Exercise selection plays an important role in inducing non-uniform acute responses on elbow flexors muscle thickness

The muscle thickness (MT) acutely increases in response to the redirection of blood flow during exercise, with this muscle swelling being a proxy to quantify the degree of muscle stimuli and involvement in an exercise. The present study aims to compare the MT acute variations between the biceps brachii (BB) and brachialis (BRA) muscles in two different unilateral exercises, the dumbbell curl (DC) and dumbbell row (DR). Sixteen well-trained young males performed a 10-repetition maximum (10RM) load test and retest for each exercise. Four sets were performed with the 10RM load for each exercise until the concentric failure. The BB and BRA muscles MT were measured pre and post-intervention with a B-mode ultrasound images. The main finding of this study was that, when DC is performed, the BB presented greater MT changes (18.67% ± 6.23) compared to BRA (12.27% ± 6.20) (p = 0.025), and compared to BB when performed in DR (12.23% ± 6.03) (p = 0.024). It was also found that BB greatest increase from BRA was not observed in DR and the BRA results were similar in both exercises. These results indicate that the structural acute responses can be muscle-specific among the elbow flexors muscles for the single-joint exercise and also exercise-specific. Therefore, either one of these two exercises can be chosen to stimulate BRA, but it would be interesting to use DC to offer greater stimuli for BB.