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The purpose of this study was to examine the effects of high-intensity, eccentric-only muscle actions of the leg extensors on (a) serum biomarkers of collagen degradation (hydroxyproline [HYP] and C-terminal telopeptide of type I collagen [C1M]) and synthesis (pro-c1a1) and (b) the time course of changes in maximal voluntary isometric contraction (MVIC) and ratings of muscle soreness after the eccentric-only exercise bout. Twenty-five recreationally active men (mean ± SD: age = 21.2 ± 2.0 years) completed 5 sets of 10 bilateral, eccentric-only dynamic constant external resistance muscle actions of the leg extensors at a load of 110% of their concentric leg extension 1 repetition maximum. Analysis of variances (p < 0.05) and a priori planned pairwise comparisons using Bonferroni corrected (p < 0.0167) paired t tests were used to examine mean changes in blood biomarkers from baseline to 48 hours postexercise as well as in MVIC and soreness ratings immediately, 24 hours, and 48 hours postexercise. There were increases in HYP (3.41 ± 2.37 to 12.37 ± 8.11 µg⋅ml-1; p < 0.001) and C1M (2.50 ± 1.05 to 5.64 ± 4.89 µg⋅L-1; p = 0.003) from preexercise to 48 hours postexercise, but no change in pro-c1 α1. Maximal voluntary isometric contraction declined immediately after the exercise bout (450.44 ± 72.80 to 424.48 ± 66.67 N-m; p = 0.002) but recovered 24 hours later, whereas soreness was elevated immediately (6.56 ± 1.58; p < 0.001), 24 hours (3.52 ± 1.53; p < 0.001), and 48 hours (2.60 ± 1.32; p = 0.001) postexercise. The eccentric-only exercise bout induced increases in collagen degradation but had no effect on collagen synthesis. These findings provide information for clinicians to consider when prescribing exercise after an acute injury or surgery. [ABSTRACT FROM AUTHOR]

The purpose of this study was to identify velocity-specific changes in electromyographic root mean square (EMG RMS), EMG frequency (EMG MPF), mechanomyographic RMS (MMG RMS), and MMG MPF during maximal unilateral isokinetic muscle actions performed at 60° and 240°·s-1 velocities within the right and left vastus lateralis (VL) after 4 weeks of dynamic constant external resistance (DCER) bilateral leg press training. Twelve resistance-trained men (age: mean ± SD = 21.4 ± 3.6 years) visited the laboratory 3d·wk-1 to perform resistance training consisting of 3 sets of 10 DCER leg presses. Four, three-way analysis of variance were performed to evaluate changes in neuromuscular responses (EMG RMS, EMG MPF, MMG RMS, and MMG MPF) from the right and left VL during 1 single-leg maximal isokinetic leg extension performed at 60° and 240°·s-1 before and after 4 weeks of DCER leg press training (p < 0.05). The results indicated a 36% increase in EMG RMS for the right leg, as well as a 23% increase in MMG RMS and 10% decrease in MMG MPF after training, collapsed across velocity and leg. In addition, EMG RMS was 65% greater in the right leg than the left leg following training, whereas EMG MPF was 11% greater for the left leg than the right leg throughout training. Thus, 4 weeks of DCER leg press training provides sufficient stimuli to alter the neuromuscular activation process of the VL but not velocity-specific neuromuscular adaptations in trained males. [ABSTRACT FROM AUTHOR]

The Effects of Anchor Scheme and Sex on Performance Fatigability and Neuromuscular Responses Following Sustained, Isometric Forearm Flexion Tasks to Failure. JEPonline 2023;26(3):69-92. The purpose of this study was to examine the effects of anchor scheme and sex on time to task failure (TTF), maximal voluntary isometric contraction (MVIC) assessments, and neuromuscular responses following sustained, isometric forearm flexion tasks. Eight males and 8 females performed MVICs before and after sustained tasks anchored to an RPE = 8 (RPEFT) and torque (TRQFT). The amplitude (AMP) and frequency (MPF) of the electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from the biceps brachii. Mixed factorial ANOVAs were used to examine the mean differences in the MVIC, as well as the normalized neuromuscular parameters. For the TTF, the RPEFT was longer (P = 0.003) than the TRQFT. There were parallel fatigue-induced decreases in MVIC (P < 0.001) and EMG AMP (P = 0.023), while MMG AMP increased (P = 0.002), regardless of anchor scheme or sex. However, the MPF for EMG and MMG remained unchanged. [ABSTRACT FROM AUTHOR]

The present study used the ratings of perceived exertion (RPE)-clamp model during a sustained, isometric forearm flexion task to failure to determine the effects of joint angle on torque and neuromuscular responses. Twelve college-aged women performed two 3-second maximal voluntary isometric contractions at elbow joint angles (EJ) of 75˚, 100˚, and 125˚ before sustained, isometric, forearm flexions anchored to RPE = 7 to task failure (defined as RPE >7, or the torque was reduced to zero) at EJ75, EJ100, and EJ125. The amplitude (AMP) and frequency (MPF) of the electromyographic (EMG) and mechanomyographic (MMG) signals from the biceps brachii were recorded. Repeated-measures ANOVAs and post hoc comparisons were used to examine differences across time and between joint angles for torque and neuromuscular parameters. A p-value ≤ 0.05 was considered significant. For each joint angle, there was a decrease (p <0.05) in torque across the sustained, isometric task. Collapsed across joint angle, there were decreases (p <0.001, η²p 5 0.378) in EMG AMP from 30 to 100% time to task failure. No changes were observed, however, for the other neuromuscular responses. The subjects voluntarily reduced torque to maintain RPE 5 7 for each joint angle, and we hypothesize that RPE was maintained by afferent feedback from group III/IV motor neurons and corollary discharge (efferent copy of an internal signal that develops from central motor commands). The RPE-Clamp Model may be extended to athletes recovering from injury because a self-selected exercise intensity may be perceived as more enjoyable and promote adherence. [ABSTRACT FROM AUTHOR]