Comparisons of Muscle Strength, Size, and Neuromuscular Function in Pre- and Post-Pubescent Males and Females

The purpose of this study was to compare measurements of muscle strength, size, and neuromuscular function of the forearm flexors in pre- and post-pubescent males and females. Forty pre-pubescent (mean ± 95% confidence interval, age = 9.79 ± 0.35 yrs, n = 10 males, n = 10 females) and post-pubescent (age = 17.23 ± 0.58 yrs, n = 10 males, n = 10 females) participants completed this study. Biceps brachii muscle cross-sectional area (CSA) and muscle volume (MV) were quantified from ultrasound images. Participants completed maximal voluntary isometric contractions (MVICs) of the forearm flexors and extensors, and submaximal isometric step muscle actions at 30, 50, and 70% of the peak MVIC, as well as one absolute low-level torque step muscle action that equaled 5 Nm. Participants also completed isometric ramp muscle actions at a constant rate of torque increase (7.5 Nm∙s-1). Percent voluntary activation (VA) was quantified during the MVIC and submaximal isometric step muscle actions, while EMG amplitude and MMG amplitude were quantified during the isometric ramp muscle actions. MVIC strength was expressed in absolute terms and normalized to CSA and MV to examine the influence of muscle size on differences in strength between groups. The post-pubertal males were 130% stronger, had 78% greater CSA, 374% greater MV, and 17% greater maximal VA than the pre-pubertal males, while the post-pubertal females were 72% stronger, had 63% greater CSA, 270% greater MV, and 23% greater maximal VA than the pre-pubertal females. Normalizing MVIC strength to CSA and MV accounted for a greater proportion of the difference in strength between males than females. The collective responses for VA, EMG amplitude, and MMG amplitude across intensity reflected differences in muscle activation and motor unit recruitment strategies between pre- and post-pubertal males and females. These results suggest that muscle size may account for a greater proportion of the growth and development-related differences in strength among males, while females may be more affected by changes in muscle activation. However, regardless of sex, changes in muscle size and neuromuscular function occur during growth and development