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Background The isokinetic dynamometer has been considered the gold-standard measurement of muscle performance. However, the reliability for the isometric and isokinetic wrist flexor and extensor strength using the Biodex isokinetic dynamometer has not been reported to date. This study evaluated test-retest reliability of isometric and isokinetic wrist strength using the Biodex System 3 isokinetic dynamometer. Methods This is a test-retest reliability study. Peak concentric and isometric torque was determined of the dominant limb wrist flexor and extensor of healthy individuals using the Biodex Multi-Joint System 3 dynamometer. The participants were evaluated by the same examiner in two different sessions separated by an interval of two to seven days. Reliability was investigated using the intraclass correlation coefficient (ICC2,1), standard error of measurement (SEM) and minimum detectable difference (MDD). Results Twenty healthy subjects participated in the study. The ICCs for concentric and isometric torque of the wrist flexor and extensor ranged from 0.79 to 0.91, revealing excellent intra-examiner test-retest reliability; SEM ranging from 0.4 to 1.5; and MDD ranged from 1.12 Nm to 4.17 Nm. Conclusions Excellent intra-examiner test-retest reliability was found regarding peak concentric toque of the wrist flexor and extensor at an angular velocity of 45°/s as well as isometric torque of the wrist flexor and extensor in healthy individuals measured using the Biodex System 3 isokinetic dynamometer.

Reactive stepping is one of the only strategies that can lead to successful stabilization following a large challenge to balance. Improving function of specific muscles associated with reactive stepping may improve features of reactive balance control. Accordingly, this study aimed to determine the relationship between lower limb muscle strength and explosive force with force plate-derived timing measures of reactive stepping. Nineteen young, healthy adults (27.6 ± 3.0 years of age; 10 women: 9 men) responded to 6 perturbations (~13-15% of body weight) using an anterior lean-and-release system (causing a forward fall), where they were instructed to recover balance in as few steps as possible. Foot-off, swing, and restabilization times were estimated from force plates. Peak isokinetic torque, isometric torque, and explosive force of the knee extensors/flexors and plantar/dorsiflexors were measured using isokinetic dynamometry. Correlations were run based on a priori hypotheses and corrected for the number of comparisons (Bonferroni) for each variable. Knee extensor explosive force was negatively correlated with swing time (r = −0.582, p = 0.009). Knee flexor peak isometric torque also showed a negative association with restabilization time (r = −0.459, p = 0.048), however this was not statistically significant after correcting for multiple comparisons. There was no significant relationship between foot-off time and knee or plantar flexor explosive force (p > 0.025). These findings suggest that there may be utility to identifying specific aspects of reactive step timing when studying the relationship between muscle strength and reactive balance control. Exercise training aimed at improving falls risk should consider targeting specific aspects of muscle strength depending on specific deficits in reactive stepping.

Hamstring strain injuries are common in sport. Supramaximal eccentric or high-intensity isometric contractions are favored in hamstring strain injury prevention. The effect of combining these contraction modes in such prevention programs as a poststretch isometric contraction is unknown. Poststretch isometric contractions incorporate an active stretch and result in greater final isometric force than isometric contractions at comparable joint angles. This study compared torque and muscle activation levels between maximal voluntary isometric contraction and maximal poststretch isometric contractions of the knee flexors. Participants (n = 9) completed baseline maximal voluntary isometric contraction at 150° knee flexion and maximal poststretch isometric contractions at 120° knee flexion actively stretching at 60°/s to 150° knee flexion for final isometric contraction. Torque of the knee flexors and surface electromyography root mean square (sEMGRMS) of biceps femoris long head were simultaneously recorded and compared between baseline and poststretch isometric at 150° knee flexion. Torque was 14% greater in the poststretch isometric condition compared with baseline maximal voluntary isometric contraction (42.45 [20.75] N·m, 14% [22.18%], P RMS of biceps femoris long head (−.03 mV, ±.06, P = .130, d = .93). Poststretch isometric contractions resulted in supramaximal levels of poststretch isometric torque without increased activation of biceps femoris long head.

Background: The anatomy, origin, function, and appearance of the Palmaris Longus Muscle (PLM) in different populations are well studied. However, little is known about its contribution to wrist flexion movements in sports. This study investigates whether the existence or absence of the PLM affects maximal torque output or torque consistency of submaximal wrist flexion moment. Methods: One hundred ninety-seven well-trained sports students were clinically examined to ascertain the presence of the PLM. Forty of them from different sport disciplines were assigned to two groups (athletes in handgrip sports: HG, athletes in non-handgrip sports: NHG). Their 80 upper limbs were divided based on the PLM-presence/absence and hand-dominance/non-dominance. Maximal Isometric Torque (MIT) at 150º, 180º, and 210º wrist angle, and torque steadiness at 150º and 180º, at 25%, 50%, and 75% of MIT were measured on a Humac Norm dynamometer. Results: In all MIT tests, HGs significantly surpassed NHGs, independently of the dominant or non-dominant side in presence of the PLM (p

Objective To compare the effectiveness of adding anteromedial versus posterolateral hip musculature strengthening to knee strengthening in women with patellofemoral pain (PFP). Design Randomized controlled trial. Setting University physiotherapy clinic. Participants Fifty-two women with PFP were randomized to receive either anteromedial (AMHG) or posterolateral (PLHG) hip musculature strengthening. Main outcome measures The primary outcomes were pain intensity by the numeric pain rating scale and function by the Anterior Knee Pain Scale in six weeks. Secondary outcomes were pain and function at six months, global perceived effect at six weeks and six months, pain in step down, isometric torque of abductors, adductors and hip rotators measured with hand-held dynamometer, and dynamic knee valgus by step down in six weeks. Results Both groups showed improvement in primary outcomes; however, no differences were found between groups in pain intensity and function in six weeks and the secondary outcomes. Group x time interaction found superior gains in abductor strength in the PLHG and increase in the strength of the adductors and internal rotators in AMHG. Conclusion There was no difference between the addition of anteromedial or posterolateral hip musculature strengthening to knee strengthening in improving pain and function in women with PFP.

The length–tension relationship affects knee extension performance; however, whether anatomical variations in different quadriceps regions affect this relationship is unknown. Regional (proximal, middle, distal) quadriceps thickness (MT), pennation angle, and fascicle length of 24 males (48 limbs) were assessed via ultrasonography. Participants also performed maximal voluntary isometric torque (MVIT) assessments at 40°, 70°, and 100° of knee flexion. Measures were recorded on 3 separate occasions. Linear regression models predicting angle-specific torque from regional anatomy provided adjusted simple and multiple correlations (√adjR2) with bootstrapped compatibility limits to assess magnitude. Middle vastus lateralis MT and MVIT at 100° (√adjR2 = 0.64) was the largest single correlation, with distal vastus lateralis MT having the greatest mean correlations regardless of angle (√adjR2 = 0.61 ± 0.05, mean ± SD). Lateral distal MT and architecture had larger (Δ√adjR2 = 0.01 to 0.43) single and multiple correlations with MVIT than the lateral proximal (√adjR2 = 0.15 to 0.69 vs −0.08 to 0.65). Conversely, middle anterior MT had greater (Δ√adjR2 = 0.08 to 0.38) single and multiple correlations than proximal MT (√adjR2 = 0.09 to 0.49 vs −0.21 to 0.14). The length–tension relationship was trivially affected by regional quadriceps architecture. The middle and distal quadriceps were the strongest predictors of MVIT at all joint angles. Therefore, researchers may wish to focus on middle and distal lateral quadriceps anatomy when performing ultrasonographic evaluations. Novelty: The length–tension relationship is minimally affected by regional quadriceps anatomical parameters. Middle and distal vastus lateralis and lateral vastus intermedius anatomy were consistently the best predictors of torque. Practitioners may focus their assessments on the middle and distal regions of the lateral quadriceps’ musculature.

Tomazin, K, Strojnik, V, Feriche, B, Garcia Ramos, A, Štrumbelj, B, and Stirn, I. Neuromuscular adaptations in elite swimmers during concurrent strength and endurance training at low and moderate altitudes. J Strength Cond Res 36(4): 1111-1119, 2022-This study evaluated neuromuscular adaptations in elite swimmers during concurrent strength and endurance training (SET) at low (295 m) and moderate (2,320 m) altitudes. Sixteen elite swimmers took part in a 3-week SET during a general preparation phase. All neuromuscular tests were performed a week before and after a SET. In posttraining, maximal knee isometric torque (TMVC) and soleus H-reflex remained statistically unchanged for sea-level (SL) and for altitude (AL) training. Rate of torque development (RTD) decreased post-SL (-14.5%; p0.01) but not post-AL (-4.7%; p0.05) training. Vastus lateralis electromyographic (EMG) activity during RTD decreased post-SL (-17.0%; P = 0.05) but not post-AL (4.8%; p0.05) training. Quadriceps twitch torque (TTW) significantly increased post-AL (12.1%; p0.01) but not post-SL (-1.0%; p0.05; training × altitude: F1,15 = 12.4; p0.01) training. Quadriceps twitch contraction time and M-wave amplitude remained statistically unchanged post-SL and post-AL training. After SL training, increment in TMVC was accompanied with increment in vastus lateralis EMG (R = 0.76; p0.01) and TTW (R = 0.48; p0.06). Posttraining in AL, increment in TMVC was accompanied with increment in TTW (R = 0.54; p0.05). Strength and endurance training at altitude seems to prompt adaptations in twitch contractile properties. In contrast, SET performed at SL may hamper the magnitude of neural adaptations to strength training, particularly during rapid voluntary contractions. In conclusion, SET at AL might benefit muscular adaptations in swimmers compared with training at SL.

Background Competitive swimmers are exposed to high training loads, which can contribute to the development of shoulder pain. There is a lack of research investigating the interactions between the accumulation of training loads and factors associated to shoulder pain in swimmers. Purpose The primary objective was to analyze the changes in shoulder physical qualities and wellness factors over a week of training in competitive swimmers. A secondary objective was to compare the changes in these variables between different swim-training volumes performed during the week. Design Cross-sectional. Methods Thirty-one national and regional-level swimmers were included (18 females, 13 males; age= 15.5 ± 2.2 years). Active shoulder external rotation (ER) range of motion (ROM), shoulder-rotation isometric torque, and wellness factors using the Hooper questionnaire were measured twice over the week: a baseline measurement (before Monday´s training session) and a follow-up during the week. Participants were divided into a high-volume group (HVG) and low-volume group (LVG) based on the day follow-up was performed. HVL (n= 15) was tested at the end of the training week (after Saturday´s session) and LVG (n= 16) during the week (after Thursday or Friday´s session). Rating of perceived exertion (RPE) of the whole week was recorded after the follow-up session. Results At follow-up, the LVG averaged a volume of 26.2 ± 2.2 km, whereas the HVG averaged a volume of 37.5 ± 3.7 km. LVG and HVG participants decreased active shoulder ER ROM on dominant (p= 0.002; p= 0.006) and nondominant sides (p= 0.001; p= 0.004), displayed increased muscular soreness (p= 0.001; p= 0.007) and worsened overall wellness (p< 0.001; p= 0.010). Fatigue (p= 0.008) and poor sleep quality were increased (p= 0.023) in HVG, but not in LVG. There were no changes in shoulder-rotation torque and stress in any group. Regarding between-groups differences, only weekly RPE was higher (p= 0.004) in HVG. Conclusions The accumulation of training loads over the week negatively affect physical and wellness factors. Greater swim-volumes were associated with an increase perception of training loads. The regular monitoring of multiple factors to assess swimmers’ response to training might be necessary. Level of evidence 3

Reliable assessment of skeletal muscle strength is arguably the most important outcome measure in neuromuscular and musculoskeletal disease and injury studies, particularly when evaluating regenerative therapies' efficacy. Additionally, a critical aspect of translating many regenerative therapies is the demonstration of scalability and effectiveness in a large animal model. Various physiological preparations have been established to evaluate intrinsic muscle function properties in basic science studies, primarily in small animal models. The practices may be categorized as: in vitro (isolated fibers, fiber bundles, or whole muscle), in situ (muscle with intact vascularization and innervation but distal tendon attached to a force transducer), and in vivo (structures of the muscle or muscle unit remain intact). There are strengths and weaknesses to each of these preparations; however, a clear advantage of in vivo strength testing is the ability to perform repeated measurements in the same animal. Herein, the materials and methods to reliably assess isometric torque produced by the hindlimb dorsiflexor muscles in vivo in response to standard peroneal electrical stimulation in anesthetized pigs are presented.

Introduction: Hip muscle strength has a good component to improve the execution of movement preventing excessive knee movements, such as dynamic valgus, which is a factor related to ACL injuries, however, the relationship between isometric torque and dynamic valgus is not yet well established. Functional tests that resemble sports have been used for movement analysis and possible injury minimizing factor. Objectives: To compare the knee medialization peak in three kinematic tests with different demands, and its correlation with the isometric torque of the abductors and hip extensors. Methods: The isometric torque was collected by the Lafayette hand dynamometer. Two-dimensional kinematics were used to evaluate three functional tests of different requirements, Single Limb Squat, Lateral Step Down Test and Single Leg Drop Landing Tests. For comparison between values we used the Student T test and for correlation the Spearman test, with p < 0.05. Results: No significant differences were found between the three right kinematic tests, different from the left. And no relationship was established between the isometric hip torque and none of the three kinematic tests. Conclusion: There is no correlation between the dynamic knee valgus peak during different tests. It is concluded that the isometric torque test does not seem to be as sensitive when related to functional tests, but it has good applicability for comparing strength between limbs.

Objective The purpose was two-fold: (1) to examine differences in maximal voluntary isometric torque (MVIT) production, and electromyographic signal amplitude (EMGAMP) and mean power frequency (EMGMPF) values obtained during traditional (MVICTRAD), rapid (MVICRAPID), and ramp (MVICRAMP) maximal voluntary isometric contractions, and (2) to determine if there were differences in the reliability of MVIT, EMGAMP and EMGMPF among the three MVIC types. Approach Twenty-two young males and females completed MVICTRAD, MVICRAPID, and MVICRAMP muscle actions on two separate visits separated by 48 h. During all MVICs, MVIT and EMGAMP and EMGMPF of the vastus lateralis (VL) and rectus femoris (RF) were quantified. Main results MVIT was greater during MVICTRAD and MVICRAPID than during MVITRAMP (both p Significance Investigators may choose MVIC type based on preference or equipment availability. However, investigators should note that MVICRAMP contractions will likely yield the greatest EMGAMP values and more reliable measurements of VL and RF EMGMPF.

The aim of the present study was to determine whether depression of maximal muscular force and neural drive subsequent to prolonged ( ≥ 60 s) passive muscle stretching is associated with altered corticospinal excitability or intracortical (GABAFourteen healthy adult males were tested before and after 5 min (5 × 60-s stretches) of intense, passive static stretching of the plantar flexor muscles. Two protocols (A and B) were conducted in a randomized order. Transcranial magnetic stimulation was delivered to the contralateral motor cortex at rest (Protocol A) and during maximal voluntary contractions (Protocol B). Changes in maximal voluntary isometric torque, voluntary surface electromyographic activity of triceps surae muscles (normalized to M-wave; EMG/M), motor-evoked potentials (MEP), and cortical silent period (cSP; Protocol B) in soleus elicited by transcranial magnetic stimulation were examined 10 min after stretch.In both protocols A and B, significant decreases were observed immediately after stretching in maximal voluntary plantar flexion torque ( - 20.1 ± 15.9%, P = 0.004; and - 17.2 ± 13.5%, P = 0.006) and EMG/M ( - 18.0 ± 18.2%, P = 0.023; and - 13.0 ± 9.3%, P = 0.003). Decreases in torque and EMG/M were highly correlated (r = 0.67-0.85, P 0.05). However, no changes were observed in MEP amplitudes during rest ( + 29.3 ± 50.0%) or maximum voluntary contraction ( + 1.9 ± 16.8%), or in cSP ( + 2.1 ± 15.1%).Impaired neural drive contributed to the stretch-induced force loss; however, changes in corticospinal excitability and intracortical inhibition could not explain the phenomenon.

Summary Introduction Recent studies reported improvements in aerobic performance after ischemic preconditioning (IPC) compared to a control or placebo condition. However, the effects of IPC on both skeletal maximal muscle strength and power have not been investigated. Summary of facts and results Considering the importance of muscle strength/power production and the potential benefits of IPC, the purpose of this study was to investigate the effects of IPC on peak isometric torque and rate of force development (RFD). Ten participants performed on separated days 4 sets of either ischemic preconditioning (5 min of ischemia [250 mmHg] and 5 min of reperfusion) or placebo (5 min of placebo [10 mmHg] and 5 min of reperfusion) alternated in both lower limbs 30 min before maximal voluntary isometric contraction test. RFD was calculated over time intervals of 0–30, 0–50, and 0–200 ms and peak isometric torque was determined from the torque-time curve. Despite no significant difference, there was a moderate effect of ischemic preconditioning on rate of force development in time intervals of 0–30 ms, small effect in 0–50 ms, and trivial effect of ischemic preconditioning on rate of force development in 0–200 ms and on peak isometric torque. Conclusions Considering that RFD is a key factor of performance in tasks with limited time (

Introduction: Both resistance and stretch-shortening cycle exercise have positive effects on physical abilities and health related factors. In the present experiment we tested the hypothesis that an 8-week-long combined strength and stretch-shortening cycle exercise training is superior to strength training alone in the development of walking and running economy in healthy untrained women. Methods: Twenty untrained female college students (age = 21.5 ± 2.1 years, body mass index = 22.3 ± 2.9) were divided into two experimental groups. Both groups performed own-body resistance exercises three times per week but one group performed additional stretch-shortening cycle exercises. Countermovement jump force as well as maximal voluntary isometric torque and elastic energy storage and re-use in quadriceps muscle were measured. Running and walking economy was quantified by measuring maximal oxygen consumption during a treadmill test. Results: Isometric torque improved uniformly in the two groups (p Conclusion: This study suggests that improved elastic energy storage and re-use rather than maximum muscle contractility may account for the changes in countermovement jump force and running economy after additional stretch-shortening cycle exercise. The present data should be taken into consideration for understanding the favourable effects of stretch-shortening cycle exercise training in the young untrained population.

INTRODUCTION The isometric force attained after active stretch is greater than that attained in a purely isometric contraction. This phenomenon is called residual force enhancement (RFE). The purpose was to examine the influence of isometric preactivation conducted just before active stretch on the magnitude of RFE in plantar flexors. METHODS In the control condition, subjects conducted isometric contraction at 15° of dorsiflexion. In the no preactivation condition, the isometric contraction at 15° of dorsiflexion was conducted after an eccentric contraction from 0° to 15° of dorsiflexion. In the isometric preactivation condition, an isometric contraction was conducted for preactivation before conducting the same routine as in the no preactivation condition. Isometric torque at the end of isometric contraction at 15° of dorsiflexion was compared among conditions to examine whether isometric preactivation affects the magnitude of RFE. The fascicle behaviors of the medial gastrocnemius were recorded by ultrasonography. RESULTS The isometric torque attained in the preactivation condition was greater than that in the control condition (P = 0.017). There was no significant difference between no preactivation and control conditions (P = 0.744). The magnitude of fascicle elongation during active stretch was greater in the preactivation than in the no preactivation condition (P = 0.002). CONCLUSION Compared to the control condition, greater isometric torque was observed only in the preactivation condition, indicating that substantial RFE was induced only in the preactivation condition. This difference would be explained by the lesser degree of fascicle elongation during active stretch in the no preactivation condition.

Purpose The present study compared knee extension explosive isometric torque, neuromuscular activation, and intrinsic contractile properties at five different knee-joint angles (35°, 50°, 65°, 80°, and 95°; 0° = full knee extension). Methods Twenty-eight young healthy males performed two experimental sessions each involving: 2 maximum, and 6–8 explosive voluntary contractions at each angle; to measure maximum voluntary torque (MVT), explosive voluntary torque (EVT; 50–150 ms after contraction onset) and quadriceps surface EMG (QEMG, 0–50, 0–100, and 0–150 ms after EMG onset during the explosive contractions). Maximum twitch and M-wave (MMAX) responses as well as octet contractions were evoked with femoral nerve stimulation at each angle. Results Absolute MVT and EVT showed an inverted ‘U’ relationship with higher torque at intermediate angles. There were no differences between knee-joint angles for relative EVT (%MVT) during the early phase (≤ 75 ms) of contraction and only subtle differences during the late phase (≥ 75 ms) of contraction (≤ 11%). Neuromuscular activation during explosive contractions was greater at more flexed than extended positions, and this was also the case during MVT. Whilst relative twitch torque (%MVT) was higher at knee flexed positions (P ≤ 0.001), relative octet torque (%MVT) was higher at knee extended positions (P ≤ 0.001). Conclusion Relative EVT was broadly similar between joint angles, likely because neuromuscular activation during both explosive and plateau (maximum) phases of contraction changed proportionally, and due to the opposing changes in twitch and octet evoked responses with joint angle.

NEW FINDINGS What is the central question of this study? Is the degree of in human muscle affected by different shortening velocities, or contraction type? What are the main findings and their importance? The PAP response following maximal concentric contractions was independent of velocity. Slow and moderate velocity maximal contractions produced PAP responses like those from maximal isometric contractions when matched for contraction duration. Despite contraction type differences in cross-bridge and Ca2+ kinetics, maximal contractions, regardless of contraction modality, likely generate sufficient Ca2+ to induce maximal PAP. ABSTRACT Post-activation potentiation (PAP) is the acute enhancement of contractile properties following a brief (

Peak knee valgus has been shown to predict anterior cruciate ligament injury. The purpose of the current study was to compare peak rate of torque development (RTD) to peak isometric torque as a predictor of peak knee valgus during landing. Twenty-three healthy females participated. Hip abductor muscle performance was quantified using 2 types of isometric contractions: sustained and rapid. Peak isometric torque was calculated from the sustained isometric contraction. Peak RTD was calculated from the rapid isometric contraction (0–50 and 0–200 ms after force initiation). Kinematic data were collected during the deceleration phase of a double-leg drop jump task. Linear regression was used to assess the ability of hip abductor muscle performance variables to predict peak knee valgus. Increased peak RTD during the 0 to 50 milliseconds window after force initiation was found to significantly predict lower peak knee valgus (P = .011, R2 = .32). In contrast, neither peak RTD from 0 to 200 milliseconds after force initiation window (P = .45, R2 = .03) nor peak isometric torque (P = .49, R2 = .03) predicted peak knee valgus. The inability of the hip abductors to rapidly generate muscular force may be more indicative of “at-risk” movement behavior in females than measures of maximum strength.

Objective The torque-producing capacity can be assessed as maximal isometric torque per muscle size. Nevertheless, the factors contributing to this capacity remain poorly understood. In general, the magnitude of joint torque production is determined not only by muscle size but also by joint moment arm (MA). Based on this background, we hypothesized that longer MA would be related to higher torque-producing capacity despite a given muscle size. To test this hypothesis, we examined the relationship between MA and toque-producing capacity in the knee extensors. The quadriceps femoris muscle volume (MV) and knee extensor MA in 30 healthy young men were measured using magnetic resonance imaging. The knee extensor isometric torque was measured using a dynamometer. The knee extensor torque-producing capacity was calculated as the knee extensor isometric torque per quadriceps femoris MV. Results The quadriceps femoris MV and knee extensor MA correlated significantly with the knee extensor isometric torque (r = 0.785 and 0.790, respectively, both Ps

Context: Traditionally, quadriceps activation failure after anterior cruciate ligament reconstruction (ACLR) is estimated using discrete isometric torque values, providing only a snapshot of neuromuscular function. Sample entropy (SampEn) is a mathematical technique that can measure neurologic complexity during the entirety of contraction, elucidating qualities of neuromuscular control not previously captured. Objective: To apply SampEn analyses to quadriceps electromyographic activity in order to more comprehensively characterize neuromuscular deficits after ACLR. Design: Cross-sectional. Setting: Laboratory. Participants: ACLR: n = 18; controls: n = 24. Interventions: All participants underwent synchronized unilateral quadriceps isometric strength, activation, and electromyography testing during a superimposed electrical stimulus. Main Outcome Measures: Group differences in strength, activation, and SampEn were evaluated with t tests. Associations between SampEn and quadriceps function were evaluated with Pearson product–moment correlations and hierarchical linear regressions. Results: Vastus medialis SampEn was significantly reduced after ACLR compared with controls (P = .032). Vastus medialis and vastus lateralis SampEn predicted significant variance in activation after ACLR (r2 = .444; P = .003). Conclusions: Loss of neurologic complexity correlates with worse activation after ACLR, particularly in the vastus medialis. Electromyographic SampEn is capable of detecting underlying patterns of variability that are associated with the loss of complexity between key neurophysiologic events after ACLR.

Objective Quadriceps dysfunction has been suggested as a complication after medial patellofemoral ligament (MPFL) reconstruction. The purpose of this study was to investigate changes in knee extensor strength before and after MPFL reconstruction. Methods Twenty patients who underwent MPFL reconstruction for unilateral recurrent patellar dislocation (18 females and 2 males; mean age 20.8 ± 7.6 years) were examined. The peak isometric torque at 60° and 90° of knee flexion and isokinetic knee extensor strength at speeds of 60°/s and 90°/s in operated and non-operated legs were measured using a dynamometer preoperatively and 6 months, 1 year, and 2 years postoperatively. The following parameters were evaluated: (1) body weight-adjusted muscle strength, (2) improvement index (post-/preoperative value × 100) (%), and (3) extensor strength ratio (operated/non-operated value × 100) (%). Results The mean knee extensor strength in both operated and non-operated legs significantly increased 2 years after surgery compared with that before surgery. At 2 years postoperatively, the improvement indexes of the isometric knee extensor strength at 60° and 90° and of the isokinetic knee extensor strength at 60°/s and 90°/s were 237%, 192%, 318%, and 186%, respectively, in the operated legs and 144%, 124%, 140%, and 140%, respectively, in the non-operated legs. At 2 years postoperatively, the mean isometric knee extensor strength ratios at 60° and 90° and the isokinetic knee extensor strength ratios at 60°/s and 180°/s were 81%, 84%, 81%, and 82%, respectively. Conclusions Knee extensor strength was improved in most patients after MPFL reconstruction, at least compared with that before surgery, although an approximately 20% deficit against the non-operated legs remained even 2 years after surgery.

INTRODUÇÃO: Dinamômetro isocinético é um equipamento eletrônico e mecânico, capaz de medir o torque gerado por um determinado segmento, bem como a potência e estimar fadiga, observando-se a variação do torque ao longo tempo. Este dispositivo também controla a velocidade do movimento angular, seja ele gerado por uma contração excêntrica ou concêntrica. Este tipo de equipamento tem sido utilizado tanto para avaliação como para treinamento de força. OBJETIVO: Verificar o efeito do treinamento de força, realizado exclusivamente no dinamômetro isocinético, na capacidade de gerar torque isométrico. MÉTODO: 2 homens, sedentários, saudáveis com idade de 23 e 24 anos realizaram 16 sessões de treinamento de força (sempre em esforço máximo e no modo concêntrico utilizando-se um dinamômetro isocinético) para os músculos flexores da articulação do cotovelo do membro dominante. As sessões foram compostas por um treinamento de quatro séries de oito repetições em uma amplitude de movimento de 130º, com velocidade fixada em 45º/s. As avaliações de contração isométrica voluntária máxima (CIVM) a 90º de flexão da articulação do cotovelo foram realizadas na primeira, oitava e décima sexta sessão. Espessura dos músculos flexores da articulação do cotovelo também foi medida, com ultrassonografia, nas mesmas sessões em que o torque máximo isométrico foi medido. RESULTADOS: Não houve diferença significativa no ganho de torque tam pouco na espessura muscular, ao final do treinamento. CONCLUSÃO: Treinamento de força, exclusivamente realizado no modo concêntrico no dinamômetro isocinético não provocou aumento da capacidade de gerar força isométrica, tam pouco aumento da espessura muscular.

Background The production of finger force control is essential for a large number of daily activities. There is evidence that deficits in the mechanisms of accuracy and control of finger force tasks are associated with children's motor difficulties. Objective To compare the effect of practice of an isometric finger force/torque task between children with significant movement difficulty and those with no difficulty movement. Methods Twenty-four children aged between 9 and 10 years (12 at risk of developmental coordination disorder and 12 with no movement difficulty – typically developing children) were asked to produce finger force/torque control in a continuous and constant 25% of maximum voluntary torque with visual feedback during 15 s. Practice was given during five consecutive days with 15 trials per day. After the practice with visual feedback, children were asked to perform five trials without visual feedback. In these trials, feedback was removed 5 s after the start of the trial. Results Typically developing children were consistently more accurate in maintaining finger force/torque control than those children at risk of developmental coordination disorder. Children from both groups improved the performance in the task according to practice sessions. Also, children at risk of developmental coordination disorder poorly performed the task without visual feedback as they did when visual feedback was available. Conclusion The present study give support to the idea that movement difficulty is associated with finger force/torque control and children at risk of developmental coordination disorder can improve finger force/torque control with practice when visual feedback is available.

Context: The Y Balance Test was developed as a test of dynamic postural control and has been shown to be predictive of lower-extremity injury. However, the relationship between hip strength and performance on the Y Balance Test has not been fully elucidated. Objective: The goal of this study was to identify the relationship between components of isometric hip strength and the Y Balance Test, to provide clinicians better guidance as to specific areas of muscle performance to address in the event of poor performance on the Y Balance Test. Design: Laboratory study. Setting: Biomechanics laboratory. Participants: A total of 73 healthy participants (40 males and 33 females) volunteered for this study. Intervention: None. Main Outcome Measures: Participants completed the Y Balance Test on the right leg. The authors then measured peak isometric torque in hip external rotation, abduction, and extension. Correlations were calculated between torque measurements, normalized for mass and Y Balance Test performance. Significant relationships were used in linear regression models to determine which variables were predictive of the Y Balance Test performance. Results: The authors found significant positive correlations between Y Balance Test performance and hip abduction strength. They also found correlations between the Y Balance Test and hip extension and external rotation strengths. Linear regression analysis showed hip abduction to be the only significant predictor of Y Balance performance. Conclusions: The authors found the strongest association between the Y Balance Test and hip abduction strength. They also showed smaller but significant associations with hip extension and external rotation strength. When entered into a linear regression analysis, hip abduction strength was the only significant predictor of Y Balance performance. Using this information, practitioners should look to hip abduction strength when patients exhibit deficits in the Y Balance Test.

Background Patellofemoral pain is common in physically active adults. Females with patellofemoral pain have been shown to have posterolateral hip muscle weakness, but there is a paucity of research examining hip muscle strength in males with patellofemoral pain. Hypothesis/Purpose The purpose of this study was to examine posterolateral hip muscle strength in males with patellofemoral pain compared to asymptomatic males. It was hypothesized that males with patellofemoral pain would have decreased strength of the hip extensor, hip external rotator, and hip abductor muscles compared to healthy, asymptomatic males. Study Design Descriptive, cross-sectional. Methods Thirty-six adult males with patellofemoral pain and 36 pain-free males participated in the study. The patellofemoral pain group were required to have retropatellar pain reproduced by activities that loaded the patellofemoral joint (squatting, descending stairs, etc.). Peak isometric torque of the hip extensors, hip external rotators, and hip abductors was measured with an instrumented dynamometer. Torque was normalized by body mass and height. Between-group differences were analyzed with parametric or non-parametric tests, as appropriate. The level of significance was adjusted for multiple comparisons. Results Hip extensor torque was significantly reduced in the patellofemoral pain group compared to the control group (p = .0165). No differences were found between groups for the hip external rotators or hip abductors (p > .0167). Conclusion Males with patellofemoral pain appear to have weakness of the hip extensors, but unlike females with patellofemoral pain, they do not appear to have weakness of the hip abductors or hip external rotators. The findings of this study suggest that muscle strength factors associated with patellofemoral pain in males may be different from muscle strength factors in females. Clinicians examining and designing plans of care for male patients with patellofemoral pain should consider that the hip abductors and hip external rotators may not be weak in men with this condition. Level of evidence Level 3.

Chu, E, Kim, Y-S, Hill, G, Kim, YH, Kim, CK, and Shim, JK. Wrist resistance training improves motor control and strength. J Strength Cond Res 32(4): 962-969, 2018-The aim of this study was to investigate the effects of a 6-week direction-specific resistance training program on isometric torque control and isokinetic torque strength of the wrist joint. Nineteen subjects were randomly assigned to either the wrist training group (n = 9) or the control group (n = 10). The training group performed wrist exercises in 6 directions (flexion, extension, pronation, supination, radial deviation, and ulnar deviation), whereas the control group did not. Data were collected on the isometric torque control, 1-repetition maximum (1RM) strength, and isokinetic maximum torque (angular velocity of 60° per second wrist movements) before and after 6 weeks of resistance training and at 2-week intervals during training. The training group showed significant decreases in isometric torque control error in all 6 directions after 2 weeks of resistance training, whereas the control group did not show significant increase or decrease. After 4 weeks of training, the training group showed significant increases in maximum strength in all 6 directions as assessed by 1RM strength and isokinetic strength tests, whereas the control group did not show any statistically significant changes. This study shows that motor control significantly improves within the first 2 weeks of resistance training, whereas the wrist strength significantly improves within the first 4 weeks of resistance training. Based on the findings of this study, coaches and trainers should consider wrist resistance training to improve athletes' muscular strength and control of the wrist muscles.

Study Design A controlled laboratory study, with a single-blind, block-randomization crossover design. Objectives To compare the electrically elicited knee extensor torque produced by 3 clinically available waveforms: 2500-Hz burst-modulated alternating current (BMAC), 1000-Hz BMAC, and 1000-Hz burst-modulated biphasic square-wave pulsed current (BMBPC). Background Neuromuscular electrical stimulation (NMES) is the therapeutic use of electrical current to strengthen muscle. Muscle torque produced by NMES is limited by discomfort. Methods The knee extensor maximal volitional isometric torque (KEMVIT) of 33 able-bodied participants (18 female) was measured and used to normalize the electrically elicited knee extensor torque to produce a percent of KEMVIT (%KEMVIT). Electrically elicited isometric knee extensor torque was measured in response to each of the waveforms at the participants' maximum tolerance. Results The average maximum tolerated stimulation produced 32.0 ± 16.7 %KEMVIT with 2500-Hz BMAC, 38.2 ± 18.4 %KEMVIT with 1000-Hz BMAC, and 42.2 ± 17.1 %KEMVIT with 1000-Hz BMBPC. Tukey honest significant difference (HSD) post hoc testing revealed a statistically significant difference between 2500-Hz BMAC and 1000-Hz BMAC (P = .046), and between 2500-Hz BMAC and 1000-Hz BMBPC (P.001). No statistically significant difference was found between 1000-Hz BMAC and 1000-Hz BMBPC (P = .267). Conclusion For eliciting maximum knee extensor muscle torque, 1000-Hz BMBPC and 1000-Hz BMAC were similarly effective, and 2500-Hz BMAC was less effective. J Orthop Sports Phys Ther 2018;48(3):217-224. Epub 19 Dec 2017. doi:10.2519/jospt.2018.7601.

The objectives of this research were to: (1) investigate the effects of handwheel height and angle of a valve on the muscle loading of shoulder, neck, and back muscles; and (2) identify a handwheel height and angle that best distributes the load of torque exertions to different muscles. Fifteen healthy male participants were recruited for this study. The handwheel heights included knee, elbow, shoulder, and overhead levels. The handwheel angles included 0°, 45°, and 90°. At each height-angle combination, participants performed an isometric torque exertion on a handwheel. During each trial, the maximum electromyography (EMG) activities were measured from the right and left anterior deltoids, trapezii, latissimi dorsi, and erector spinae muscles. EMG data were normalized and reported as percentages of reference contractions (RC). A two factor split-plot analysis of variance (ANOVA) and Tukey multiple pairwise comparison tests were performed to determine the significant effects. Results show that a handwheel at overhead 45°, which allows the greatest torque production, is associated with a concentrated load on the right anterior deltoid (94.1 %RC). At elbow level, participants were exposed to low loads on the shoulder and neck muscles, but that was compensated with higher loads on the back muscles. Based on the EMG results, the best handwheel height and angle appeared to be at shoulder 0°. At this height and angle, seven of the eight muscles were working at or close to their lowest EMG activities, while also allowing the production of relatively large torques (65.2 Nm).

Introduction Volumetric muscle loss (VML) occurs following significant traumatic injury or surgical removal of skeletal muscle, resulting in nonrecoverable loss of tissue and long-term dysfunction. Perhaps less recognized is that VML injuries inherently disrupt the neuromuscular unit, resulting in fiber denervation and presumptive motor unit rearrangement, expansion, and/or loss. To characterize neural dysfunction we quantified motoneuron axotomy, in efforts to understand how this relates to the temporal coordination of neuromuscular and morphological alterations due to injury. Methods In an established rat tibialis anterior (TA) VML injury model, we examined the motoneuron, skeletal muscle, and maximal isometric torque at 3, 7, 14, and 21 days postinjury. Results Significant axotomy of 57-79% of all TA muscle motoneurons was observed through 21 days postinjury, which was coupled with a 45-90% TA maximal torque deficit. Discussion A ∼20% partial ablation of the TA muscle causes disproportionate damage across the motor unit acutely postinjury. Muscle Nerve 57: 799-807, 2018.

The purpose of this study was to compare the benefits and possible problems of 4 weeks stretching when taken to the point of pain (POP) and to the point of discomfort (POD). Twenty-six physically active women (20 ± 1.1 years) took part in group-based stretching classes of the hamstring muscles, 4 times per week for 4 weeks, one group one stretching to POD, the other to POP. Passive stiffness, joint range of motion (ROM), maximal isometric torque and concentric knee flexion torque, were measured before training and 2 days after the last training session. Hip flexion ROM increased by 14.1° (10.1°–18.1°) and 19.8° (15.1°–24.5°) and sit-and-reach by 7.6 (5.2–10.0) cm and 7.5 (5.0–10.0) cm for POD and POP, respectively (Mean and 95% CI; p

Objective: To analyze the effect of maximal voluntary isometric contractions and of electroestimulation on isometric torque and muscle activation of the brachii triceps in physically active adult males. Methods: Nineteen men underwent isometric force tests as pre-test, through 10-second long maximal voluntary isometric contractions and conditioning activities randomized: isometric contraction during 7, 10 and 12 seconds and electric stimulation in 70 and 120 Hz for 10 seconds each. After the conditioning activities, two voluntary isometric contractions were performed for 10 seconds with interval of 4 and 8 minutes, respectively. The muscle electrical activity of brachii triceps (medial and lateral portion’s) was measured. Results: It was not verified effect in any conditions to maximal or mean torque (P>0.05), likewise to muscle electrical activity of brachii triceps (P>0.05). Conclusion: The interval adopted among the conditioning activities and the isometric force test was not enough to induce the isometric torque improvement.

Introduction Despite assumptions, there is an absence of research on acute fatigue responses to high- and low-load and advanced technique resistance exercise. Methods Trained males (n = 8; age 27.2 ± 7.4 years, height 180.0 ± 6.6 cm, weight: 86.6 ± 10.3 kg) were assessed for decrement in maximal voluntary isometric torque (MVIT) and perceived effort and discomfort after heavier load (HL; 80% MVIT), lighter load (LL; 30% MVIT), forced repetition (FR), and breakdown set (BD) training protocols. Results Analyses revealed a significant reduction in MVIT (P 0.05). Discussion Fatigue as a decrement in force production appears to follow a more complex relationship than simply 100% minus the force requirements of the task relative to a maximal voluntary contraction. Muscle Nerve 56: E141–E146, 2017

Following exercise-induced muscle damage (EIMD), masters athletes take longer to recover than younger athletes. The purpose of this study was to determine the effect of higher than recommended postexercise protein feedings on the recovery of knee extensor peak isometric torque (PIT), perceptions of recovery, and cycling time trial (TT) performance following EIMD in masters triathletes. Eight masters triathletes (52 ± 2 y, V̇O2max, 51.8 ± 4.2 ml•kg-1•min-1) completed two trials separated by seven days in a randomized, doubleblind, crossover study. Trials consisted of morning PIT testing and a 30-min downhill run followed by an eight-hour recovery. During recovery, a moderate (MPI; 0.3 g•kg-1•bolus-1) or high (0.6 g•kg-1•bolus-1) protein intake (HPI) was consumed in three bolus feedings at two hour intervals commencing immediately postexercise. PIT testing and a 7 kJ•kg-1 cycling TT were completed postintervention. Perceptions of recovery were assessed pre- and postexercise. The HPI did not significantly improve recovery compared with MPI (p > .05). However, comparison of within-treatment change shows the HPI provided a moderate beneficial effect (d = 0.66), attenuating the loss of afternoon PIT (-3.6%, d = 0.09) compared with the MPI (-8.6%, d = 0.24). The HPI provided a large beneficial effect (d = 0.83), reducing perceived fatigue over the eight-hour recovery (d = 1.25) compared with the MPI (d = 0.22). Despite these effects, cycling performance was unchanged (HPI = 2395 ± 297 s vs. MPI = 2369 ± 278 s; d = 0.09). In conclusion, doubling the recommended postexercise protein intake did not significantly improve recovery in masters athletes; however, HPI provided moderate to large beneficial effects on recovery that may be meaningful following EIMD.

Purpose: The aim of the study was to assess the usefulness of isometric torque (IT) and peak torque (PT) of the hamstring to quadriceps muscles ratio (H/Q ratio) in monitoring the effectiveness of physiotherapy (PH) in males after ACLR. Hypothesis: The H/Q ratio is a diagnostic tool for monitoring of the effectiveness of the 6- month PH after ACLR. Methods: Twenty males 6 months after ACLR (ACLR group) and 20 male controls underwent IT and PT (60°/s and 180°/s) bilateral measurements of H and Q muscles. The IT and PT were normalized to body mass, and expressed as relative IT (RIT) and relative PT (RPT). The RIT and RPT H/Q ratios, and Limb Symmetry Index (LSI) were calculated. Results: In the ACLR group, the RIT for the H and Q, the RIT for the H/Q ratio and most of the RPT, as well as the H/Q ratio, ROM and LSI values of the operated knee, were not significantly different (NSD) than those of the non-operated side (NOS) or the control group. The between-group comparison of the H/Q ratio for RIT and RPT weren’t NSD. The isokinetic test at 180°/s showed lower RPT, H/Q ratio and LSI values for the Q muscle than those of the NOS (p = 0.042, p = 0.001). Conclusions: The H/Q ratio, in combination with the RIT, RPT and LSI, is a useful diagnostic tool for monitoring the effectiveness of 6-month PH after ACLR. Restoring the correct H/Q ratio can reduce the risk factor for ACL graft rupture.

Context: Myofascial self-release is performed using a roller to exert pressure on the soft tissues and to promote effects similar to those of traditional massage. However, there is no standardization regarding its application, mainly in relation to time. Objective: To evaluate the effects of myofascial self-release with a rigid roller on range of motion (ROM), pressure pain threshold (PPT), and hamstring strength in asymptomatic individuals following 2 different times of intervention. Design: Randomized, controlled, blind, clinical trial comparing preintervention and immediately postintervention within 2 groups. Setting: Institutional physiotherapy clinic. Participants: A total of 40 university students (18–30 y), who had no symptoms, participated. Intervention: Foam roller for 30 seconds and 2 minutes for group 2. Main Outcome Measures: Hamstring PPT, knee-extension ROM, and peak knee-flexion torque measured before and immediately after the intervention. Results: Both groups experienced a statistically significant increase in ROM compared with baseline (30 s and 2 min for group 2 P Conclusions: Hamstring myofascial self-release using a roller for 30 seconds or 2 minutes produced an increase in ROM in healthy individuals. PPT and peak knee-flexion isometric torque showed no effects.

Made available in DSpace on 2018-12-11T17:38:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-10-01 Background: Pilates exercises help stabilize the vertebral segments by recruiting the abdominal and spinal muscles. Pilates training may increase joint stability and improve neuromuscular efficiency (NME). Objective: This study aimed to evaluate NME of the multifidus (MU) muscle through electromyography (EMG) analysis and torque test, applied to practitioners and non-practitioners of Pilates. Methods: Participants included thirty women: Pilates practitioners (n = 15) and non-practitioners (n = 15). They were tested for trunk extension. Their right and left MU muscles were submitted to EMG to estimate NME. Results concerning torque, EMG, and NME from all participants were compared. Results: Statistical analysis concerning isometric torque peak (p = 0.0275) and NME (p = 0.0062) showed significant difference (Student t test; p < 0.05) between practitioners and control. No significant difference (p = 0.3387) in EMG was observed. Conclusion: Our results suggest Pilates exercises is effective in training spinal muscles to improve NME in women. Department of Morphology (Anatomy) Piracicaba Dental School University of Campinas (UNICAMP) Department of Physical Education São Paulo State University (UNESP) Department of Physical Education São Paulo State University (UNESP)

Neuromuscular fatigue (NMF) is usually assessed non-invasively in healthy, athletic or clinical populations with the combination of voluntary and evoked contractions. Although it might appear relatively straightforward to magnetically or electrically stimulate at different levels (cortical/spinal/muscle) and to measure mechanical and electromyographic responses to quantify neuromuscular adjustments due to sustained/repeated muscle contractions, there are drawbacks that researchers and clinicians need to bear in mind. The aim of this opinion paper is to highlight the pitfalls inevitably faced when NMF is quantified. The first problem might arise from the definition of fatigue itself and the parameter(s) used to measure it; for instance, measuring power vs. isometric torque may lead to different conclusions. Another potential limitation is the delay between exercise termination and the evaluation of neuromuscular function; the possible underestimation of exercise-induced neural and contractile impairment and misinterpretation of fatigue etiology will be discussed, as well as solutions recently proposed to overcome this problem. Quantification of NMF can also be biased (or not feasible) because of the techniques themselves (e.g. results may depend on stimulation intensity for transcranial magnetic stimulation) or the way data are analyzed (e.g. M wave peak-to-peak vs first phase amplitude). When available, alternatives recently suggested in the literature to overcome these pitfalls are considered and recommendations about the best practices to assess NMF (e.g. paying attention to the delay between exercise and testing, adapting the method to the characteristics of the population to be tested and considering the limitations associated with the techniques) are proposed.

The purpose of this study was to demonstrate the differences in shoulder muscle strength, cross-sectional area of the rotator cuff muscles, acromiohumeral distance, and supraspinatus tendon thickness between symptomatic and asymptomatic patients with rotator cuff tears.Thirty-two symptomatic patients and 23 asymptomatic patients with rotator cuff tears participated in this study. Data of the patients with any type of tear and supraspinatus tear were analyzed. We evaluated the isometric torque, cross-sectional area of the rotator cuff muscles, supraspinatus tendon thickness, acromiohumeral distance, range of motion, and Western Ontario Rotator Cuff Index.Asymptomatic patients showed greater isometric torque of shoulder abduction and internal rotation than symptomatic patients with any type of tear (P ≤ .01). Asymptomatic patients also demonstrated greater cross-sectional area of the supraspinatus (P.01); however, there was no significant difference in the cross-sectional area of the other cuff muscles. There was also no significant difference in the supraspinatus tendon thickness (P = .10). The acromiohumeral distance at 90° of shoulder abduction was larger (P = .04) in asymptomatic patients. Additionally, similar tendencies were observed in the results of patients with supraspinatus tears, except for the isometric torque of shoulder external rotation. This torque was greater (P.01) in asymptomatic patients.Asymptomatic patients showed greater shoulder range of motion, muscle strength of shoulder abduction and internal rotation, small occupation ratio of supraspinatus tendon thickness as a percentage of acromiohumeral distance, and large cross-sectional area of supraspinatus.

This study examined whether changes in strength following a moderate-duration strength training program were associated with changes in specific combinations of anatomical and neuromuscular variables. 36 men (18–40 y) completed 10 weeks of lower-limb heavy resistance (6-RM) strength training. Measurements included cross-sectional area (CSA), fascicle length (lf) and fascicle angle (θf) from proximal, middle and distal regions of the four quadriceps components; agonist (EMG:M), antagonist (EMG) muscle activities and percent voluntary quadriceps activation (%VA; interpolated twitch technique); patellar tendon moment arm distance; and maximal isometric, concentric and eccentric (60° s–1) torque. Multiple regression models were developed to quantify the relationship between the change in maximum torque and the changes in combinations of anatomical and neuromuscular variables. The best model for each contraction mode was determined using Akaike’s Information Criterion (AICc), an information-theoretic approach for model selection. Strength increased significantly following training (mean range = 12.5–17.2%), and moderate relationships were observed between modeled data (using best-fit prediction models) and the change in torque for each contraction mode. The change in isometric torque was best (although weakly) predicted by the linear combination of the change in proximal-region vastus lateralis (VL) CSA and fascicle angle (R2 = 0.27, p < 0.05; AICcwi = 0.52, i.e., the probability the model would be selected as the “best model”). The models best predicting the change in concentric and eccentric torque both included the combination of the change in quadriceps (i.e., mean of all muscles) EMG:M and the change in vastus intermedius fascicle angle combined with either a change in proximal-region VL (R2 = 0.40, p < 0.001; AICcwi = 0.15) or whole quadriceps (R2 = 0.41, p < 0.001; AICcwi = 0.30) CSA (concentric and eccentric, respectively). Models incorporating the change in proximal CSA typically received substantial support (AICC < 2) for concentric torque prediction models, and the change in % VA and pre-training moment arm distance had substantial support for use in eccentric torque prediction models. In conclusion, adaptations varied between individuals, however strength training programs targeted to improve a group of variables that particularly includes agonist muscle activation might yield the greatest improvements in concentric and eccentric knee extension strength, whereas proximal muscle size and fascicle angle appear most important for isometric torque improvements.

Background and Purpose: The effect of knee angle on electrically elicited quadriceps muscle torque has not been established. The goal of this study was to determine which knee angle allowed for the production of the greatest knee extensor maximal voluntary isometric torque (KEMVIT), the greatest electrically elicited torque, and the highest percent of KEMVIT from the knee extensor muscles. Case Description: Eighteen participants were secured in a force dynamometer with the knee positioned at 30°, 60°, and 90° flexion. Participants performed KEMVITs followed by electrically elicited contractions to their maximum tolerance. Outcomes: The mean ± SD of the peak KEMVITs was 123.7 ± 35.7 Nm, 222.6 ± 67.1 Nm, and 248.2 ± 81.1 Nm at 30°, 60°, and 90°, respectively. Significantly greater KEMVITs were produced at 60° and 90° than at 30° (p < 0.001). The mean ± SD of the maximally tolerated electrically elicited torques was 71.8 ± 18.8 Nm, 170.9 ± 70.4 Nm, and 134.6 ± 72.6 Nm at 30°, 60°, and 90°, respectively. Significantly higher torques were tolerated at 60° than at 30° (p < 0.001) and 90° (p = 0.018). The mean ± SD of the percent KEMVITs was 59.7 ± 11.7%, 78.2 ± 23.8%, and 52.6 ± 18.7% at 30°, 60°, and 90°, respectively. Significantly greater percent KEMVITs were produced at 60° than at 30° (p = 0.001) and 90° (p < 0.001). Discussion: Electrically elicited quadriceps torque production is greater at 60° as compared to 30° and 90° knee flexion.

NEW FINDINGS What is the central question of this study? Why do some subjects recover slowly following a bout of eccentric exercise and why is recovery faster following a repeated bout? What is the main finding and its importance? The results are consistent with two major causes of the reduction of quadriceps torque, the onset of low-frequency fatigue which recovered relatively fast and a second, delayed form of damage. Differences in the delayed damage process largely accounted for the differences in the rate of torque recovery between subjects after a first bout and it was suppression of the delayed damage which accounted for the faster recovery following a repeated bout of eccentric exercise. ABSTRACT The purpose of this study was to determine the extent to which low-frequency fatigue (LFF) accounts for the loss of quadriceps strength and time course of recovery following a series of drop jumps (DJs). Seventeen female subjects (20.8 ± 1.4 years) undertook 100 DJs, which were repeated 4 weeks later. Maximum isometric torque (MIT) and the ratio of torque generated by 20 and 100 Hz electrical stimulation (20/100), as a measure of LFF, were measured over 7 days following each series of DJs. After the first series the 20/100 ratio fell to a greater extent than MIT (to 35 ± 8.7% and 69 ± 11%, respectively) but recovered over 2-3 days, while MIT showed little recovery over this time. Changes of the 20/100 ratio were similar between subjects with fast or slow MIT recovery. Following the second series of DJs, changes in the 20/100 ratio were similar to those of the first bout and there were no differences between fast and slow recovering subjects. MIT, however, recovered more rapidly than after the first bout; the faster recovery was confined to the subjects who recovered slowly following the first bout. The results are consistent with two major causes of the reduction of quadriceps torque, the onset of low-frequency fatigue which recovered relatively fast and a second, delayed, form of damage. The latter largely accounted for the differences in MIT recovery between subjects after the first bout, while suppression of the delayed damage accounted for the faster recovery following the repeated bout.

Previous results have shown experimental evidence that the muscle response to neuromuscular electrical stimulation (NMES) is delayed; the time lag is often referred to as electromechanical delay. NMES closed-loop control methods have been developed to compensate for a known constant input delay. However, as a muscle fatigues, this delay increases. This paper develops a feedback controller that robustly compensates for the time-varying delay of an uncertain muscle model during isometric contractions. The controller is proven to yield global uniformly ultimately bounded torque tracking error. Experimental results illustrate the effectiveness of the developed controller and the time-varying nature of the delayed response.

BACKGROUND We tested the hypothesis that, in patients participating in 17 weeks of postoperative physiotherapy after anterior cruciate ligament reconstruction (ACLR), maximal isometric torque (IT) and peak torque (PT) generated by the muscles affecting the operated knee joint in the sagittal and transverse planes are not restored. We also present the application of IT and PT measurements of the muscles affecting the knee joint in 2 planes of motion. MATERIAL AND METHODS IT and PT of the knee extensor and flexor muscles and the muscles internally rotating the shin were measured in 30 males who participated in postoperative physiotherapy for 17 weeks after ACLR (ACLR group) and 30 males with no injuries (control group). RESULTS Significantly lower IT and PT values were noted in the operated knee extensors and flexors. The differences were also noted in the PT for the muscles internally rotating the shin and in the IT of those muscles in the position of 25° of internal rotation. Significantly lower relative IT and PT values were noted for studied muscle groups in comparison to the control group. CONCLUSIONS Seventeen weeks of postoperative physiotherapy after ACLR did not result in complete restoration of IT and PT of the muscles affecting the operated knee joint, suggesting that even after 17 weeks of physiotherapy following ACLR, athletes may not be ready to return to sports. The results demonstrate the usefulness of biplanar analysis of muscle strength under isometric and isokinetic conditions in the monitoring and assessment of physiotherapeutic procedures.

Objective To determine if maximal isometric contraction (MVIC) method (i.e., ramp (MVICRAMP) versus traditional MVIC) influences (1) maximal voluntary isometric torque (MVIT) production of the knee extensors, (2) electromyographic signal amplitude (EMGAMP), and (3) EMG mean power frequency (EMGMPF) of the rectus femoris and vastus lateralis in moderately-to highly-activated subjects. We hypothesized that EMGAMP would be greater during the MVICRAMP than MVIC muscle contractions, but that there would be no difference in MVIT. Approach Twenty-five males (23.4 ± 3.4 y; % voluntary activation = 93.9 ± 5.1%) visited the laboratory and completed MVICRAMPs and MVICs. During all contractions, leg extensor torque and sEMG signals from the vastus lateralis (VL) and rectus femoris (RF) were recorded. Main results There was no significant difference in the MVIT produced (p = 0.65) or in EMGMPF (p = 0.052) during MVICRAMP versus MVIC. However, EMGAMP was 18.1% higher during the MVICRAMP than MVIC (p = 0.004). Significance Maximal isometric muscle contraction method significantly influenced EMGAMP, and had a moderate effect on EMGMPF (d = 0.49). Investigators who utilize MVICs to determine maximal EMG signal amplitude and frequency to normalize their EMG signals should be aware of these differences.

The purpose of this study was to investigate the effects of a single-dose of β-hydroxy-β-methylbutyrate free acid (HMB-FA) supplementation on muscle recovery after a high-intensity exercise bout. Twenty-three trained young males were randomly assigned to receive either a single-dose supplementation of 3 g of HMB-FA (n = 12; age, 22.8 ± 3.0 years) or placebo (PLA; n = 11; age, 22.9 ± 3.1 years). A muscle damage protocol was applied 60 min after supplementation, and consisted of 7 sets of 20 drop jumps from a 60-cm box with 2-min rest intervals between sets. Muscle swelling, countermovement jump (CMJ), maximal voluntary isometric torque (MVIT), and work capacity (WC) were measured before, immediately after, and 24, 48, and 72 h after the exercise protocol. Muscle swelling, CMJ, and MVIT changed similarly in both groups after the exercise protocol (p < 0.001), but returned to pre-exercise levels after 24 h in both groups. WC decreased similarly in both groups after the exercise protocol (p < 0.01). For HMB-FA, WC returned to pre-exercise level 24 h after exercise protocol. However, for PLA, WC did not return to pre-exercise level even 72 h after the exercise protocol. In summary, a single-dose of HMB-FA supplementation improved WC recovery after a high-intensity exercise bout. However, HMB-FA did not affect the time-course of muscle swelling, MVIT, and CMJ recovery.

New Findings What is the central question of this study? Does contraction influence the fascicle length, pennation angle and effective physiological cross-sectional area (effPCSA) of the quadriceps femoris muscle? Is there a stronger relationship between effPCSA and maximal strength if effPCSA is measured during maximal contraction rather than at rest? What is the main finding and its importance? Fascicle length decreased, pennation angle increased and effPCSA increased in a non-linear manner with isometric torque. The effPCSA during maximal contraction and rest were correlated in a similar manner to maximal strength. The effPCSA at rest is sufficient to characterize the muscle size–strength relationship. The primary purpose of this study was to document the influence of muscle contraction on quadriceps femoris (QF) muscle architecture [fascicle length (Lf) and pennation angle (θp)] and effective physiological cross-sectional area (effPCSA). Secondarily, we aimed to determine whether effPCSA measured during maximal voluntary contraction (MVC) had a stronger relationship to maximal strength than effPCSA at rest. Fifteen young men performed a series of voluntary knee-extension isometric ramp contractions. Isometric maximal voluntary torque (MVT) was recorded during separate MVCs. Measurements of architecture and effPCSA of each constituent muscle of the QF and, subsequently, the whole QF were made at rest, during 20% increments of maximal voluntary torque and during an MVC. The QF muscle architecture and morphology changed in a curvilinear manner with relative torque (%MVT), with significant differences being observed between incremental torque levels for Lf, θp and effPCSA. Specifically, from rest to MVC, QF Lf decreased (–23.5 ± 3.3%), whereas θp increased (+39.7 ± 6.6%). The QF effPCSA was +26.5 ± 5.7% greater during MVC than at rest. Similar moderate correlations existed for MVT and effPCSA at rest (r = 0.519, P = 0.047) and for MVT and effPCSA during MVC (r = 0.530, P = 0.042). Substantial changes in QF architecture (Lf, θp) and effPCSA occur in a curvilinear manner with relative torque production. The effPCSA during MVC was no more strongly associated with MVT than effPCSA measured at rest, which implies that resting measurements of muscle size are suitable for characterizing the muscle size–strength relationship.

It is believed that sport massage after intensive exercise might improve power and perceptual recovery in athletes. However, few studies have been done in this area. This study aimed to examine the effect of massage on the performance of bodybuilders. Thirty experienced male bodybuilders were randomly assigned to either a massage group (n = 15) or a control group (n = 15). Both groups performed five repetition sets at 75-77% of 1RM of knee extensor and flexor muscle groups. The massage group then received a 30-min massage after the exercise protocol while the control group maintained their normal passive recovery. Criteria under investigation included: plasma creatine kinase (CK) level, agility test, vertical jump test, isometric torque test, and perception of soreness. All variables were measured over 6 time periods: baseline, immediately after the DOMS inducing protocol, right after the massage, and 24, 48, and 72 h after the massage. Both groups showed significant (P .001) decreases in jumping, agility performance, and isometric torque, but significant (P .001) increases in CK and muscle soreness levels. The massage group in general demonstrated a better recovery rate. As such, a post-exercise massage session can improve the exercise performance and recovery rate in male bodybuilders after intensive exercise.

One of the fundamental adaptations observed with resistance training (RT) is muscle hypertrophy. Conventional and isokinetic machines provide different forms of mechanical stress, and it is possible that these two training modes could promote differing degrees of hypertrophic adaptations. There is a lack of data comparing the selective hypertrophy of the quadriceps musculature after training with a conventional knee extension machine versus an isokinetic machine. The purpose of this study was to evaluate the selective hypertrophy of the quadriceps musculature and knee extension maximal isometric torque after 14 weeks of conventional versus isokinetic RT. Thirty-five men were assigned to three groups: control group and training groups (conventional and isokinetic) performed three sets of unilateral knee extensions per session with a progressive loading scheme twice a week. Prior to and following the intervention, maximal isometric knee extensor torque was measured using an isokinetic dynamometer, and muscle thickness (MT) of quadriceps femoris muscles was assessed via ultrasound. The results indicated non-uniform changes in MT between the muscles that comprise the quadriceps femoris group. For the conventional group, significantly greater increases in rectus femoris thickness were evident versus all other quadriceps muscles (14%). For the isokinetic group, increases in RF thickness (11%) were significantly greater in comparison with the vastus intermedius only. Although the muscle thickness did not increase for all the quadriceps femoris muscles, the relative rectus femoris adaptation suggested a selective hypertrophy favouring this portion.

Animal studies suggest that regular exposure to whole-body vibration (WBV) induces an anabolic response in bone and tendon. However, the effects of this type of intervention on human tendon properties and its influence on the muscle-tendon unit function have never been investigated. The aim of this study was to investigate the effect of WBV training on the patellar tendon mechanical, material and morphological properties, the quadriceps muscle architecture and the knee extension torque-angle relationship. Fifty-five subjects were randomized into either a vibration, an active control, or an inactive control group. The active control subjects performed isometric squats on a vibration platform without vibration. Muscle and tendon properties were measured using ultrasonography and dynamometry. Vibration training induced an increase in proximal (6.3%) and mean (3.8%) tendon cross-sectional area, without any appreciable change in tendon stiffness and modulus or in muscle architectural parameters. Isometric torque at a knee angle of 90° increased in active controls (6.7%) only and the torque-angle relation remained globally unchanged in all groups. The present protocol did not appreciably alter knee extension torque production or the musculo-tendinous parameters underpinning this function. Nonetheless, this study shows for the first time that WBV elicits tendon hypertrophy in humans.