Inter-Set Static Stretching does not Impair Muscle Performance and Acute Muscle Architecture

Background. Inter-set static stretching has emerged as a potential strategy for enhancing skeletal muscle adaptations. However, its impact on acute performance remains unclear. Objective. To investigate the acute effects of inter-set static stretching on isokinetic knee extension total work and muscle swelling measured by the longitudinal muscle area variation of the vastus lateralis. Methods. Fourteen resistance-trained men performed four sets of ten maximal repeti- tions of knee extension at 60º/s in an isokinetic dynamometer with 90 s of rest interval. In the inter-set stretching protocol, passive static stretching was applied until the posi- tion of maximum discomfort in knee flexion for 30s, while the other limb remained relaxed and extended as established by the control protocol. The total work performed during each repetition was summed for each set. Panoramic ultrasound images of the vastus lateralis were acquired immediately before and after the interventions and the whole longitudinal muscle area was measured. The significance level of the study was set to P < 0.05. Results. There was a decrease in performance throughout the series in both protocols (F = 58.334; P < 0.001) and equally affected total work (F = 1.016; P = 0.316). Increases in the vastus lateralis longitudinal muscle area were observed in the control (14.8%) and experimental (20.9%) protocols, with no difference between them (P = 0.274). Conclusions. Inter-set static stretching lasting 30s had no impact on knee extensor performance or muscle swelling. Coaches and practitioners can use this stretching approach without compromising exercise performance.