RESUMEN
This study aimed to investigate if ACTN3 gene polymorphism impacts the susceptibility to exercise-induced muscle damage (EIMD) and changes in running economy (RE) following downhill running. Thirty-five healthy men were allocated to the two groups based on their ACTN3 gene variants: RR and X allele carriers. Neuromuscular function [knee extensor isometric peak torque (IPT), rate of torque development (RTD), and countermovement, and squat jump height], indirect markers of EIMD [muscle soreness, mid-thigh circumference, knee joint range of motion, and serum creatine kinase (CK) activity], and RE (oxygen uptake, minute ventilation, blood lactate concentration, and perceived exertion) for 5-min of running at a speed equivalent to 80% of individual maximal oxygen uptake speed were assessed before, immediately after, and 1-4 days after a 30-min downhill run (-15%). Neuromuscular function was compromised (P < 0.05) following downhill running with no differences between the groups, except for IPT, which was more affected in the RR individuals compared with the X allele carriers immediately (-24.9 ± 6.9% vs. -16.3 ± 6.5%, respectively) and 4 days (-16.6 ± 14.9% vs. -4.2 ± 9.5%, respectively) post-downhill running. EIMD manifested similarly for both the groups except for serum CK activity, which was greater for RR (398 ± 120 and 452 ± 126 U L-1 at 2 and 4 days following downhill running, respectively) compared with the X allele carriers (273 ± 121 and 352 ± 114 U L-1 at the same time points). RE was compromised following downhill running (16.7 ± 8.3% and 11 ± 7.5% increases in oxygen uptake immediately following downhill running for the RR and X allele carriers, respectively) with no difference between the groups. We conclude that although RR individuals appear to be more susceptible to EIMD following downhill running, this does not extend to the changes in RE.
RESUMEN
NEW FINDINGS: What is the central question of this study? What role do neuromuscular fatigue mechanisms play in resistance training-induced adaptations of the impulse above end-test torque (IET) after the training period? What is the main finding and its importance? IET and global and peripheral fatigue were increased after a short period of resistance training. Thus, resistance training-induced adaptations in neuromuscular fatigue seem to contribute to enhanced IET after the training period. ABSTRACT: Short-term resistance training has a positive influence on the curvature constant of the power-duration relationship (W'). The physiological mechanism of W' enhancement after resistance training is unclear. This study aimed to determine whether one-leg maximal isometric resistance training influences (1) impulse above end-test torque (IET; an analogue of W') during a 5 min all-out isometric test; and (2) exercise tolerance (limit of tolerance, Tlim) and neuromuscular fatigue during severe exercise (i.e. above end-test torque; ET). Sixteen healthy active males participated in a 3-week unilateral knee extensor resistance-training programme, and 10 matched subjects participated as controls. The subjects were instructed to ramp up to 100% of maximal voluntary contraction (MVC) over 1 s, hold it for 3 s, and relax. Each repetition had a 2 s interval (10) and each set, a 2 min interval (3). MVC (18.6%) and muscle thickness (12.8%) were significantly improved after training. Significantly greater global (i.e. reduced MVC, 43.2 ± 13.5% vs. 58.9 ± 6.9%) and peripheral (51.7 ± 13.6% vs. 57.3 ± 15.3%) fatigue, IET (26%) and Tlim (92%) were obtained after resistance training. Moreover, both global (r = 0.57, P < 0.05) and peripheral fatigue (r = 0.55, P < 0.05) accrued during severe exercise were associated with IET. However, echo intensity, which reflects muscle quality, ET and central fatigue remained unchanged throughout the training period. No significant changes in the control group for any variable were observed. Resistance training-induced adaptations in muscle size and neuromuscular fatigue seem to contribute to enhanced IET and Tlim after the training period.