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The Journal of Strength and Conditioning Research: Vol. 13, No. 4, pp. 325–329.
The Impact of Menstrual Phases on Anaerobic Power Performance in Collegiate Women
GERALD MASTERSON
Department of Health Physical Education and Recreation, Southwest Missouri State University, Springfield, Missouri 65804.
ABSTRACT
The purpose of this study was to explore the impact of the menstrual phases on power performance in fairly active collegiate women. After the initial screening of 100 potential subjects who engaged in exercise 2 and no more than 3 days a week for 30 minutes or less, 32 subjects were selected to completed the study. The subjects underwent 2 Wingate tests to estimate anaerobic power, anaerobic capacity, and fatigue. One test was administered during the follicular phase; the other test was administered during the luteal phase. The data from this study indicate that there are differences between power performance during the follicular and luteal phases for these women. The women in this study demonstrated greater anaerobic capacity, produced greater peak power, and were less fatigued by the end of the exercise during the luteal phase than during the follicular phase. The results indicate that menstrual phase in fairly active collegiate women can have an influence on anaerobic performance.
Key Words: menstrual cycle, exercise performance, Wingate testing.
Introduction Identifying key elements that contribute to performance is an exhaustive process. Anaerobic power has been recognized as a key element and can be an indicator of success in athletics (2, 4, 12). Past studies of anaerobic power have focused on men (17). Of 17 studies reviewed by Bar-Or (2), 14 included only men as subjects. The 3 remaining studies included both men and women. This leaves unanswered questions regarding the response of women to power tests. Although past studies report that both sexes respond or adapt in much the same way to short-term and long-term exercise, Willmore and Costill (22) list some special factors that should be considered when working with women. One of these factors is menstruation. According to the National Strength and Conditioning Association (20, 21), there are cultural and social stigmas that a woman must overcome; however, there is little evidence that menstruation affects athletic performance. However, these authors recognize that there is tremendous variability in the physical and psychological ways in which women respond to menses and highlight the need for investigation into the effect of the ovarian hormones on exercise performance.
Golub (8) suggests that misconceptions associated with the menstrual cycle continue to exist. She cites a study done by the Tampax Corporation, in which more than 1,000 Americans, ranging in age from 14–65 years and representing all ethnic, educational, and economic groups, were sampled. The results indicate that a substantial number of women believe that they cannot function normally during menstruation. Some believe that they should restrict their physical activities during menses, and most experience dysmenorrhea at some point.
Studies examining the impact of the menstrual cycle on exercise have yielded mixed findings. For example, Schoene et al. (18) reported time to exhaustion on a incremental exercise test was shorter during the luteal phase than during the follicular phase for controls but not in competitive athletes. In other studies (7, 16), endurance performance was enhanced during the luteal phase in trained women. Jurkowski et al. (10) reported an increase of high-intensity work (exercise lasting less than 3 minutes), including lower lactate levels, during the luteal phase for “healthy females.”
No evidence for different phases of the menstrual cycle affecting maximal exercise performance has been found for highly active (5, 12), moderately active (6), or “healthy females” (19). Menstrual cycle phase also does not appear to affect submaximal endurance performance for “healthy females” (19) or for athletes (11, 15). Thus, there appear to be some discrepancies in the findings regarding the effects of menstrual status.
Differences in past findings may be related to the activity level of subjects used. Many studies that found no differences in performance involved highly active or athletic women (5, 11, 15). Perhaps active women have overcome negative effects associated with menstruation to a greater extent than less active women. This notion is supported in Golub by research performed by Bates (8), who studied 28 women participating in a daily exercise program for 8 weeks. Bates suggests that women who participate in regular physical activity 4 or more days a week have less menstrual pain and premenstrual tension. Including women who are not as physically active, as those described by Bates, might help answer the question concerning relatively inactive women's response to exercise. For example, women enrolled in college physical education classes participate in class activities but may not get additional exercise outside class. Perhaps the performance of women whose activity is at such a level would vary as a result of the different phases of the menstrual cycle.
Differences may also be due to sample size. Restricted sample sizes are a problem for this area of research, since most studies include no more than 16 subjects and are vulnerable to variations among individuals (5, 7, 9, 10, 11, 13, 14, 19). Because of large variances associated with the menstrual cycle, a larger sample should help account for wide individual variability and be more representative of the population.
The present study was designed to explore whether anaerobic power performance of women differs during the 2 phases of the menstrual cycle. These women participated in exercise fewer than 3 days a week and less than 30 minutes a session. Their performance during the follicular phase, within 48 hours of the onset of menstrual flow, was compared with their performance during the luteal phase, days 18–21 of the cycle (17). Anaerobic power was measured using the Wingate anaerobic test because of its high test-retest reliability (2). Power performance was characterized by measures of anaerobic capacity, peak power, and fatigue indices.
Methods
Subjects
One hundred apparently healthy women were recruited for this study. The women were enrolled in a college wellness course at the time of the study. All subjects volunteered and were provided written, university-approved informed consent forms. After being instructed as to the purpose of the study and signing consent forms to participate, each subject completed a medical history form and menstrual cycle history form (8, 9, 15). Those demonstrating contraindication for exercise and amenorrhea, users of oral contraceptives, and those who exercised 3 or more days a week were not included as subjects. The subjects typically exercised at least once a week as part of the course, and some reported additional activity. The average exercise level was 2.5 workouts per week. Consequently, they were considered “fairly active.”
After the initial screening process, 48 subjects with normal menstrual cycles were chosen to participate in the study. The length of the menstrual cycle was considered to be the number of days from the first day of a bleeding episode through the day before the start of the next bleeding episode. Menstrual cycles were considered normal if the subject reported regular monthly menstruation that occurred between 25- and 31-day intervals (8). Of the 48 individuals identified as eligible to participate, 32 subjects completed both trials. The remaining 16 subjects withdrew because of scheduling conflicts or illness. Subject characteristics were as follows: age: 20 ± 1.8 years; weight: 61 ± 6.5 kg; and body fat: 24 ± 4%.
Procedures
This study used a repeated-measures design. Each subject was asked to participate in 2 Wingate anaerobic power tests. One was completed during the follicular phase of the menstrual cycle, and the other during the luteal phase of the cycle. Test order was counterbalanced so that results would not be threatened by practice effects. As a result of counterbalancing, approximately half (n = 15) of the subjects underwent the first power test during the follicular phase and the others underwent their first test during the luteal phase.
Menstrual status was determine based on cycle history (8, 9, 15). Subjects were asked to report the onset of menstrual flow so that test dates could be set accordingly. Subjects assigned to take their first test during the follicular phase were instructed to come to the laboratory within 48 hours of the first noticeable sign of menstruation. Subjects assigned to take their first test during the luteal phase reported the end of their flow and were then scheduled for a test within 14–15 days. This manner of scheduling was followed because the luteal phase starts at approximately day 14 of the menstrual cycle and is when ovulation is supposed to occur. According to the World Health Organization, the average length of the bleeding episode is 4–5 days. Scheduling the test 14–15 days after the end of flow placed the test around days 18–21 and in the luteal phase of the cycle (8, 9, 15, 22). These procedures were similar to those used and described in previous studies (9, 15). Although direct measurement of menstrual cycle phase was not taken, our testing dates were dramatically displaced from one another, making it unlikely that the 2 measures would have been taken during the follicular phase.
Subjects who completed trial 1 during the luteal phase completed trial 2 during the follicular phase. Subjects who completed trial 1 during the follicular phase completed trial 2 during the luteal phase. Trials were done during the same time of day for each subject to limit the possible effects of circadian rhythm.
Testing
Subjects completed the Wingate test (1) to estimate the power and capacity of the anaerobic energy system. The Wingate test requires the subject to pedal as rapidly as possible for 30 seconds at a resistance setting that is based on body mass (0.075 kg per kilogram of body weight). Before beginning each test, the subject was weighed, and her weight was used to set the appropriate resistance. Seat height was positioned according to Adams' test protocol (1) to control for variations in leg length. Height was set so that the subject's knees were almost completely extended through the bottom of the pedaling cycle. Once the resistance was determined, the subject completed a 3-minute warm-up, followed by a 3-minute recovery. The subject was then asked to pedal against the predetermined resistance as rapidly as possible for 30 seconds. The subject was instructed to give an all-out effort and not to pace herself. Throughout the testing period, each subject was verbally encouraged to do her best. Pedal revolutions were counted by a trip sensor located on the back of the ergometer. Assessments were made during each exercise bout and included anaerobic capacity (i.e., the total number of revolutions in 30 seconds expressed in Watts), anaerobic power (i.e., maximum number of revolutions in a 5-second period expressed in Watts), and fatigue index (i.e., the percent difference between the maximum number and minimum number of revolutions in a 5-second period).
Statistical Analysis
A t-test for repeated measures (SPSS 6.11) was used to detect differences between the follicular and luteal phases for each of the three dependent measures: anaerobic capacity, anaerobic power, and fatigue index. Significance was set at the p 0.05 level.
Results
Indices of the women's power performance are shown in Table 1 A t-test for repeated measures was used to compare the scores for each of the 3 dependent measures (3). As seen in Table 1 and illustrated in Figure 1, the difference in anaerobic capacity between the follicular phase and the luteal phase was significant. Anaerobic capacity was higher during the luteal phase than during the follicular phase.
As seen in Table 1 and illustrated in Figure 2, the difference in anaerobic power between the follicular phase and luteal phase also was significant. Anaerobic power was greater during the luteal phase than during the follicular phase.
As seen in Table 1 and illustrated in Figure 3, the difference in fatigue index between the follicular phase and the luteal phase was significant. The fatigue index was greater during the follicular phase than during the luteal phase.
Discussion
Similar to the findings of other studies (7, 10, 16, 18), the data from this study indicate that there are differences between performance during the follicular and luteal phases of the menstrual cycle. The women in this study demonstrated greater anaerobic capacity, produced greater peak power, and were less fatigued by the end of the exercise during the luteal phase than during the follicular phase. This is in contrast to other studies reporting no significant reduction in performance across different menstrual phases (5, 6, 11, 12, 15, 19).
The results of this study should not be compromised by a limited sample size, since the number of subjects was twice the number used in previous studies. Neither should the results be attributable to sequencing or practice effects, since the testing order for the 2 phases was counterbalanced.
Although the Wingate anaerobic test is a highly reliable task, with a test-retest reliability correlation average of 0.94, its procedures might have contributed to the outcome of the present study (2). The Wingate protocol requires that pedal resistance be based on body mass (0.075 kg per kilogram of body weight). Consequently, it is possible that differences in the anaerobic power measures attributed to menstrual phase may have actually been related to changes in the resistance setting that accompanied changes in weight between the 2 tests (or phases). Mean resistance settings for the 2 conditions were checked to see if they were different. Although the difference in subject weight between the 2 tests was significant, the resistance settings were not significantly different. The mean setting for the follicular phase was 5.28 (SD = 0.628), and the mean resistance setting for the luteal phase was 5.27 (SD = 0.637). The fact that these settings are virtually identical indicates that the differences in power performance between menstrual phases were not simple artifacts of changes in the resistance settings.
It is likely that the differences between the subjects and their activity level included in the present study and those involved in previous studies are responsible for the variation in findings. Although it is difficult to pinpoint the cause for the differences in performances, it would appear that both psychological and physiological factors are involved. Our fairly active subjects' perceptions of menstrual cycle and their capabilities may be different from those of regularly active or competitive women, and these perceptions could have affected the outcome of this study. It is estimated that up to 75% of all women suffer from premenstrual tension (8). Perhaps, as Bates (8) suggests, women who participate in regular physical activity 4 or more days a week have less menstrual pain and premenstrual tension than those who are less active. It is unclear whether the women in the present study varied in attitude or actual menstrual discomfort from the active women who participated in previous studies. In either case, these results demonstrate a difference in power performance across the ovarian phases for this group of women.
In summary, competing explanations such as testing protocol, sample size, and sequencing effects do not appear to account for the significant findings. Rather, the differences were likely due to differences in subject responses to the ovarian phase during which the testing took place. These differences were significant in the fairly active women who served as subjects for this study.
Practical Applications
Questions still exist as to whether menstruation adversely affects performance. The results of this study suggest that the follicular phase compromises indices of power performance in fairly active women ages 18–24 years. Scientists and physical educators, who might use fairly active or sedentary women for a study or to start an exercise program, need to be aware of this potential influence on performance. They should implement appropriate control procedures when performing preexercise and postexercise measures. If ovarian phase is not held constant, potential benefits of exercise might be misrepresented. For example, if the pretraining measure is conducted during the luteal phase and the posttraining measure is conducted during the follicular phase, positive effects of exercise might be masked. It is also reasonable to expect that the reverse might be true. It should be emphasized, however, that these findings and principles relate to fairly active women. This study did not include athletes, and the results from previous studies do not indicate the necessity for control between pretraining and posttraining measures in athletes and highly trained women.
References
1. Adams, G.M. Exercise Physiology Laboratory Manual. Dubuque, Iowa: Wm C. Brown Publisher. 1990.
2. Bar-Or, O. The Wingate anaerobic test: An update on methodology, reliability and validity. Sports Med. 4:381–394. 1987. [PubMed Citation]
3. Baumgartner, T.A., and C.H. Strong. Conducting and reading research. In:. Health and Human Performance. Boston: WCB McGraw-Hill. 1998.
4. Beckenholdt, S., and J.L. Mayhew. Specificity among anaerobic power tests in males. J. Sports Med. 23:326–331. 1983.
5. Bemben, D.A., P.C. Salm, and A.J. Salm. Ventilatory and blood lactate responses to Maximal treadmill exercise during the menstrual cycle. J. Sports Med. Phys. Fitness. 35:257–262. 1995. [PubMed Citation]
6. De Souza, M.J., K.R. Maguire, K.R. Rubin, and C.M. Maresh. Effects of menstrual phase and amemorrhea on exercise performance in runners. Med. Sci. Sports Exerc. 22:575–580. 1990.
7. Doskin, V.A., T.V. Kozeeva, T.S. Listskay, and E.V. Shokina. Changes in working capacity of female athletes in different phases of menstrual cycle. Hum. Physiol. 5:144–149. 1980.
8. Golub, S. Periods: From Menarche to Menopause. Newbury Park: Sage Publications Inc. 1992.
9. Higgs, S.L., and L.A. Robertson. Cyclic variations in perceived exertion and physical work capacity in females. Can. J. Appl. Sports Sci. 6:191–196. 1981.
10. Jurkowski, J.E., N.L. Jones, C. Walker, E.V. Younglai, and J.R. Sutton. Ovarian hormonal responses to exercise. J. Appl. Physiol. 44:109–114. 1978. [PubMed Citation]
11. Kanaley, J.A., R.A. Boileau, J.A. Bahr, J.E. Misner, and R.A. Nelson. Substrate oxidation and GH responses to exercise are independent of menstrual phase and status. Med. Sci. Sports Exerc. 24:873–880. 1992. [PubMed Citation]
12. Komi, P.V. Training of muscle strength and power: Interaction of neuromotoric, hypertrophic, and mechanical factors. Int. J. Sports Med. 7:10–15. 1986. [PubMed Citation]
13. Lavoie, J.M., N. Dionne, R. Helie, and G.R. Brisson. Menstrual cycle phase dissociation of blood glucose homeostasis during exercise. J. Appl. Physiol. 62:1084–1089. 1987. [PubMed Citation]
14. Lebrun, C.M., D.C. McKenzie, J.C. Prior, and J.L. Taunton. Effects of menstrual cycle phase on athletic performance during exercise. Med. Sci. Sports Exerc. 27:437–444. 1995. [PubMed Citation]
15. Miskec, C.M., J.A. Potteiger, K.L. Nau, and C.J. Zebras. Do varing enviromental and menstrual cycle conditions affect anaerobic power output in female athletes. J. Strength Cond. Res. 11:219–223. 1995.
16. Nicklas, B.A., A. Hackney, and R. Sharp. The menstrual cycle and exercise: Performance, muscle glycogen, and substrate responses. Int. Sports Med. 10:264–269. 1989.
17. Pankey, R.B., D.W. Bacharach, and R.A. Gaugler. Anaerobic power differences in fit women across age. J. Strength Cond. Res. 10:62–64. 1996.
18. Schoene, R.B., H.T. Robertson, D.J. Pierson, and A.P. Peterson. Respiratory drives and exercise in menstrual cycles of athletic and nonathletic women. J. Appl. Physiol. 50:1300–1305. 1981. [PubMed Citation]
19. Stephenson, L.A., M.A. Kola, and J.E. Wilkerson. Perceived exertion and anaerobic threshold during the menstrual cycle. Med. Sci. Sports Exerc. 14:218–222. 1982. [PubMed Citation]
20. Strength training for female athletes: A position paper: part I. Natl. Strength Cond. Assoc. J. 11
4)43–55. 1989.
21. Strength training for female athletes: A position paper: part II. Natl. Strength Cond. Assoc. J. 114)43–55. 1989.
22. Willmore, J.H., and D.L. Costill. Physiology of Sports and Exercise. Champaign, IL: Human Kinetics. 1994.
The Impact of Menstrual Phases on Anaerobic Power Performance in Collegiate Women
GERALD MASTERSON
Department of Health Physical Education and Recreation, Southwest Missouri State University, Springfield, Missouri 65804.
ABSTRACT
The purpose of this study was to explore the impact of the menstrual phases on power performance in fairly active collegiate women. After the initial screening of 100 potential subjects who engaged in exercise 2 and no more than 3 days a week for 30 minutes or less, 32 subjects were selected to completed the study. The subjects underwent 2 Wingate tests to estimate anaerobic power, anaerobic capacity, and fatigue. One test was administered during the follicular phase; the other test was administered during the luteal phase. The data from this study indicate that there are differences between power performance during the follicular and luteal phases for these women. The women in this study demonstrated greater anaerobic capacity, produced greater peak power, and were less fatigued by the end of the exercise during the luteal phase than during the follicular phase. The results indicate that menstrual phase in fairly active collegiate women can have an influence on anaerobic performance.
Key Words: menstrual cycle, exercise performance, Wingate testing.
Introduction Identifying key elements that contribute to performance is an exhaustive process. Anaerobic power has been recognized as a key element and can be an indicator of success in athletics (2, 4, 12). Past studies of anaerobic power have focused on men (17). Of 17 studies reviewed by Bar-Or (2), 14 included only men as subjects. The 3 remaining studies included both men and women. This leaves unanswered questions regarding the response of women to power tests. Although past studies report that both sexes respond or adapt in much the same way to short-term and long-term exercise, Willmore and Costill (22) list some special factors that should be considered when working with women. One of these factors is menstruation. According to the National Strength and Conditioning Association (20, 21), there are cultural and social stigmas that a woman must overcome; however, there is little evidence that menstruation affects athletic performance. However, these authors recognize that there is tremendous variability in the physical and psychological ways in which women respond to menses and highlight the need for investigation into the effect of the ovarian hormones on exercise performance.
Golub (8) suggests that misconceptions associated with the menstrual cycle continue to exist. She cites a study done by the Tampax Corporation, in which more than 1,000 Americans, ranging in age from 14–65 years and representing all ethnic, educational, and economic groups, were sampled. The results indicate that a substantial number of women believe that they cannot function normally during menstruation. Some believe that they should restrict their physical activities during menses, and most experience dysmenorrhea at some point.
Studies examining the impact of the menstrual cycle on exercise have yielded mixed findings. For example, Schoene et al. (18) reported time to exhaustion on a incremental exercise test was shorter during the luteal phase than during the follicular phase for controls but not in competitive athletes. In other studies (7, 16), endurance performance was enhanced during the luteal phase in trained women. Jurkowski et al. (10) reported an increase of high-intensity work (exercise lasting less than 3 minutes), including lower lactate levels, during the luteal phase for “healthy females.”
No evidence for different phases of the menstrual cycle affecting maximal exercise performance has been found for highly active (5, 12), moderately active (6), or “healthy females” (19). Menstrual cycle phase also does not appear to affect submaximal endurance performance for “healthy females” (19) or for athletes (11, 15). Thus, there appear to be some discrepancies in the findings regarding the effects of menstrual status.
Differences in past findings may be related to the activity level of subjects used. Many studies that found no differences in performance involved highly active or athletic women (5, 11, 15). Perhaps active women have overcome negative effects associated with menstruation to a greater extent than less active women. This notion is supported in Golub by research performed by Bates (8), who studied 28 women participating in a daily exercise program for 8 weeks. Bates suggests that women who participate in regular physical activity 4 or more days a week have less menstrual pain and premenstrual tension. Including women who are not as physically active, as those described by Bates, might help answer the question concerning relatively inactive women's response to exercise. For example, women enrolled in college physical education classes participate in class activities but may not get additional exercise outside class. Perhaps the performance of women whose activity is at such a level would vary as a result of the different phases of the menstrual cycle.
Differences may also be due to sample size. Restricted sample sizes are a problem for this area of research, since most studies include no more than 16 subjects and are vulnerable to variations among individuals (5, 7, 9, 10, 11, 13, 14, 19). Because of large variances associated with the menstrual cycle, a larger sample should help account for wide individual variability and be more representative of the population.
The present study was designed to explore whether anaerobic power performance of women differs during the 2 phases of the menstrual cycle. These women participated in exercise fewer than 3 days a week and less than 30 minutes a session. Their performance during the follicular phase, within 48 hours of the onset of menstrual flow, was compared with their performance during the luteal phase, days 18–21 of the cycle (17). Anaerobic power was measured using the Wingate anaerobic test because of its high test-retest reliability (2). Power performance was characterized by measures of anaerobic capacity, peak power, and fatigue indices.
Methods
Subjects
One hundred apparently healthy women were recruited for this study. The women were enrolled in a college wellness course at the time of the study. All subjects volunteered and were provided written, university-approved informed consent forms. After being instructed as to the purpose of the study and signing consent forms to participate, each subject completed a medical history form and menstrual cycle history form (8, 9, 15). Those demonstrating contraindication for exercise and amenorrhea, users of oral contraceptives, and those who exercised 3 or more days a week were not included as subjects. The subjects typically exercised at least once a week as part of the course, and some reported additional activity. The average exercise level was 2.5 workouts per week. Consequently, they were considered “fairly active.”
After the initial screening process, 48 subjects with normal menstrual cycles were chosen to participate in the study. The length of the menstrual cycle was considered to be the number of days from the first day of a bleeding episode through the day before the start of the next bleeding episode. Menstrual cycles were considered normal if the subject reported regular monthly menstruation that occurred between 25- and 31-day intervals (8). Of the 48 individuals identified as eligible to participate, 32 subjects completed both trials. The remaining 16 subjects withdrew because of scheduling conflicts or illness. Subject characteristics were as follows: age: 20 ± 1.8 years; weight: 61 ± 6.5 kg; and body fat: 24 ± 4%.
Procedures
This study used a repeated-measures design. Each subject was asked to participate in 2 Wingate anaerobic power tests. One was completed during the follicular phase of the menstrual cycle, and the other during the luteal phase of the cycle. Test order was counterbalanced so that results would not be threatened by practice effects. As a result of counterbalancing, approximately half (n = 15) of the subjects underwent the first power test during the follicular phase and the others underwent their first test during the luteal phase.
Menstrual status was determine based on cycle history (8, 9, 15). Subjects were asked to report the onset of menstrual flow so that test dates could be set accordingly. Subjects assigned to take their first test during the follicular phase were instructed to come to the laboratory within 48 hours of the first noticeable sign of menstruation. Subjects assigned to take their first test during the luteal phase reported the end of their flow and were then scheduled for a test within 14–15 days. This manner of scheduling was followed because the luteal phase starts at approximately day 14 of the menstrual cycle and is when ovulation is supposed to occur. According to the World Health Organization, the average length of the bleeding episode is 4–5 days. Scheduling the test 14–15 days after the end of flow placed the test around days 18–21 and in the luteal phase of the cycle (8, 9, 15, 22). These procedures were similar to those used and described in previous studies (9, 15). Although direct measurement of menstrual cycle phase was not taken, our testing dates were dramatically displaced from one another, making it unlikely that the 2 measures would have been taken during the follicular phase.
Subjects who completed trial 1 during the luteal phase completed trial 2 during the follicular phase. Subjects who completed trial 1 during the follicular phase completed trial 2 during the luteal phase. Trials were done during the same time of day for each subject to limit the possible effects of circadian rhythm.
Testing
Subjects completed the Wingate test (1) to estimate the power and capacity of the anaerobic energy system. The Wingate test requires the subject to pedal as rapidly as possible for 30 seconds at a resistance setting that is based on body mass (0.075 kg per kilogram of body weight). Before beginning each test, the subject was weighed, and her weight was used to set the appropriate resistance. Seat height was positioned according to Adams' test protocol (1) to control for variations in leg length. Height was set so that the subject's knees were almost completely extended through the bottom of the pedaling cycle. Once the resistance was determined, the subject completed a 3-minute warm-up, followed by a 3-minute recovery. The subject was then asked to pedal against the predetermined resistance as rapidly as possible for 30 seconds. The subject was instructed to give an all-out effort and not to pace herself. Throughout the testing period, each subject was verbally encouraged to do her best. Pedal revolutions were counted by a trip sensor located on the back of the ergometer. Assessments were made during each exercise bout and included anaerobic capacity (i.e., the total number of revolutions in 30 seconds expressed in Watts), anaerobic power (i.e., maximum number of revolutions in a 5-second period expressed in Watts), and fatigue index (i.e., the percent difference between the maximum number and minimum number of revolutions in a 5-second period).
Statistical Analysis
A t-test for repeated measures (SPSS 6.11) was used to detect differences between the follicular and luteal phases for each of the three dependent measures: anaerobic capacity, anaerobic power, and fatigue index. Significance was set at the p 0.05 level.
Results
Indices of the women's power performance are shown in Table 1 A t-test for repeated measures was used to compare the scores for each of the 3 dependent measures (3). As seen in Table 1 and illustrated in Figure 1, the difference in anaerobic capacity between the follicular phase and the luteal phase was significant. Anaerobic capacity was higher during the luteal phase than during the follicular phase.
As seen in Table 1 and illustrated in Figure 2, the difference in anaerobic power between the follicular phase and luteal phase also was significant. Anaerobic power was greater during the luteal phase than during the follicular phase.
As seen in Table 1 and illustrated in Figure 3, the difference in fatigue index between the follicular phase and the luteal phase was significant. The fatigue index was greater during the follicular phase than during the luteal phase.
Discussion
Similar to the findings of other studies (7, 10, 16, 18), the data from this study indicate that there are differences between performance during the follicular and luteal phases of the menstrual cycle. The women in this study demonstrated greater anaerobic capacity, produced greater peak power, and were less fatigued by the end of the exercise during the luteal phase than during the follicular phase. This is in contrast to other studies reporting no significant reduction in performance across different menstrual phases (5, 6, 11, 12, 15, 19).
The results of this study should not be compromised by a limited sample size, since the number of subjects was twice the number used in previous studies. Neither should the results be attributable to sequencing or practice effects, since the testing order for the 2 phases was counterbalanced.
Although the Wingate anaerobic test is a highly reliable task, with a test-retest reliability correlation average of 0.94, its procedures might have contributed to the outcome of the present study (2). The Wingate protocol requires that pedal resistance be based on body mass (0.075 kg per kilogram of body weight). Consequently, it is possible that differences in the anaerobic power measures attributed to menstrual phase may have actually been related to changes in the resistance setting that accompanied changes in weight between the 2 tests (or phases). Mean resistance settings for the 2 conditions were checked to see if they were different. Although the difference in subject weight between the 2 tests was significant, the resistance settings were not significantly different. The mean setting for the follicular phase was 5.28 (SD = 0.628), and the mean resistance setting for the luteal phase was 5.27 (SD = 0.637). The fact that these settings are virtually identical indicates that the differences in power performance between menstrual phases were not simple artifacts of changes in the resistance settings.
It is likely that the differences between the subjects and their activity level included in the present study and those involved in previous studies are responsible for the variation in findings. Although it is difficult to pinpoint the cause for the differences in performances, it would appear that both psychological and physiological factors are involved. Our fairly active subjects' perceptions of menstrual cycle and their capabilities may be different from those of regularly active or competitive women, and these perceptions could have affected the outcome of this study. It is estimated that up to 75% of all women suffer from premenstrual tension (8). Perhaps, as Bates (8) suggests, women who participate in regular physical activity 4 or more days a week have less menstrual pain and premenstrual tension than those who are less active. It is unclear whether the women in the present study varied in attitude or actual menstrual discomfort from the active women who participated in previous studies. In either case, these results demonstrate a difference in power performance across the ovarian phases for this group of women.
In summary, competing explanations such as testing protocol, sample size, and sequencing effects do not appear to account for the significant findings. Rather, the differences were likely due to differences in subject responses to the ovarian phase during which the testing took place. These differences were significant in the fairly active women who served as subjects for this study.
Practical Applications
Questions still exist as to whether menstruation adversely affects performance. The results of this study suggest that the follicular phase compromises indices of power performance in fairly active women ages 18–24 years. Scientists and physical educators, who might use fairly active or sedentary women for a study or to start an exercise program, need to be aware of this potential influence on performance. They should implement appropriate control procedures when performing preexercise and postexercise measures. If ovarian phase is not held constant, potential benefits of exercise might be misrepresented. For example, if the pretraining measure is conducted during the luteal phase and the posttraining measure is conducted during the follicular phase, positive effects of exercise might be masked. It is also reasonable to expect that the reverse might be true. It should be emphasized, however, that these findings and principles relate to fairly active women. This study did not include athletes, and the results from previous studies do not indicate the necessity for control between pretraining and posttraining measures in athletes and highly trained women.
References
1. Adams, G.M. Exercise Physiology Laboratory Manual. Dubuque, Iowa: Wm C. Brown Publisher. 1990.
2. Bar-Or, O. The Wingate anaerobic test: An update on methodology, reliability and validity. Sports Med. 4:381–394. 1987. [PubMed Citation]
3. Baumgartner, T.A., and C.H. Strong. Conducting and reading research. In:. Health and Human Performance. Boston: WCB McGraw-Hill. 1998.
4. Beckenholdt, S., and J.L. Mayhew. Specificity among anaerobic power tests in males. J. Sports Med. 23:326–331. 1983.
5. Bemben, D.A., P.C. Salm, and A.J. Salm. Ventilatory and blood lactate responses to Maximal treadmill exercise during the menstrual cycle. J. Sports Med. Phys. Fitness. 35:257–262. 1995. [PubMed Citation]
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