Author(s): CHANEL, B., BABAULT, N., COMETTI, C., Institution: SPORT SCIENCE FACULTY, UNIVERSITY OF BOURGOGNE-FRANCHE-COMTÉ, Country: FRANCE, Abstract-ID: 1200

INTRODUCTION:
The current literature has shown a lower fatigue following muscular-type exercises for prepubertal boys in comparison with adults. While, isometric contractions are frequently explored, less is known in dynamic conditions. Given that fatigue is contraction mode dependent in adults, one can expect similar findings in prepubertal children. Thus, the aim of this study was to compare the fatigue development between prepubertal boys and men, during maximal concentric and eccentric knee extensors contractions.
METHODS:
This cross-over, randomized study consisted in three visits at the laboratory (one familiarization session and two experimental sessions). Twelve boys (9-11 years old) and 12 men (20-25 years old) were included. Tests and exercises were conducted on the right knee extensor muscles using an isokinetic ergometer. The fatiguing protocol was composed of three sets of 30 concentric (CONC) or eccentric (ECC) knee extensor maximal contractions realized at 60°/s, separated with 30 seconds rest between each set. Maximal voluntary isometric contractions (MVIC) were conducted before the fatiguing exercise (PRE) and were repeated immediately after each sets (POST S1, POST S2, POST S3), five minutes (POST R5), and one hour (POST R60) after the end of the exercise. Torque (MVIT) and electromyographic activity (EMG) of vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF) were recorded during MVIC. MVIT and EMG values were analyzed with a three-way (age x contraction mode x time) analysis of variances (ANOVA). Age corresponded to boys vs. men. Contraction Mode corresponded to the fatiguing exercise (CONC vs. ECC). Time corresponded to differences between all time points.
RESULTS:
A significant Time x Age interaction was found for MVIT, revealing a decrease after both fatiguing protocols. Post-hoc revealed a signitificant difference with PRE from POST S1 to POST R60 for men (P < 0.05). For boys no difference with PRE values was observed with the post-hoc. When considering relative torque values, a significant Time x Age interaction was also observed. Post-hoc test revealed a significant group effect at POST S2 and POST S3 indicating a significant lower torque decrease (P < 0.05) for boys than for men.
A significant Contraction Mode x Age interaction was found for RF EMG. Post-hoc tests revealed a significant higher EMG decrease during MVIC for boys than for men in CONC conditions (P < 0.05). No difference was obtained between boys and men in ECC.
CONCLUSION:
This study shown a lower MVIT decrease for boys than for adults. During concentric exercise, the EMG revealed a higher decrease for boys, like already shown with isometric fatiguing protocol. However, no difference was observed during the eccentric exercise, suggesting a similar central fatigue development during this exercise modality between prepubertal boys and adults. These observations confirmed that fatigue development between men and prepubertal boys was contraction mode dependent.