Maximal Voluntary Contraction Torque Research Articles

Modified Pulvertaft on Weave Technique Restores Full Active Knee Extension in Patients With Large Chronic Quadriceps Tendon Rupture: A Case Series

We aimed to investigate the clinical and functional outcomes, including maximal and explosive strength, after chronic quadriceps tendon rupture repair with Modified Pulvertaft on Weave (MPW) technique METHODS: Knee joint range of motion (ROM), patella height, thigh circumference, and Lysholm and International Knee Documentation Committee (IKDC) scores were assessed preoperatively and postoperatively. The knee extensors maximal (isokinetic peak torque and isometric maximal voluntary contraction (MVC) torque) and explosive strength-rate of torque development (RTD) early [RTD50 and RTD100] and late [RTD250]-were performed. We assessed the thigh circumference and vastus lateralis muscle thickness (MT) as indicators of quadriceps muscle mass, and the voluntary quadriceps activation using surface electromyography (EMG50). Nine patients (mean age: 53 ± 11 years) took part in the study. We observed a significant increase in the knee active ROM and a decreased extension deficit (both, P < .001), but not for pain (P= .07), IKDC (P= .07), and Lysholm (P= .21) after the surgery. We did not observe a difference between involved (n= 8) and uninvolved (n= 10) limbs for ROM, thigh circumference, and MT. We observed differences for extensors peak torque, MVC torque, and late RTD (all, P < .05). However, we did not observe differences for early RTD and EMG50. Significant positive correlations were observed for RTD50 (ρ= .80) and RTD100 (ρ= .81) vs EMG50. Both the IKDC and Lysholm were better correlated with the early than with later RTD. The MPW reestablished the active knee extension. The same level of quadriceps muscle mass was observed in both limbs, suggesting a lack of hypotrophy due to the injury. Although the involved limb had demonstrated lower knee extensors maximal strength, they demonstrate an equivalent early RTD when compared to the uninvolved limb. The early RTD seems to be better correlated with the patient's functionality than the later RTD and maximal strength. IV, case series.

Inter-Person Differences in Isometric Coactivations of Triceps Surae and Tibialis Anterior Decrease in Young, but Not in Older Adults After 14 Days of Bed Rest

We examined activation patterns of the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), soleus (SO), and tibialis anterior (TA) muscles in eight older (58.4 ± 3.3 years) and seven young (23.1 ± 2.9 years) participants, before and after 14 days of horizontal bed rest. Visual feedback on the exerted muscle torque was provided to the participants. The discharge patterns of individual motor units (MUs) were studied in three repetitions of isometric plantar flexion at 30 and 60% of Maximum Voluntary Contraction (MVC), before, and 1 day after the 14-day bed rest, respectively. In the GL and GM muscles, the older participants demonstrated higher MU discharge rates than the young, regardless of the contraction level, both before and after the bed rest. In the TA and SO muscles, the differences between the older and young participants were less consistent. Detailed analysis revealed person-specific changes in the MU discharge rates after the bed rest. To quantify the coactivation patterns we calculated the correlation coefficients between the cumulative spike trains of identified MUs from each muscle, and measured the root mean square difference of the correlation coefficients between the trials of the same session (intra-session variability) and between different sessions (inter-session variability) in each participant (intra-person comparison) and across participants (inter-person comparison). In the intra-person comparison, the inter-session variability was higher than the intra-session variability, either before or after the bed rest. At 60% MVC torque, the young demonstrated higher inter-person variability of coactivation than the older participants, but this variability decreased significantly after the bed rest. In older participants, inter-person variability was consistently lower at 60% than at 30% MVC torque. In young participants, inter-person variability became lower at 60% than at 30% MVC torque only after the bed rest. Precaution is required when analyzing the MU discharge and coactivation patterns, as individual persons demonstrate individual adaptations to aging or bed rest.

Maximum isometric torque at individually-adjusted joint angles exceeds eccentric and concentric torque in lower extremity joint actions

BackgroundPrevious research indicates the high relevance of optimal joint angles for individual isometric strength assessment. The objective was to compare lower limb peak isometric muscle strength abilities at the strongest joint angles with those of dynamic contractions in healthy young adults.MethodsEighteen young male adults performed maximum concentric, isometric, and eccentric contractions of the ankle, knee, and hip flexors and extensors, and hip adductors and abductors in a randomized sequence on an isokinetic dynamometer (ISOMED 2000). Angular velocity was set at 60°/s. The peak of concentric contraction torque curves was used to define optimal joint angles best suited to generate maximum torque during isometric contractions. Maximum voluntary contraction torque of all contraction conditions was adjusted for limb weight and analyzed via a generalized linear mixed gamma regression model (GLMM).ResultsThe gamma GLMM revealed strongly significant effects for all three categorical covariates (contraction types, muscle group, and test order) (p < 2 times 10^{ - 16}). Eccentric contraction increases the muscle torque (hat{beta }_{k} = 0.147) compared to concentric contraction, and isometric contraction even more (hat{beta }_{k} = 0.258). A moderate individual-specific variation was found (random effects standard deviation sigma_{b} = 0.093).ConclusionThe results support the importance of optimal joint angles for isometric maximum strength assessment. When such conditions are given, isometric contractions can produce higher muscle torques than eccentric contractions in the lower body.

Acute Effects of Local Ischemic Hypoxia and Systemic Hypoxemia on Neuromuscular and Cognitive Function

Rivera, Paola M., Chris E. Proppe, Esther Beltran, and Ethan C. Hill. Acute effects of local ischemic hypoxia and systemic hypoxemia on neuromuscular and cognitive function. High Alt Med Biol. 23:18-25, 2022. Background: The application of blood flow restriction (BFR) induces local ischemic hypoxia within the muscle(s) distal to the restriction device. Systemic hypoxemia via oxygen or barometric pressure manipulation achieves whole-body hypoxia and thus may be a more potent exercise adjunct than BFR. Therefore, the purpose of this study was to examine the acute effects of local ischemic hypoxia versus systemic hypoxemia on maximal voluntary isometric contraction (MVIC) torque, electromyographic amplitude (EMG AMP), EMG mean power frequency (MPF), and cognition. Materials and Methods: Twelve recreationally trained women (mean age ± standard deviation = 21 ± 1.6 years) performed 75 submaximal (1 × 30, 3 × 15) unilateral leg extension muscle actions under normoxia, local ischemic hypoxia, and systemic hypoxemia. Before and immediately after the 75 repetitions, MVIC muscle actions were performed, and surface EMG was simultaneously assessed from the vastus lateralis. Cognitive function was assessed immediately after each exercise using the Automated Neuropsychological Assessment Metrics (ANAM). Separate repeated-measures analyses of variance (ANOVAs) were performed to examine changes in MVIC, reaction time, EMG AMP, and EMG MPF responses during the MVIC muscle actions. Results: There were no significant (p = 0.21-0.953) Condition × Time interactions for MVIC, EMG AMP, or EMG MPF but a significant (p < 0.001-0.005) main effect for the Time collapsed across Condition for MVIC torque (pretest 238.8 ± 19.5, posttest 212.7 ± 20.1 Nm) and EMG MPF (88.5% ± 1.4% of pretest). There were no significant (p = 0.503) differences in reaction time among Conditions. Conclusions: The findings of the present study suggest that all three conditions elicited comparable acute changes in performance as assessed by MVIC torque that were associated with no changes in muscle activation but decrease in action potential conduction velocity. Therefore, the application of local ischemic hypoxia or systemic hypoxemia during low-load resistance exercise can be used to elicit similar acute physiological responses and not adversely affect cognitive function relative to nonhypoxic conditions.

Severe acute hypoxia impairs recovery of voluntary muscle activation after sustained submaximal elbow flexion.

The purpose of this study was to determine how severe acute hypoxia alters neural mechanisms during, and following, a sustained fatiguing contraction. Fifteen participants (25±3.2years, six female) were exposed to a sham condition and a hypoxia condition where they performed a 10min elbow flexor contraction at 20% of maximal torque. For hypoxia, peripheral blood oxygen saturation ( ) was titrated to 80% over a 15min period and maintained for 2h. Maximal voluntary contraction torque, EMG root mean square, voluntary activation, rating of perceived muscle fatigue, and corticospinal excitability (motor-evoked potential) and inhibition (silent period duration) were then assessed before, during and for 6min after the fatiguing contraction. No hypoxia-related effects were identified for neuromuscular variables during the fatigue task. However, for recovery, voluntary activation assessed by motor point stimulation of biceps brachii was lower for hypoxia than sham at 4min (sham: 89%±7%; hypoxia: 80%±12%; P=0.023) and 6min (sham: 90%±7%; hypoxia: 78%±11%; P=0.040). Similarly, voluntary activation (P=0.01) and motor-evoked potential area (P=0.002) in response to transcranial magnetic stimulation of the motor cortex were 10% and 11% lower during recovery for hypoxia compared to sham, respectively. Although an of 80% did not affect neural activity during the fatiguing task, motor cortical output and corticospinal excitability were reduced during recovery in the hypoxic environment. This was probably due to hypoxia-related mechanisms involving supraspinal motor circuits. KEY POINTS: Acute hypoxia has been shown to impair voluntary activation of muscle and alter the excitability of the corticospinal motor pathway during exercise. However, little is known about how hypoxia alters the recovery of the motor system after performing fatiguing exercise. Here we assessed hypoxia-related responses of motor pathways both during active contractions and during recovery from active contractions, with transcranial magnetic stimulation and motor point stimulation of the biceps brachii. Fatiguing exercise caused reductions in voluntary activation, which was exacerbated during recovery from a 10min sustained elbow flexion in a hypoxic environment. These results suggest that reductions in blood oxygen concentration impair the ability of motor pathways in the CNS to recover from fatiguing exercise, which is probably due to hypoxia-induced mechanisms that reduce output from the motor cortex.

Muscle Damage Indicated by Maximal Voluntary Contraction Strength Changes From Immediately to 1 Day After Eccentric Exercise of the Knee Extensors.

The present study examined if the magnitude of changes in indirect muscle damage markers could be predicted by maximal voluntary isometric contraction (MVIC) torque changes from immediately to 1 day after eccentric exercise. Twenty-eight young men performed 100 maximal isokinetic (60°/s) eccentric contractions of the knee extensors. MVIC torque, potentiated doublet torque, voluntary activation (VA) during MVIC, shear modulus of rectus femoris (RF), vastus medialis and lateralis, and muscle soreness of these muscles were measured before, immediately after, and 1–3 days post-exercise. Based on the recovery rate of the MVIC torque from immediately to 1-day post-exercise, the participants were placed to a recovery group that showed an increase in the MVIC torque (11.3–79.9%, n = 15) or a no-recovery group that showed no recovery (−71.9 to 0%, n = 13). No significant difference in MVIC torque decrease immediately post-exercise was found between the recovery (−33 ± 12%) and no-recovery (−32 ± 9%) groups. At 1–3 days, changes in MVIC torque (−40 to −26% vs. −22 to −12%), potentiated doublet torque (−37 to −22% vs. −20 to −9%), and proximal RF shear modulus (29–34% vs. 8–15%) were greater (p < 0.05) for the no-recovery than recovery group. No significant group differences were found for muscle soreness. The recovery rate of MVIC torque was correlated (p < 0.05) with the change in MVIC torque from baseline to 2 (r = 0.624) or 3 days post-exercise (r = 0.526), or peak change in potentiated doublet torque at 1–3 days post-exercise from baseline (r = 0.691), but not correlated with the changes in other dependent variables. These results suggest that the recovery rate of MVIC torque predicts changes in neuromuscular function but not muscle soreness and stiffness following eccentric exercise of the knee extensors.

Runners with chronic mid-portion Achilles tendinopathy have greater Triceps surae intracortical inhibition than healthy controls

Background: Achilles tendinopathy (AT) is an overload injury, affecting mostly runners. Persistent triceps surae muscle weakness has been reported in AT patients. Muscle force is influenced by inhibitory and excitatory circuits, and imbalances between these (e.g., increased short-interval intracortical inhibition - SICI) may negatively affect strength. Increased SICI has been observed with patella tendinopathy; however, it is unclear if this increased inhibition is present in chronic mid-portion AT patients. Thus, this study aimed to investigate the intracortical inhibitory mechanisms in runners with mid-portion AT. Methods: Runners with chronic mid-portion AT (n=11; 44.1±8.4 years) and healthy controls (n=13; 33.9±4.25 years), with a running routine of at least twice weekly for more than 4 months, were recruited. All completed the VISA-A questionnaire AT (AT= 70.7±7.0) and Control (100±0). The most symptomatic leg (8 unilateral AT and 3 bilateral AT) was compared with control group dominant legs. Plantar flexor maximal voluntary isometric contraction (MVIC) torque was measured via isokinetic dynamometer (knee fully extended, ankle at 0°). Triceps surae endurance was measured with standing single leg heel raise to failure (SLHR) test. SICI was assessed using paired-pulse transcranial magnetic stimulation to the motor cortex area associated with the leg, delivering 20 paired-pulses at 0.8x (first pulse) and 1.2x (second pulse) of active motor threshold (AMT) with 3ms interval and 20 single pulse stimulation at 1.2 AMT, all during a 10% plantar flexion contraction. Two-way repeated measures ANOVA was used to compare SICI between muscles (Soleus, and Gastrocnemii) and groups. Independent t-test was used to compare SLHR and MVIC peak torque between groups. Results: SICI was higher in AT group (67.4±9.0) than controls (54.0±9.0); (p=0.039,) independent of the tested muscle (no muscle vs group interaction; p =0.828). AT group performed ~28% fewer SLHR repetitions than the controls (AT, 27.5.0±6.8 and control 38.5±5.3 repetitions, p=0.004). There was no difference in MVIC peak torque corrected for body mass (N.m/Kg), (AT=1.4±0.3; Control=1.6±0.4, p =0.093). Discussion: The AT group displayed greater intracortical inhibition of the triceps surae muscles and reduced SLHR endurance, without deficit in maximal isometric torque. SICI could be negatively influencing SLHR endurance in AT; thus, rehabilitation aiming to reduce intracortical inhibition should be considered for better outcomes. Conflict of interest: The authors declare no conflict of interest related to the present work.

Neuromuscular responses to isometric, concentric and eccentric contractions of the knee extensors at the same torque-time integral.

The present study compared isometric, concentric and eccentric contractions at the same torque-time integral for changes in neuromuscular fatigue and muscle damage parameters. Healthy men (18-24years) were placed to either isometric (ISO), concentric (CONC), or eccentric (ECC) group (n = 11/group) that performed corresponding contractions of the knee extensors to exert the same amount of torque-time integral (24,427 ± 291 Nm·s). Changes in maximal voluntary contraction (MVC) torque, voluntary activation, evoked torque at 10Hz and 100Hz and its ratio, M-wave amplitude, and muscle soreness were assessed immediately before and after, 1h, 1day and 2days after each exercise, and were compared among the groups. MVC torque decreased immediately after ISO (-17.0 ± 8.3%), CONC (-21.7 ± 11.5%) and ECC (-26.2 ± 15.6%) similarly (p = 0.35), but the decrease sustained longer (p < 0.05) for ECC (2days post-exercise: -12.9 ± 14.8%) and ISO (-5.5 ± 7.9%) than CONC (+ 5.0 ± 11.0%). Muscle soreness developed after ECC (25.1 ± 19.8mm) and ISO (17.5 ± 21.0mm) similarly (p = 0.15). Voluntary activation decreased immediately (-3.7 ± 6.6%) and 1h post-exercise (-4.7 ± 7.6%) for all groups similarly. Electrically evoked forces decreased greater immediately (-30.1 ± 15.6%) and 1h post-exercise (-35.0 ± 12.8%) for ECC than others, and the decrease in 10/100Hz ratio was also greater immediately (-30.5 ± 12.6%) and 1h after ECC (-23.8 ± 10.3%) than others. ISO, CONC and ECC with the same torque-time integral produced similar neuromuscular fatigue at immediately post-exercise, but the force loss was longer-lasting after ISO and ECC than CONC, and the changes in peripheral fatigue parameters were the greatest after ECC, suggesting greater muscle damage.

Concentric versus eccentric cycling at equal power output or effort perception: Neuromuscular alterations and muscle pain.

This study aimed to compare neuromuscular alterations and perceptions of effort and muscle pain induced by concentric and eccentric cycling performed at the same power output or effort perception. Fifteen participants completed three 30-min sessions: one in concentric at 60% peak power output (CON) and two in eccentric, at the same power output (ECCPOWER ) or same perceived effort (ECCEFFORT ). Muscle pain, perception of effort, oxygen uptake as well as rectus femoris and vastus lateralis electromyographic activities were collected when pedaling. The knee extensors maximal voluntary contraction (MVC) torque, the torque evoked by double stimulations at 100Hz and 10Hz (Dt100; Dt10), and the voluntary activation level (VAL) were evaluated before and after exercise. Power output was higher in ECCEFFORT than CON (89.1±23.3% peak power). Muscle pain and effort perception were greater in CON than ECCPOWER (p<0.03) while muscle pain was similar in CON and ECCEFFORT (p>0.43). MVC torque, Dt100, and VAL dropped in all conditions (p<0.04). MVC torque (p<0.001) and the Dt10/ Dt100 ratio declined further in ECCEFFORT (p<0.001). Eccentric cycling perceived as difficult as concentric cycling caused similar muscle pain but more MVC torque decrease. A given power output induced lower perceptions of pain and effort in eccentric than in concentric yet similar MVC torque decline. While neural impairments were similar in all conditions, eccentric cycling seemed to alter excitation-contraction coupling. Clinicians should thus be cautious when setting eccentric cycling intensity based on effort perception.

Relationship between changes in passive properties and muscle strength after static stretching

BackgroundThe association between decreased muscle strength of rate of force development (RFD) immediately after static stretching (SS) and change in muscle stiffness or muscle slack has remained unclear. ObjectiveThis study aimed to investigate the association between changes in muscle strength and RFD and muscle stiffness or muscle slack immediately after SS. MethodsSixteen healthy male non-athlete volunteers participated in this study. The maximal voluntary contraction torque and shear elastic modulus of medial gastrocnemius muscle were measured before and after 300 s of SS intervention. ResultsThe results showed that maximal voluntary contraction torque and RFD at 100, 150, and 200 ms decreased significantly after the 300-s SS (p < 0.01). Additionally, shear elastic modulus at 0° (decrease in muscle stiffness) and slack angle decreased (increase in slack length) significantly after the 300-second SS (p < 0.01). However, no significant association was observed between changes in muscle strength and changes in mechanical properties of the MG. ConclusionThese results suggested that the decrease in muscle strength and RFD could not be associated with changes in the passive mechanical properties of the medial gastrocnemius muscle.

Elbow Joint Angles in Elbow Flexor Unilateral Resistance Exercise Training Determine Its Effects on Muscle Strength and Thickness of Trained and Non-trained Arms.

The present study compared two unilateral arm curl resistance exercise protocols with a different starting and finishing elbow joint angle in the same ROM for changes in elbow flexors strength and muscle thickness of the trained and non-trained arms. Thirty-two non-resistance trained young adults were randomly assigned to one of the three groups: extended joint training (0°–50°; EXT, n = 12); flexed joint training (80°–130°; FLE, n = 12); and non-training control (n = 8). The exercise training was performed by the dominant arms twice a week for 5 weeks with gradual increases in the training volume over 10 training sessions, and the non-dominant (non-trained) arms were investigated for the cross-education effect. Maximal voluntary contraction torque of isometric (MVC-ISO), concentric (MVC-CON), and eccentric contractions (MVC-ECC), and thickness (MT) of biceps brachii and brachialis of the trained and non-trained arms were assessed at baseline and 4–8 days after the last training session. The control group did not show significant changes in any variables. Significant (P < 0.05) increases in MVC-ISO torque (16.2 ± 12.6%), MVC-CON torque (21.1 ± 24.4%), and MVC-ECC torque (19.6 ± 17.5%) of the trained arm were observed for the EXT group only. The magnitude of the increase in MT of the trained arm was greater (P < 0.05) for EXT (8.9 ± 3.9%) than FLE (3.4 ± 2.7%). The cross-education effect was evident for MVC-ISO (15.9 ± 14.8%) and MVC-CON (16.7 ± 20.0%) torque of the EXT group only. These results suggest that resistance training at the extended elbow joint induces greater muscle adaptations and cross-education effects than that at flexed elbow joint.

Comparison Between Foam Rolling With and Without Vibration on Passive and Active Plantar Flexor Muscle Properties.

Nakamura, M, Sato, S, Kiyono, R, Yoshida, R, Yasaka, K, Yahata, K, and Konrad, A. Comparison between foam rolling with and without vibration on passive and active plantar flexor muscle properties. J Strength Cond Res XX(X): 000-000, 2021-Although foam rolling interventions with and without vibration have been used to increase flexibility in the field of sports, their effects on passive and active properties remain unclear. Hence, this study aimed to investigate the effects of foam rolling interventions on range of motion (ROM), shear elastic modulus, plantar flexor muscle strength, and jump performance. This randomized, controlled, crossover study included 16 healthy male subjects who visited the laboratory 3 times (control condition, foam rolling condition, and vibration foam rolling condition), each with an interval of >72 hours. In both foam rolling and vibration foam rolling conditions, subjects were instructed to perform 60-second bouts of intervention for 3 sets, with 30-second rest between each set. In the vibration foam rolling condition, the intensity of vibration was set at a frequency of 48 Hz. Dorsiflexion (DF) ROM, shear elastic modulus, plantar flexor muscle strength, and drop jump height were determined before and after the rolling intervention. Our results showed a similar increase in dorsiflexion range of motion (p < 0.01, d = 0.51; p < 0.01, d = 0.65, respectively) and passive torque at dorsiflexion range of motion (p = 0.02, d = 0.51 and p < 0.01, d = 0.65, respectively) after foam rolling and vibration foam rolling. Medial gastrocnemius shear elastic modulus decreased only after vibration foam rolling (p < 0.01, d = 0.44). No significant main effects of time were observed in maximal voluntary isometric contraction torque (F = 2.0, p = 0.15, = 0.119) and drop jump height (F = 1.5, p = 0.24, = 0.091) after both interventions. Maximal voluntary concentric contraction torque showed a significant main effect of time (F = 7.59, p = 0.02, = 0.336). However, only after foam rolling, the maximal voluntary concentric contraction torque significantly decreased (p = 0.01, d = 0.39). Our results suggest that vibration foam rolling effectively alters passive muscle properties without decreasing muscle strength and performance.

Changes in neural drive to calf muscles during steady submaximal contractions after repeated static stretches

Repeated static-stretching interventions consistently increase the range of motion about a joint and decrease total joint stiffness, but findings on the changes in muscle and connective-tissue properties are mixed. The influence of these stretch-induced changes on muscle function at submaximal forces is unknown. To address this gap in knowledge, the changes in neural drive to the plantar flexor muscles after a static-stretch intervention were estimated. Neural drive to the plantar flexor muscles during a low-force contraction increased after repeated static stretches. These findings suggest that adjustments in motor unit activity are necessary at low forces to accommodate reductions in the force-generating and transmission capabilities of the muscle-tendon unit after repeated static stretches of the calf muscles. Static stretching decreases stiffness about a joint, but its influence on muscle-tendon unit function and muscle activation is unclear. We investigated the influence of three static stretches on changes in neural drive to the plantar flexor muscles, both after a stretch intervention and after a set of maximal voluntary contractions (MVCs). Estimates of neural drive were obtained during submaximal isometric contractions by decomposing high-density electromyographic signals into the activity of individual motor units from medial gastrocnemius, lateral gastrocnemius and soleus. Motor units were matched across contractions and an estimate of neural drive to the plantar flexors was calculated by normalizing the cumulative spike train to the number of active motor units (normalized neural drive). Mean discharge rate increased after the stretch intervention during the 10% MVC task for all recorded motor units and those matched across conditions (all, P=0.0046; matched only, P=0.002), recruitment threshold decreased for motor units matched across contractions (P=0.022), and discharge rate at recruitment was elevated (P=0.004). Similarly, the estimate of normalized neural drive was significantly greater after the stretch intervention at 10% MVC torque (P=0.029), but not at 35% MVC torque. The adjustments in motor unit activity required to complete the 10% MVC task after stretch may have been partially attenuated by a set of plantar flexor MVCs. The increase in neural drive required to produce low plantar-flexion torques after repeated static stretches of the calf muscles suggests stretch-induced changes in muscle and connective tissue properties.

Inhomogeneous and Anisotropic Mechanical Properties of the Triceps Surae Aponeuroses in Older Adults: Relationships With Muscle Strength and Walking Performance.

This study investigated (a)site- and direction-dependent variations of passive triceps surae aponeurosis stiffness and (b)the relationships between aponeurosis stiffness and muscle strength and walking performance in older individuals. Seventy-nine healthy older adults participated in this study. Shear wave velocities of the triceps surae aponeuroses at different sites and in two orthogonal directions were obtained in a prone position at rest using supersonic shear imaging. The maximal voluntary isometric contraction torque of the plantar flexors and normal (preferred) and fast (fastest possible) walking speeds (5-m distance) were also measured. The shear wave velocities of the adjoining aponeuroses were weakly associated with plantar flexion torque (r = .23-.34), normal (r = .26), and fast walking speed (r = .25). The results show clear spatial variations and anisotropy of the triceps surae aponeuroses stiffness in vivo, and the aponeurosis stiffness was associated with physical ability in older adults.

Peripheral Alterations Affect the Loss in Force after a Treadmill Downhill Run.

Downhill running has an important effect on performance in trail running competitions, but it is less studied than uphill running. The purpose of this study was to investigate the cardiorespiratory response during 15 min of downhill running (DR) and to evaluate the neuromuscular consequences in a group of trail runners. Before and after a 15-min DR trial (slope: −25%) at ~60% of maximal oxygen consumption (V̇O2max), we evaluated maximal voluntary contraction torque (MVCt) and muscle contractility in a group of seventeen trail running athletes. Additionally, during the DR trial, we measured V̇O2 and heart rate (HR). V̇O2 and HR increased as a function of time, reaching +19.8 ± 15.9% (p < 0.001; ES: 0.49, medium) and +15.3 ± 9.9% (p < 0.001; ES: 0.55, large), respectively, in the last minute of DR. Post-exercise, the MVCt decreased (−22.2 ± 12.0%; p < 0.001; ES = 0.55, large) with respect to the pre-exercise value. All the parameters related to muscle contractility were impaired after DR: the torque evoked by a potentiated high frequency doublet decreased (−28.5 ± 12.7%; p < 0.001; ES: 0.61, large), as did the torque response from the single-pulse stimulation (St, −41.6 ± 13.6%; p < 0.001; ES: 0.70, large) and the M-wave (−11.8 ± 12.1%; p < 0.001; ES: 0.22, small). We found that after 15 min of DR, athletes had a decreased MVCt, which was ascribed mainly to peripheral rather than central alterations. Additionally, during low-intensity DR exercise, muscle fatigue and exercise-induced muscle damage may contribute to the development of O2 and HR drift.

Effect of race distance on performance fatigability in male trail and ultra-trail runners.

The etiology of changes in lower-limb neuromuscular function, especially to the central nervous system, may be affected by exercise duration. Direct evidence is lacking as few studies have directly compared different race distances. This study aimed to investigate the etiology of deficits in neuromuscular function following short versus long trail-running races. Thirty-two male trail runners completed one of five trail-running races as LONG (>100km) or SHORT (<60km). Pre- and post-race, maximal voluntary contraction (MVC) torque and evoked responses to electrical nerve stimulation during MVCs and at rest were used to assess voluntary activation and muscle contractile properties of knee-extensor (KE) and plantar-flexor (PF) muscles. Transcranial magnetic stimulation (TMS) was used to assess evoked responses and corticospinal excitability in maximal and submaximal KE contractions. Race distance correlated with KE MVC (ρ=-0.556) and twitch (ρ=-0.521) torque decreases (p≤.003). KE twitch torque decreased more in LONG (-28±14%) than SHORT (-14±10%, p=.005); however, KE MVC time×distance interaction was not significant (p=.073). No differences between LONG and SHORT for PF MVC or twitch torque were observed. Maximal voluntary activation decreased similarly in LONG and SHORT in both muscle groups (p≥.637). TMS-elicited silent period decreased in LONG (p=.021) but not SHORT (p=.912). Greater muscle contractile property impairment in longer races, not central perturbations, contributed to the correlation between KE MVC loss and race distance. Conversely, PF fatigability was unaffected by race distance.

Effect of whole-body vibration therapy on lower extremity function in subacute stroke patients.

This study aimed to investigate the effect of whole-body vibration therapy on lower extremity function in subacute stroke patients. Subacute stroke patients who were able to undergo gait training were randomly divided into a vibration therapy group and a control group. All patients attended 20-min training sessions twice daily, 5 times a week for 2 weeks. Each session included 45 squats. The vibration group trained on a vibration platform and the control group trained on the ground. The degree of maximal isokinetic voluntary contraction torque was evaluated, and manual muscle tests of hip and knee flexion and extension were performed. The Berg Balance Scale, 10-m walk test, Timed Up and Go Test, and Functional Ambulation Category were used. A total of 38 patients, 20 in the vibration group and 18 in the control group, were included in the analysis. After the 2-week therapy, the vibration group showed significant improvements in lower extremity strength, balance, and gait performance. The vibration group showed significantly better performance on the Berg Balance Scale, 10-m walk test, and Functional Ambulation Category than the control group. There were no significant differences in maximal isokinetic voluntary contraction torque or manual muscle tests between the groups. Our results suggest that additional training with whole-body vibration may effectively improve the balance and gait performance of subacute stroke patients. Further studies on large populations are required to determine the therapy’s clinical efficacy.

The torque-frequency relationship is impaired similarly following two bouts of eccentric exercise: No evidence of a protective repeated bout effect

High-intensity eccentric exercise can lead to muscle damage and weakness. The ‘repeated bout effect’ (RBE) can attenuate these impairments when performing a subsequent bout. The influence of eccentric exercise-induced muscle damage on low-frequency force production is well-characterized; however, it is unclear how eccentric exercise and the RBE affect torque production across a range of stimulation frequencies (i.e., the torque-frequency relationship). We investigated the influence of an initial (Bout 1) and repeated bout (Bout 2) of eccentric exercise on the elbow flexor torque-frequency relationship. Eleven males completed two bouts of high-intensity eccentric elbow flexions, 4 weeks apart. Torque-frequency relationships were constructed at baseline and 0.5, 24, 48, 72, 96, and 168 h following both bouts via percutaneous stimulation at 1, 6, 10, 20, 30, 40, 50, and 100 Hz. Serum creatine kinase activity, self-reported muscle soreness, and isometric maximum voluntary contraction torque indirectly inferred the presence of muscle damage following Bout 1, and attenuation of muscle damage following Bout 2. Torque amplitude at all stimulation frequencies was impaired 30 min following eccentric exercise, however, torque at lower (1–10 Hz) and higher frequencies (40–100 Hz) recovered within 24 h while torque across the middle frequency range (20–30 Hz) recovered by 48 h. No between-bout differences were detected in absolute or normalized torque at any stimulation frequency, indicating no protective RBE on the elbow flexor torque-frequency relationship.

Quercetin ingestion modifies human motor unit firing patterns and muscle contractile properties

Quercetin is a polyphenolic flavonoid that has reported to block the binding of adenosine to A1 receptors at central nervous system and increase calcium release from the sarcoplasmic reticulum at skeletal muscle. The aim of the present study was to investigate the acute effect of quercetin ingestion on motor unit activation and muscle contractile properties. High-density surface electromyography during submaximal contractions and electrically elicited contraction torque in knee extensor muscles were measured before (PRE) and 60 min after (POST) quercetin glycosides or placebo ingestions in 13 young males. Individual motor units of the vastus lateralis muscle were identified from high-density surface electromyography by the Convolution Kernel Compensation technique. Firing rates of motor units recruited at 30–50% of the maximal voluntary contraction torque (MVC) were increased from PRE to POST only with quercetin (9.0 ± 2.3 to 10.5 ± 2.0 pps, p = 0.034). Twitch torque during doublet stimulation was decreased from PRE to POST with placebo (77.1 ± 17.1 to 73.9 ± 17.6 Nm, p = 0.005), but not with quercetin (p > 0.05). For motor units recruited at < 10% of MVC, normalized firing rate were decreased with quercetin (1.52 ± 0.33 to 1.58 ± 0.35%MVC/pps, p = 0.002) but increased with placebo (1.61 ± 0.32 to 1.57 ± 0.31%MVC/pps, p = 0.005). These results suggest that ingested quercetin has the functional roles to: mitigate reduction in the muscle contractile properties, enhance activations of relatively higher recruitment threshold motor units, and inhibit activation of relatively lower recruitment threshold motor units.

Urinary N-terminal fragment of titin: A surrogate marker of serum creatine kinase activity after exercise-induced severe muscle damage

ABSTRACT We aimed to evaluate whether changes in the noninvasively assessed urinary N-terminal fragment of titin (U-titin) concentration may be associated with those of serum creatine kinase (CK) activity, transverse relaxation time (T2), maximal voluntary contraction (MVC) torque, range of motion (ROM), and muscle soreness, following high-intensity eccentric exercise. Twenty-eight healthy young men performed 30 maximal isokinetic (120°/s) eccentric elbow flexor contractions using an isokinetic dynamometer. U-titin concentration, serum CK activity, T2, MVC torque, ROM, and muscle soreness were measured before and after a maximum of 4 days. Both U-titin concentration and serum CK activity increased post-exercise in a similar manner, though the former elevated slightly earlier (p < 0.05). The peak values of log U-titin concentration following eccentric exercise were strongly correlated with those of log serum CK activity (r = 0.90, p < 0.05) and T2 (r = 0.84, p < 0.05). There were moderate correlations between peak values of U-titin concentration and those of MVC torque (r = 0.69, p < 0.05) and ROM decline rate (r = 0.45, p < 0.05). These results suggest that in healthy young men, the non-invasive marker, U-titin, may be used as a serum CK surrogate following exercise-induced severe muscle damage.