Author(s): LEDERGERBER, R., LICHTENSTEIN, E., ROTH, R., Institution: PREVENTIVE BIOMECHANICS, Country: SWITZERLAND, Abstract-ID: 872

INTRODUCTION:
Prepubertal children exhibit distinct neuromuscular characteristics when compared to adults, including reduced voluntary activation and fatigability, and a possibly lower recruitment of larger motor units that innervate predominantly fast-twitch fibers (1,2). Depending on exercise modality, childrens fatigue is also more pronounced centrally rather than peripherally (1). Additionally, there is evidence that females may experience less fatigue than males, though studies focusing on this aspect in children are sparse (3). Hence, this study was designed to examine neuromuscular differences by age and sex in knee extensor muscle endurance until failure.
METHODS:
A cohort of 23 prepubertal children (9.4±0.9y) and 23 adults (23.4±2.4y, 54% F), undertook a maximal voluntary isometric contraction (MVCpre), a task to failure at 60% of MVCpre, and a subsequent MVCpost in knee extensors. Surface electromyography (EMG) was recorded for the rectus femoris (RF), vastus medialis (VM), and vastus lateralis (VL) at 0, 25, 50, 75, and 100% of individual time to failure (TTF). Age and sex differences were quantified for TTF, MVCpre-post, and the root mean square (RMS) and median frequency (MDF) values of the EMG signals using linear models and Cohens d effect sizes.
RESULTS:
Moderate age-related differences were noted in TTF (d=-0.54), along with a large age*sex interaction (d=1.06). Children experienced a greater change in MVCpost (d=0.42), with negligible age*sex interactions (d≤0.2). At the onset of the trial (0% TTF), children showed less activation in all muscles (d≥1.18), and as the failure-task progressed, age-related differences were observed in the RMS and MDF for RF, VL, and VM (d≥0.14), with minimal differences attributable to sex and age*sex interaction (d≤0.19).
CONCLUSION:
Childrens reduced capacity to produce MVCpost and the smaller changes in EMG readings could indicate a dominance of central over peripheral fatigue. This is further suggested by the lower initial muscle activation in adults, indicating a conservation of larger, more fatigue-prone motor units, which might be less recruited in children (2). The observed differences in neuromuscular fatigability, especially in girls, emphasize the need for further in-depth studies that should also address sex-specific differences in training and developmental changes.

References
1. Souron R, Carayol M, Martin V, Enzo P, Duché P, Gruet M. Differences in time to task failure and fatigability between children and young adults: A systematic review and meta-analysis. Front Physiol. 2022;13:1026012. doi:10.3389/fphys.2022.1026012
2. Dotan R, Mitchell C, Cohen R, Klentrou P, Gabriel D, Falk B. Child-adult differences in muscle activationa review. Pediatr Exerc Sci. 2012;24(1):2-21. doi:10.1123/pes.24.1.2
3. Hunter SK. The Relevance of Sex Differences in Performance Fatigability. Med Sci Sports Exerc. 2016;48(11):2247. doi:10.1249/MSS.0000000000000928