Does the mixed grip compromise symmetry? Kinetic stability and eccentric biceps overload in the deadlift

The deadlift is highly effective for improving maximal force and muscular power. Double-overhand (DOH) and mixed grip (MG) are widely used, their effects on upper-limb neuromuscular activation and lower-limb kinetic symmetry remain underexplored. This study investigated mechanical performance, bilateral lower-limb kinetic asymmetry (asymmetry index, ASI), and upper-limb surface electromyography (sEMG) of the biceps brachii (BB), brachioradialis (BR), and flexor carpi ulnaris (FCU) between DOH and MG. In a single-session repeated-measures design, nineteen sub-elite powerlifters performed isometric mid-thigh pulls (IMTP) and deadlifts under both conditions. Maximum force, rate of force development (RFD), ASI, and sEMG across total, concentric, and eccentric phases were analyzed. MG produced a significantly higher one-repetition maximum ( p < 0.001, d = 2.69), maximum force ( p = 0.015, d = 0.61), and RFD ( p = 0.045, r = 0.32) versus DOH. Lower-limb symmetry was maintained, with no ASI differences between DOH (4.29%) and MG (4.02%; p = 0.568, r = 0.09). However, sEMG showed pronounced upper-limb asymmetries during MG: the pronated arm exhibited higher BR and FCU activation across all phases (eccentric FCU: 14.79% vs. 4.18% MVC; p < 0.001, d = 1.81), while the supinated arm showed greater eccentric BB activation (5.53% vs. 4.21% MVC; p = 0.002, d = 0.50). MG enhances maximal force production while preserving lower-limb symmetry but induces substantial upper-limb neuromuscular asymmetries. The eccentric overload on the supinated biceps brachii may partly explain elevated distal tendon injury risk. Therefore, MG should be reserved for maximal attempts, whereas DOH is preferable for submaximal training.