INTRODUCTION:
Eccentric exercises are recommended as an interesting training approach for physical performance improvement and more generally for health benefits. Unfortunately, eccentric exercise has been shown to induce a force alteration and muscle damage for several days (1). While these alterations are well documented in adults, less is known in children, more particularly considering structural modifications. Thus, the main aim of this study was to compare the modifications of the musculotendinous elastic properties after an eccentric exercise in prepubertal boys as compared to adult men.
METHODS:
Ten prepubertal boys (8-12 years old) and ten men (20-25 years old) participated in the present study. The first session included a fatiguing protocol composed of five sets of 30 maximal eccentric knee extensors contractions. Muscle-tendon elastic properties were evaluated using shear wave elastography videos (SWV) of the vastus lateralis (VL), rectus femoris (RF), and the patellar tendon (Tendon). SWV was measured before (PRE), immediately after the exercise (POST), after 30 minutes (POST 30 min), and during a second session 48 hours after the first one (POST 48h). SWV raw and relative values were analyzed using a two-way (Time x Age) analysis of variance (ANOVA). Time corresponds to differences between all time-points. Age corresponds to boys vs. men.
RESULTS:
A significant Time effect was observed for SWV in VL (p < 0.001). Post-hoc revealed greater values at POST 30 min than at PRE (p = 0.003). A significant Time effect was observed for SWV RF (p = 0.035). Post-hoc revealed greater values at Post (p = 0.024). A significant Age effect was observed for SWV RF relative values. After fatigue, greater increases were obtained for men than for boys (POST: BOYS mean: +0.86% ± 16.92 / MEN mean: +24.37% ± 36.67).
Significant Time (p < 0.001) and Age (p < 0.001) effects were observed for SWV Tendon. Post-hoc revealed greater values at POST (p < 0.001) and POST 30 min (p = 0.002) as compared to PRE. Post-hoc also revealed lower values for boys than for men. No significant Age effect was observed for SWV Tendon relative values (POST: BOYS mean: +10.90% ± 6.94 / MEN mean: +11.25% ± 7.51).
CONCLUSION:
As previously enounced in the literature, boys presented lower modifications of muscle properties than men, potentially attributed to fewer muscle damages. However, a similar modification of the tendon tissue properties was observed for both age groups. Tendon properties changes could have an impact on the force transmission and stretch-shortening cycle and need some further investigations (2).
REFERENCES:
1 Clarkson PM, Hubal MJ. Exercise-induced muscle damage in humans. 2002
2 Waugh CM, Korff T, Fath F, Blazevich AJ. Rapid force production in children and adults: mechanical and neural contributions. 2013