The Influence of Menstrual Cycle Phase upon Postexercise Hypotension JOSEPH I. ESFORMES, FRANCES NORMAN, JOANNE SIGLEY, and KAREN M. BIRCH Centre fbr Sports and Exercise Sciences, Institute of Membranes and Systems Biology, University of Leeds, Leeds, UNITED KINGDOM ABSTRACT ESFORMES, J. I., F. NORMAN, J. SIGLEY, and K. M. BIRCH. The Influence of Menstrual Cycle Phase upon Postexercise Hypotension. Med. Sci. Sports Exerc., Vol. 38, No. 3, pp. 484-491, 2006. Purpose: Postexercise hypotension (PEH) has been observed in males and females; however, the impact of menstrual cycle phase upon PEH has not been evaluated. We examined the pattem of PEH in the early follicular (EF), late follicular (LF), and midluteal (ML) phases of the menstrual cycle in eight eumenorrheic women following 30 min of exercise at 80% lactate threshold. Methods: Supine hemodynamic measurements were assessed at rest and then for 45 min following exercise. Blood pressure was measured with manual sphygmomanometry, calf vascular resistance (CVR) via venous occlusion plethysmography, and central hemodynamics with echocardiography. Results: Cardiovascular parameters did not differ between menstrual phases at rest (P > 0.05). The pattern of PEH was unaffected by menstrual phase, but mean arterial and diastolic (DBP) pressures dropped to significantly lower levels across the recovery period in the EF phase than in the LF and ML phases (mean DBP EF: 69 + 4; LF 74 ± 3; ML 72 ± 5; P < 0.05). Postexercise cardiac output, stroke volume, ejection fraction, left ventricular dimensions, and heart rate did not differ across menstrual phases (P > 0.05). These parameters, except for left ventricular dimensions in systole and heart rate, varied with recovery time, increasing to a peak between 5 and 10 min postexercise (P < (0.05). CVR displayed a significant interaction between cycle phase and recovery time as resistance increased to greater values in the ML phase compared with the EF and LF phases following 30 min of postexercise recovery (P < 0.05). Conclusion: Buffering of PEH appears to be enhanced in the LF and ML phases of the cycle where estrogen concentrations are known to be elevated. Key Words: HEMODYNAMICS, ECHOCARDIOGRAPHY, VENOUS OCCLUSION PLETHYSMOGRA- PHY, ESTROGEN, PROGESTERONE he decreases in blood pressures that instantly follow a single bout of exercise (postexercise hypotension (PEH)) are well documented in both hypertensive and normotensive individuals (3,31). Indeed, resting blood pressure becomes normalized for hours following acute exercise in hypertensives (1), and this acute effect is thought to be one of the mechanisms explaining the longer-term positive impact of repetitive exercise training upon hyper- tension. Postexercise hypotension has been seen to occur following both moderate- and higher-intensity exercise (12), and following exercise of differing durations (23) and mo- dalities (24), and its length of persistence has been seen to vary from I to 12 h (18). The mechanisms explaining PEH are not clearly understood, but have been postulated to be related to a decreased postexercise baroreflex set point (34), a decreased vascular responsiveness to sympathetic vaso- constrictor outflow (15) via either impaired a-adrenergic receptor stimulation (30) or a metaboreflex effect of accu- mulated vasoactive substances (13), an elevated sympathetic Address for correspondence: Dr. Karen Birch, Centre for Sports and Exercise Sciences, Institute of Membranes and Systems Biology, University of Leeds, Leeds, LS2 9JT, UK; E-mail: k.m.birch@leeds.ac.uk. Submitted for publication February 2005. Accepted for publication October 2005. 0195-9131/06/3803-0484/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE, Copyright © 2006 by the American College of Sports Medicine DOI: 10.1249/01 .mss.0000193559.98095.ea nerve activation (16,22), and/or an adaptive mechanism for maintenance of plasma volume (18). Establishing the occurrence of PEH has historically been undertaken in male subjects, although the influence of gender upon the magnitude and temporal pattern of PEH has recently been evaluated. Carter et al. (5) reported a greater magnitude of nadir in mean arterial pressure in men, compared with women, during 5 min of recovery from a 3-min bout of exercise conducted at 60% maximal heart rate. However, the magnitude and pattern of PEH during 60 min of recovery, following 60 min of exercise at 60% peak oxygen uptake, was shown to be similar in endurance-trained women and sedentary men and women (33). The authors reported that in these subjects, PEH occurred as a result of peripheral vasodilation, but that in an additional group of endurance-trained men, PEH was explained by a reduced postexercise cardiac output com- pared with resting values. It would thus appear that the pattern of PEH is similar in males and females, but that the magnitude and underlying mechanisms may differ depend- ing upon fitness status and the exercise stressor. Given the variability in reproductive hormones across the menstrual cycle in females, gender comparisons of PEH have examined female subjects in a standardized menstrual cycle phase. Indeed, the hormone estrogen has been seen to initiate arteriolar vasodilation, and thus to increase blood flow in eumenorrheic females (21), whereas progesterone is known to act antagonistically (32). Estrogenically mediated variability in peripheral vasodilation throughout 484