Influence of Pennation Angle and Muscle Thickness on Mechanomyographic Amplitude-Torque Relationships and Sex-Related Differences in the Vastus Lateralis.

This study examined potential sex-related differences and correlations among the pennation angle (PA), muscle thickness (MT), and mechanomyographic amplitude (MMGRMS)-torque relationships of the vastus lateralis (VL) in 11 healthy males and 12 healthy females. The PA and MT of the VL were quantified with ultrasound. Participants performed an isometric muscle action of the knee extensors that linearly increased to 70% of maximal strength followed by a 12 s plateau. MMG was recorded from the VL. Linear regression models were fit to the log-transformed MMGRMS-torque relationships to calculate b terms (slopes) for the linearly increasing segment. MMGRMS was averaged during the plateau. Males exhibited greater PA (p < 0.001), MT (p = 0.027), b terms (p = 0.005), and MMGRMS (p = 0.016). The b terms were strongly (p < 0.001, r = 0.772) and moderately correlated (p = 0.004, r = 0.571) with PA and MT, respectively, while MMGRMS was moderately correlated with PA (p = 0.018, r = 0.500) and MT (p = 0.014, r = 0.515). The greater mechanical behavior of individuals possessing a larger PA and MT of the VL may reflect increased cross-bridge activity within the muscle fibers. Additionally, PA may help explain sex-related differences in MMGRMS between sexes.

Chronic training status affects muscle excitation of the vastus lateralis during repeated contractions.

This study examined electromyographic amplitude (EMGRMS)-force relationships during repeated submaximal knee extensor muscle actions among chronic aerobically-(AT), resistance-trained (RT), and sedentary (SED) individuals. Fifteen adults (5/group) attempted 20 isometric trapezoidal muscle actions at 50% of maximal strength. Surface electromyography (EMG) was recorded from vastus lateralis (VL) during the muscle actions. For the first and last successfully completed contractions, linear regression models were fit to the log-transformed EMGRMS-force relationships during the linearly increasing and decreasing segments, and the b terms (slope) and a terms (antilog of y-intercept) were calculated. EMGRMS was averaged during steady force. Only the AT completed all 20 muscle actions. During the first contraction, the b terms for RT (1.301 â€‹± â€‹0.197) were greater than AT (0.910 â€‹± â€‹0.123; p â€‹= â€‹0.008) and SED (0.912 â€‹± â€‹0.162; p â€‹= â€‹0.008) during the linearly increasing segment, and in comparison to the linearly decreasing segment (1.018 â€‹± â€‹0.139; p â€‹= â€‹0.014), respectively. For the last contraction, the b terms for RT were greater than AT during the linearly increasing (RT â€‹= â€‹1.373 â€‹± â€‹0.353; AT â€‹= â€‹0.883 â€‹± â€‹0.129; p â€‹= â€‹0.018) and decreasing (RT â€‹= â€‹1.526 â€‹± â€‹0.328; AT â€‹= â€‹0.970 â€‹± â€‹0.223; p â€‹= â€‹0.010) segments. In addition, the b terms for SED increased from the linearly increasing (0.968 â€‹± â€‹0.144) to decreasing segment (1.268 â€‹± â€‹0.126; p â€‹= â€‹0.015). There were no training, segment, or contraction differences for the a terms. EMGRMS during steady force increased from the first- ([64.08 â€‹± â€‹51.68] â€‹µV) to last-contraction ([86.73 â€‹± â€‹49.55] â€‹µV; p â€‹= â€‹0.001) collapsed across training statuses. The b terms differentiated the rate of change for EMGRMS with increments in force among training groups, indicating greater muscle excitation to the motoneuron pool was necessary for the RT than AT during the linearly increasing and decreasing segments of a repetitive task.

Contralateral protective effect against repeated bout of damaging exercise: A meta-analysis.

The purpose was to summarize the studies examining the contralateral protective effect on the maximal strength in the subsequent bout of muscle-damaging exercise. The literature search was conducted through CINAHL plus, SportDiscus, and PubMed. Hedge's g effect size (ES) and 95% confidence intervals (CIs) were computed using a random effects model. From 14 papers and 25 ESs, the mean ES for contralateral repeated bout effect (CL-RBE) on 1-, 2-, and 3-day post maximal strength were -0.61 (95% CI = -0.80, -0.41), -0.50 (95% CI = -0.67, -0.33), and -0.74 (95% CI = -1.01, -0.48), respectively. For moderator analyses, the mean ESs were not influenced by type (isometric vs. isokinetic) of strength, but CL-RBE on maximal strength was influenced by duration (≤6 weeks) between bouts. Therefore, the meta-analysis demonstrated that an initial bout of exercise induces the protective effect on contralateral limb muscles regardless of the different type of strength, but can be affected by different duration (≤6 weeks) between exercise bouts.

Effect of repeated eccentric exercise on muscle damage markers and motor unit control strategies in arm and hand muscle.

To examine the contralateral repeated bout effect (CL-RBE) on muscle damage markers and motor unit (MU) control strategies, seventeen healthy adults performed two bouts of 60 eccentric contractions with elbow flexor (EF group; n â€‹= â€‹9) or index finger abductor (IA group; n â€‹= â€‹8) muscles, separated by 1 week. All participants randomly performed eccentric exercise on either the right or left arm or hand muscles, and muscle damage markers and submaximal trapezoid contraction tests were conducted pre, post, 1- and 2-day post eccentric protocol. One week after the first bout, the same exercise protocol and measurements were performed on the contralateral muscles. Surface electromyographic (EMG) signals were collected from biceps brachii (BB) or first dorsal interosseous (FDI) during maximal and submaximal tests. The linear regression analyses were used to examine MU recruitment threshold versus mean firing rate and recruitment threshold versus derecruitment threshold relationships. EMG amplitude from BB (bout 1 vs. bout 2 â€‹= â€‹65.71% â€‹± â€‹22.92% vs. 43.05% â€‹± â€‹18.97%, p â€‹= â€‹0.015, d â€‹= â€‹1.077) and the y-intercept (group merged) from the MU recruitment threshold versus derecruitment threshold relationship (bout 1 vs. bout 2 â€‹= â€‹-7.10 â€‹± â€‹14.20 vs. 0.73 â€‹± â€‹16.24, p â€‹= â€‹0.029, d â€‹= â€‹0.513) at 50% MVIC were significantly different between two bouts. However, other muscle damage markers did not show any CL-RBE in both muscle groups. Therefore, despite changes in muscle excitation and MU firing behavior, our results do not support the existence of CL-RBE on BB and FDI muscles.

Effect of Arm Eccentric Exercise on Muscle Damage of the Knee Flexors After High-Intensity Eccentric Exercise.

Repeated bout effect (RBE) describes a phenomenon that an initial unaccustomed eccentric exercise (ECC) bout can confer a protective effect against muscle damage from the subsequent same exercise. This protection has been observed in the same muscle, as well as the contralateral homologous (CL-RBE) muscle. But it is unknown whether the RBE is evident for non-local unrelated heterogonous muscles. The purpose of this study was to examine whether an initial elbow flexion (EF) muscle-damaging ECC could confer RBE against muscle damage from the subsequent ECC performed in the remote lower limb knee flexor (KF) muscle group. Twenty-seven young individuals were randomly assigned into the experimental (EXP: n = 15) and the control (CON: n = 12) groups. All participants performed a baseline unilateral KF ECC (six sets of 10 repetitions) on a randomly chosen leg. After a washout period (4 weeks), the EXP group performed 60 high-intensity unilateral EF ECC on a randomly chosen arm, followed by the same intensity exercise using the contralateral KF muscle group 2 weeks later. The CON group performed the same contralateral KF ECC, but with no prior EF ECC bout. Changes in the KF muscle damage indirect markers (muscle soreness, range of motion, and maximal isometric strength) after the ECC were compared between the baseline and second bouts for both groups with mixed factorial three-way (group × bout × time) ANOVA. Additionally, index of protection for each damage marker was calculated at 1 and 2 days after the ECC and compared between groups with independent t-tests. For both groups, the magnitude of the changes in the damage markers between the baseline and the second ECC bouts were not significantly different (all values of p > 0.05). As for the index of protection, relative to the CON, the EXP showed an exacerbating damaging effect on the KF isometric strength following the second ECC bout, particularly at the 1-day post-exercise time point (index of protection: EXP vs. CON mean ± SD = -29.36 ± 29.21 vs. 55.28 ± 23.83%, p = 0.040). Therefore, our results do not support the existence of non-local RBE.

Downhill running impairs peripheral but not central neuromuscular indices in elbow flexor muscles.

The purpose of this study was to examine the effects of a 1-h downhill running exercise on the elbow flexor muscles' neuromuscular functions. Seventeen adults (Control [CON]: n = 9; Experimental [EXP]: n = 8) completed this study. The CON rested for 30 min while the EXP performed the downhill running. Before, 10 min, 24 h, and 48 h after the interventions, dependent variables (knee extensor muscle soreness, elbow flexion and knee extension isometric strength, elbow flexion resting twitch and voluntary activation [VA], and the biceps surface electromyography [EMG] amplitude) were measured. Knee extensor muscle soreness was significantly greater in the EXP than the CON group following the intervention throughout the entire 48 h. This was accompanied by the greater decline in the knee extension strength in the EXP than the CON (mean ±â€¯SD: -6.9 ±â€¯3.4% vs. 1.0 ±â€¯3.2%, p = 0.044). The elbow flexion strength, VA, and EMG amplitude were not affected by the exercise. However, the decline of the elbow flexion resting twitch was greater in the EXP than the CON (-19.6 ±â€¯6.3% vs. 8.7 ±â€¯5.9%, p = 0.003). Therefore, the downhill running impaired the remote elbow flexor muscles at a peripheral level.

Does Performance-Related Information Augment the Maximal Isometric Force in the Elbow Flexors?

The effects of different feedback conditions on the elbow flexors maximal voluntary isometric (MVIC) force were examined. In a single visit, twenty participants (10 males) were exposed to four conditions including, Visual only; (i.e., knowledge of results [VI]); Verbal encouragement (i.e., verbally stating pull, pull [VE]); VI and VE (VIVE); and no VI or VE (NOVIVE). Three, 5-s MVIC trials were completed for each condition. Separate 2 × 4 (sex × condition) repeated measures analyses of variance (ANOVA) were used to examine MVIC force, rate of force development (RFD200), and rate of electromyography (EMG) rise (RER200) for the 0-200-ms window. There was a significant main condition effect for MVIC force (p < 0.001). Significantly greater MVIC force was shown for VIVE compared to VE (p < 0.001) and NOVIVE (p = 0.002) conditions, and VI compared to VE (p = 0.011) and NOVIVE (p = 0.009) conditions. A significant sex × condition interaction (p = 0.036) was observed for RFD200, with significantly (p = 0.003) greater RFD200 in males compared to females, in the VI condition only. There were no significant differences in RFD200 among condition for males (p = 0.033) or females (p = 0.194). There was a significant main effect for sex (p = 0.006) for RER200, with significantly greater (p = 0.003) RER200 (conditions merged) in males (mean ± standard deviation (SD): 422.99 ± 124.67%), compared to females (220.68 ± 134.01%). Here we suggest the importance of providing VI feedback alone, or in conjunction with VE, for the measurement of elbow flexion MVIC. Additionally, these results provide a foundational framework for future studies aiming to improve feedback modalities during training or rehabilitation.

The Effects of a Preconditioning Rolling Session on Subsequent Eccentric Exercise-Induced Muscle Damage.

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

A Comparison of Motor Unit Control Strategies between Two Different Isometric Tasks.

BACKGROUND: This study examined the motor unit (MU) control strategies for non-fatiguing isometric elbow flexion tasks at 40% and 70% maximal voluntary isometric contraction. METHODS: Nineteen healthy individuals performed two submaximal tasks with similar torque levels: contracting against an immovable object (force task), and maintaining the elbow joint angle against an external load (position task). Surface electromyographic (EMG) signals were collected from the agonist and antagonist muscles. The signals from the agonist were decomposed into individual action potential trains. The linear regression analysis was used to examine the MU recruitment threshold (RT) versus mean firing rates (MFR), and RT versus derecruitment threshold (DT) relationships. RESULTS: Both agonist and antagonist muscles' EMG amplitudes did not differ between two tasks. The linear slopes of the MU RT versus MFR and RT versus DT relationships during the position task were more negative (p = 0.010) and more positive (p = 0.023), respectively, when compared to the force task. CONCLUSIONS: To produce a similar force output, the position task may rely less on the recruitment of relatively high-threshold MUs. Additionally, as the force output decreases, MUs tend to derecruit at a higher force level during the position task.

An examination of acute cross-over effects following unilateral low intensity concentric and eccentric exercise.

We compared the effects of low intensity concentric (CON) and eccentric (ECC) exercise on the force and neural responses of the dominant (exercised) elbow flexors (EFs), and studied if these conditions could induce cross-over effects to the contralateral (non-exercised) EFs. Fifteen subjects (8 males) completed all conditions (CON and ECC: 6 sets of low intensity exercise to failure; control: rest) in separate visits with a randomized order. Maximal isometric force and electromyography (EMG) of the dominant and contralateral EFs were assessed at pre, immediate-, 24-, and 48-h-post. Two-factor (condition and time) linear mixed-model analyses were performed to examine the force and EMG responses. Immediately post CON, contralateral EFs force was significantly (p = 0.026) higher (12.41%) than control, but no cross-over effects regarding the neural responses were observed. Immediately post ECC, dominant EFs force was significantly lower in ECC, compared to CON (p = 0.003) and control (p < 0.001). This force remained depressed at 24- and 48-h post ECC, when compared to CON (p < 0.001) and control (p < 0.001). Our data suggests that submaximal unilateral exercises are not likely to impair contralateral muscle strength performance. Instead, concentric exercises may acutely improve muscle strength for the contralateral limb. However, this effect is not explained by changes in muscle excitation.

Effects of Maximal vs. Submaximal Isometric Fatiguing Exercise on Subsequent Submaximal Exercise Performance.

Miller, WM, Ye, X, and Jeon, S. Effects of maximal vs. submaximal isometric fatiguing exercise on subsequent submaximal exercise performance. J Strength Cond Res 34(7): 1875-1883, 2020-Exercise-induced muscle fatigue directly influences subsequent exercise performance. Thus, we examined task failure times for submaximal intermittent fatiguing isometric contractions performed after a bout of sustained maximal vs. submaximal isometric fatiguing contractions with the dominant elbow flexors. Twenty physically active individuals 8 men (mean ± SD = 21.4 ± 1.8 years; 80.9 ± 12.5 kg; 180 ± 6.4 cm) and 12 women (mean ± SD = 21.4 ± 2.7; 66.8 ± 15.6 kg; 165.7 ± 7.1 cm) participated in a 3-visit randomized cross-over study. Visit 1 included familiarization, and 2 and 3 were randomized for sustained maximal (until force was below 50% of the maximal force value) or submaximal conditions (50% of maximal force until task failure), followed by submaximal intermittent isometric contractions to task failure. Surface electromyography was recorded through the biceps brachii during all fatiguing contractions. Task failure time was significantly shorter for the maximal compared with submaximal condition, and no significant difference in sex or condition was found for the subsequent fatiguing condition. Electromyography amplitude significantly increased in the submaximal intermittent isometric contractions from prefatigue and first and final postfatigue with no condition or sex differences. Electromyography mean frequency significantly decreased from prefatigue and first and final postfatigue for both sexes, with no condition or sex differences. With both maximal and submaximal exercises inducing the same level of force deficit, our results suggested that both exercises might have imposed a similar burden on the neuromuscular system, thereby not providing differential effects on the subsequent submaximal exercise performance.

Unilateral hamstring foam rolling does not impair strength but the rate of force development of the contralateral muscle.

BACKGROUND: Self-administered foam rolling (SAFR) is an effective massage technique often used in sport and rehabilitation settings to improve range of motion (ROM) without impairing the strength performance. However, the effects of unilateral SAFR on contralateral non-intervened muscle's rate of force development (RFD) are unknown. Therefore, the purpose of this investigation was to examine the acute effects of unilateral hamstrings SAFR on the contralateral limb flexibility, the isometric strength, and the RFD parameters. METHODS: Thirty-four subjects (21 women) completed two separate randomly sequenced experimental visits, during which the control (rested for 10 min) or ten, 30-second SAFR were performed with the dominant hamstring muscle group. Before (Pre) and after (Post) the interventions, the contralateral hip flexion passive ROM, the maximal explosive isometric strength of the contralateral knee flexors with the corresponding prime mover muscles' surface electromyographic (EMG) amplitude were measured. Separate two-way (time ×intervention) repeated measures analyses of variance (ANOVAs) were used to examine the potential changes of the dependent variables. RESULTS: The SAFR significantly improved the contralateral limb ROM (Pre vs. Post: 68.3 ± 21.0 vs. 73.2 ± 23.2 degrees, p < 0.001; d = 0.22). No change was found for the contralateral isometric strength or the maximal EMG amplitude. For the RFD parameters, the percent changes of the RFDs for the first 50, 100, and 200 ms of the maximal explosive isometric contraction were -31.2%, -16.8%, and -10.1%, respectively, following the unilateral SAFR, relative to the control condition. In addition, the decrement of the first 50-ms RFD reached statistical significance (p = 0.007; Cohen's d = 0.44). CONCLUSION: Ten sets of 30-second unilateral hamstring SAFR improved the ROM of the non-intervened contralateral limb, but decreased its ability to generate force, especially during the early phase (e.g., 50 ms) of the maximal explosive contraction.

Sex comparisons of agonist and antagonist muscle electromyographic parameters during two different submaximal isometric fatiguing tasks.

To examine the task failure time of the force- and position-based submaximal elbow flexion fatiguing tasks for both sexes, twelve men and eight women visited the laboratory for two separate experimental occasions. During the experiment, they pulled against a rigid restraint for the force task and maintained a constant elbow joint angle to support an equivalent inertial load for the position task. For both fatiguing tasks (50% of the isometric strength at the elbow joint angle of 135 degree), the task failure time, along with the surface electromyographic (EMG) amplitude and mean frequency (MNF) were measured. The average failure time was longer for the force task than that for the position task (sexes combined: 39.6 ± 16.6 sec vs. 33.9 ± 14.9 sec, P = 0.033). In addition, men were overall less fatigable than women (tasks combined: 42.0 ± 14.7 sec vs. 28.7 ± 10.3 sec, P = 0.020). The multiple regression analyses showed that the task failure time in women was solely predicted by the rate of change of the triceps EMG MNF. Thus, more fatigability of women in this study was likely due to the quicker fatiguing rate of the antagonist triceps brachii muscle. Different from most previous studies that have used 90-degree elbow joint angle, the current 135-degree joint angle setup might have created a situation where greater muscle activity from the related muscles (e.g., the antagonist) were required for women than for men to stabilize the joint, thereby resulting in a shorter task failure time.

Sex comparisons of the bilateral deficit in proximal and distal upper body limb muscles.

Bilateral deficit (BLD) describes a phenomenon that the force produced during maximal simultaneous bilateral contraction is lower than the sum of those produced unilaterally. The aim of this study was to examine the potential sex-related differences in BLD in upper body proximal and distal limb muscles. Ten men and eight women performed single-joint maximal contractions with their elbow flexors and index finger abductors at separate laboratory visits, during which the maximal isometric voluntary contractions (MVICs) were performed unilaterally and bilaterally with a randomized order in the designated muscle group. Surface electromyographic (EMG) signals were recorded from the prime movers of the designated muscle groups (biceps brachii and first dorsal interosseous) during the maximal contractions. Both men and women demonstrated BLD in their elbow flexors (deficit: men = -11.0 ±â€¯6.3%; women = -10.2 ±â€¯5.0%). Accompanied by this force deficit was the reduced EMG amplitude from the dominant biceps brachii (collapsed across sex: p = 0.045). For the index finger abductors, only men (deficit = -13.7 ±â€¯6.1%), but not women showed BLD. Our results suggested that the BLD in the proximal muscle group is likely induced by the decreased maximal muscle activity from the dominant prime mover. The absence of BLD in women's index finger muscle is largely due to the inter-subject variability possibly related to the sex hormone flux and unique levels of interhemispheric inhibition.