Effects of grip variation on biceps brachii and brachioradialis electromyographic activity during concentric and eccentric phases of the barbell curl exercise

This study investigated the effects of grip variations (supinated, semi-supinated, and neutral) and contraction phases (concentric, eccentric, and combined) on surface electromyographic (sEMG) activity of the biceps brachii (BB) and brachioradialis (BRR) during the barbell biceps curl (BBC). Twelve resistance-trained males performed BBCs under three grip conditions. sEMG activity was recorded bilaterally following SENIAM guidelines and normalized to maximal voluntary isometric contractions. A Bayesian framework evaluated activation differences within and between muscles across contraction phases. Concentric contractions elicited greater activation than eccentric phases in both muscles, while combined concentric-eccentric (CON/ECC) repetitions produced the highest activation, with strong to extreme evidence for hypothesis H1. Between-muscle comparisons showed higher BRR activation than BB during the eccentric phase, whereas concentric and CON/ECC actions yielded similar activations, supporting anecdotal evidence. These findings indicate that contraction phase and grip-bar configuration influence acute neuromuscular activation patterns during the barbell biceps curl. Across the examined conditions, combined concentric-eccentric repetitions elicited the greatest normalized activation in both muscles, whereas brachioradialis activation was greater than biceps brachii activation during eccentric actions, particularly in the supinated and semi-supinated grip-bar configurations. These results characterize acute muscle-activation patterns during the tested barbell curl conditions.