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.

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.

The purpose of this study was to examine peak torque (PT), mean power (MP), electromyographic (EMG) amplitude, mechanomyographic (MMG) amplitude, and neuromuscular efficiency from EMG and MMG amplitude (NME_EMG and NME_MMG, respectively) across the velocity spectrum in children versus adolescents.

Seventeen children (n = 8 males, n = 9 females) and 22 adolescents (n = 11 males, n = 11 females) participated. Participants completed maximal concentric isokinetic leg extensions at 60, 120, 180, 240 and 300°/s. PT, MP, EMG amplitude, and MMG amplitude were quantified during all muscle actions. NME_EMG and NME_MMG were quantified by expressing PT relative to EMG and MMG amplitude, respectively, for each muscle action.

PT, MP, NME_EMG, and NME_MMG were greater for the adolescents than the children collapsed across sex and velocity (P ≤ 0.021). There were no significant differences for EMG amplitude (P ≥ 0.051), while MMG amplitude increased significantly from 60 to 240°/s (P < 0.001) then decreased significantly from 240 to 300°/s (P < 0.001) for all groups.

Overall, regardless of velocity, the expression of PT relative to EMG and MMG amplitude (NME_EMG and NME_MMG, respectively), in conjunction with measurements of torque and power production, may provide practitioners a unique method of examining growth and development-related augmentations in neuromuscular function during dynamic movements.

This study examined changes in vertical jump performance with progressively greater eccentric pre-loading in relation to growth and development in young female athletes.

Twenty young female athletes ranging from 9 to 17 years old performed the following vertical jumps in random order: static jumps (SJs), counter-movement jumps (CMJs), and drop jumps (DJs) from drop heights of 20, 30, and 40 cm (DJ20, DJ30, and DJ40, respectively). Measurements included peak force (PF), peak rate of force development (RFD), peak power (PP), eccentric impulse (ECC), and concentric impulse (CON). Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and thigh muscle cross-sectional area (CSA).

PF increased from the SJ-DJ20 (P ≤ 0.009), then plateaued from DJ20-DJ40 (P = 1.000). RFD remained the same from SJ-CMJ (P = 1.000), increased from CMJ-DJ20 (P < 0.001), and plateaued from DJ20-DJ40 (P = 0.874). PP increased from the SJ-CMJ (P < 0.001), then plateaued from the CMJ-DJ40 (P ≥ 0.486). CON remained the same across all vertical jumps (P = 1.000), while ECC increased from the SJ-DJ40 (P ≤ 0.038). Jump height (JH) increased from the SJ-CMJ (P < 0.001), decreased from CMJ-DJ20 (P < 0.001), and plateaued from DJ20-DJ40 (P = 1.000). The change in PP from the SJ-CMJ (ΔCMJ-SJ) was related to all measurements of growth except CSA (r = 0.558–0.815).

Young females produced greater power during the CMJ than SJ, but equivalent power from the CMJ-DJ40, despite increases in ECC. Additionally, ΔCMJ-SJ was not related to CSA, which suggests other underlying mechanisms affect stretch–shortening cycle utilization in young female athletes.