Effects of Menstrual Phase on Performance and Recovery in Intense Intermittent Activity BY
Laura Elizabeth Middleton
B.H.K., University of British Columbia, 2000
A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE
in the School of Physical Education
O Laura E. Middleton, 2004, University of Victoria
All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author.
Supervisor: Dr. Howard Wenger
Abstract
This study examined differences and relationships between high intensity, intermittent work and menstrual phase. Six performed (10) 6-second sprints on a cycle ergometer in the luteal (LP) and follicular phase (FP) of the menstrual cycle.
The average 6-second work was greater in the LP (39.3 (3.4)Jkg) than during the FP (38.3 (3.1)Jkg). There was no difference in peak 6-second power (6.8(0.6)W/kg in FP, 6.9(0.6)W/kg in LP) and the drop-off in work (1.2(3.5)J/kg in FP and 1.0(2.7)J/kg in LP) between menstrual phases.
There was no significant difference in sprint V 0 2 or recovery V 0 2 between FP (2.3 (O.S)rnL/kg/min and 24.1 (2.5)mL/kg/min) and LP (2 1.8(1.6)mL/kg/rnin and 23.7(2.8)mL/kg/min). In sprints 2 to 10, recovery V 0 2 was greater in LP
(26.3(2.4)mL/kg/min) than FP (25.0(2.6)rnL/kg/min). Recovery V 0 2 and average 6- second work positively correlated (0.78 in FP, 0.77 in LP).
In summary, oxygen consumption between sprints 2-10 and average work was greater in LP than FP.
Table of Contents Title Page Abstract Table of Contents List of Tables List of Figures Acknowledgements Introduction
Hypotheses and Research Questions Limitations Delimitations Operational Definitions Methodology Subjects Instrumentation Design Procedures Statistical Procedures Results Discussion Literature Cited
Appendix One - Informed Consent Form Appendix Two - Raw Data
Appendix Three - Review of Literature Literature Cited
Table 1 Table 2
List of Tables Table 1
Average physical measurements in the follicular phase (FP) and in the luteal phase (LP).
Table 2 14
Comparison between follicular (FP) and luteal phase (LP) of the menstrual cycle in mean 6-s work (MW), peak 6-second power (PP), and drop-off in work over
10 sprints (DO). Table 3
Comparison between follicular (FP) and luteal phases (LP) of the menstrual phase in resting V02, Sprint V02 (intervals 2 to 1 O), Recovery V02 (intervals 2 to lo), and post-exercise V02.
List of Figures
Figure 1
Experimental design.
Figure 2 10
Testing procedures for each laboratory session.
Fimre 3 15
Comparison of the 6-second power (P) achieved during a series of 10 sprints in the follicular (FP) and in the luteal phase (LP).
F i m e 4
Comparison of the recovery period V 0 2 during the follicular (FP) and the luteal phase (LP).
vii Acknowledgements
Howie, your help and guidance was invaluable. Thank you for allowing me the flexibility to train and compete while pursing my studies. Thank you to my committee members, Dr. Kathy Gaul and Dr. John Anderson, who helped me along the way.
Introduction
Adult females experience fluctuating, cyclical levels of reproductive hormones. During the reproductive years, the variation in these hormones during the menstrual cycle is a generally predictable pattern (Frankovich & Lebrun, 2000). Exercise is associated with alteration of circulating hormone concentration (Bonen et al., 1979; Jurkowski, Jones, Walker, Younglai, & Sutton, 1978) and hormone metabolism (Keizer, Poortman, & Bunnik, 1980) and with menstrual irregularities (Bonen et al., 1983, Keizer et al., 1980). Although the effect of intense training on the menstrual cycle has been extensively studied, the relationship between the menstrual cycle and physical performance is still unclear (Lebrun & Rumball, 1994).
Reproductive hormones influence many systems within the human body. For example, estrogen is known to influence the hypothalamic-pituitary-adrenal axis (Puder, Freda, Goland, & Wardlaw, 2002) while progesterone stimulates respiration (Schoene, Thomas Robertson, Pierson, & Peterson, 1981). These hormones vary within the menstrual cycle, suggesting a possible relationship between the menstrual cycle and exercise performance. However, the relationship is still unclear (Lebrun & Rumball, 2001).
There are two major phases of the menstrual cycle, the follicular phase and the luteal phase. The follicular phase begins at the onset of menses and ends at ovulation. The follicular phase can be fiu-ther divided into the menstrual phase and the pre-ovulatory phase. The menstrual phase occurs during menstrual bleeding and is characterized by low levels of estrogen, progesterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). During the pre-ovulatory phase, a mature follicle develops under the
influence of LH and FSH. A surge in LH occurs immediately preceding ovulation. During the pre-ovulatory phase, estrogen levels are high but progesterone levels are still low. The luteal phase begins at ovulation and ends at the onset of the next menses. It is characterized by high levels of estrogen and progesterone and low levels of LH and FSH.
Of the studies examining physiological variation in exercise performance during the menstrual cycle, many have examined the effect on maximal aerobic power
(VOamax) (Beidleman et al., 1999; Bemben, Salm, & Salm, 1995; Bonekat, Dombovy, & Staats, 1987; Bryner, Toffle, Ullrich, & Yeater, 1996; DeSouza, Maguire, Rubin, and Maresh, 1990; Lebrun, McKenzie, Prior, & Taunton, 1995; Pivarnik, Marichal, Spillman, & Morro, 1992; Schoene, Thomas Robertson, Pierson, & Peterson, 1981), substrate metabolism (Bonen et al., 1983; Campbell, Angus, & Febbraio, 2001; Hackney, 1999; Hackney, McCracken-Compton, & Ainsworth, 1994; Hackney, Muoio, & Meyer, 2000; Nicklaus, Hackney, & Sharp, 1989), and thermoregulation (Frye, Kamon, & Webb,
1982; Giacomoni, Bernard, Gavarry, Altare & Falgairette, 2000; Horvath & Drinkwater, 1982; Stachenfeld, Silva, & Keefe, 2000). Other research has examined the effects on muscular function (Chen & Tang, 1989), sympathetic activity (Minson, Halliwill, Young, & Joyner, 2000), and recovery fiom aerobic activity (Fukuba, Yano, Murakami, Kan, & Miura, 2000; Matsuo, Saitoh, & Suzuki, 1999). Only four studies have examined the effect of the menstrual cycle on performance in high intensity (anaerobic) activity (Giacomoni et al., 2000; Lebrun et al., 1995; Lynch & Nimrno, 1998; Sunderland & Nevill, 2003).
High intensity, intermittent activity is present in most game sports, for example, rugby, field hockey, and soccer, where intense bursts of effort are interspersed with
periods of low intensity activity or rest. Also, training sessions for many sports include interval training where repeated bouts of high intensity work are required. There have been two studies that examined the effects of the menstrual cycle on intermittent performance. Neither found a significant effect of menstrual phase on performance. However, both studies had design problems. Lynch and Nimrno (1998) used intervals of progressive intensity which is not a valid simulation of game sport. The study by
Sunderland and Nevill (2003) involved intervals of varying intensities, maximal sprints, cruising (-95% VOzmax), jogging (-55% V02max), and walking. However, they did not monitor the performance in each interval. The effect of menstrual phase may be different on various intensities of effort. Also, the primary purpose of the Sunderland and Nevill study was to monitor the ability of the participants to cope with heat in the luteal phase and the follicular phase.
Despite the studies performed to date, there is some evidence to suggest that high intensity intermittent activity may be affected by the menstrual cycle. High intensity intermittent activity requires high power output which is generated mainly fiom the anaerobic system (Gaitanos, Williams, Boobis, & Brooks, 1993). Alactic anaerobic metabolism may be enhanced during the luteal phase due to increased intramuscular phosphogen (adenosine triphosphate, phosphocreatine) stores associated with high estrogen levels (Shivaji, Devi, Ahmad, & Sundaram, 1995). Strength endurance is also required to produce repeated, powerful bursts. In a study of inspiratory muscle, Chen and Tang (1989) found improved strength endurance in the luteal phase.
Recovery between high intensity intervals may also be affected by menstrual phase. For complete recovery, metabolic systems must return to the pre-exercise
condition. There is some evidence of enhanced lactate clearance at high intensities (Jwkowski et al., 198 1 ; McCracken, Ainsworth, & Hackney, 1994) and increased excess post-exercise oxygen consumption (EPOC) (Matsuo et al., 1999) during the luteal phase relative to the follicular phase. Also, there is evidence of enhanced blood flow with high progesterone levels (Charkoudian, 2001), as seen in the luteal phase. These three factors suggest that metabolic products may be cleared faster and energy stores may be
replenished faster during the luteal phase.
It was the purpose of this study to determine: (a) the difference between power production during high intensity, intermittent activity in the follicular phase and the luteal phase of the menstrual cycle; (b) the difference between the ability to resist fatigue over repeated sprints in the follicular phase and the luteal phase of the menstrual cycle; and (c) the difference between oxygen consumption during and between repeated sprints in the follicular phase and the luteal phase of the menstrual cycle.
Hypotheses and Research Questions
1. Will the power production during high intensity, intermittent activity be different in the follicular phase than in the luteal phase of the menstrual cycle?
Research Hypothesis: PFP < PLP Null Hypothesis: PFP = PLP
2. Will the ability to resist fatigue over repeated sprints be different in the follicular phase than in the luteal phase of the menstrual cycle?
Research Hypothesis: PFP < PLP Null Hypothesis: PFP = PLP
3. Will the V 0 2 consumption before and between repeated sprints be different in the follicular phase than the luteal phase of the menstrual cycle?
Research Hypothesis: PFP < PLP Null Hypothesis: PFP = PLP
Limitations
The participants were required to use toe clips as clipless shoes were not available for all. Because of this, there were slips during some of the sprints, making the data of that sprint unusable.
The progesterone tests were carried out at a separate, independent testing facility. Although they went to be tested immediately before the cycle ergometer session, there was still a delay between the progesterone testing and the performance testing protocol. Within this delay, progesterone levels may change.
The V 0 2 data was collected on a breath-by-breath basis. However, in a 6-second sprint, there was often only two breaths. This made estimating the V 0 2 consumption during the sprint difficult. Also, some subjects occasionally held their breath for an entire sprint, although instructed not to do so.
Delimitations
The subjects involved in this study were active women, aged 19-29 years, with eumenorrheic cycles, not on oral contraceptives. The goal of this study was to examine the effects of menstrual phase on high intensity intermittent activity similar to game sport. Generalizations to specific athlete groups or athletes of higher or lower training
Mean Work (MW)
Peak Power (PP)
Drop-off (DO)
Eumenorrheic
status may not be appropriate. Also, women taking oral contraceptives may not find the same results as women with regular menstrual cycles.
The work protocol was performed on a cycle ergometer. This allowed work and power data to be more accurately measured than on a treadmill. However,
generalizations to the running involved in most game sports may not be appropriate. Operational Definitions
6-second Work (W) the work per kilogram body weight produced over one 6-second sprint interval in jouleskilogram ( J k )
the mean of all the 6-second work intervals produced in the 10 sprint series in J k g
the maximum 6-second mean power per kilogram body weight produced in the 10 sprint series in watts per kilogram (Wkg)
the decrement between the average of the first (3) 6- second work intervals and the average of the last (3) 6-second works in J k g
Having regular, ovulatory menstrual cycles occurring every 24 to 36 days.
Methodology Subjects
Nine women were recruited from the University of Victoria and the Gorge
Rowing Club for this study. The nature and purpose of the investigation was explained to each participant before she signed an informed consent form (Appendix 1). An
information sheet describing the research was given to all participants. All subjects were informed that participation was voluntary and withdrawal from the study was permitted at any time.
Subjects were required to satisfy several criteria: (a) female 19-29 years; (b) participate in moderate physical activity at least four times per week; (c) free of metabolic, cardiovascular, or respiratory disease; (d) non-smoker; (e) not an oral
contraceptive user for 6 months or more; (f) eumenorrheic menstrual cycles for 1 year or more; and (g) menstruating for at least 3 years. Eumenorrhea was operationally defined as regularly occurring menstrual cycles, 24 to 35 days in length (Lebrun, McKenzie, Prior, & Taunton, 1995).
Instrumentation
All exercise tests were performed on a friction-loaded cycle ergometer (model 8 18, Monark) interfaced with an electronic revolution counter (Micro Projects). The product of flywheel revolutions and the load were used to determine power measures.
Expired gases were collected through a low resistance valve (Rudolph 2700) using breath by breath mode with a Vmax 229 Metabolic Measurement Cart
(Sensormedics) for determination of oxygen consumption (V02), ventilation (VE), carbon dioxide produced (VC02), and respiratory exchange ratio (RER).
Prior to exercise testing, subjects had their blood progesterone level tested via radioimrnunoassay by MDS Metro Lab Services. Blood lactate was tested by finger tip (Lactate Pro).
Design
Subjects participated in three laboratory sessions: a familiarization session, a luteal phase testing session; and a follicular phase testing session. The follicular phase session was at 6 to 10 days and the luteal phase session at 20 to 24 days after the beginning of menstrual bleeding. The luteal and the follicular phase sessions were in a randomly assigned order. All sessions were identical except that blood testing did not occur prior to the familiarization session.
Figure 1
Experimental design.
Follicular Phase Luteal Phase
/
TestF HllA Test
Participant
-
Familiarization,-'
Recruitment Session\
Luteal Phase Follicular Phase HllA Test HllA TestFollicular Phase = day 6 to 10 Luteal Phase = day 20 to 24
Procedures
Each session took place after a two hour fast to reduce the thennogenic effect of food on oxygen consumption. Subjects traveled to the laboratory by motorized vehicle to eliminate unnecessary activity (Gore & Withers, 1990). Subjects also abstained from caffeine, alcohol, and drugs for the four hours prior to the testing session and from intense physical exercise for 24 hours prior to the session (Short & Sedlock, 1997). Intense exercise was defined as any exercise session longer than 30 minutes perceived as intense by the participant (Tomlin, 1998). In each testing session, participant weight and resting V O a was established prior to the intense intermittent exercise test.
Prior to each testing session, the participants had their blood sampled at a MDS Metro Lab Services to test serum progesterone levels. Upon arrival to the exercise laboratory, the subject rested for 30 minutes. The average oxygen consumption during the last 10 minutes of the rest period was taken as resting oxygen consumption. Next, the subject performed a submaximal cycling warm-up consisting of five minutes at 50 rpm against a resistance of 0.5 kp. A moderate intensity warm-up followed, consisting of two 30-second periods of submaximal cycling, one at 85 and one at 11 5 rpm separated by 60 seconds of recovery. Finally, the warm-up was completed by a five-minute stretching period. A similar warm-up has been shown to result in only minor metabolic
disturbances (Wootton & Williams, 1983).
The intense intermittent exercise test consisted of 10 maximal 6-second sprints interspersed with 30 seconds of recovery. The cycling ergometer was loaded with 0.075 kp.kga'. To standardize the measure, the subjects started each sprint from a stationary, seated position with the same starting pedal position. Each sprint was performed in a
seated position with feet secured to pedals with toe clips. Subjects were instructed to ensure that they breathed during the sprints.
During the 30 second rest period, the subjects remained quietly seated on the cycle ergometer. All subjects were verbally encouraged during each sprint to give maximal effort. Following the 10 sprints, the subjects rested on a chair for 10 minutes. During the intense intermittent exercise test and for 10 minutes post-exercise, VOz, VC02, VE, and RER were monitored, measured on a breath by breath basis. Blood lactate levels were measure at one minute and three minutes into the post-exercise rest period.
Average revolutions per minute were recorded after each sprint and were used to determine work and power.
Figure 4
Testing procedures for each laboratory session. Blood
Test 30 minute rest period
-
Warm upPost-exercise Rest
-
Arrival 10' Resting VO, Warm up 5' @ SOrprn, 0.5kp; 30" @ 85rpm, I .Okp (I ' Rest) 30" @ 1 1 Srpm, I .Okp 5' Stretch or choice10 x {(6", 0.75kpikg)DO" Stationary Rest
HllA
Statistical Procedures
The differences between menstrual phases in Ws, MW, PP, DO, lactate levels as well as V 0 2 during, between, and after the sprints was examined using t-tests.
Correlations were also investigated between lactates, V 0 2 and mechanical parameters. Statistical significance was set at 0.05.
Results
Thirteen participants were recruited for this study. Nine participants completed the testing. The data of only six participants was used in data analysis. One participant did not have her progesterone tested during the luteal phase so menstrual phase could not be confirmed. The second subject was excluded because her progesterone during the luteal phase was not high enough to confirm ovulation. The final participant was
excluded because her foot slipped fi-om the clip in four of the 10 sprints during the luteal phase testing, making proper comparison between phases impossible. For the remaining six subjects, the progesterone levels were significantly higher during the LP (19.0 (6.7) nmoVL) than during the FP (1.2 (0.4) nmoVL) (Table 1).
The MW over the series of 10 sprints was significantly greater in the LP (39.3 (3.4) Jlkg) than in the FP (38.2 (3.1) Jkg). The W for individual sprints was only significantly different in sprint 4 where it was greater in the LP (40.4 (3.4) Jkg) than in the FP (38.7 (3.3) Jkg) (Figure 3). There was no significant difference between the menstrual phases in PP (6.8 (0.6) W k g in FP, 6.9 (0.6) W k g in LP) or in DO (1.2 (3.5) J k g in FP, (1.0 (2.7) J k g in LP) (Table 2).
The lactate samples were not significantly different between menstrual phases either at 1 minute (9.2 (2.7) mmoVL in FP, 9.2 (3.1) mmoVL in LP) or at 3 minutes (9.0 (2.2) mmoVL in FP, 9.2 (2.2) mmoVL in LP) (Table 1). The decrement in lactate from minute 1 to minute 3 was also similar between menstrual phases (-0.2 (0.8) mmol/L in FP, 0.0 (1.4) mmoVL in LP).
There were no significant differences in the average VOz during rest or post - exercise (Table 3). Over the 10 intervals, there was no difference between menstrual
phase for sprint
13 ntervals (Above resting: 21.8 (1.6) mL/kg/min in FP, 21.3 (0.8)
mL/kg/min in LP) or recovery intervals (25.0 (2.6) mL/kg/min in FP, 26.3 (2.4)
mLikg/min in LP). If calculated only for sprints 2 through 10, the average V02 during the recovery periods is significantly higher during the LP than in the FP. However, there was still no significant difference in sprint V 0 2 (Table 3). The recovery V02 was
significantly higher for individual intervals in recovery 2 (21.7 (3.2) mL/kg/min in FP; 23.9 (2.7) mL/kg/min in LP), recovery 4 (24.1 (2.5) mL/kg/min in FP; 25.5 (2.7)
mL/kg/min in LP), recovery 6 (24.8 (2.9) mL/kg/min in FP, 26.6 (1.9) mL/kg/min in LP), 7 (25.0 (2.5) mL/kg/min in FP; 26.6(2.5)mL/kg/min in LP), and recovery 9 (25.7 (3 .O) mL/kg/min in FP, 27.4 (2.4) mL/kg/min in LP).
There was a positive correlation between average recovery V 0 2 and MW in both the FP (0.78) and the LP (0.77). There was also significant correlations between lactate at 3 minutes post exercise and drop off (0.963 in FP, 0.836 in LP). There were no other significant correlations amongst lactate, sprint V02, or recovery V02 and MW, PP, or DO.
Table 1
Physical measurements in the follicular (FP) and in the luteal phases (LP).
Menstrual Progesterone Mass Lactate 1 Lactate 2
Phase (nmol1L) (kg) (mmolIL) (mmol1L)
FP Mean 1.2 71.7 9.2 9
(SD) (0.4) (7.6) (2.7) (2.2)
Table 2
Comparison between follicular (FP) and luteal phases (LP) of the menstrual phase in average mean work (MW), peak 6-second power (PP), and drop-off in work (DO) over
10 sprints. Menstrual MW MW PP DO Phase Jlkg
1
Jlk FP Mean 38.3 2.74 6.8 1.2 (SD) (3-1) (0.27) (0.6) (3.5) LP Mean 39.3 2.82 6.9 1 .O (SD) (3.4) (0.24) ***
*
(0.6) (2.7)*
= significant difference between FP and LP (p < 0.001).**=
significant difference between FP and LP (p < 0.05).Figure 3
Comparison of the mean 6-second work (MW) between the follicular (FP) and luteal phase (LP) achieved during a series of 10 sprints.
0
1
I I I I I I I I I
1 2 3 4 5 6 7 8 9 1 0
Sprint
Table 3
Comparison between follicular (FP) and luteal phases (LP) of the menstrual phase in resting V02, Sprint V 0 2 (intervals 2 to 10). Recoverv VO:, - (intervals 2 to lo), and post- exercise V02. --
Menstrual V02 Rest Sprint Recovery Post
Phase (mL/kg/min) (2-1 0) (2-1 0)
FP Mean 3.1 24.3 25.0 8.3
Figure 4
Comparison of the follicular (FP) and the luteal phase (LP) for recovery period V02: -
Recovery
Discussion
Eumenorrheic cycles have been operationally defined as regularly occurring, ovulatory menstrual cycles (24-35 days in length) (Lebrun et al., 1995). In this study, the progesterone levels were significantly higher during LP than FP (p < 0.001). According to Millar and Soules (1996), a progesterone level of greater than 9nmolIL confirms that ovulation has occurred. All progesterone values during the luteal phase of subjects whose data was used were 1 InrnolIL or greater, confirming eumenorrheic cycles.
Compared to female soccer players completing a similar protocol (Tomlin & Wenger, 2002), both mean 6-second power and PP are slightly lower in both menstrual phases (averages of 44.3 J k g and 7.9 W k g in the Tomlin and Wenger study versus 38.8 J k g and 6.8 W k g in this study). However, the subjects in the Wenger and Tomlin study used clipless shoes. This may have allowed for more efficient power transfer to the pedals. The higher power may also be due to the type of training of the subjects have performed. Soccer requires fiequent bwsts of speed, interspersed with periods of lower intensity. In contrast, the subjects in this study are involved in endurance sport, requiring a fairly constant level of effort. Hamilton, Nevill, Brooks, & Williams (1991) found that games players produced greater peak power and peak speed than did endurance trained- runners using a similar protocol. The soccer players of the Tomlin and Wenger study may have higher power than the subjects of the current study because the energy patterns in a soccer game are more similar to the testing protocol than the energy patterns of an
endurance training session or an endurance race. The V02 during and between the sprints was similar to that of the women in the low aerobic power group in the Wenger &
Tomlin study (an average of 2 1.5 mLkg/min in this study versus 2 1.8 mLkg/min in Wenger & Tomlin).
There was no significant difference between PP in the follicular phase and PP in the luteal phase in this study. Similarly, in a study examining maximal anaerobic performance, there was no difference between menstrual phase for power in an 8 second bicycle ergometer sprint (Giacomoni et al., 2000). They also found that maximum power, as measured by a multi-jump test or a squat jump test, was also similar over the menstrual cycle phases.
The anaerobic alactic (ATP-PCr) system can produce energy much faster
(approximately 4 ATP per minute) than either the anaerobic lactic (2.5 ATP per minute) or the aerobic energy system (1 ATP per minute) (Axen & Vermitsky Axen, 2001). The rate of energy production fiom the ATP-Cr system is related to the enzymatic action of creatine kinase which facilitates the release of energy from PCr to fund the production of ATP. The concentration of creatine kinase limits the production of ATP from PCr. It appears that creatine kinase stores may not be affected by menstrual phase.
Although most W were not significantly different between menstrual phases, the MW was greater during the LP (39.3 (3.4) Jkg) than the FP (38.3 (3.1) Jlg). This may be due to greater PCr and adenosine triphosphate (ATP) stores associated with high estradiol levels (Shivaji et al., 1995) as in the luteal phase. The decline in ATP utilization during exercise and subsequent production of work may be related to the decrease in PCr concentrations (Hargreaves et al., 1998). According to Gaitanos et al. (1993), 84% of the anaerobic ATP production in the last of 10 sprints is from phosphogen stores. Therefore,
increased PCr and ATP stores may sustain higher ATP utilization levels and allow for more consistent work levels.
No previous studies have examined average power over a series of sprints relative to menstrual phase. Giacomoni et al. (2000) tested women in a series of 8 second sprints on a bicycle ergometer. However, only peak power values were reported. The rest interval was also much greater than in this study in an effort to achieve peak power.
Two other studies have examined intermittent activity (Lynch & Nimmo, 1998; Sunderland & Nevill, 2003). Unlike the present study, neither found a significant
difference in performance between menstrual phases. However, unlike the current study, power exerted during the intervals was not measured, nor was maximal exertion required in every interval.
Lynch and Nirnmo (1998) had subjects perform work intervals of progressive intensity to exhaustion, meaning only the last interval or two were of maximal exertion. Both the work interval (20 seconds) and the rest interval (100 seconds) were far longer than in the current study. Intervals of different length will influence the energy sources that the body uses. A 6-second sprint requires nearly equal contribution fiom alactic and glycolytic energy sources (Gaitanos et al., 1993). A 20 second sprint requires more contribution from the aerobic systems because the contribution of the anaerobic energy systems is less (Bogdanis, Nevill, Lakomy, & Boobis, 1998). The recovery time in the Lynch and Nimmo study (100-seconds) was also much longer than in the current study (30-seconds). This difference will greatly affect the amount of recovery prior to the subsequent sprint and would account for the lack of differences in performance between menstrual phase.
Sunderland and Nevi11 (2003), required participants to complete 20m intervals of varying speed for repeats of 15 minutes until exhaustion. Although some of the intervals were maximal sprints, others were walk, jog (-55%), or cruising (-95% V02max) speed. Intervals at each speed contributed to the final performance results (total distance
completed). In contrast to the present study, they found no difference in performance. It may be the contribution of the sub-maximal intervals that caused there to be no
significant difference in performance between menstrual phases. Time to exhaustion at submaximal V 0 2 has been found to be similar in the follicular phase and in the luteal phase (De Souza et al., 1990; Lebrun et al., 1995; McCracken et al., 1994).
Muscular endurance is required to produce repeated sprints. In a previous study of inspiratory muscle, Chen and Tan (1989) found improved strength endurance during the luteal phase. If this can be generalized to skeletal muscle in the legs, then improved strength endurance may have contributed to the greater MW in this study. However, two studies (Dibrezzo, Fort, & Brown, 1991; Friden, Hirshberg, & Saartok, 2003) found no significant difference in muscle endurance over the menstrual cycle. The use of isokinetic contractions in these studies may have influenced maximal power output differently.
Oxygen consumption between intervals may also contribute to the ability to maintain power through a series of sprints by replenishing ATP and PCr stores
(McMahon & Jenkins, 2002). The fast phase of recovery, lasting 10 seconds to 5 minutes is associated with phosphagen (ATP, PCr) recovery (Gaesser & Brooks, 1984). In this study, there was no significant difference in average V02 during either the sprints or the recovery periods. However, for intervals 2 to 10, the average recovery period V02 is significantly greater during the recovery period in the LP (26.3 (2.4) mL/kg/min) than the
FP (25.0 (2.6) mL/kg/min). The trend for higher oxygen consumption during the luteal phase than during the follicular phase can be seen in Figure 4. The increased oxygen consumption during recovery may reflect increased ATP and PCr levels and usage. This would confirm the results of Shivaji et al. (1995) who found increased phosphogen stores with higher estradiol levels. Since ATP and PCr produce energy more quickly than other energy systems, increased levels and usage of ATP and PCr would allow the greater MW observed in the LP.
Despite the higher MW during the luteal phase, there was no significant
difference in the DO in the follicular phase and in the luteal phase. It was hypothesized that there would be less DO during the luteal phase due to enhanced lactate clearance at high intensities (Jurkowski et al., 198 1 ; McCracken et al., 1999) and increased EPOC (Matsuo et al., 1999) associated with the luteal phase. Elevations in lactate are associated with the onset of fatigue (Sahlin, 1992). This fatigue may be due to the accumulation of protons (H+) in the muscle and blood (Hochachka & Mommsen, 1983; Roos & Boron,
198 1 ; Sahlin, 1978). However, enhanced lactate clearance is only associated with the luteal phase at intensities above 90% V02max (Jurkowski et al., 1981; McCracken et al., 1999). At intensities below 90% VOzmax, several studies have found no difference in lactate clearance (Bonen et al, 1983; DeSouza et al., 1990; Hessemer & Bruck, 1985).
During recovery, lactate is either converted to pyruvate by lactate dehydrogenase or to glucose or glycogen (Parkhouse & McKenzie, 1984). The increased lactate
clearance associated with the luteal phase at intensities above 90% of V02max (Jurokowski et al., 198 1 ; McCracken et al., 1994) suggest that lactate dehydrogenase stores may be higher. Increased lactate dehydrogenase stores will only increase the
clearance of lactate if the active sites are saturated at the current levels. Lactate clearance may be enhanced only at intensities above 90% of V02max because lactate
dehydrogenase is not saturated with lactate until this intensity. Despite the maximal effort in this study, there was no difference in lactate clearance between menstrual phases. The intermittent protocol versus the steady state protocol of previous studies may have caused this conflict in results.
A portion of the EPOC includes oxygen that is being used to replenish energy stores. The V02 consumed between the sprints can be termed EPOC since it is consumed after a sprint. EPOC is associated with PCr recovery (Taylor, Bore, Styles, Gadian, & Radda, l983), lactate removal, and H+ removal (Gaesser & Brooks, 1984; Sahlin, 1992).
In this study, an increased V02 between sprints may contribute to the ability of athletes to maintain consistent W, relating to a higher MW. However, there was no significant difference in average oxygen consumption either during the sprints (22.9 (9.0)
mL/kg/min in FP, 21.7 (8.3) mL/kg/min in LP) or during the recovery period between the sprints (25.7 (10.5) mL/kg/min in FP, 24.9 (9.6) mL/kg/min in LP), suggesting that the recovery between sprints is similar in the two menstrual phases. However, as in displayed in figure 4, there is a tendency for the V02 during the recovery periods to be higher in the luteal phase than in the follicular phase. There is also a positive correlation between the average recovery period V02 and the MW (0.75 in LP, 0.80 in FP).
Although Matsuo et al. (1999) found a higher EPOC during the luteal phase of the menstrual cycle than during the follicular phase, Fukuba et al. (2000), found no
significant difference in EPOC between the two phases. However, these studies examined EPOC over a period of six and seven hours, respectively. This study examined V02
consumed between sprints, a 30 second EPOC, and for 10 minutes post-exercise. The average VOz consumed after sprints two to 10 was significantly greater in the luteal phase than the follicular phase. However, there was no significant difference between menstrual phases for V02 consumed post-exercise. This suggests that there may be a difference in EPOC for this fast phase (up to 5 minutes) but not in the slow phase of recovery. The fast phase is associated with a rapid decline in oxygen consumption and with phosphogen (ATP, PCr) replenishment and may last 10 seconds to 5 minutes (Gaesser & Brooks, 1984). The increase in EPOC between sprints may have enhanced phosphogen replenishment and allowed the subjects to maintain power production.
Conclusions
The MW was significantly higher during the luteal phase than the follicular phase of the menstrual cycle. The higher recovery period VOz during the LP relative to the FP may reflect increased usage and replenishment of phosphogen stores which may have allowed for greater MW.
These results suggest that athletes can maintain a higher power output for a series of sprints during the luteal phase than during the follicular phase.
Future Research
More research is needed using larger subject populations to confirm these
findings and to determine contributing factors. A cycle ergometer with a stop mechanism could be used to regulate start times more precisely. Muscle phosphogen stores should
be examined between menstrual phases as a possible factor in enhanced work production over a series of sprints.
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Letter of C O ~ S ~ ~ ~ U N I V E R S I T Y OF VICTORIA
OFFICE OF THE VICE-PRESIDENT, RESEARCH
HUMAN RESEARCH ETHICS COMMITTEE
Effects of Menstrual Phase on Intense Intermittent Activity
You are being invited to participate in a study entitled Effects of Menstrual Phase on Intense Intermittent Activity that is being conducted by myself, Laura Middleton. I am a graduate student in the department of physical education at the University of Victoria. You may contact me if you have further questions by phone at 721-9254 or by e-mail at middleton-l@hotmail.com.
As a graduate student, I am required to conduct research as part of the requirements for a Master of Science degree in sport and exercise science. It is being conducted under the supervision of Professor Howard Wenger. You may contact my supervisor at 721-8386 or at hwenger@uvic.ca.
The purpose of this research project is to examine the relationship between menstrual phase and performance during 10 repeated bursts of 6 second cycling. Your participation in this study will help to understand the relationship between the menstrual cycle and physical performance. The results of this study may help coaches and female athletes better prepare for training and competitions.
I have recruited women aged 19 to 29 years for this study. You must be recreationally active and used to high intensity exercise. You must be free of cardiovascular, respiratory, and metabolic diseases and have regularly occurring menstrual cycles 24-35 days in length. You must not smoke or have taken birth control pills in the last 6 months. We are looking for participants who have had regularly occurring menstrual cycles for the past year. At the familiarization session, you will be asked about your menstrual history and pattern so that eligibility for the study can be determined and the appropriate lab testing scheduled. If not the case, you will be required to withdraw from the study. If you agree to voluntarily participate in this research, your participation will include 3 laboratory sessions within 2 months - 1 familiarization session and 2 sprint test sessions. Participation in this study may cause some inconvenience to you because of the time commitment and travel required. Each laboratory session will take approximately 1 '/z hours. You will also be required to give one blood sample prior to each of the sprint test sessions. The morning of each of the sprint test sessions, you will travel to the MDS metro laboratory at 124-3749 Shelbourne Street to have a blood sample taken. This sample will be tested for progesterone to confirm menstrual phase. Including travel time, blood testing, and laboratory sessions, less than 7 hours of your time will be required.
Prior to the sprint test sessions, it is requested that you refrain from intense physical exercise for 24 hours and abstain from alcohol, caffeine, and drugs for 2 hours. We also ask that you travel to the laboratory by motorized vehicle in order to eliminated unnecessary activity. The sprint test sessions will take place 4 to 5 hours after your last meal. During the familiarization session, the test protocol will be the same but you may eat, drink, and exercise freely prior to the laboratory session.
Upon arrival to the laboratory, resting oxygen consumption and heart rate will be established as you sit quietly for 30 minutes. During this time, you are free to read, write andor listen to music but must remain seated. Following the resting period, you will perform a standard 10 minute warm up. The sprint test will then include 10 6-second all-out sprints on a stationary bike with 30 seconds of rest between each sprint. Your heart rate and oxygen consumption will be measured during the sprints and for 10 minutes afterwards. During the recovery period, blood lactate will be collected by finger prick at 1 minute and 3 minutes into the recovery period.
There are some potential risks to you by participating in this research. There risks infection with any blood testing is low. The blood sample will be taken in a sterile environment with sterile instruments by qualified personnel. The lactate samples are taken by finger prick in the laboratory. All equipment that may come in contact with the finger and blood is sterilized before and after each session. The fmger is sterilized before the sample is taken by alcohol swab and the finger puncture unit is a new, sterile instrument for each subject (one use only). The tester will be wearing gloves on freshly cleaned hands with hair tied back.
You may experience nausea or dizziness during the laboratory session. However, the loads imposed will not exceed those which might be expected during game of soccer or basketball. If you experience any symptoms, please inform the investigator and the test will be terminated. You can either reschedule another appointment to complete the test or withdraw from the study. Following the exercise session, you may experience some minor muscle soreness. Gentle stretching of the affected muscles should alleviate the stiffness. If the muscle soreness persists for more than 48 hours or if you would describe it as more than minor stiffness, please contact the researcher (721-9254).
Your anonymity cannot be completely protected since the researcher and assistants will know of your involvement and other subjects in the study may see you at the lab. However, you will be assigned a code number and this code number will be the only identifyrng information on the data sheets. The key for the code number will be kept in a separate location from the data sheets and know only to the primary researcher, Laura Middleton. Your name will not be attached to any results and your
anonymity will be protected by describing all results in terms of the group. Any data collected in this study will remain confidential, kept in a filing cabinet in a locked room.
In order to assure myself that you are continuing to give your consent to participate in this research, I will remind you of your right to withdraw at the beginning each laboratory session. Your participation in this research must be completely voluntary. If you do decide to participate, you may withdraw at any time without any consequences or any explanation. If you do withdraw from the study your data collected to that point will not be used without your written approval.
It is anticipated that the results of this study will be shared with others in my thesis and possibly in the publication of further scientific papers
In addition to being able to contact the researcher and the supervisor at the above phone numbers, you may verify the ethical approval of this study, or raise any concerns you might have, by contacting the Associate Vice-president, Research at the University of Victoria (250-472-4362).
Your signature below indicates that you understand the above conditions of participation in this study and that you have had the opportunity to have your questions answered by the researchers.
Name of Participant Signature Date
APPENDIX TWO
Table A-1
Mean power (W/kg) for 10 6-second sprint for follicular phase (FP) and luteal phase (LP).
Subj. Jlkg Jlkg Wlkg Jlkg 1 2 3 4 5 6 7 8 9 10 FP 1 44.7 44.4 42.1 42.7 39.3 42.0 38.3 42.9 41.0 38.8 41.6 7.4 2.81 2 44.2 44.3 41.1 39.6 38.8 37.2 39.1 38.7 38.1 35.3 39.6 7.4 5.81 3 30.5 30.7 34.7 33.3 32.4 32.4 33.8 33.8 34.5 35.4 33.1 5.9 -2.61 4 38.7 35.6 37.5 38.6 37.1 38.5 38.1 38.7 39.1 39.5 38.1 6.6 -1.80 5 36.2 36.6 35.9 37.1 36.5 33.2 37.2 36.7 38.2 37.3 36.5 6.4 -1.16 6 43.8 43.3 41.4 40.8 40.5 39.9 39.6 41.3 37.4 38.1 40.6 7.3 3.87 Mean 39.7 39.1 38.8 38.7 37.4 37.2 37.7 38.7 38.0 37.4 38.3 6.8 1.2 (sd) (5.7) (5.7) (3.2) (3.3) (2.9) (3.8) (2.1) (3.2) (2.1) (1.7) (3.1) (0.6) (3.5) Mean 38.8 40.6 39.9 40.4 38.8 39.3 38.8 38.5 39.1 38.7 39.3 6.9 1.0 (sd) (5.0) (4.2) (3.3) (3.4) (3.0) (3.7) (3.9) (3.1) (3.6) (3.8) (3.4) (0.6) (2.7)
Table A-2
Oxygen consumption (mL/kdmin) above pre-exercise levels for each 6-second sprint for follicular phase (FP) and luteal phase (LP).
Mean Subj. Sprint Mean 2-10
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 Mean (sd) LP 1 2 3 4 5 6 Mean (sd)
Table A-3
Oxygen consumption (mL/k~/min) above pre-exercise levels for each 30-second recovery period for follicular phase (FP) and luteal phase (LP).
Mean 2-1 0 Subject Recovery Mean
1 2 3 4 5 6 7 8 9 10 Ave. 1 2 3 4 5 6 Average (sd) LP 1 2 3 4 5 6 Average (sd)
APPENDIX THREE
During her reproductive years, like all women, the female athlete experiences fluctuating levels of sex hormones. This variation in hormones over the menstrual cycle is a generally predictable pattern (Frankovich & Lebrun, 2000). Although the effect of intense training on the menstrual cycle has been extensively studied, the relationship between the menstrual cycle and physical performance is still unclear (Lebrun & Rumball, 1994).
Of the studies examining the physiological aspects of exercise performance during the menstrual cycle, many have examined the effect on maximal aerobic power (V02max) (Beidleman et al., 1999; Bemben, Salm, & Salm, 1995; Bonekat, Dombovy, & Staats, 1987; Bryner, Toffle, Ullrich, & Yeater, 1996; DeSouza, Maguire, Rubin, and Maresh, 1990; Lebrun, McKenzie, Prior, & Taunton, 1995; Pivarnik, Marichal, Spillman, & Mono, 1992; Schoene, Thomas Robertson, Pierson, & Peterson, 198 I), substrate metabolism (Bonen et al., 1983; Campbell, Angus, & Febbraio, 2001; Hackney, 1999; Hackney, McCracken-Compton, & Ainsworth, 1994; Hackney, Muoio, & Meyer, 2000; Nicklas, Hackney, & Sharp, 1989), and thermoregulation (Frye, Kamon, & Webb, 1982; Giacomoni, Bernard, Gavarry, Altare & Falgairette, 2000; Horvath & Drinkwater, 1982; Stachenfeld, Silva, & Keefe, 2000). Other research has examined the effects on muscular function (Chen & Tang, 1989), sympathetic activity (Minson, Halliwill, Young, & Joyner, 2000), and recovery fiom aerobic activity (Fukuba, Yano, Murakami, Kan, & Miwa, 2000; Matsuo, Saitoh, & Susuki, 1999). However, only four studies have examined performance in high intensity (anaerobic) activity (Giacomoni et al., 2000; Lebrun et al., 1995, Lynch & Nimmo, 1998; Sunderland & Nevill, 2003).
Many sports require highly intense, anaerobic performance. Games sports (for example, basketball, field hockey, and soccer) require bouts of high intensity interspersed with periods of low intensity. This type of performance is referred to as high intensity, intermittent activity. Also, training sessions for many sports include interval training where repeated bouts of high intensity are required. It is valuable for coaches and athletes to know the effects of the menstrual cycle on performance and recovery during high intensity, intermittent activity so that competition and training can be properly planned.
Neither of the two studies that have examined the menstrual cycle and intermittent activity (Lynch & Nirnmo, 1998; Sunderland & Nevill, 2003) have found a significant difference between menstrual phases. However, the Lynch and Nimmo (1998) used intervals of progressive intensity to exhaustion rather than maximal intensity bursts as occur in game and interval training sessions. Sunderland and Neville (2003) used intervals of maximal intensity interspersed with low intensity intervals but had only 7 normally menstruating subjects. Even if a real menstrual phase effect occurs, this subject pool may be too small to achieve statistical significance. More research is needed to determine the menstrual cycle effects on high intensity, intermittent activity.
This paper will discuss: the menstrual cycle during exercise; the nature of high intensity, intermittent work; recovery fiom high intensity intermittent work; the effect of the menstrual cycle on exercise performance; and the effect of the menstrual cycle on recovery fiom exercise.
Menstrual Cycle During Exercise
The escalation of training is associated with the alteration of circulating hormone concentration (Bonen, Ling, MacIntyre, Neil, McGrail, & Belcastro, 1979; Jurkowski, Jones, Walker, Younglai, & Sutton, 1978) and hormone metabolism (Keizer, Poortman, & Bunnik, 1980) and with menstrual irregularities (Bonen et al., 1983; Keizer et al., 1980). Common menstrual irregularities associated with exercise include delayed
menarche, shortened luteal phase, anovulation, and amenorrhea. This section will discuss the long-term and short-term effects of exercise on reproductive hormone concentrations as well as the menstrual irregularities associated with vigorous activity.
The acute effects of exercise on serum hormone levels are different than the long- term effects of exercise. There is a higher concentration of bound estradiol (Jurkowski, Jones, Walker, Younglai, & Sutton, 1978; Keizer et al., 1992; Brown, 1992; Bunt, 1990; Bunt, Bahr, & Bemben, 1987) and of testosterone (Baker et al., 1982; Shangold, Gatz, & Thysen, 1981) immediately after exercise as compared to resting levels. There is also an increase in plasma progesterone over an exercise session during the luteal phase (Bonen, Belcastro, Ling, & Simpson, 1981 ; Bonen & Keizer 1984; Keizer, Kuipers, de Haan, Beckers, & Habets, 1987) but not in the follicular phase. In contrast, training for at least one menstrual cycle seems to decrease progesterone (Ellison & Lager, 1986; Loucks, Mortola, Girton, & Yen, 1989; Ronkainen, 1985), estradial (Broocks, Pirke, & Schweiger, 1990; Consitt, Copeland, & Tremblay, 200 1 ; Ronkainen 1985), and
testosterone (Consitt et al., 2001) in both phases of the menstrual cycle. However, one study by Baker and Demers (1988) found no change in either progesterone or in estradiol. However, this study compared college athletes and sedentary college student rather than
examining the hormonal levels before and after a period of training. It is impossible to know whether the sample of group of sedentary students accurately represents the hormonal levels the athletes would have if they did not train.
Previous research has found that girls who trained pre-pubertally reached menarche later than their sedentary peers in track and field athletes (Malina, Harper, Avent, & Campbell, 1973), ballet dancers (Frisch, Wyshak, & Vincent, l98O), and college athletes (Mesaki, Sasaki, shoji, & Iwasaki, 1984). Warren (1980) also found that girls trained in ballet had later menarche than a sedentary control group and also later than a group of music students. Music students would face the same psychological stress as the ballet students but not the physiological stress. This suggests that the delayed menarche is related to the physiological stress that athletes face, not the psychological stress. Malina, Spirduso, Tate, and Baylor (1973) found that age at menarche further correlated with the level of sports activity achieved. Olympic athletes experienced later onset of menses than did high school or college athletes.
A higher prevalence of shortened luteal phases (fewer than seven days) has been found in trained athletes than in sedentary controls (Bonen et al., 1981; Boyden,
Pamenter, Stanforth, Rotkis, & Wilmore, 1983; Loucks et al, 1989). Bullen et al. (1985) used untrained subjects to examine the effects of training on menstrual cycle length during an eight week, longitudinal study. The subjects trained progressively until they were running 16 km per day, 5 days per week as well as swimming or cycling 3 % hours per day. After the eight weeks, 25% of participants developed shortened luteal phases. All luteal phases returned to normal within 3 months after the activity ceased.
Boyden et al. (1983) found that training heightens the prevalence of anovulation in adolescent swimmers. Morris and Wark (2001) found that 35% of menstrual cycles in adolescent rowers, and 75% of menstrual cycles in lightweight rowers had anovulatory cycles. In the longitudinal study of previously untrained athletes (Bullen et al., 1985), half of the subjects who developed a shortened luteal phase during training (25% of subjects) also developed anovulatory cycles.
Investigations have found an occurrence of amenorrhea of 1-50% in athletes and of 2-5% in the general population (Bonen, 1994; Feicht, Sanborn, & Martin, 1982; Frisch, Wyshak, & Vincent, 1980; Schwartz et al., 1981 ; Wakat, Sweeney, & Rogol, 1982). The variety in findings may be due to different definitions of amenorrhea. Amenorrhea has been defined variably as three months without menstruation
,
four months without menstruation, six months without menstruation, and less than one menstrual cycle in the last ten months (Loucks & Horvath, 1985). According to De Cree (1998), when studies examining of athletes and the general population are matched for operational definition of amenorrhea, amenorrhea is 20 times more prevalent in athletes than in the general population. In a longitudinal design, 16 cynomolgus monkeys were studied (Williams, Helmreich, Parfitt, Caston-Balderrama, & Cameron, 2001). Eight monkeys were trained with progressive intensity until they were running 12 kilometres a day. Eight monkeys matched for weight served as sedentary controls. Within 24 months, all eight exercising monkeys developed amenorrhea while no amenorrhea occurred in the sedentary control suggesting that increases in physical activity may be related to the incidence of amenorrhea. In three of the eight exercising monkeys, the amenorrheiccycle was preceded by an anovulatory cycle suggesting that anovulation may be a precursor to amenorrhea.
Frisch and colleagues (Frisch et al., 198 1; Frisch, Revelle, & Cook, 1973; Frisch & MacArthur, 1974) have theorized that menstrual irregularities occur below a threshold percent of body fat. The theory was developed after the observation that both ballet and distance running have participants who are lean and have high incidences of menstrual irregularities. Gray and Dale (1983) also found a significant correlation between mass, percent body mass, and the number of menstrual cycles occurring per year, suggesting that a low body mass may lead to an increased incidence of amenorrhea. However, the cause of exercise-induced menstrual irregularities is now thought to be multi-factorial (Keizer & Rogol, 1990; Prior, Vigna, Schulzer, Hall, & Bonen, 1990), including factors such as rapid weight loss (Wells, 1991), a sudden onset of strenuous training (Bonen & Keizer, 1984), inadequate nutritional intake to meet energy requirements (Laughlin, Dominguez, & Yen, 1998; Lloyd et al., 1987), and psychological or physiological stress (Arendt, 1993; Sanborn & Jankowski, 1994).
Caloric deficit has recently been examined in several studies in regards to menstrual irregularities. Studies have found that eumenorrheic athletes consume 1700- 2500 kcal per day whereas amenorrheic athletes consume 1250-2150 kcal per day (Brooks, Sanborn, Albrech, & Wagner, 1984; Deuster et al., 1986; Kaiserauer, Snyder, Steeper, & Zierath, 1989; Myerson et al., 1991; Nelson et al., 1986). However, the caloric deficit (difference between calories required and calories consumed) for amenorrheic and eumenorrheic athletes is also in the same range (500-700kcal) as amenorrheic athletes (Wilmore et al., 1992; Dueck, Manore, & Matt, 1996). In a survey
of 73 healthy females, Dale & Goldberg (1982) found that there was no significant correlation between caloric intake and menstrual status but a positive relationship between meat consumption, not protein consumption, and menstrual status.
Longitudinal studies on the effect of energy intake on the menstrual cycle have been performed on hamsters (Schweiger et al., 1987), cynomolgus monkeys (Williams et al., 2001), and humans (Loucks & Verdun, 1998; Williams et al., 1995). These studies have all produced menstrual irregularities in participants after periods of energy
deficiency. In a study of moderately trained women, an abrupt increase in training did not bring about changes in luteal hormone (LH) pulse frequency. Only when combined with nutritional deficiency did a decrease in LH pulse frequency occur (Williams et al., 1995). This implies that energy deficiency is required in addition to training to produce the change in LH pulse frequency. Although there is no effect on the amount of LH that is release with each pulse (LH pulse amplitude), the total amount of LH is still less with nutritional deficiency because of fewer LH pulses (Loucks & Verdun, 1998; Williams et al., 1995). Williams et al. (2001) found that an increase in physical activity with no increase in caloric intake produced amenorrhea in all 8 cynomolgus monkeys tested. In the four monkeys who were then given supplemental calories, the menstrual cycles were reestablished in 12 to 72 days. Exercise-induced amenorrhea seems to be related to energy deficiency.
It has been proposed that the metabolic stress created by energy deficiency stimulates the hypothalamus-pituitary-adrenal axis (Bonen, 1994), a major regulator of the endocrine system. The stimulation of the hypothalamus-pituitary-adrenal axis may cause the release of corticotrophic-releasing hormones and the down-regulation of
gonadotrophin releasing hormone (GnRH). Or, it may be cortisol which stilmulates the hypothalamus-pituitary-adrenal axis to depress the release of GnRH. GnRH controls the release of LH and of FSH. The hypothetical down-regulation of GnRH would suppress LH pulse frequency causing the disturbance of the menstrual cycle.
Despite the menstrual irregularities that are common in athletes (Bonen et al., 1983; Keizer et al., 1980), athletes seem to perform well. Gray and Dale (1983) found a negative correlation between menstrual irregularity and time per mile in runners, greater menstrual irregularity with lower time per mile. Feicht et al. (1 982) also found that amenorrheic middle-distance runners perform significantly better than eumenorrheic runners. However, the occurrence of amenorrhea was positively correlated with miles of training per week. The effect of the menstrual cycle on performance must now be determined.
High Intensity Intermittent Exercise
High intensity intermittent activity requires repeated bouts of high quality performance and rapid recovery. According to Parkhouse and McKenzie (1 984), high rate performance requires a high rate of adenosine triphosphate (ATP) synthesis, a maintenance of redox balance through the clearing of metabolites and cofactors, and adequate buffering of protons @+). This section will discuss the processes of ATP resynthesis and of metabolic recovery. Methods of measuring recovery in high intensity intermittent activity will also be discussed.
ATP Resynthesis
ATP is the direct form of energy for muscular contraction. However, ATP stores in the muscle are limited. In order to sustain power output, ATP stores must be
replenished at the rate they are depleted. ATP can be regenerated by three metabolic systems: the anaerobic alactic system, the anaerobic lactic system, and the aerobic system. In very short, intense bursts, ATP is regenerated by the phosphorylation of adenosine diphosphate (ADP) by phosphocreatine (PCr), catalyzed by creatine kinase. This procedure regenerates ATP quickly, but PCr stores are also limited. Therefore, other systems must be used to regenerate ATP. ATP and PCr stores are important for high power output for the first 10 seconds of activity (Bogdanis, Nevill, Boobis, & Lakomy, 1996).
For intervals as short as 6 seconds, half the energy is supplied by the anaerobic lactic system (Gaitanos, Williams, Boobis, & Brooks, 1993). Anaerobic glycolysis converts glucose or glycogen to lactate and produces ATP. However, during anaerobic glycolysis, ADP, inorganic phosphate (Pi), and lactic acid are formed. Lactic acid
dissociates into lactate and H+. High lactate levels are associated with decreased athletic performance (Karlsson, Bonde-Petersen, Henriksson, & Knuttgen, 1975) and fatigue (Sahlin, 1992). This inhibition of performance may be due to the accumulation of H+ in the muscle and in the blood (Hochachka & Mommsen, 1983; Roos & Boron, 1981; Sahlin, 1978) that is associated with high lactate levels (Sahlin, 1978).. The drop in pH is associated with a decreased rate of glycolysis (Roos & Boron, 1981), a decreased time to exhaustion (Fitts and Holloszy, 1976), and decreased force generation (Dawson, Gadian, & Wilkie, 1978). Possible mechanisms for this decreased performance include inhibition of enzymes regulating ATP production such as phosphofi-uctose kinase, lactate
