Standing balance is not affected by estrogen fluctuations during the menstrual cycle

Abstract

When people stand still, they exhibit a phenomenon called postural sway, or spontaneous movement of the bodys center of pressure, which is related to balance control. In general females show less sway than males, but this difference only begins to appear around puberty, pointing to different levels of sex hormones as one potential mechanism for sway sex differences. In this study, we followed one group of young females using oral contraceptives (n = 32) and one group not using oral contraceptives (n = 19), to investigate associations between estrogen availability and postural sway, both over the course of the menstrual cycle (in the group not using oral contraceptives) and long-term (between the two groups). All participants visited the lab four times over the putative 28-day menstrual cycle. At each visit, we performed blood draws to measure plasma estrogen (estradiol) levels, and tests of postural sway using a force plate. Due to the hormone-stabilizing effects of oral contraceptives, estradiol levels were higher in participants not using oral contraceptives (690.45 pmol/L versus 464.50 pmol/L), reflecting higher estradiol concentrations during the late follicular and luteal phase. Postural sway was similar on average for participants not using oral contraceptives (21.47 cm versus 23.56 cm). Overall, we found no significant effects of the estimated menstrual cycle phase - or absolute levels of estradiol - on postural sway.