Joint angle-specific neuromuscular time course of recovery after isometric resistance exercise at shorter and longer muscle lengths

McMahon, G and Onambele-Pearson, G ORCID: https://orcid.org/0000-0002-1466-3265 (2024) Joint angle-specific neuromuscular time course of recovery after isometric resistance exercise at shorter and longer muscle lengths. Journal of Applied Physiology, 136 (4). pp. 889-900. ISSN 8750-7587

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Abstract

Resistance training at longer muscle lengths induces greater muscle hypertrophy and different neuromuscular functional adaptations than training at shorter muscle lengths. However, the acute time course of recovery of neuromuscular characteristics after resistance exercise at shorter and longer muscle lengths in the quadriceps has never been described. Eight healthy young participants (4 M, 4 F) were randomly assigned to perform four sets of eight maximal isometric contractions at shorter (SL; 50° knee flexion) or longer (LL; 90° knee flexion) muscle lengths in a crossover fashion. During exercise, peak torque (PT), muscle activity [electromyogram (EMG)], and internal muscle forces were assessed. PT and EMG at shorter (PT50, EMG50) and longer (PT90, EMG90) muscle lengths, creatine kinase (CK), and muscle soreness were measured at baseline, immediately after exercise (Post), after 24 h (24 h), and after 48 h (48 h). During exercise, EMG (P ¼ 0.002) and internal muscle forces (P ¼ 0.017) were greater in LL than in SL. During recovery, there was a main effect of exercise angle, with PT50 (P ¼ 0.002), PT90 (P ¼ 0.016), and EMG50 (P ¼ 0.002) all significantly reduced to a greater degree in LL compared with SL. CK and muscle soreness increased after resistance exercise, but there were no differences between SL and LL. The present results suggest that if the preceding isometric resistance exercise is performed at longer muscle lengths, function and muscle activity at shorter and longer muscle lengths are inhibited to a larger degree in the subsequent recovery period. This information can be used by practitioners to manipulate exercise prescription. NEW & NOTEWORTHY: Despite the established long-term benefits of training at longer muscle lengths for muscle size and strength, acutely performing resistance exercise at longer muscle lengths may require a longer time course of neuromuscular recovery compared with performing resistance exercises at shorter muscle lengths. Furthermore, there appear to be different joint angle-specific recovery profiles, depending on the muscle length of the preceding exercise.