Maximal Voluntary Isometric Contraction Torque Research Articles

Well-Trained Elders Have Antioxidant Responses and an Equal Magnitude of EIMD as Young Adults

Aim The aim of the study was to investigate acute and chronic effects of a two-week eccentric concentric, dynamometric training concerning the time-course changes of blood antioxidant parameters (total antioxidant capacity, catalase enzyme activity, thiol concentration), and to compare the adaptability of young and older muscle to this type of training. Methods Seventeen moderately trained young and older men participated in this research. Subjects performed six eccentric concentric exercise bouts during the training period and maximal voluntary isometric contraction torque, plasma CK and intensity of muscle soreness were determined before and 24 h after the first exercise. During five testing sessions (baseline, 24 h, 48 h, week 1, week 2) the level of blood antioxidants were measured. Results No significant changes were registered in total antioxidant capacity and catalase enzyme activity for any time points; furthermore, no difference was found between groups during the training period. However, total thiol concentrations measured two weeks after the first exercise bout significantly differed between the young and elderly groups. Plasma CK and the subjective intensity of soreness elevated significantly 24 h following the first training, while maximal voluntary isometric contraction torque decreased at the same time. Conclusions Our results do not support previous findings that chronic, short-term eccentric concentric training programs enhance the antioxidant defense of well-trained older and young men. This type and setting of exercise did not cause a different time course of changes in the markers of exercise-induced muscle damage (EIMD) in the studied population. Subjects may already have adapted to maintain constant levels of antioxidants and isometric torque due to their active lifestyle.

Sex-related differences and effects of short and long trail running races on resting muscle-tendon mechanical properties.

The purpose of the study was to assess sex-related differences in resting mechanical properties and adaptations of skeletal muscles and tendons in response to trail running races of different distances using multi-site shear wave elastography assessments of the lower limb, force capacity and blood analyses. Sex differences in resting mechanical properties of knee extensor and plantar flexor muscles and tendons were characterized by shear wave velocity (SWV) measurements in healthy males (N=42) and females (N=25) trained in long-distance running. Effects of running distance on muscle and tendon properties were assessed in short (<60 km, N=23) vs. long (>100 km, N=26) distance races. Changes in isometric maximal voluntary contraction torque, serum C-reactive protein and creatine kinase activity were also quantified after running races. Higher SWV of relaxed triceps surae muscle was detected in females as compared to males before running races (+4.8%, p=0.006), but the significant increases in triceps surae muscle group (+7.0%, p=0.001) and patellar tendon SWV (+15.4%, p=0.001) after short-distance races were independent of sex. A significant decrease in triceps surae muscle SWV was found after long-distance races in the whole experimental population (-3.1%, p=0.049). Post-races increase in C-reactive protein and creatine kinase activity were significantly correlated to the relative decreases in triceps surae and quadriceps femoris skeletal muscle SWV (ρ=-0.56, p=0.001 and ρ=-0.51, p=0.001, respectively). Resting mechanical properties of muscles and tendons are affected by sex, and adaptations to trail races are related to running distance. Exercise-induced changes in resting skeletal muscle mechanical properties are associated with enhanced indirect markers of inflammation and muscle damage.

Greater neuromuscular fatigue following low-load blood flow restriction than non-blood flow restriction resistance exercise among recreationally active men.

The purpose of this study was to examine the acute effects of low-load blood flow restriction (LLBFR) and low-load non-BFR (LL) on neuromuscular function after a bout of standardized fatiguing leg extension muscle actions. Fourteen men (mean age ± SD = 23 ± 4 yr) volunteered to participate in this investigation and randomly performed LLBFR and LL on separate days. Resistance exercise consisted of 75 isotonic unilateral leg extension muscle actions performed at 30% of one-repetition maximum. Before (pretest) and after (posttest) performance of each bout of exercise, strength and neural assessments were determined. There were no pretest to posttest differences between LLBFR and LL for maximal voluntary isometric contraction (MVIC) torque or V wave/M wave responses (muscle compound action potentials assessed during a superimposed MVIC muscle action), which exhibited decreases (collapsed across condition) of 41.2% and 26.2%, respectively. There were pretest to posttest decreases in peak twitch torque (36.0%) and surface electromyography amplitude (sEMG) (29.5%) for LLBFR but not LL and larger decreases in voluntary activation for LLBFR (11.3%) than for LL (4.5%). These findings suggested that LLBFR elicited greater fatigue-induced decreases in several indexes of neuromuscular function relative to LL. Despite this, both LLBFR and LL resulted in similar decrements in performance as assessed by maximal strength.NEW & NOTEWORTHY The application of blood flow restriction induces greater acute neuromuscular fatigue relative to nonrestricted conditions. Resistance exercise with blood flow restriction elicited a greater reduction in twitch responses. These neuromuscular differences might explain the more favorable adaptations achieved with blood flow restriction that are likely a function of metabolic stress and subsequent changes in efferent neural drive.

Comparison between 6-week foam rolling intervention program with and without vibration on rolling and non-rolling sides.

The chronic effects of unilateral foam rolling (FR) or FR with vibration (VFR) intervention on the rolling and non-rolling sides (cross-education effects) are still unclear. Thus, this study aimed to investigate the effects of unilateral 6-week FR or VFR intervention on ankle dorsiflexion range of motion (DF ROM), muscle stiffness, and muscle strength in both rolling and non-rolling sides. Thirty healthy young men were randomly allocated into the FR (n = 15) or the VFR intervention group (n = 15). Participants performed three sets of unilateral FR or VFR interventions for 60s of the calf muscles twice/week, for 6weeks. DF ROM, gastrocnemius muscle stiffness, and maximal voluntary isometric contraction (MVIC) torque were assessed in the rolling and non-rolling sides before and after the intervention. The DF ROM increased significantly (p < 0.05) to the same extent in the FR and VFR intervention groups on both rolling (FR: d = 0.58, VFR: d = 0.63) and non-rolling (FR: d = 0.39, VFR: d = 0.50) sides. Similarly, the passive torque at DF ROM increased significantly (p < 0.05) to the same extent in the FR and VFR intervention groups on both rolling (FR: d = 0.85, VFR: d = 0.77) and non-rolling (FR: d = 0.76, VFR: d = 0.68) sides. However, there were no significant changes in muscle stiffness and MVIC after FR and VFR interventions on both the rolling and non-rolling sides. FR and VFR interventions could increase the ROM in both the rolling and non-rolling sides but could not change muscle stiffness and strength. The results showed that it is not necessarily needed to perform VFR to increase ROM in the long term.

Sex differences in central and peripheral fatigue induced by sustained isometric ankle plantar flexion

The main aim of this study was to determine sex differences in central and peripheral fatigue produced by a sustained isometric exercise of ankle plantar flexors in healthy young adults. Ten males and fourteen females performed a sustained isometric ankle exercise until task failure. Maximal voluntary isometric contraction (MVIC) torque (plantarflexion), voluntary activation level (using the twitch interpolation technique), and resting twitch contractile properties [twitch peak torque (ST), twitch half relaxation time, and low frequency fatigue (LFF) ratio] were measured before, immediately after, and throughout a recovery period (1, 2, 5, and 10 min) following the exercise protocol in order to characterize neuromuscular fatigue. Fatigue had effects (p≤ 0.05) on all dependent variables (reduction in MVIC, VA and twitch torque and slowing of relaxation time). However, no significant differences in performance fatigability markers (MVIC torque decline and time to fatigue) and only minor differences in the variables reflecting central and peripheral fatigue mechanisms were found between males and females. A regression analysis did suggest a somewhat greater role of central fatigue in males compared with females. Females also showed a slightly greater and more prolonged decline in ST and LFF after exercise compared with males. The presence of only minor differences in central and peripheral fatigue mechanisms between males and females in the present study could be explained by the lack of important sex differences in performance fatigability, which could be due to lesser sex differences in the relative area of type I muscle fibers and in contractile function (muscle strength) of ankle plantar flexors as compared with other muscle groups.

Neuromuscular function of the shoulder girdle and upper extremity musculature in individuals with a history of glenohumeral labral repair.

The purpose of this study was to compare neuromuscular function in the upper extremity musculature between individuals with glenohumeral labrum repair and uninjured controls. This cross-sectional study examined 16 individuals with a primary, unilateral glenohumeral labral repair (male/female: 13/3, age: 24.1 ± 5.0 years, time from surgery: 36.7 ± 33.3months) and 14 uninjured individuals (male/female: 11/3, age: 23.8 ± 2.7 years) matched by age, sex, activity level, and limb dominance participated. Mass-normalized shoulder abduction and wrist flexion maximal voluntary isometric contraction (MVIC) torque, motoneuron pool excitability of the flexor carpi radialis (Hoffmann reflex), and corticospinal excitability of the upper trapezius, middle deltoid, and flexor carpi radialis (active motor threshold [AMT]) were evaluated. Dependent and independent t-tests were used to assess between-limb and between-group comparisons. Cohen's d effect sizes with 95% confidence intervals were used to quantify the magnitude of differences observed. Within the injured group, the involved limb had lesser shoulder abduction MVIC torque (p < 0.001, d=1.16) and higher AMT for the upper trapezius (p=0.01, d=0.81) compared with the contralateral limb. The labral repair group had lesser shoulder abduction MVIC torque (p < 0.001, d=1.17) and Hoffmann reflex (p=0.01, d=0.99), as well as higher AMT for the upper trapezius (p < 0.001, d=1.23) in their involved limb compared with the control group. Large magnitude neuromuscular impairments are present beyond 6months from glenohumeral labral repair, suggesting potential origins of impairments to be addressed during post-operative rehabilitation.

Quantifying Knee Strength Deficits and Muscular Contribution to Torque Generation in ACL-Injured Adolescents Using A Simple Musculoskeletal Model

Background:Surface electromyography (sEMG) is commonly used to elucidate the effect of anterior cruciate ligament (ACL) injury on neuromuscular function. To facilitate comparisons, sEMG is normalized to a known value, such as peak activation during a maximum voluntary isometric contraction (MVIC). However, voluntary muscle inhibition after an injury compromises one’s ability to achieve a true MVIC value. Musculoskeletal modeling can be used to quantify this strength deficit by comparing a theoretical MVIC torque to the actual MVIC torque.Purpose:This study sought to evaluate voluntary knee extensor and flexor strength deficits and individual muscle contribution to peak torque generation in ACL injured (ACLi) and uninjured (CON) adolescent populations using a simplified subject-specific modeling framework.Methods:Thirty-nine ACLi (25 females) and 39 CON (25 females) adolescents (12-17years) completed knee extension and flexion MVICs on an isokinetic dynamometer. Peak experimental torque (TE) was identified. A subject-specific modeling framework used normalized sEMG of the quadriceps, hamstrings, and gastrocnemius muscles to determine theoretically ideal torque (TI) for each exercise, assuming agonist muscles were fully activated. Strength deficit ratios (TE/TI) and individual muscle contribution to TE were computed. Group mean differences were compared using independent t-tests.Results:ACLi demonstrated significantly lower extension (2.53±0.94 vs 3.07±0.57Nm/kg, p<0.001) and flexion (1.14±0.50 vs 1.37±0.31Nm/kg, p<0.001) peak TE compared to CON (FIG 1.A). Significant between group differences in sEMG of antagonist muscles were observed. Both groups demonstrated similar TI values (FIG 1.B-upper). Significantly lower trends in strength ratios (TE/TI) were maintained between groups (FIG 1.B-lower). However, percent between group differences were minimized from 17.8% to 6.3% for knee extension, and 16.7% to 10.0% for knee flexion, when TE is expressed relative to TI. Significantly lower medical gastrocnemius contribution to flexion TE was also observed in the ACLi (24.7±0.08%) compared to CON (30.9±10.1%, p=0.037).Conclusion:Significant between group differences in peak extensor or flexor torques were observed. Our model confirmed a strength deficit in ACLi compared to CON, however, between group differences were less prominent when described relative to TI. This may be attributed to between group differences in antagonist contributions (i.e. co-contraction) during MVIC exercise. Simplified modeling frameworks that can incorporate muscle activations as well as torque generation may be more appropriate for evaluating functional outcomes of ACLi populations in a clinical setting.Figure 1:

The Relationship Between Acute Exercise-Induced Changes in Extramuscular Connective Tissue Thickness and Delayed Onset Muscle Soreness in Healthy Participants: A Randomized Controlled Crossover Trial

BackgroundThe extramuscular connective tissue (ECT) has been shown to play a significant role in mechanical force transmission between musculoskeletal structures. Due to this and owing to its tight connection with the underlying muscle, the ECT may be vulnerable to excessive loading. The present study aimed to investigate the effect of eccentric elbow flexor exercise on the morphology of the biceps brachii ECT. In view of the high nociceptive capacity of the ECT, an additional objective was to elucidate the potential relationship between ECT damage and the occurrence of delayed onset muscle soreness (DOMS).MethodsEleven healthy participants (♂ = 7; 24 ± 2 years) performed fatiguing dumbbell elbow flexor eccentric exercise (EE) for one arm and concentric exercise (CE) for the other arm in random order and with random arm allocation. Before, immediately after and 24–96 h post-exercise, maximal voluntary isometric contraction torque of the elbow flexors (dynamometer), pressure pain (algometer), palpation pain (100 mm visual analog scale), biceps brachii ECT thickness and ECT/muscle mobility during passive movement (both high-resolution ultrasound) were examined.ResultsPalpation pain, suggestive of DOMS, was greater after EE than CE, and maximal voluntary isometric contraction torque decreased greater after EE than CE (p < .05). Relative to CE, EE increased ECT thickness at 48 (+ 17%), 72 (+ 14%) and 96 (+ 15%) hours post-exercise (p < .05). At 96 h post-EE, the increase in ECT thickness correlated with palpation pain (r = .68; p < .05). ECT mobility was not different between conditions, but compared to CE, muscle displacement increased at 24 (+ 31%), 72 (+ 31%) and 96 (+ 41%) hours post-EE (p < .05).ConclusionCollectively, these results suggest an involvement of the ECT changes in delayed onset muscle soreness.

Neural and muscular alterations of the plantar flexors in middle-aged women.

Considering the large population of middle-aged adults, it is important to understand the age-related change in lower limb muscles and the possible mechanisms before old age (> 65years old). The purpose of this study was to investigate age-related neural and muscular alterations of the plantar flexors in young and middle-aged women. Twenty two middle-aged (54.0±5.8yrs) and 17 young (21.8±1.4yrs) recreationally active women performed rapid maximal voluntary isometric contractions (MVIC) of the plantar flexors. Absolute and normalized rate of torque development (RTD) and electromyography (EMG) were examined. Electrical stimulation was used to examine voluntary activation and contractile properties of the muscle. Ultrasonography was used to examine medial and lateral gastrocnemius muscle thickness and pennation angle. A 6-minute walk and sit to stand task were also performed by all participants. The middle-aged women had significantly lower MVIC torque (141±49 vs. 109±30Nm, P=0.031), absolute RTD (753.0±313.6 vs. 423.0±156.1Nm/s, P=0.001), and normalized peak RTD (554.0±191.0 vs. 388.0±91.9% MVIC/s, P=0.001). Normalized early RTD0-50 and late RTD100-200, voluntary activation, and EMG were similar between groups. Resting twitch data showed that time to peak (124.0±20.4 vs. 143.0±16.7ms, P=0.002) and half relaxation time (73.1±15.2 vs. 107.0±28.2ms, P<0.001) was significantly faster for the young women. Thickness was greater in the lateral gastrocnemius (1.6±0.2 vs. 1.4±0.2cm, P=0.006) for the young women. Pennation angle of both muscles were greater for the young women (15.8±3.9 vs. 13.1±2.7 degrees, P<0.05). Performance of the 6-minute walk was similar between groups, however, the young women performed more repetitions during the sit to stand task (25.6±6.7 vs. 18.3±4.7 reps, P<0.001). Compared to young women, middle-age women were shown to have lower MVIC torque, peak RTD, and functional performance. Muscle architecture and contractile properties are affected by aging.

Effect of daily 3-s maximum voluntary isometric, concentric, or eccentric contraction on elbow flexor strength.

The present study compared a 3-s isometric maximal voluntary contraction (MVC), concentric MVC and eccentric MVC of the elbow flexors performed daily for 5days a week for 4weeks for changes in muscle strength and thickness. Young sedentary individuals were assigned to one of three training groups (n=13 per group) that performed either 3-s isometric, concentric, or eccentric MVC once a day for 20days, or to a control group (n=10) that had measurements without training. The participants in the isometric group performed isometric MVC at 55° (0.96rad) elbow flexion, and those in the concentric or eccentric group performed concentric MVC or eccentric MVC between 10° (0.17rad) and 100° (1.75rad) elbow flexion at 30°/s (0.52rad/s) on an isokinetic dynamometer. MVC isometric torque at 20° (0.35rad), 55° (0.96rad), and 90° (1.57rad) elbow flexion, MVC concentric and eccentric torque at 30°/s (0.52rad/s) and 180°/s (3.14rad/s), and muscle thickness (MT) of biceps brachii and brachialis were measured before and several days after the 20th exercise session. The control group did not show any changes. The eccentric group showed increases (p<0.01) in isometric (three angle average: 10.2±6.4%), concentric (two velocity average: 12.8±9.6%), and eccentric MVC torque (12.2±7.8%). An increase (p<0.05) was limited for isometric MVC torque (6.3±6.0%) in the concentric group, and for eccentric MVC torque (7.2±4.4%) in the isometric group. No significant changes in MT were evident for all groups. Performing one 3-s MVC a day increased muscle strength, but eccentric MVC produced more potent effects than isometric or concentric MVC.

Immediate voluntary activation deficits following submaximal eccentric contractions of knee extensors are associated with alterations of the sense of movement

The mechanisms underlying movement sense alterations following repeated eccentric contractions remain unclear. This study concomitantly investigated the effects of unilateral eccentric contractions on movement sense and on neuromuscular function at the knee before, immediately after (POST), 24 (POST24) and 48 (POST48) h after the exercise. Twelve participants performed sets of submaximal knee extensors (KE) eccentric contractions until a 20% decrease in maximal voluntary isometric contraction (MVIC) torque was reached. Threshold to detect passive movement (TTDPM) tasks were used to assess movement sense during both knee flexion (TTDPMFLEX) and extension (TTDPMEXT). KE fatigability was assessed using the interpolated twitch technique. TTDPM values expressed in seconds and the percentage of unsuccessful trials only increased at POST during TTDPMFLEX and TTDPMEXT. The 20%-MVIC decrease was associated with significant decreases in voluntary activation level (− 12.7%, p < 0.01) and potentiated doublet torque at 100 Hz (− 18.1%, p < 0.001). At POST24, despite persistent reductions of maximal voluntary and electrically evoked torques associated with increased perceived muscle soreness, TTDPM values and the percentage of unsuccessful trials returned to baseline values. Consequently, movement sense alterations were only observed in the presence of voluntary activation deficits, suggesting that some exercise-induced central alterations may affect the somatosensory function.

Fasting-Mimicking-Diet does not reduce skeletal muscle function in healthy young adults: a randomized control trial.

The aim of this study was to evaluate the short- and long-term effects of the Fasting-Mimicking-Diet (FMD) intervention on neuromuscular parameters of force production in healthy young men. Twenty-four physically active men completed the study. Participants were randomly assigned to Fasting-Mimicking (FMD) or Normal Diet (ND) and asked to follow three cycles of dietary intervention. Neuromuscular parameters of force production during maximalvoluntary isometric contractions (MVCs) with the leg extensors muscles and anthropometrics were measured at baseline (T0), at the end of the first cycle (T1), and 7-10days after the 3rd cycle of the nutritional intervention (T2). The study was registered on Clinicaltrials.gov (No. NCT04476615). There was a significant decrease in body mass at T1 for FMD (- 2.6kg, ∆ from baseline, on average; p < 0.05) but not in ND (- 0.1kg;). Neuromuscular parameters of force production, muscle volume, and MVC torque did not change or differ between groups across visits. Results were similar even when parameters were normalized by muscle volume. The consumption of FMD in a group of young healthy male subjects showed to be feasible, and it did not affect neuromuscular parameters of force production. The results suggest that FMD could be safely adopted by strength athletes without detrimental effects on force and muscle volume. Further research in clinical population at risk of muscle mass loss, such as elderly and obese subjects with sarcopenia, is warranted.

Rate of force development in the quadriceps of individuals with severe knee osteoarthritis: A preliminary cross-sectional study.

Knee osteoarthritis (KOA) is a leading cause of knee pain and disability due to irreversible cartilage degeneration. Previous studies have not identified modifiable risk factors for KOA. In this preliminary cross-sectional study, we aimed to test the following hypotheses: individuals with severe KOA would have a significantly lower quadriceps rate of force development (RFD) than individuals with early KOA, and the decrease in quadriceps RFD would be greater than the decrease in maximum quadriceps strength in individuals with severe KOA. The maximum isometric strength of the quadriceps was assessed in individuals with mild (Kellgren and Lawrence [K&L] grade 1-2) and severe KOA (K&L grade 3-4) using a handheld dynamometer. The RFD was analyzed at 200 ms from torque onset and normalized to the body mass and maximum voluntary isometric contraction torque. To test whether the quadriceps RFD was lowered and whether the lower in the quadriceps RFD was greater than the lower in maximum quadriceps strength in individuals with severe knee OA, the Mann-Whitney U-test and analysis of covariance were performed, respectively. The effect size (ES) based on Hedges' g with a 95% confidence interval (CI) was calculated for the quadriceps RFD and maximum quadriceps strength. Sixty-six participants were analyzed. Individuals with severe KOA displayed significantly lower quadriceps RFD (p = 0.009), the lower being greater than the lower in maximum quadriceps strength (between-group difference, ES: 0.88, -1.07 vs. 0.06, -0.22). Our results suggest that a decreased quadriceps RFD is a modifiable risk factor for progressive KOA. Our finding could help in the early detection and prevention of severe KOA.

Effect of the Knee and Hip Angles on Knee Extensor Torque: Neural, Architectural, and Mechanical Considerations.

This study examined the influence of knee extensors’ hip and knee angle on force production capacity and their neuromuscular and architectural consequences. Sixteen healthy men performed sub-maximal and maximal voluntary isometric contractions (MVIC) of knee extensors with four different combinations of the knee and hip angles. Muscle architecture, excitation-contraction coupling process, muscular activity, and corticospinal excitability were evaluated on the vastus lateralis (VL) and rectus femoris (RF) muscles. MVIC and evoked peak twitch (Pt) torques of knee extensors increased significantly (p < 0.05) by 42 ± 12% and 47 ± 16% on average, respectively, under knee flexed positions (110° flexion, 0° = full extension) compared to knee extended positions (20° flexion) but were not different between hip positions (i.e., 0° or 60° flexion). Knee flexion also affected VL and RF muscle and fascicle lengths toward greater length than under knee extended position, while pennation angle decreased for both muscles with knee flexion. Pennation angles of the VL muscle were also lower under extended hip positions. Alternatively, no change in maximal muscle activation or corticospinal activity occurred for the VL and RF muscles across the different positions. Altogether these findings evidenced that MVIC torque of knee extensors depended particularly upon peripheral contractile elements, such as VL and RF muscle and fascicle lengths, but was unaffected by central factors (i.e., muscle activation). Furthermore, the hip position can affect the pennation angle of the VL, while VL muscle length can affect the pennation angle of the RF muscle. These elements suggest that the VL and RF muscles exert a mutual influence on their architecture, probably related to the rectus-vastus aponeurosis.

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.

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.

Cross-education and detraining effects of eccentric vs. concentric resistance training of the elbow flexors

BackgroundUnilateral resistance training increases the strength of the contralateral non-trained homologous muscles known as the cross-education effect. We tested the hypothesis that unilateral eccentric resistance training (ET) would induce greater and longer-lasting cross-education effect when compared with concentric resistance training (CT).MethodsYoung (20–23 y) participants were allocated to ET (5 males, 4 females) or CT (5 males, 4 females) group that performed unilateral progressive ET or CT of the elbow flexors, twice a week for 5 weeks (10 sessions) followed by a 5-week detraining, and control group (7 males, 6 females) that did not perform any training. Maximum voluntary isometric contraction torque of the elbow flexors (MVIC), one-repetition maximum of concentric dumbbell curl (1-RM), and biceps brachii and brachialis muscle thickness (MT) were measured from the trained and non-trained arms before, several days after the last training session, and 5 weeks later. A ratio between the trained and non-trained arms for the change in MVIC or 1-RM from pre- to post-training (cross-body transfer ratio) was compared between ET and CT groups.ResultsThe control group did not show significant changes in any variables. Both ET and CT increased (P < 0.05) MVIC (22.5 ± 12.3 % vs. 26.0 ± 11.9 %) and 1-RM (28.8 ± 6.6 % vs. 35.4 ± 12.9 %) of the trained arm without a significant difference between groups. MVIC was maintained after detraining for ET but returned to the baseline for CT, and 1-RM was maintained after detraining for both ET and CT. For the non-trained arm, MVIC (22.7 ± 17.9 % vs. 12.2 ± 10.2 %) and 1-RM (19.9 ± 14.6 % vs. 24.0 ± 10.6 %) increased similarly (P > 0.05) after ET and CT, and MVIC returned to the baseline after detraining, but 1-RM was maintained for both groups. An increase (P < 0.05) in MT was found only after ET for the trained arm (7.1 ± 6.1 %). The cross-body transfer ratio for MVIC was greater (P < 0.05) for ET (90.9 ± 46.7 %) than CT (49.0 ± 30.0 %).ConclusionsThese results did not support the hypothesis and showed similar changes in the most of the variables between ET and CT for the trained and non-trained arms, and strong cross-education effects on MVIC and 1-RM, but less detraining effect after ET than CT on MVIC of the trained arm.Trial registrationUniversity Hospital Medical Information Network Clinical Trials Registry (UMIN000044477; Jun 09, 2021).

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.

The single-leg heel raise does not predict maximal plantar flexion strength in healthy males and females.

IntroductionThe single-leg heel raise test (SLHR) is commonly used in clinical settings to approximate plantar flexor strength, yet this is neither validated nor supported physiologically. The purposes of this study were to: determine (1) associations between SLHR repetitions, maximal plantar flexor strength, and reductions in strength; and (2) whether sex differences exist in performance of the SLHR.MethodsTwenty-eight young, healthy participants (14 males,14 females, 19–30 years) performed repeated single-leg heel raises to task failure. Pre- and post-task measures included maximal voluntary isometric contractions (MVIC), and voluntary activation and contractile properties of the plantar flexor muscles, assessed using peripheral electrical stimulation of the tibial nerve. Surface electromyography was recorded for the medial and lateral gastrocnemius, soleus, and anterior tibialis muscles.ResultsThe SLHR resulted in 20.5% reductions in MVIC torque (p<0.001). However, the number of SLHR repetitions was not correlated with either the baseline MVIC (maximal strength; p = 0.979) or the reduction in MVIC following the SLHR (p = 0.23). There were no sex differences in either the number of SLHR repetitions (p = 0.14), baseline MVIC torque (p = 0.198), or the reduction of MVIC (p = 0.14). MVIC decline was positively associated with the reduction in voluntary activation (r = 0.841, p<0.001), but was not associated with the change in twitch amplitude (p = 0.597).ConclusionsThe SLHR was similar in young males and females yet was a poor predictor of maximal plantar flexor strength but evaluates performance fatigability of the lower extremity specific to dynamic contractions. The reduction in maximal strength at task failure was explained by reduced neural drive to the plantar flexor muscles in both males and females.Impact statementSLHR performance is not a clinical assessment of plantar flexor strength but assesses dynamic lower extremity fatigability that is similar in males and females. Alternate clinical measures for maximal plantar flexion strength need to be developed.