Per-session Improvement Of Biceps Brachii Power Among Males Performing Concentric Unilateral Curls

Muscular power is important in athletic settings and activities of daily living. Skeletal muscle is a highly adaptable tissue; however, the rate of power improvement upon novel unilateral training requires further investigation. PURPOSE: To evaluate changes in power output of the biceps brachii during concentric unilateral exercise against a 3D isotonic load. METHODS: We tracked 26 male subjects for a minimum of 5 consecutive workout sessions involving unilateral bicep curls (dominant and non-dominant) using a Proteus device. Owing to inconsistency of performance during the first session, we evaluated sessions 2 through 10. We retained 15 subjects through 8 sessions, and 8 subjects through 10 sessions. We performed paired-samples t-tests comparing power output of the dominant arm to the non-dominant arm at days 2, 5, 8, and 10. We also compared the rate of progress of each arm from day 2 to day 5 and from day 5 to day 8. Linear regression, holding age constant, evaluated power improvement from day 2 to day 5. RESULTS: Subject age was 30.6 ± 15.5 yr, height was 71.0 ± 3.9 in, and weight was 179.3 ± 25.8 lb. On day 2, dominant arm power was 75.8 ± 37.9 w and non-dominant power was 74.9 ± 39.5 w. No difference was observed between arms at day 2 (p = 0.817), day 5 (p = 0.885), day 8 (p = 0.108), or day 10 (p = 0.396). From day 2 to day 5, subjects improved 25.2 ± 40.6 w (33.2%) in the dominant arm (p = 0.004) and 26.1 ± 42.7 w (34.0%) in the non-dominant arm (p = 0.005). From day 5 to day 8, power improvement was not significant for dominant (p = 0.739) or non-dominant (p = 0.629) arms. From day 5 to day 10, differences in power were not significant for dominant (p = 0.376) or non-dominant (p = 0.967) arms. In the dominant arm, between sessions 2 and 5, each additional exercise session predicted a power increase of 8.7 w (p = 0.015; 95% CI: 1.8, 15.7) when holding age constant (p = 0.026). In the non-dominant arm, each additional day predicted an increase of 8.4 w (p = 0.030; 95% CI: 0.9, 16.0). Age was not significant (p = 0.120); removing it from the model did not affect the relationship between exercise session and power (β = 8.4; p = 0.031). CONCLUSION: Five consecutive sessions of a novel training stimulus were sufficient to elicit significant improvements in power of the biceps brachii. Improvement tapered after 5 exercise sessions, indicating a neurophysiological explanation.