Research has shown that total testosterone (tT) levels in women increase acutely during a prolonged bout of aerobic exercise. Few studies, however, have considered the impact of the menstrual cycle phase on this response or have looked at the biologically active free testosterone (fT) form responses. Therefore, this study examined the fT concentration response independently and as a percentage (fT%) of tT to prolonged aerobic exercise during phases of the menstrual cycle with low estrogen-progesterone (L-EP; i.e., follicular phase) and high estrogen-progesterone (H-EP; i.e., luteal phase). Ten healthy, recreationally trained, eumennorrheic women (X ± SD: age = 20 ± 2 y, mass = 58.7 ± 8.3 kg, body fat = 22.3 ± 4.9 %, VO2max = 50.7 ± 9.0 ml/kg/min) participated in a laboratory based study and completed a 60-minute treadmill run during the L-EP and H-EP menstrual phases at ~70% of VO2max. Blood was drawn prior to (PRE), immediately after (POST) and following 30 minutes of recovery (30POST) with each 60-minute run. During H-EP, there was a significant increase in fT concentrations from PRE to POST (p < 0.01) while in L-EP fT levels were unchanged; which resulted in fT being significantly higher at H-EP POST versus L-EP POST (p < 0.03). Area-under-the-curve (AUC) responses were calculated, for fT the total AUC was greater in H-EP than L-EP (p < 0.04). There was no significant interaction of fT% between phases and exercise sampling time. There was, however, a main effect for exercise where fT% POST was a greater proportion of tT than at PRE (p < 0.01). In summary, hormonal changes associated with the menstrual cycle impact fT response to a prolonged aerobic exercise bout; specifically, there being higher levels under H-EP conditions. This suggests more biologically active T is available during exercise in this phase. This response may be a function of the higher core temperatures found with H-EP causing greater sex hormone binding protein release of T, or could be a function of greater degrees of glandular production. Further work is warranted to elucidate the mechanism of this occurrence. It is recommended that researchers examining T responses to exercise in women look at both tT and fT forms in order to have an accurate endocrine assessment in women.
Bunt JC : Metabolic actions of estradiol: significance for acute and chronic exercise responses. Med. Sci. Sports Exerc. 22(3), 286–290 (1990)
Cadoux-Hudson TA , Few JD, Imms FJ: The effect of exercise on the production and clearance of testosterone in well-trained young men. Eur. J. Appl. Physiol. 54(3), 321–325 (1985)
Enea C , Boisseau N, Ottavy M, Mulliez J, Millet C, Ingrand I, Diaz V, Dugué B: Effects of menstrual cycle, oral contraception, and training on exercise-induced changes in circulating DHEA-sulphate and testosterone in young women. Eur. J. Appl. Physiol. 106(3), 365–373 (2009)
Fahrner CL , Hackney AC: Effects of endurance exercise on free testosterone concentration and the binding affinity of sex hormone binding globulin (SHBG). Int. J. Sport Med. 19(1), 12–15 (1998)
Hall JE (2009) : Neuroendocrine control of the menstrual cycle. In: Yen & Jaffe’s Reproductive Endocrinology: Physiology, Pathophysiology, and Clinical Management, eds Strauss JF, Barbieri RL, 6th ed. Elsevier, New York, pp. 139–154
Kolka MA , Stephenson LA: Effect of luteal phase elevation in core temperature on forearm blood flow during exercise. J. Appl. Physiol. 82(4), 1079–1083 (1997)
Marsh SA , Jenkins DG: Physiological responses to the menstrual cycle: implications for the development of heat illness in female athletes. Sports Med. 32(10), 601–614 (2002)
O’Leary CB , Lehman C, Koltun K, Smith-Ryan A, Hackney AC: Response of testosterone to prolonged aerobic exercise during different phases of the menstrual cycle. Eur. J. Appl. Physiol. 113(9), 2419–2424 (2013)
American College of Sports Medicine (2005): ACSM’s Guidelines for Exercise Testing and Prescription, 7th ed. Lippincott Williams & Wilkins, Philadelphia, pp. 287–290