Optimizing neuromuscular symmetry through load-progressive closed-chain upper limb training: An EMG-based approach

Bilateral neuromuscular symmetry is a critical factor for safe and effective resistance training. Limited evidence exists on how progressive closed-chain resistance exercises influence upper-limb muscle activation and interlimb balance.

Forty healthy, recreationally trained males (mean age 22.8 ± 1.9 years; height 176.2 ± 4.7 cm; weight 73.5 ± 6.2 kg) performed bilateral elbow flexion and extension at 50 %, 75 %, and 90 % of one-repetition maximum (1RM). Surface electromyography (EMG) was recorded bilaterally from the biceps brachii and triceps brachii. Muscle activity was quantified using root mean square (RMS) values, and bilateral coordination was assessed through symmetry indices.

EMG amplitude increased significantly with higher load intensities (p < 0.001). Bilateral symmetry improved at 90 % 1RM, as reflected by lower symmetry index values and non-significant interlimb differences. At lower intensities, moderate asymmetries persisted, particularly in antagonist muscles.

Progressive closed-chain resistance training enhances neuromuscular activation and promotes interlimb symmetry in the upper limbs, especially under near-maximal loading. These findings suggest that higher load intensities acutely enhance muscle coordination and reduce asymmetry during bilateral resistance exercise.