Raymond W. McCoy

Neuromuscular disturbance outlasts other symptoms of exercise-induced muscle damage

This study examined the biochemical, immunological, functional, and neuromuscular responses associated with exercise-induced muscle damage in the quadriceps of untrained men. Muscle damage and soreness was elicited with maximal concentric/eccentric muscle actions at 0.53 rads s(-1). Significant (P<0.05) soreness was evident 1, 2, and 3 days following muscle insult, while plasma creatine kinase, a marker of muscle damage, was elevated 3 and 5 days post-insult. Plasma interleukin-Ibeta was significantly increased within 5 min, and remained elevated 1, 2, 5, and 7 days post-insult. Maximal isometric quadriceps function was impaired (P<0. 05) for 5 days following muscle challenge. Maximal isokinetic performance at 1.09 rads s(-1) was diminished (P<0.05) for 2 days post-insult; no significant decrements at 3.14 rads s(-1) were noted. Average electrical activation (iEMG) of the quadriceps was unaltered, but iEMG activity of the rectus femoris - where soreness was focused - was significantly increased. Neuromuscular efficiency (torque/iEMG) was compromised throughout the 10-day post-insult period investigated. While other symptoms of exercise-induced muscle damage dissipate within 7 days, neuromuscular perturbation persists for at least 10 days.

Adaptations to Short-Term Muscle Unloading in Young and Aged Men

INTRODUCTION The purpose of this investigation was to determine whether young (21.7 yr) and aged (68.5 yr) men experienced similar responses to 7 d of muscle unloading (N = 10 per group). METHODS Unilateral lower limb suspension (ULLS) was used to impose muscle unloading of the knee extensors. To compare the effects of unloading on aged and young men, a repeated-measures factorial ANOVA was used to assess those effects on isometric strength, as well as strength, total work, and average power during isokinetic contractions conducted at 0.53, 1.05, and 2.09 rad.s(-1). RESULTS Data showed that at slower speeds of movement, only a main effect of unloading was identified with young and aged men displaying similar and significant (P < 0.05) ULLS-induced decrements in strength, work, and power. The decrease in isometric strength correlated well with loss of electromyographic activity of contracting muscles (r = 0.79, P = 0.0002). At higher speeds of isokinetic contractions, not only was a main effect of age detected (young > aged), but it was also revealed that aged men, but not young men, experienced significant unloading-induced declines in muscle performance. Moreover, unloading resulted in a significant increase in plasma cortisol, a potent catabolic hormone, only among aged men. In contrast to other variables assessed, muscle endurance, quantified during 30 repetitions completed at 3.14 rad.s(-1), did not differ between age groups, nor was it altered by unloading. CONCLUSION These findings suggest that young and aged men respond differently to muscle unloading, but in assessing muscle performance, these differences are manifested only during faster contractile velocities.

Factors relating to gender specificity of unloading-induced declines in strength.

Introduction: This investigation aimed to: (1) confirm whether women were more vulnerable to the negative neuromuscular adaptations elicited by muscle unloading and if so, (2) determine which physiological mechanism(s) explain those gender‐related differences. Methods: Healthy young men (20.7 ± 0.3 years) and women (20.3 ± 0.3 years)—(N = 12/group)—participated by completing neuromuscular functional tests before and after 7 days of unloading. Results: During isokinetic testing of peak torque, work performed, and power, women displayed significantly (P ≤ 0.05) greater declines in performance than men at 1.05 and 2.09, but not 0.53 rads/s. During maximal isometric contractions, women experienced greater strength decrements. Similar gender‐specific adaptations to unloading were found in EMG activity, but not muscle mass, neuromuscular transmission, or force relative to EMG. Conclusions: Women are more susceptible to the adaptations of muscle unloading, and disturbances in neural drive from the central nervous system are probably responsible. Muscle Nerve 46: 210–217, 2012

The efficacy of prehabilitative conditioning: ameliorating unloading-induced declines in the muscle function of humans.

Deschenes MR, McCoy RW, Davis JM, McGinn MC, Eason MK: The efficacy of prehabilitative conditioning: ameliorating unloading-induced declines in the muscle function of humans. Objective:To determine whether prehabilitation, or exercise performed before muscle unloading, can effectively mitigate decreases in neuromuscular function typically elicited by unloading. Design:Ten healthy, untrained young men (20.9 ± 1.3 yrs; mean ± SD) were initially tested for strength, work, power, and electromyography. After completing six prehabilitative resistance training sessions, they repeated testing of neuromuscular function. Immediately after the second neuromuscular function test, participants began 7 days of muscle unloading that was immediately followed by a third testing session for neuromuscular function. Results:Prehabilitative conditioning failed to prevent significant (P ≤ 0.05) unloading-induced decrements in neuromuscular function. Performance in each measure quantified was significantly less during the third test session than during both of the first two sessions. Moreover, the declines in strength observed here were similar to those noted in a previous study featuring 1 wk of unloading without prehabilitation (13% vs. 16%, respectively, P > 0.05). Also similar to that study, the decline in strength noted here was significantly correlated with a decline in electromyography. Conclusions:The prehabilitation program used here did not moderate unloading-induced reductions in neuromuscular function. It remains to be determined whether more extensive prehabilitation protocols may be more effective.

Chronic Resistance Training Does Not Ameliorate Unloading-Induced Decrements in Neuromuscular Function.

Objective The aim of this study was to assess the efficacy of long-term resistance training in preventing the detrimental effects of muscle unloading on neuromuscular function. Design Eleven untrained men and 11 men with extensive backgrounds in resistance training were tested for several parameters of neuromuscular function at various isokinetic contractile velocities before and after 7 days of muscle unloading. Measurements included muscle mass, strength, power, total work, electromyography, and neuromuscular transmission efficiency using superimposed electrical stimulation of maximally contracting muscles. Results Muscle performance was superior in resistance-trained subjects before and after unloading. In both groups of participants, unloading resulted in significantly (P < 0.05) diminished muscle performance, but only at isometric or slower isokinetic contractile velocities. Electromyography activity was significantly higher in trained than in untrained subjects before and after unloading. Thigh muscle mass was greater among trained subjects before and after unloading. Neither electromyography activity, thigh muscle mass, nor neuromuscular transmission efficiency was significantly altered by unloading in trained or untrained participants. Conclusions Chronic resistance training was found to be ineffective in neutralizing the deleterious effects of unloading on neuromuscular function. It appears that positive adaptations associated with long-term resistance training provide no prophylactic effect when neuromuscular systems are subjected to unloading.