AGE-RELATED DIFFERENCES IN HORMONE RESPONSES TO ENDURANCE VS RESISTANCE EXERCISE IN FEMALES

Abstract

The purpose of this study was to examine the acute endocrine response to exercise in females of varying age. Thirty healthy, cross-trained, female subjects (age range 19–69) volunteered for this study. Subjects were divided into 5 age quintiles (mean ages: Q1:25.0, Q2:34.5, Q3:43.8, Q4:52.8: Q5:62.3). All subjects completed an endurance exercise session (ES), a resistance exercise session (RS), and a resting control session (CS). The ES consisted of 40 min. of cycling at 75% max heart rate and the RS consisted of 3 sets of 10 reps of 8 exercises at 10RM intensity. During the CS subjects rested quietly for 35 minutes. Sessions were performed in random order, at the same time of day, and same phase of menstrual cycle. Subjects consumed the same pre-testing meal before all three testing sessions. Pre-exercise, post-exercise, and 30 minute recovery blood samples were analyzed in duplicate for plasma lactate and serum levels of growth hormone (GH), IGF-I, cortisol (C), testosterone (T), estradiol (E2), and DHEA. Samples were taken during the control session at the same intervals as during the exercise sessions. Statistical significance was set at p < .05. Q5 had significantly lower baseline levels of T and E2 than all other groups, and Q1 had significantly higher baseline levels of DHEA and IGF-I than all other groups. Lactate and average RPE were significantly higher in the RS compared to the ES or CS, while average heart rate was higher in the ES. There were no age-related differences in any intensity measures during the exercise sessions. Percent change from baseline in T and E2 was significantly greater in the ES and RS compared to the CS. Percent change in DHEA was significantly greater in the RS only and percent change in GH was significantly greater in the ES only. There were no age-related differences in any of these exercise-induced hormone changes. There was, however, a significant correlation between several intensity measures and percent change in DHEA, T, E2, and GH, indicating that hormone changes with exercise are more dependent on the relative intensity of the exercise than chronological age. Supported by NSERC and Medical Research Fund of New Brunswick