The Relationship Between Changes in Aerobic Power and Cortisol in Youth Undergoing Weight Status Alteration

Abstract

PURPOSE: To determine if changes in aerobic power and cortisol are related in youth who underwent weight status alterations. METHODS: Data were collected from 60 youth at baseline (t1) and two years later (t2), (mean age t1 = 9.6 yr). Participants were selected from a larger study (CHIC III) and divided into two groups based upon their weight status: N-O (normal weight at t1 and overweight at t2), and O-N (overweight at t1 and normal weight at t2). Normal weight was defined as >5th and <85th BMI percentile, while overweight was ≥ 85th BMI percentile. Aerobic power was estimated using the submaximal PWC195, and expressed per kg of fat free mass (VO2/kgffm). Blood was taken in the morning (standardized) at t1 and t2, and cortisol was analyzed via radioimmunoassay procedures. The relationship between changes in VO2/kgffm and cortisol was examined using Pearson correlations. Multiple regression analyses were also computed to determine the influence of changes in VO2/kgffm and BMI percentile, race and gender on change in cortisol. RESULTS: When both groups were analyzed together, there was a correlation (r=0.32, p<0.02) between the two-year changes in VO2/kgffm and cortisol. In the overall multiple regression model, we found that changes in VO2/kgffm and BMI percentile each accounted for 11% of the variance in change in cortisol (Total Rfs = 0.21, p<0.02). When the groups were analyzed separately, the relationship between changes in VO2/kgffm and cortisol was only significant for the O-N group (r=0.45, p<0.03). Similarly, in the regression model for each of the O-N and N-O groups, change in VO2/kgffm was the only predictor of cortisol change, although it was only significant for the O-N group, accounting for 20% of the variance. Change in BMI percentile was not a significant predictor of change in cortisol for either group. CONCLUSIONS: Changes in cortisol and VO2/kgffm are related in youth who underwent weight status alterations, independent of changes in BMI percentile. The influence of VO2/kgffm on cortisol change is stronger in youth who were overweight and became normal weight, compared to youth who increased their weight status by becoming overweight. Supported by NINR #NR01-1837.