Time-Course of Neuromuscular Changes during and after Maximal Eccentric Contractions

Aging and Recovery After Resistance-Exercise-Induced Muscle Damage: Current Evidence and Implications for Future Research

Aging is anecdotally associated with a prolonged recovery from resistance training, though current literature remains equivocal. This brief review considers the effects of resistance training on indirect markers of muscle damage and recovery (i.e., muscle soreness, blood markers, and muscle strength) in older males. With no date restrictions, four databases were searched for articles relating to aging, muscle damage, and recovery. Data from 11 studies were extracted for review. Of these, four reported worse symptoms in older compared with younger populations, while two have observed the opposite, and the remaining studies (n = 6) proposed no differences between age groups. It appears that resistance training can be practiced in older populations without concern for impaired recovery. To improve current knowledge, researchers are urged to utilize more ecologically valid muscle-damaging bouts and investigate the mechanisms which underpin the recovery of muscle soreness and strength after exercise in older populations.

Influence of fascicle strain and corticospinal excitability during eccentric contractions on force loss

NEW FINDINGS

What is the central question of this study? Do neural and/or mechanical factors determine the extent of muscle damage induced by eccentric contractions? What is the main finding and its importance? The extent of muscle damage induced by eccentric contractions is related to both mechanical strain and corticospinal excitability measured at long muscle lengths during eccentric contractions.

ABSTRACT

In this study, we investigated whether the mechanical and neural characteristics of maximal voluntary eccentric contractions would determine the extent of change in postexercise maximal voluntary isometric contraction (MVC) torque and muscle soreness. Eleven men performed 10 sets of 15 isokinetic (45 deg s^-1 ) maximal voluntary eccentric knee extensions. Knee-extension torque and vastus lateralis fascicle length were assessed at sets 1, 5 and 9. Vastus lateralis motor evoked potential, maximal M wave (MEP/M) and the cortical silent period (CSP) were measured at 75 and 100 deg of knee flexion (0 deg = full extension) during contractions and were normalized to MEP/M (MEP/M_ecc/iso ) and CSP (CSP_ecc/iso ) recorded during isometric MVC at each angle. The MVC torque and muscle soreness of the knee extensors were assessed before, 24, 48 and 96 h after the eccentric contractions. The extent of relative decrease in MVC torque at 24 h postexercise (r²  = 0.38) and peak muscle soreness (r²  = 0.69) were correlated (P < 0.05) with MEP/M_ecc/iso measured at 100 deg, but not at 75 deg. The average torque on the descending limb of the torque-angle relationship (r²  = 0.16), fascicle elongation (r²  = 0.18) and CSP_ecc/iso at both 75 (r²  = 0.00) and 100 deg (r²  = 0.02) were not significantly correlated with the relative decrease in MVC torque. The relative decrease in MVC torque was best predicted by a combination of mean torque on the descending limb, fascicle elongation and MEP/M_ecc/iso (R²  = 0.93). It is concluded that the extent of muscle damage based on the reduction in MVC torque is determined by mechanical strain and corticospinal excitability at long muscle lengths during maximal voluntary eccentric contractions.

Internal Loads, but Not External Loads and Fatigue, Are Similar in Young and Middle-Aged Resistance-Trained Males during High Volume Squatting Exercise †

Little is known about the internal and external loads experienced during resistance exercise, or the subsequent fatigue-related response, across different age groups. This study compared the internal (heart rate, OMNI ratings of perceived exertion (RPE), session RPE) and external loads (peak velocity and power and volume load) during high volume squatting exercise (10 × 10 at 60% one-repetition maximum (1RM)) and the fatigue-related response (maximal voluntary contraction (MVC), voluntary activation (VA), resting doublet force, peak power, and blood lactate) in young (n = 9; age 22.3 ± 1.7 years) and middle-aged (n = 9; age 39.9 ± 6.2 years) resistance-trained males. All internal load variables and peak velocity illustrated unclear differences between groups during exercise. Peak power and volume load were likely higher in the young group compared to their middle-aged counterparts. The unclear differences in MVC, VA and blood lactate between groups after exercise were accompanied by very likely greater decrements in resting doublet force and peak power at 20 and 80% 1RM in the middle-aged group compared to the young group. These data indicate that internal load is not different between young and middle-aged resistance-trained males, though certain external load measures and the fatigue response are.

Specific joint angle dependency of voluntary activation during eccentric knee extensions

INTRODUCTION

This study compared voluntary activation during isometric, concentric, and eccentric maximal knee extensions at different joint angles.

METHODS

Fifteen participants performed isometric, concentric, and eccentric protocols (9 contractions each). For each protocol, the central activation ratio (CAR) was randomly measured at 50°, 75°, or 100° of knee joint angle (0° = full knee extension) using superimposed supramaximal paired nerve stimulations during contractions.

RESULTS

CAR increased between 50° and 100° during isometric (93.6 ± 3.1 vs. 98.5 ± 1.4%), concentric (92.4 ± 5.4 vs. 99.2 ± 1.2%), and eccentric (93.0 ± 3.5 vs. 96.6 ± 3.8%) contractions. CAR was lower during eccentric than both isometric and concentric contractions at 75° and 100°, but similar between contraction types at 50°.

CONCLUSIONS

The ability to activate muscle maximally is impaired during eccentric contractions compared with other contraction types at 75° and 100°, but not at 50°. Muscle Nerve 56: 750-758, 2017.