AUTONOMIC RESPONSES TO L.B.N.P. FOLLOWING TEN WEEKS OF RESISTANCE TRAINING IN FEMALES

Abstract

Following exposure to microgravity there is a decreased ability of the vasculature of the body to maintain necessary blood pressure upon return to earth. The resulting orthostatic intolerance may jeopardize the crew's ability to perform an emergency egress from the shuttle. Little is known about the efficacy of resistance training as a countermeasure especially in females who make up an increasingly larger segment of space travelers. PURPOSE: The purpose of this study was to determine the effect of ten weeks of lower limb resistance training on orthostatic tolerance in females. METHODS: Sixteen apparently healthy female subjects, ages 19–45 yrs. (mean ± SD: weight = 68.4 ± 8.5kg, height = 168.3 ± 5.6cm, sum of skinfold = 20.7 ± 6.7%) were age-matched and then randomized into either a control (CON) group (N = 8) or a resistance training (RT) group (N = 8). Maximal O2 consumption, autonomic nervous system (ANS) responses to LBNP, and 1-RM's for leg press, leg curl, thigh adduction, and thigh abduction were obtained for both CON and RT groups prior to and following ten weeks of resistance training. The LBNP protocol used began at -10 mmHg of suction with suction increasing by -10 mmHg every six minutes until culminating at -40 mmHg of suction. HRV data was used to assess ANS responses to LBNP. Subjects in the RT group trained 3 x week for 50 minutes each session. Of those three sessions, two were allocated for lower body resistance training and one for upper body resistance training. RESULTS: RT increased 1-RM leg press (mean δ = 132.5, 95%CI = 173.9 to 91.1) and 1-RM leg curl (mean δ = 28.1, 95%CI = 43.91 to 12.3) demonstrating increased strength at post-test, while VO2max (mean δ = 1.7, 95%CI = 3.0 to 6.4) showed little change. Wilcoxon tests examined the time and frequency domain responses to LBNP in the CON and RT groups. A significant difference was found in the LF/HF ratio (Z = 2.100, p > .036). The LF/HF ratio was significantly lower for the RT group post-test indicating a reduced shift toward sympathetic in response to suction. CONCLUSION: The challenge of an orthostatic stress was more appropriately met by females following the resistance training protocol used in this study. This study was supported by a Murdock Summer Research Grant.