(41) EXAMINING THE EFFECTS OF EXERCISE-INDUCED, PHYSICAL OVERSTRESS ON STRESS BIOMARKERS IN ADOLESCENT, C57BL/6 MICE

Background: Exercise is known to improve fitness, sports performance, and injury/ health risk reduction. Conversely, exercise overstress (i.e. overtraining syndrome) has shown inverse outcomes in both athletes and general populations. Youth and adolescent training programs have increased exponentially prompting the NSCA to develop the Long-Term Athletic Development Model. Still, there remains a lack of research investigating the negative effects of exercise overstress in adolescents.

Purpose: The objective of this study was to examine hormone biomarkers, anthropometrics, and behavioral traits associated with exercise overstress, in adolescent C57BL/6 mice.

Methods: Twenty-four adolescent mice, aged 4 to 5 weeks, were randomly assigned to one of three groups: Sedentary Group (SG), Moderate-trained Exercise Group (MEG), and Overtrained Exercise Group (OEG) during an 8-week intervention. An incremental load test was performed at baseline to determine exhaustion velocity (EV) for the MEG and OEG. MEG performed exercise at 60% EV with progressive duration between 15-60 minutes over 8 weeks. The OEG performed downhill running progressing from 60-90% EV and 15-90 minutes over 8 weeks. The SG did not participate in any exercise outside of normal cage activity. Corticosterone, IGF-1, and body composition were conducted at baseline, mid, and post-intervention along with behavioral measures of food consumption, edge and center time. Measures of central tendencies and percentages were used for demographics within and between groups. ANOVA and MANOVA with repeated measures were used to determine if interactions occurred within and between groups for all pre, mid and post intervention data.

Results: There were no significant differences in baseline hormone concentrations, food consumption, edge or center time between groups. There was a significant difference between OEG and SG for lean mass (p=0.034059). Following intervention, significant differences were found in plasma corticosterone concentrations across time between OEG and SG (p=0.0022) and OEG and MEG (p=0.0098), respectively with the OEG displaying the highest levels. No significant differences were found in IGF-1 results among groups across time (p=0.9754); however, all groups decreased in IGF-1 levels across time (p=0.0168). All groups significantly increased body weight across time (p< 0.0001) with the OEG gaining the least (p=.73). Also, all groups decreased percent fat mass over time (p< 0.0001). Behavioral results showed food consumption was significantly greater in the OEG group compared to MEG and SG (p< 0.0001) between weeks 4-8. A significant difference was found in edge time between OEG and SG across time (p= 0.0223) but not between OEG and MEG (p=.76). There was no significant difference among groups for center time (p=0.0651).

Conclusion: Results indicate that exercise overstress in adolescent mice demonstrate negative physiological and behavioral outcomes. Further research is needed to determine which biomarkers can be practically assessed to recognize and reduce potential overtraining and their relevant implications to physicians, coaches, parents, and exercise specialists. PRACTICAL APPLICATIONS: While biomarkers can confirm maladaptation to training stress, feeding and behavior modifications may be practical indicators to observe in adolescent exercise programs to avoid chronic exercise overstress and potential risk of growth rate consequences and injury.

Acknowledgements: None