Differences in Neuromuscular Responses During Isometric Muscle Actions Before and After Pubescence

The purpose of this study was to examine the responses of electromyographic (EMG) and mechanomyographic (MMG) amplitude across the torque spectrum in pre- and post-pubescent males and females.

Forty pre-pubescent (mean ± 95% confidence interval, age = 9.79 ± 0.35 years, n = 10 males, n = 10 females) and post-pubescent (age = 17.23 ± 0.58 years, n = 10 males, n = 10 females) participants completed this study. Participants completed maximal voluntary isometric contractions (MVICs) of the forearm flexors and extensors, as well as isometric ramp muscle actions. EMG and MMG amplitude were quantified from the biceps brachii, brachialis, and brachioradialis during all muscle actions. EMG and MMG amplitude during the isometric ramp muscle actions were normalized to EMG and MMG amplitude from the MVICs.

The pre-pubertal group tended to have greater relative EMG amplitude across intensity (P < 0.050), while the post-pubertal group had a more pronounced increase in EMG amplitude at higher intensities. Similarly, the pre-pubertal group tended to have greater relative MMG amplitude across intensity (P ≤ 0.004) that plateaued earlier than the post-pubertal group (55% vs. 65%–75% of MVIC). Additionally, the pre-pubertal group had greater coactivation across intensity (P ≤ 0.001).

The greater relative EMG and MMG amplitude in the pre-pubertal group, in conjunction with the earlier plateau in MMG amplitude for the pre-pubertal group and greater coactivation, suggests less efficient muscle activation and motor unit recruitment strategies during pre-pubescence. Taken together, the findings of the present study suggest that growth-mediated changes in neuromuscular function lead to improvements in the efficiency of muscular activation and augmentations in motor unit recruitment strategies.