JEPonline

Official Journal of The American

Society of Exercise Physiologists (ASEP)

ISSN 1097-9751

An International Electronic Journal

Volume 3 Number 4 October 2000

Menstrual Phase Effects on Fat and Carbohydrate Oxidation During Prolonged Exercise in Active Females

CANDI D. ASHLEY1, PHILIP BISHOP2, JOE F. SMITH2, PAUL RENEAU3 AND CINDY PERKINS4

1School of Physical Education, Wellness and Sport Studies, University of South Florida, Tampa FL; 2Department of Human Performance Studies, University of Alabama, Tuscaloosa, AL; 3Department of Physical Education, Tennessee Wesleyan College, Athens, TN; 4College of Nursing, University of Alabama, Tuscaloosa, AL.

CANDI D. ASHLEY, PHILIP BISHOP, JOE F. SMITH, PAUL RENEAU AND CINDY PERKINS. Menstrual Phase Effects On Fat And Carbohydrate Oxidation During Prolonged Exercise In Active Females. JEPonline, 3(4):67-73, 2000. The purpose of this study was to examine between-phase effects of resting levels of estradiol (E2) on fat and carbohydrate oxidation during a 60 minute submaximal exercise bout. Ten physically active females performed two 60-minute treadmill runs at an intensity of 70% of maximal aerobic capacity (VO2max) once each in the follicular phase (FP) and luteal phase (LP) of the menstrual cycle. Resting levels of E2 were assessed prior to exercise. Participants also completed four-day food and activity diaries. Data analysis revealed a significant between-phase difference (p>0.05) in E2 and respiratory exchange ratio (RER) between the FP and LP runs. Further, there was no relationship between E2 and RER in either the FP or LP. However, there were significant correlations between FP RER and average protein intake (r=0,68; p<0.05). In conclusion, our results suggest that there was a between-phase difference in RER concomitant with a between-phase difference in resting E2 levels. However, it appears that the difference in fat oxidation is not related to differences in E2 between the FP and LP of the menstrual cycle.

Key words: estrogen, substrate oxidation

It has been postulated that estradiol (E2) may have enhance fat metabolism (1). A number of studies have examined the relationship between menstrual cycle phase and substrate metabolism at rest and have found higher resting levels of free fatty acids in the blood (2), and a lower respiratory exchange ratio (RER) in the luteal phase (LP) when E2 is elevated (2).

During exercise, there appears to be a tendency toward greater endurance and decreased lactate concentration (3) as well as enhanced fat metabolism in the LP (4). However, the results of Hackney et al. (5) suggest a greater fat oxidation and utilization during ovulation than during the mid-LP. Further, most researchers have found no significant menstrual phase or menstrual status effect on fat metabolism during exercise (6,7,8).

Based on the aforementioned studies, the influence of E2 on fat metabolism has not been fully established. There are several possible reasons for the discrepancies in prior research. A number of researchers have examined menstrual effects of metabolism in healthy participants with “normal menstrual cycles” (5,7,9), while other researchers have examined between-phase differences in substrate metabolism in eumenorrheic participants (4,6,9,10). Researchers have also utilized participants of varied training levels. There appears to be a direct relationship between training and menstrual dysfunction (11,12,13). Highly trained females may not experience characteristic fluctuations of hypothalamic-pituitary-ovarian hormones over the menstrual cycle. Further, several authors employed an incremental exercise protocol (3,4,8) or had participants perform multiple submaximal exercise bouts in one testing session (8,13) which might affect substrate availability in subsequent exercise bouts. In addition, nutritional status and diet may have an effect on substrate utilization during exercise, however, most researchers did not specify or control the nutritional status of participants (2,3,4). Berend et al. (15) reported that a carbohydrate-rich diet, which is common among athletes, appears to negate between-phase differences in the lactate response to exercise. Therefore, the primary purpose of this study was to examine the relationship between resting levels of E2 and fat metabolism during a prolonged submaximal exercise bout in physically active females.