The Effects of Exercise Training on Oxygen Uptake Kinetics in Post-menopausal Women

Abstract

Adaptations to exercise training in older women differ from those observed in men. Additionally, adaptations in older women may be dependent on hormone status, since for example, blood flow delivery (i.e. O2 delivery) to working limb muscles has been shown to be dependent on hormone status. Research is lacking regarding exercise training and O uptake (VO2) kinetics in post-menopausal women. PURPOSE: To describe the effects of exercise training on VO2 kinetics in women and to determine if hormone replacement therapy (HRT) influences training adaptations. METHODS: Prior to, and following exercise training, 15 sedentary post-menopausal women (7 nonHRT, age 56 ± 4yr; and 8 HRT, age 60 ± 5yr) performed an initial fatigue-limited ramp cycle test and, on other days, 4–6 step-transitions (6 min) from 15 W to moderate-intensity (80% lactate threshold) constant-load exercise on a cycle ergometer. Exercise training sessions were 30 min, conducted 3 times per week for 6 weeks on a cycle ergometer. VO2 was measured breath-by-breath. Data were interpolated, time-aligned, and ensemble-averaged into 5-s time bins. Phase II VO2 kinetics (τVO2) were estimated using a mono exponential model and nonlinear regression techniques, with data fit from the phase 1 – phase 2 transition to 4 min exercise. RESULTS: Pre-training VO2peakwas 21±3 ml kg−1·min−1 (mean± SD) and was similar between nonHRT (21 ±3) and HRT (21 ±3). After training, VO2peak increased ∼12%. τVO2decreased∼31%(pre: 46 ±8s; post: 32 ±4s) (p<0.01). nonHRT and HRT showed similar speeding of τVO2of 30% (45 ±9s to 32 ±6 s) and 34% (47 ±7s to 31 ±3s) respectively. The τHR2 did not change (p=0.058) from pre- (38 ±9s) to post-training (36 ±5s) in either group. The decrease in τVO2 was correlated to the increase in VO2peak (p<0.037), but only 13% of the variance was explained. The change in the τVO2was not correlated with the change in τHR (p=0.055). CONCLUSIONS: Six weeks of exercise training resulted in appreciably faster phase II VO2 kinetics during moderate exercise in older women. The speeding of τVO2 was similar to that reported for older men (Babcock et al., 1994), with τVO2 approaching values seen in young adults. The speeding of τVO2was not affected by HRT. Supported by NSERC