muscle activation and self-reported stress indicators. Analysis of individual performances using smallest worthwhile change showed that two participants improved under the simulated competition condition, while two declined, and three remained unaffected. In conclusion, sub-elite youth air pistol shooters were able to exhibit good neuromuscular control under high anxiety situations and thus their performance was largely unaffected. [ABSTRACT FROM AUTHOR]

Breaststroke is the only competitive stroke characterised by propulsive discontinuity. It is consequently paramount that swimmers optimally coordinate limb movements in order to maintain the highest average velocity possible. The present study aimed to investigate the temporal patterns of elite breaststroke swimmers. 50 m long-course competition footage of (1) 20 male 100 m races, (2) 24 female 100 m races, (3) 15 male 200 m races, and (4) 27 female 200 m races from 2018 to 2020 were digitised and analysed. Six points within each stroke cycle were identified and used to calculate 15 temporal parameters. Analyses revealed multiple temporal pattern differences between groups based on sex and race distance. It is recommended that coaches individualise swimmers' breaststroke temporal patterns based on individual needs, strengths, and morphological characteristics. [ABSTRACT FROM AUTHOR]

Objective: The main objective of this study was to investigate the effect of a self-regulated dual task on muscle endurance within a single rehabilitation session in patients recovering from an elbow fracture. Design: This is a cross-sectional study of individuals recovering from elbow fractures (N = 20). Muscle endurance was tested using elastic bands at Borg’s CR10 intensity 3—during four conditions: singletask and dual-task for elbow flexion and extension. Results: The cognitive condition significantly influenced muscle endurance ( P < 0.001), while the type of elbow exercise (flexion or extension) did not show significant differences ( P = 0.592). The perceived difficulty of the tasks showed a significant interaction effect ( P = 0.032). The dual-task condition showed an average increase of about 15 repetitions. A moderate negative correlation was found between the differences in repetitions and the perceived difficulty of the flexion exercise (r = 0.677, P = 0.001). Conclusions: Dual-task with self-regulation enhances muscle endurance among patients recovering from an elbow fracture. However, the improvements seem to depend on the perceived difficulty of the cognitive task. Future randomized controlled trials are required to understand the therapeutic implications of dual-tasking. [ABSTRACT FROM AUTHOR]

BACKGROUND: Trolley bags have gained popularity among students, but there is limited research comparing them to backpack-style school bags. OBJECTIVE: This study aimed to compare how carrying a backpack versus a trolley bag affects the activity of trunk and lower limb muscles in secondary school students. METHODS: Electromyographic activity was measured in 25 students (13.4±1.1 years) as they walked on level ground and up/down stairs while carrying both types of bags. The activity of the gastrocnemius, tibialis anterior, semitendinosus, rectus femoris, lumbar erector spinae, and rectus abdominis muscles was assessed on both the dominant and non-dominant sides. RESULTS: The study found significantly reduced muscle activation in most of the targeted muscles when walking on level ground with the trolley bag and when going up/down stairs with the backpack. CONCLUSIONS: Lifting a trolley bag depends on the slope of the walking surface and is more efficient on level ground, while carrying a backpack is more efficient when going up and down stairs. Since it is not practical to switch bags when encountering stairs in schools, a bag with a mixed model design incorporating features of both trolley and backpack may be more beneficial and practical for students to use. Students, parents, and teachers should be aware of the injury risks associated with carrying different types of bags. [ABSTRACT FROM AUTHOR]

Background: The body of literature regarding the use of an upper limb exoskeleton during authentic working conditions is sparse. Objective: The aim of this study was to evaluate the effectiveness of an upper limb exoskeleton in reducing muscle strain during authentic industrial construction work. Methods: Fifteen male participants, comprising of roofers, scaffolders, builders, bricklayers, and graders performing overhead work participated in the study. During work without (REF) and with exoskeleton (EXO), muscle activity from 8 muscles, heart rate (HR), metabolic equivalent (MET), and upper arm elevation angles were recorded. Results: When using the exoskeleton, a significant reduction of 20.2% in average muscle activity of 8 muscles was found. The largest effect focused on m. deltoideus, where 46.2 and 32.2% reduction occurred in medial and anterior parts of the muscle, respectively. HR and MET were unaffected. Upper arm elevation angles were similar between REF and EXO, indicating equal biomechanical loading. Conclusions: This study indicates that exoskeletons show great promise in reducing the potential for musculoskeletal strain during authentic overhead construction work. [ABSTRACT FROM AUTHOR]

The rate of proximal femur fractures (PFF) in the structure of musculoskeletal system injuries among all fractures of long bones ranges from 3.9 to 18%. According to Russian Ministry of Health 2020 data, the incidence of femoral fractures in Russia was up to 61 cases per 100,000 population (90,000 per year); and femoral neck fractures incidence was 4 times higher among people over 75 years of age. The choice of surgical technique and the fixator used depend on many factors, such as fracture location and its nature, the age of the patient, comorbidities, and the quality of bone tissue. Internal osteosynthesis, is the current treatment method of choice for extra-articular proximal femur fracture, but every treatment method has its limitations. a significant number of complications caused by technical errors, vicious union or nonunion with the subsequent development of false joints, the development of femoral head aseptic necrosis, which leads to coxarthrosis and persistent pain syndrome. To solve the above-described problems, it is necessary to use a conversion surgery - total hip replacement. long-term analysis of the results of total hip replacement in patients with proximal femur pseudarthrosis. The study was based on clinical and laboratory data analysis and on the results of total hip arthroplasty (THA) in 45 patients aged 56–84 years (mean age 68.3), including 32 (71.1%) women and 13 (26.1%) men. 12 patients initially received conservative treatment, and 33 patients received initial surgical treatment using various metal osteosynthesis procedures. The time from osteosynthesis or from the moment of injury to admission to the hospital for hip arthroplasty ranged from 12 to 30 months. All patients, before conversion arthroplasty and after discharge, were repeatedly invited to the clinical diagnostic department for a clinical examination and for assessment using rating scales. 3, 6 and 12 months after the surgery, pain syndrome and patient quality of life were assessed using the following questionnaire scales: Harris Hip Score, MOS SF-36, VAS. The maximum follow-up period ranged from 12 to 60 months. Based on the results obtained, patients of all 4 groups after conversion arthroplasty noted a significant quality of life improvement, a decrease in pain severity and functional results improvement. This was probably due to the presence of a severe limitation of range of movements in the joint, intense pain, absence of support ability of the extremity, as well as low operative efficacy expectations. In 1 (2%) patient, acute PJI was diagnosed in the early postoperative period, followed by sepsis and death. In 4 patients (9%) the result was considered unsatisfactory. At 1 year of follow-up after surgery, they complained of pain and claudication in the operated joint. 3 (6%) patients underwent reduction of dislocation. Strict adherence to the recommended treatment algorithm for patients with proximal femur pseudarthrosis made it possible to achieve good treatment results in 90% of surgically treated patients. An important step in the treatment of this patients is a careful preoperative planning with thorough assessment of bone tissue quality and muscles condition in the proximal femur area, allowing to choose the optimal endoprosthesis components. [ABSTRACT FROM AUTHOR]

Background: The chronic effect of static stretching (SS) on muscle hypertrophy is still unclear. This study aimed to examine the chronic effects of SS exercises on skeletal muscle hypertrophy in healthy individuals. Methods: A systematic literature search was conducted in the PubMed, Web of Science, Cochrane Library, and SPORTDiscus databases up to July 2023. Included studies examined chronic effects of SS exercise compared to an active/passive control group or the contralateral leg (i.e., utilizing between- or within-study designs, respectively) and assessed at least one outcome of skeletal muscle hypertrophy in healthy individuals with no age restriction. Results: Twenty-five studies met the inclusion criteria. Overall, findings indicated an unclear effect of chronic SS exercises on skeletal muscle hypertrophy with a trivial point estimate (standardised mean difference [SMD] = 0.118 [95% prediction interval [95% PI] = − 0.233 to 0.469; p = 0.017]) and low heterogeneity (I2 = 24%). Subgroup analyses revealed that trained individuals (β = 0.424; 95% PI = 0.095 to 0.753) displayed larger effects compared to recreationally trained (β = 0.115; 95% PI = − 0.195 to 0.425) and sedentary individuals (β = − 0.081; 95% PI = − 0.399 to 0.236). Subanalysis suggested the potential for greater skeletal muscle hypertrophy in samples with higher percentages of females (β = 0.003, [95% confidence interval [95% CI] = − 0.000 to 0.005]). However, the practical significance of this finding is questionable. Furthermore, a greater variety of stretching exercises elicited larger increases in muscle hypertrophy (β = 0.069, [95% CI = 0.041 to 0.097]). Longer durations of single stretching exercises (β = 0.006, [95% CI = 0.002 to 0.010]), time under stretching per session (β = 0.006, [95% CI = 0.003 to 0.009]), per week (β = 0.001, [95% CI = 0.000 to 0.001]) and in total (β = 0.008, [95% CI = 0.003 to 0.013]) induced larger muscle hypertrophy. Regarding joint range of motion, there was a clear positive effect with a moderate point estimate (β = 0.698; 95% PI = 0.147 to 1.249; p < 0.001) and moderate heterogeneity (I2 = 43%). Moreover, findings indicated no significant association between the gains in joint range of motion and the increase in muscle hypertrophy (β = 0.036, [95% CI = − 0.123 to 0.196]; p = 0.638). Conclusions: This study revealed an overall unclear chronic effect of SS on skeletal muscle hypertrophy, although interpretation across the range of PI suggests a potential modest beneficial effect. Subgroup analysis indicated larger stretching-induced muscle gains in trained individuals, a more varied selection of SS exercises, longer mean duration of single stretching exercise, increased time under SS per session, week, and in total, and possibly in samples with a higher proportion of females. From a practical perspective, it appears that SS exercises may not be highly effective in promoting skeletal muscle hypertrophy unless a higher duration of training is utilized. PROSPERO registration number: CRD42022331762. Key points: Chronic static stretching exercises result in an overall unclear effect on skeletal muscle hypertrophy. However, the range of the prediction interval reveals that the chance of a positive effect is greater than that of a negative effect, suggesting a potential hypertrophic benefit of static stretching. Subgroup analysis indicated that individuals with greater training experience achieved larger muscle gains compared to less-trained individuals following chronic static stretching. Meta-regression analyses suggested that a more varied selection of static stretching exercises, longer mean duration of single stretching exercise, and increased time under static stretching per session, week, and in total are associated with greater skeletal muscle hypertrophy. [ABSTRACT FROM AUTHOR]

Extremely low-frequency electromagnetic fields (ELF-EMFs) are ubiquitous in industrialized environments due to the continuous use of electrical devices. Our previous studies demonstrated that ELF-EMFs affect muscle cells by modulating oxidative stress and enhancing myogenesis. This pilot study investigated these effects on the skeletal muscles of sedentary adult mice, assessing physiological responses to ELF-EMF exposure and potential modulation by antioxidant supplementation. Male C57BL/6 mice were exposed to ELF-EMFs (0.1 or 1.0 mT) for 1 h/day for up to 5 weeks and fed a standard diet without or with N-acetyl-cysteine (NAC). The results showed transient increases in muscle strength (after 2 weeks of exposure at 1.0 mT), potentially linked to muscle fiber recruitment and activation, revealed by higher PAX7 and myosin heavy chain (MyH) expression levels. After ELF-EMF exposure, oxidative status assessment revealed transient increases in the expression levels of SOD1 and catalase enzymes, in total antioxidant capacity, and in protein carbonyl levels, markers of oxidative damage. These effects were partially reduced by NAC. In conclusion, ELF-EMF exposure affects skeletal muscle physiology and NAC supplementation partially mitigates these effects, highlighting the complex interactions between ELF-EMFs and antioxidant pathways in vivo. Further investigations on ELF-EMFs as a therapeutic modality for muscle health are necessary. [ABSTRACT FROM AUTHOR]

BACKGROUND: Lumbopelvic movement patterns during prone hip extension has been proposed as a clinical screening method for trunk muscle dysfunction in patients with chronic low back pain (CLBP). However, correlations between trunk muscle onset and pelvic kinematics have not been investigated. OBJECTIVE: To examine the correlation between trunk muscle onset and pelvic kinematics during prone hip extension in participants with CLBP. METHODS: Fifteen patients with CLBP and 15 healthy individuals participated. We evaluated the muscle activities of the lumbar multifidus, the longissimus, and the semitendinosus via electromyogram and the displacement angles of the pelvic tilt, oblique and rotation. RESULTS: The onset of the multifidus at the ipsilateral side of hip extension was significantly delayed in the patients with CLBP compared to the control group (P < 0.001). The onset of the ipsilateral multifidus in the control group was significantly correlated with increased anterior pelvic tilt angle (P = 0.019, r = 0.597), whereas no significant correlation was observed in the CLBP group (P = 0.810, r = - 0.068). CONCLUSION: The results suggest that pelvic kinematics during prone hip extension does not predict the delayed trunk muscle onset in patients with CLBP. [ABSTRACT FROM AUTHOR]

BACKGROUND: Patients who underwent total knee arthroplasty (TKA) often experience muscle loss due to pain and limited mobility. Nutritional supplementation and rehabilitation may positively affect the decline in muscle function. OBJECTIVE: The purpose of this study is to evaluate whether whey protein intervention, in addition to conventional rehabilitation training, is beneficial in improving muscle function and quality of life in patients after TKA. METHODS: 72 patients who met the criteria were selected for this randomized controlled study. For the experimental group, whey protein was used as a daily supplement for 12 weeks, while the control group was given a placebo, during which both groups received conventional rehabilitation training. Muscle strength and each of the secondary observables needed to be measured and statistically analyzed preoperatively and at 4, 8, and 12 weeks post-intervention. RESULTS: In total, 62 subjects completed the study: 32 in the experimental group and 30 in the control group. Both groups showed significant improvement in muscle strength, VAS, ROM, AKS and leg circumference after 12 weeks of treatment. Compared to the control group, patients in the experimental group showed significant improvement in muscle strength, VAS, ROM, AKS and leg circumference (p = 0.001, p = 0.002, p = 0.001, p = 0.001, p = 0.001, respectively) after 12 weeks of treatment. CONCLUSION: The 12-week intervention of whey protein nutritional supplement showed significant improvement in muscle mass and function among post-TKA patients besides aiding with conventional rehabilitation exercise. [ABSTRACT FROM AUTHOR]

Monitoring the metabolic cost or oxygen consumption associated with rest and exercise is crucial to understanding the impact of disease or physical training on the health of individuals. Traditionally, measuring the skeletal muscle oxygen cost associated with exercise/muscle contractions can be rather expensive or invasive (i.e., muscle biopsies). More recently, specific protocols designed around the use of near-infrared spectroscopy (NIRS) have been shown to provide a quick, noninvasive easy-to-use tool to measure skeletal muscle oxygen consumption (M V ˙ o 2 ). However, the data and results from NIRS devices are often misunderstood. Thus the primary purpose of this sourcebook update is to provide several experimental protocols students can utilize to improve their understanding of NIRS technology, learn how to analyze results from NIRS devices, and better understand how muscle contraction intensity and type (isometric, concentric, or eccentric) influence the oxygen cost of muscle contractions. NEW & NOTEWORTHY: Compared to traditional methods, near-infrared spectroscopy (NIRS) provides a relatively cheap and easy-to-use noninvasive technique to measure skeletal muscle oxygen uptake following exercise. This laboratory not only enables students to learn about the basics of NIRS and muscle energetics but also addresses more complex questions regarding skeletal muscle physiology. [ABSTRACT FROM AUTHOR]

The StartReact test, increasingly popular for assessing cortico‐reticular functioning, is a valid method to influence the firing of reticulospinal tract neurons noninvasively. However, there remains limited evidence on how different stimuli employed in the StartReact test impact motor output in humans. The present study tested elbow flexor responses of 33 adults (aged 26–48 years) to visual stimuli only (LED light), audio‐visual (80 dB) stimuli, and startle‐inducing audio‐visual (120 dB) stimuli sitting with the arm supinated in an electromechanical dynamometer. Surface electromyogram (EMG) recorded muscle activity from the right biceps brachii muscle. Participants were presented with 20 stimuli for each of the three conditions in pseudorandom order with interstimulus intervals of ~8 s. Reaction times were calculated from the stimulus trigger to the initial rise in the EMG signal above 7 × SD from baseline. Rate of torque development (RTD) and EMG signals were recorded throughout and analyzed over their initial 50 ms and 100 ms time‐windows. Reaction times were reduced from visual (169 ± 23) to audio‐visual (140 ± 23) and further reduced to startle‐inducing audio‐visual stimuli (108 ± 19, p < 0.001). While RTD and EMG were consistently greatest following startle‐inducing stimuli (p < 0.001), they were also enhanced following all audio‐visual stimuli over 100 ms (p < 0.05). It appears that startle‐inducing audio‐visual stimuli result in shorter reaction times, increased RTD, and enhanced muscle activity within the initial 50 ms, likely from subcortical upregulation. However, the 100 ms time‐window suggests cortical upregulation following all audio‐visual stimuli considering the longer transmission times. [ABSTRACT FROM AUTHOR]

Low‐load blood‐flow‐restriction resistance training (LL‐BFR‐RT) is gaining popularity, but its physiological effects remain unclear. This study aimed to compare LL‐BFR‐RT with low‐load resistance exercise (LL‐RT) and high‐load resistance exercise (HL‐RT) on metabolism, electrolytes, and ions in the lower extremities by invasive catheter measurements, which are crucial for risk assessment. Ten healthy men (27.6 ± 6.4 years) completed three trials of knee‐extensor exercises with LL‐RT (30% 1RM), LL‐BFR‐RT (30% 1RM, 50% limb occlusion pressure), and HL‐RT (75% 1RM). The exercise protocol consisted of four sets to voluntary muscle failure with 1 min of rest between sets. Blood gas analysis was collected before, during, and after each trial through intravenous catheters at the exercising leg. LL‐BFR‐RT had lower total workload (1274 ± 237 kg, mean ± SD) compared to LL‐RT (1745 ± 604 kg), and HL‐RT (1847 ± 367 kg, p < 0.01), with no difference between LL‐RT and HL‐RT. Pain perception did not differ significantly. Exercise‐induced drop in oxygen partial pressure, lactate accumulation and electrolyte shifts (with increased [K+]) occurred during under all conditions (p < 0.001). Creatine kinase and lactate dehydrogenase increased significantly 24‐ and 48‐h postexercise under all three conditions (p < 0.001). This study, using invasive catheter measurements, found no significant differences in metabolic, ionic, and electrolyte responses among LL‐BFR‐RT, LL‐RT, and HL‐RT when exercised to voluntary muscular failure. LL‐BFR‐RT reduced time to failure without specific physiological responses. [ABSTRACT FROM AUTHOR]

Basketball victory relies on an athlete's skill to make precise shots at different distances. While extensive research has explored the kinematics and dynamics of different shooting distances, the specific neuromuscular control strategies involved remain elusive. This study aimed to compare the differences in muscle synergies during basketball shooting at different distances, offering insights into neuromuscular control strategies and guiding athletes' training. Ten skilled shooting right-handed male basketball players participated as subjects in this experiment. Electromyographic (EMG) data for full-phase shooting were acquired at short (3.2 m), middle (5.0 m), and long (6.8 m) distances. Non-negative matrix decomposition extracted muscle synergies (motor modules and motor primitives) during shooting. The results of this study show that all three distance shooting can be broken down into three synergies and that there were differences in the synergies between short and long distances, with differences in motor primitive 1 and motor primitive 2 at the phase of 45% - 59% (p < 0.001, t* = 4.418), and 78% - 88% (p < 0.01, t* = 4.579), respectively, and differences in the motor module 3 found in the differences in muscle weights for rectus femoris (RF) (p = 0.001, d = -2.094), and gastrocnemius lateral (GL) (p = 0.001, d = -2.083). Shooting distance doesn't affect the number of muscle synergies in basketball shooting but alters synergy patterns. During long distance shooting training, basketball players should place more emphasis on the timing and synergistic activation of upper and lower limbs, as well as core muscles. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare the acute effects of compression contrast therapy (CT) and dry needling therapy (DN) on muscle tension (MT), muscle strength (Fmax), pressure pain threshold (PPT), and perfusion (PU) following fatigue of forearm muscles (e.g., flexor carpi radialis) in combat sports athletes. A single-blind randomized controlled trial was employed. Participants first underwent muscle fatigue induction, which involved sustaining an isometric handgrip at 60% of their maximum voluntary contraction in 5-second cycles. This was followed by exposure to one of the regenerative therapies. Forty-five participants were randomly assigned to one of three groups: CT/DN (n = 15), CT/ShDN (n = 15), and ShCT/DN (n = 15). The sham condition (Sh) involved a simulated version of the technique. Measurements were taken at four time points: (i) at rest; (ii) immediately after exercise that led to a state of fatigue; (iii) 5 minutes after therapy (PostTh5min); and (iv) 24 hours after therapy (PostTh24h). Each participant was exposed to one experimental condition and one control condition, thereby undergoing evaluation in two sessions. Significant differences between groups were found in MT during the PostTh5min (p = 0.005), as well as in PU during the PostTh5min (p < 0.001) and PU during the PostTh24h (p < 0.001). All groups showed significant improvements at 5 minutes post-therapy compared to immediately post-muscle fatigue. As conclusions, CT/DN seems to be significantly better for enhancing MT and PU after 5 minutes of muscle fatigue induction. Using either CT, DN, or both combined is recommended to enhance the recovery of muscle functionality and properties, favoring recovery and potentially speeding up performance enhancement. [ABSTRACT FROM AUTHOR]

Sports injuries pose significant challenges in athlete welfare and team dynamics, particularly in high-intensity sports like soccer. This study used machine learning algorithms to assess non-contact injury risk in professional male soccer players from physiological and mechanical load variables. Twenty-five professional male soccer players with a first-time, non-contact muscle injury were included in this study. Recordings of external load (speed, distance, and acceleration/deceleration data) and internal load (heart rate) were obtained during all training sessions and official matches over a 4-year period. Machine learning model training and evaluation features were calculated for each of nine different metrics for a 28-day period prior to the injury and an equal-length baseline epoch. The acute surge in the values of each workload metric was quantified by the deviation of maximum values from the average, while the variations of cumulative workload over the last four weeks preceding injury were also calculated. Seven features were selected by the model as prominent estimators of injury incidence. Three of the features concerned acute load deviations (number of sprints, training load score-incorporating heart rate and muscle load- and time of heart rate at the 90 - 100% of maximum). The four cumulative load features were (total distance, high speed and sprint running distance and training load score). The accuracy of the muscle injury risk assessment model was 0.78, with a sensitivity of 0.73 and specificity of 0.85. Our model achieved high performance in injury risk detection using a limited number of training load variables. The inclusion, for the first time, of heart rate related variables in an injury risk assessment model highlights the importance of physiological overload as a contributor to muscle injuries in soccer. By identifying the important parameters, coaches may prevent muscle injuries by controlling surges of training load during training and competition. [ABSTRACT FROM AUTHOR]

This study evaluated the effects of a 10-month neuromuscular training (NMT) intervention on muscle architecture, isometric force production, and stretch-shortening cycle (SSC) function. Thirty-seven girls aged 6-12 years were placed into gymnastics + NMT (gNMT; n = 15), gymnastics only (GYM; n = 10), or maturity-matched control (CON; n = 12) groups. The gNMT group followed a 10-month NMT program in addition to gymnastics training, whereas the GYM group only participated in gymnastics training. Isometric midthigh pull (IMTP) and drop jump (DJ) kinetics were measured, in addition to muscle thickness, fascicle length, and pennation angle of the gastrocnemius medialis at baseline and at 4, 7, and 10 months. A3 x 4 (group x time) repeated-measures ANCOVA (covariate, % predicted adult height) was used to evaluate within-group changes. Significance level was set at p < 0.05. Significant interaction effects were observed in muscle thickness, absolute (PFabs) and relative peak force (PFrel) in the IMTP and various DJ variables. The gNMT group demonstrated improvements in muscle thickness, IMTP PFabs and PFrel, and DJ kinetics, most commonly evidenced from 7 months onward. The GYM group's muscle thickness also significantly improved, accompanied by improvements in some DJ kinetics. The CON group did not experience any desirable changes. Overall, NMT elicited positive changes in muscle thickness, PFabs and PFrel, and SSC function to a greater extent than gymnastics training alone or growth and maturation. As most adaptations took 7 months, longer-term NMT programs should be implemented with youth female gymnasts. [ABSTRACT FROM AUTHOR]

The purpose of this study was to compare the muscle-to-bone ratio (MBR) in National Collegiate Athletic Association Division I football players (collegiate football players [CFP]) to healthy, age-matched controls. In addition, we examined MBR in CFP by position. A total of 553 CFP and 261 controls had their total and regional lean mass (LM), fat mass (FM), and bone mineral content (BMC) determined by dual x-ray absorptiometry (DXA). College football players were categorized by positions defined as offensive linemen (OL), defensive linemen (DL), tight end, linebacker (LB), running back (RB), punter or kicker, quarterback (QB), defensive back (DB), and wide receiver (WR). There were significant differences between CFP and controls for total LM (80.1 ± 10.0 vs. 56.9 ± 7.8 kg), FM (22.2 ± 12.5 vs. 15.2 ± 7.1 kg), and BMC (4.3 ± 0.5 vs. 3.1 ± 0.5 kg). Although there were significant differences in body composition between CFP and controls, there was no significant differences in total MBR between CFP and controls (18.6 ± 1.4 vs. 18.8 ± 1.7). Regionally, CFP had significantly lower trunk MBR than controls (26.7 ± 2.7 vs. 28.7 ± 4.2), but no difference was seen in leg or arm MBR. Positional differences in CFP were noted as total MBR being significantly higher in DL (19.0 ± 1.4) than in DB (18.1 ± 1.3), WR (18.1 ± 1.3), and LB (18.2 ± 1.3). OL had a significantly higher total MBR (19.2 ± 1.3) than DB(18.1 ± 1.3), LB (18.2 ± 1.3), QB (18.1 ± 1.0), and WR (18.1 ± 1.3). In addition, RB had significantly higher total MBR (18.8 ± 1.3) than DB (18.1 ± 1.3) and WR (18.1 ± 1.3). This study may provide athletes and training staff with normative values when evaluating total and regional MBR with DXA. [ABSTRACT FROM AUTHOR]