Date of Award
Master of Science (MS)
Medical Sciences (Blood and Cardiovascular)
In the work described in this theses, hormonal and physiological responses to exercise were investigated in women in relation to the menstrual cycle. Alterations in estradiol, progesterone, luteinizing or follicle stimulating hormones with exercise may interfere with the delicate hormonal balance which is necessary for regular ovulatory menstrual cycles. At rest, estradiol and progesterone have effects on carbohydrate and lipid metabolism, on pulmonary and cardiovascular function and on the plasma concentrations of a number of other hormones, all of which may also be important during exercise. As wide fluctuations in resting levels of the ovarian steroids occur during a normal menstrual cycle, they may influence exercise performance or the physiological adaptations to exercise at different times in the cycle.
To investigate these issues, nine subjects were studied during cycle ergometer exercise at three exercise intensities on two occasions in the menstrual cycle. Tests were conducted when resting levels of estradiol and progesterone were low, in the early follicular phase, and when the concentrations of both hormones were elevated, in the mid-luteal phase. Separation into the two phases was confirmed by hormone analysis.
For the first time, it has been shown that in women, exercise is associated with an increase in the plasma levels of estradiol, progesterone, luteinizing hormone and follicle stimulating hormone. The response of the ovarian hormones is more marked in the luteal phase while the gonadotropins are affected only in the follicular phase. The magnitude of the increase in all four hormones is related to the intensity of exercise. These alterations in ovarian and gonadotropic hormone levels with exercise may possibly help to explain the occurrence of menstrual, irregularities in women engaged in strenuous physical activity.
In the luteal phase, at a time when resting levels of estradiol and progesterone are higher, exhaustive exercise was maintained for longer than in the follicular phase. The difference was associated with a lower blood lactate concentration in the luteal phase, in the absence of differences in heart rate, oxygen uptake or cardiac output. This suggests that the effect of the menstrual cycle on the capacity to exercise is exerted at a local level in exercising muscle rather than through changes in oxygen delivery. A final study in this thesis showed an increased epinephrine response to exercise in the follicular phase. Further studies are required to investigate the part played by epinephrine in modulating the biochemical responses to exercise.
Exercise results in increases in the plasma levels of estradiol, progesterone, luteinizing and follicle stimulating hormones that are dependent on both the intensity of exercise and the phase of the menstrual cycle. In addition, there is an improvement in performance of high intensity exercise in the luteal phase, in association with lower levels of plasma lactate. The mechanisms which underlie these findings remain to be elucidated.
With the exception of the catecholamine assays, the work reported in this thesis was performed by the author. This includes the remaining hormone assays, lactate analysis, exercise tests and calculation of the data and most of the statistical analysis.
Portions of this work have been published and/or presented previously:
Jurkowski, J.E., N.L.Jones, W.C.Walker, E.V.Younglai and J.R.Sutton Ovarian hormonal responses to exercise. J.Appl.Physiol:Respirat,Environ. Exercise Physiol. 44:109-114.1978.
Jurkowski, J.E.,N.L.Jones, J.R.Sutton, C.J.Toews Exercise performance and blood lactate levels in relation to the menstrual cycle. Med Sci Sports 9:70,1977. (abstract)
Jurkowski, J.E.,J.R.Sutton.and P.M.Keane Effect of the menstrual cycle on the plasma catecholamine response to exercise in normal females. Canadian J.Appl.Sport Sci. 3:194,1978. (abstract)
Jurkowski, Janet E., "Hormonal and Physiological Responses to Exercise in Females in Relation to the Menstrual Cycle" (1979). Open Access Dissertations and Theses. Paper 2790.