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

Purpose: 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 following resistance exercise at shorter and longer muscle lengths in the quadriceps has never been described. Methods: Eight healthy, young participants, (4M, 4F) were randomly assigned to perform 4 sets of 8 maximal isometric contractions at shorter (SL; 50o knee flexion) or longer muscle lengths (LL; 90o knee flexion) in a crossover fashion. During exercise peak torque (PT), muscle activity (EMG) and internal muscle forces were assessed. PT and EMG at shorter (PT50, EMG50) and longer muscle lengths (PT90, EMG90), creatine kinase (CK) and muscle soreness were measured at baseline, immediately post (Post), post-24hrs (24hrs) and post-48hrs (48hrs). Results: During exercise, EMG (p=0.002) and internal muscle forces (p=0.017) were greater in LL than SL. During recovery, there was a main effect of exercise angle with PT50 (p=0.002), PT90 (p=0.016) and EMG50 (p=0.002) all significantly reduced to a greater degree in LL compared to SL. CK and muscle soreness increased following resistance exercise but there were no differences between SL and LL. Conclusion: The current 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 is inhibited to a larger degree in the subsequent recovery period. This information can be used by practitioners to manipulate exercise prescription.