EFFECT OF CYCLICAL CHANGES IN BIOAVAILABLE OESTRADIOL AND TESTOSTERONE ON MAXIMUM FORCE PRODUCTION IN FEMALES

Abstract

Muscle strength has been shown to increase, decrease or remain unchanged at different phases of the menstrual cycle. In examining the relationship between muscle strength and hormonal status, previous studies have only measured the total concentrations of reproductive hormones rather than their bioavailability. Therefore the PURPOSE of this study was to investigate the effect of menstrual cycle phase on muscle strength and the bioavailability of oestradiol and testosterone. METHODS Maximum voluntary isometric force (MVIF) of the first dorsal interosseus (FDI) muscle was measured during the early follicular and mid-luteal phases of the menstrual cycle in seven eumenorrheic females. These phases were chosen for testing, as the concentration of total oestradiol is significantly different between these two phases. Strength was measured using a custom-built finger dynamometer. The concentration of total and bioavailable oestradiol and testosterone was measured, and the total concentration of progesterone. Total concentrations were measured using a Enzyme Linked Fluorescent Assay technique. Bioavailable concentrations were analysed using a radio assay technique. RESULTS Concentrations of total progesterone (1.03 ± 0.5 and 11.3 ± 8.8 ng.ml-1) and oestradiol (110.8 ± 61.59 and 464.7 ± 83.5 pmol.l-1) were significantly different between phases. The concentration of total testosterone and the ratio of oestradiol to progesterone did not significantly change. The bioavailability of testosterone (102.2 ± 66.3 and 105.0 ± 90.2 pmol.l-1) and oestradiol (90.5 ± 35.5 and 120.0 ± 60.6 pmol.l-1) did not significantly differ between phases. There were no significant differences in muscle strength during the menstrual cycle (p = 0.1). In addition, MVIF of the FDI muscle did not significantly correlate with any of the reproductive hormones measured, in either phase. CONCLUSION Despite significant changes in the concentration of total oestradiol and progesterone, menstrual cycle phase had no effect on the bioavailability of oestradiol and testosterone or muscle strength.