Normalizing for Differences in Muscle Size and Strength Does Not Eliminate Differences in Muscle Power or Acceleration Between Pre- and Post-Pubescent Males and Females

This study compared absolute and relative measurements of peak torque (PT), mean power (MP), and rate of velocity development (RVD) during isometric and isokinetic elbow flexion muscle actions in pre- and post-pubescent males and females.

Forty children participated (pre-pubescent: mean ± 95% confidence interval age = 9.79 ± 0.35 years, n = 10 males, n = 10 females; post-pubescent: 17.23 ± 0.58 years, n = 10 males, n = 10 females). Ultrasound images quantified muscle cross-sectional area (CSA) of the elbow flexors. Participants completed maximal elbow flexion muscle actions at 0, 60, 120, 180, 240, and 300°/s.

As expected, the post-pubescent group achieved greater absolute measures of PT, MP, and RVD at all velocities (P ≤ 0.015). When normalized to CSA and strength, differences in PT were mostly eliminated (P ≥ 0.136), but differences in MP and RVD remained (P ≤ 0.012).

The post-pubescent groups maintained greater MP and RVD at each movement velocity, suggesting that muscle size and strength cannot fully account for age-related differences in time-dependent measurements of muscle performance, such as power and acceleration. Instead, these performance indicators may be related to neuromuscular adaptations during normal growth, development, and biological maturation processes, such as augmentations in motor unit recruitment strategies and increases in action potential conduction velocities.