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Physical Fitness and Performance
Measuring Performance during the Menstrual
Cycle: A Model Using Oral Contraceptives
LEANNE M. REDMAN
1
and ROBERT P. WEATHERBY
2
1
Exercise Physiology Laboratory, Department of Physiology, University of Adelaide, Adelaide, SA, AUSTRALIA; and
2
School of Exercise Science and Sport Management, Southern Cross University, Lismore, NSW, AUSTRALIA
ABSTRACT
REDMAN, L. M., and R. P. WEATHERBY. Measuring Performance during the Menstrual Cycle: A Model Using Oral Contraceptives.
Med. Sci. Sports Exerc., Vol. 36, No. 1, pp. 130–136, 2004. Purpose: The aim of the study was to use a low-dose oral contraceptive
(OC) pill to generate consistent estrogen and progestogen concentrations and investigate the relationship between steroid hormone
concentrations during the OC cycle and anaerobic performance. Methods: Five female rowers taking a low-dose OC performed tests
of anaerobic power (10-s all-out effort) and capacity (1000-m row) on the Concept IIC rowing ergometer at two time points in each
of three OC cycles. These time points corresponded to high estrogen and high progestogen (pill day 16–18; TDH) and low estrogen
and low progestogen (pill day 26-28; TDL). Blood samples were collected at rest and postexercise for the quantification of 17

-estradiol
(E
2
), progesterone (P
4
), glucose, triglyceride, and lactate concentrations. Results: Endogenous E
2
and P
4
concentrations were not
significantly different between testing days or OC cycles (P⬎0.05). Peak power output was higher (P⬍0.05) and 1000-m rowing
ergometer time faster (P⬍0.05) at TDL. Pre- and postexercise glucose concentrations were increased (P⬍0.05) at TDL, whereas
rest and postexercise plasma triglyceride concentrations were significantly (P⬍0.05) lower during this time. Conclusions: This study
found that alterations in anaerobic performance throughout the OC cycle occurred with improved performances corresponding to low
estrogen and progestogen concentrations. The OC provided a consistent hormonal milieu reducing inter- and intra-individual variations
in sex steroids and standardized all performance and metabolic variables across each OC cycle tested. Given that OC use has a high
prevalence among female athletes and provides a controlled hormonal environment, it serves as a good model in which the acute effects
of female sex steroids on exercise performance can be studied. Key Words: ESTRADIOL, PROGESTERONE, METABOLISM,
ANAEROBIC PERFORMANCE, ROWING
Although the potential impact of the menstrual cycle
phase on aerobic performance has been the focus of
several investigations (2,12,19), the potential effect
of the menstrual cycle on anaerobic performance has re-
ceived little attention. There is no consensus on whether
there is a relationship between hormone changes during the
menstrual cycle and the level of anaerobic performance.
Some studies have concluded that anaerobic performance is
unaffected by cycle phase (10,11,23,26,31), whereas others
have reported menstrual cycle phase differences in anaero-
bic performances (5,9,28,34). Both Brooks-Gunn et al. (5)
and Davies and coworkers (9) found performance to be
improved during menstruation, whereas an earlier study (34)
found performance worse at this time point.
The lack of consensus may in part be due to a lack of
adequate experimental controls and the wide variation in the
types of methods used to determine the phase of the men-
strual cycle (e.g., body temperature vs hormonal assay) and
the timing of the exercise tests (e.g., menstruation vs early
and/or mid-follicular phase vs ovulation vs mid and/or late
luteal phase (LP)) during the menstrual cycle. The wide
inter- and intra-individual variation in estradiol (E
2
) and
progesterone (P
4
) concentrations within the natural men-
strual cycle and varying lengths of the menstrual cycle
between individuals make valid interpretations of previous
investigations difficult. In addition, the subject selection
criteria in some studies were not clearly defined (with regard
to age, menstrual cycle history, fitness status, menstrual
cycle length, and gynecological problems), and there has
often been limited standardization of preexercise status in-
cluding controlled dietary intakes and activity levels.
Estrogens and progestogens are known to influence sev-
eral physiological processes such as regulation of energy
metabolism (21), body water (14,33), respiration (25), and
temperature (32) throughout the course of a menstrual cycle.
Short duration, high intensity exercise, which is dependent
Address for correspondence: Leanne M. Redman, Department of Biolog-
ical Sciences, Ohio University, Athens, OH 45701-2979; E-mail:
redman@ohio.edu.
Submitted for publication January 2003.
Accepted for publication September 2003.
0195-9131/04/3601-0130
MEDICINE & SCIENCE IN SPORTS & EXERCISE
®
Copyright © 2004 by the American College of Sports Medicine
DOI: 10.1249/01.MSS.0000106181.52102.99
130
on intramuscular stores of ATP, CP, and glycogen, and the
simultaneous production of lactate could potentially be in-
fluenced by the level of ovarian steroid hormones. Estradiol
has been shown to increase the relative contribution of fat
metabolism during the LP of the menstrual cycle
(4,7,18,23,35) and could therefore by limiting carbohydrate
metabolism cause a restriction of anaerobic metabolism.
However, it could also be postulated that the increased
glycogen storage recorded in response to exogenous estro-
gens (21) and during the LP of the menstrual cycle (when
the levels of estradiol are high) (16,17) could result in
increased substrate availability enhancing the anaerobic pro-
duction of ATP and thereby increasing anaerobic perfor-
mance. Additionally, given the antagonistic relationship of
progesterone to aldosterone at the aldosterone receptor (33),
and that falling levels of progesterone on transition from the
luteal to follicular phases results in fluid and electrolyte
retention (14), one could expect an improvement in buffer-
ing capacity and a greater capacity for anaerobic perfor-
mance at this time point.
Oral contraceptives (OC) suppress normal menstrual cy-
cle levels of E
2
and P
4
by inhibiting the pituitary secretion
of gonadotropins (FSH and LH) (30) and provide consistent
pharmacological control of the reproductive cycle by sys-
tematically controlling concentrations of endogenous sex
hormones. Thus, the inter- and intra-individual variations in
circulating endogenous sex hormone concentrations typical
within the menstrual cycle of the non-OC user can be
limited. A multi-phasic OC pill contains a changing dosage
of both an estrogen and progestogen throughout three
phases of the OC cycle. This reliable pattern of administra-
tion begins with 21-d “active”steroid administration fol-
lowed by 7-d nonsteroid administration in which a placebo
is given (Fig. 1). Given that endogenous production of E
2
and P
4
is suppressed during OC usage, the serum concen-
tration of active sex steroids are directly related to the OC
dosage administered (13).
Despite the wide incidence of OC pill use in the community
since its development in the 1950s, reports in the early 1980s
indicated that OC pill use was not as predominant among
athletic females (20). However, since then, with the introduc-
tion of the lower-dose preparations, it is estimated that OC pill
use in female athletes is more widespread and matches the
prevalence of OC use within the general community (29).
There is a growing body of evidence in support of the
notion that aerobic capacity is impaired by OC pill use
(8,23,27), which has not be explained by changes in stroke
volume, muscle blood flow, or hemoglobin levels but could
be due to blunting of the sympathetic nervous system by the
high ovarian hormone concentrations characteristic of OC
use (8). It is interesting, given these findings, that few
studies have sought to determine the impact of the OCP on
anaerobic performance.
To better understand the relationship between the men-
strual cycle and anaerobic performance, this study used a
low-dose OC pill to pharmacologically generate consis-
tently low and high circulating equivalent E
2
and P
4
con-
centrations. It was hypothesized that anaerobic performance
would be altered in cyclic patterns throughout the OC cycle
with the best performances observed when the level of
exogenous hormone administration was low and these levels
of female sex steroids might facilitate carbohydrate metab-
olism and improve buffering capacity.
METHODS
Approach to the problem and experimental de-
sign. Research concerned with examining the impact of
steroid hormones on exercise performance has been com-
plicated by wide inter- and intra-individual variations of
endogenous estrogen and progesterone concentrations
within the natural course of the human menstrual cycle.
Further, inconsistent menstrual cycle lengths make the ac-
curate determination and validation of exercise testing days
between subjects almost impossible. Triphasic OC are com-
bined estrogen-progestogen preparations whereby the re-
gime consists of three phases, each with a different proges-
togen dose and some with increased estrogen in the second
phase. Triphasic OC closely mimic the endogenous or nat-
ural menstrual cycle given the regular changes in hormone
concentrations. Because the OC pill regains control over the
hypothalamic-pituitary-ovarian axis and the amount of the
“active”circulating sex steroids are related to the daily
dosage administered (13), the triphasic OC pill would be a
reliable experimental model to use in these studies where the
aim is to assess the impact of female sex steroids on per-
formance outcomes.
The aim of this study was to use a triphasic OC pill to
pharmacologically generate consistently low and high levels of
estrogens and progestogens to study the impact of low and high
ovarian steroid concentrations on anaerobic performance. To
assess the efficacy of the OC as the model for this research,
anaerobic performances were assessed at two hormonally dif-
ferent time points in each of three consecutive OC pill cycles.
The independent variables for this study were level of exoge-
FIGURE 1—Pattern of estrogen and progestogen administration for
Triphasil-28 or equivalent showing test days TDH and TDL. Proges-
togen refers to the levonorgestrel dosage (
g) and estrogen to the
ethinyl estradiol dosage (
g) of the triphasic preparation taken by
subjects in the study.
ORAL CONTRACEPTIVES AND ANAEROBIC PERFORMANCE Medicine & Science in Sports & Exercise姞
131
nous hormone concentration (high E and high P vs low E and
low P) and OC pill cycle (cycle 1, cycle 2, and cycle 3),
whereas the dependent variables were anaerobic performance
(power and capacity) and biochemical indicators of metabo-
lism (glucose, triglycerides, and lactate).
Subjects. Elite and sub-elite female rowers (18–25 yr)
were invited to participate in this study; all had a V
˙O
2max
⬎
50 mL·kg
⫺1
·min
⫺1
and were currently competing at an
Australian national or state level, and had done so for the
previous 2–6 yr. All subjects were in the same rowing squad
and were completing a preparatory-training phase at the
time of the study that involved six to eight rowing sessions
(100–150 km) per week as well as five to six additional
sessions of cross-training (e.g., weights and cycling). Sub-
jects were required to have a gynecological age greater than
3 yr and to have been taking a low-dose OC pill continu-
ously throughout the past 12 months. Twelve potential par-
ticipants completed a subject selection questionnaire that
assessed gynecological health, general health, and OC his-
tory, and six women taking Triphasil-28 or equivalent (hor-
monally similar to 50- to 125-
g levonorgestrel and 30- to
40-
g ethinylestradiol) were chosen to participate in the
study. Subjects did not smoke, were free from illness and/or
medication, dietary interventions, and menstrual abnormal-
ities. Physical characteristics of the subject group are dis-
played in Table 1. Before the commencement of the study,
one subject was excluded due to illness and a subsequent
antibiotic that presented potential contraindications to exer-
cise testing.
Subjects (N⫽5) were required to continue taking the OC
pill at the same time each day as specified for OC usage. The
number of hours from pill ingestion to the exercise test was
estimated to be between 2 and 8 h but was constant for each
subject. Subjects were informed of the nature of the study,
testing protocols, possible risks, or discomforts and signed a
written informed consent. The Human Research Ethics Com-
mittee of Southern Cross University approved the study.
Experimental overview. All subjects completed a test
of anaerobic power (10-s all-out effort) and anaerobic ca-
pacity (1000-m row) at two different time points throughout
the OC cycle. These time points corresponded to a day of
low estrogen and low progestogen and a day of high estro-
gen and high progestogen. All performance tests were con-
ducted on a rowing ergometer (Concept II Inc., Morrisville,
VT) and were repeated for three consecutive OC cycles.
Blood samples were collected at rest and postexercise for
the quantification of glucose, triglyceride, and lactate
concentrations.
Determination of testing days. Exercise tests were
conducted at two hormonally different days during the OC
cycle, and test days were chosen based on daily hormone
dosages within the low-dose triphasic OC administration
(Fig. 1). A day of high estrogen and high progestogen
(TDH), pill days 16–18 and a day of low estrogen and low
progestogen applicable to pill days 26–28 (TDL) were used.
Exercise testing took place between 0800 and 1600 h on pill
days 16 ⫾1 (TDH) and 26 ⫾0 (TDL) and time of day for
each testing session was kept constant for each subject.
Testing commenced at either TDH or TDL, depending on
when the subject was recruited into the study and three
subjects first commenced testing during TDH while two
began at TDL.
Preexercise controls. On the day of testing, subjects
reported to the laboratory following a 4-h fast (water only)
having abstained from alcohol, caffeine, and strenuous
physical activity for the previous 24 h. Subjects were re-
quired to keep a daily record of menstrual cycle symptom-
atology and physical activity profiles. A menstrual cycle
diary was used to assess individual perception and presence
of common menstrual cycle symptomatology such as men-
strual bleeding, bloatedness/fluid retention, breast tender-
ness, headache, backache, and tiredness and to confirm OC
compliance throughout the study. There were no reports of
missed OC pills throughout the study, and subjects reported
taking the pill at the same time each day (⫾1.5 h). Daily
physical activity was monitored using the training diary
adapted from the Queensland Academy of Sport Perfor-
mance Enhancement Center to assess physical activity,
training volume, and intensity throughout the study and
specifically in the 48 h before each experimental session.
Preexercise dietary intakes were recorded 48 h before the
first testing session. This diet was replicated in the 48 h
preceding each subsequent testing session and was analyzed
for compositions of carbohydrate, fat, and protein and total
energy intake using SERVE Nutritional Management Sys-
tem for Windows (M. H. Williams Pty. Ltd, 1995).
Anaerobic performance tests. On the subjects’ ar-
rival at the laboratory, the menstrual cycle diary, training
diary, and dietary logs were collected. Anthropometric mea-
sures including body mass (Wedderburn Precision Scales,
Australia) and skinfold thickness at nine sites: bicep, tricep,
subscapular, mid-axilla, abdominal, supraspinale, su-
prailiac, anterior thigh, and medial calf (Harpenden Skinfold
Caliper, British Indicators Ltd.) were recorded. After 5 min
of seated rest, subjects’ blood samples were drawn for
analysis of basal sex hormone concentrations (17

-estradiol
and progesterone) and metabolite (plasma glucose, triglyc-
eride and lactate) concentrations.
The two assigned anaerobic protocols were chosen for its
sports specificity in these athletes and were designed to
mimic different components of a 2000-m rowing event, a
standard race distance at Australian and International Row-
ing Regattas. The 10-s all-out row replicates the explosive
power executed by these athletes at the onset of a race,
whereas the 1000 m was chosen to assimilate the standard
2000-m race distance. To avoid the likelihood of improved
TABLE 1. Physical characteristics and demographic data of the subject group (N ⫽5).
Characteristic
Mean ⴞ
SD
Chronological age (yr) 20.0 ⫾1.9
Height (cm) 174.5 ⫾5.3
Body mass (kg) 69.6 ⫾4.3
Body mass index (kg䡠m
⫺2
) 22.9 ⫾1.6
Gynaecological age (yr) 5.2 ⫾2.3
Oral contraceptive use (yr) 2.6 ⫾1.3
Competitive rowing
experience
4.6 ⫾1.9
132
Official Journal of the American College of Sports Medicine http://www.acsm-msse.org
performances with learning, all subjects were familiarized
with both exercise protocols before the commencement of
the study and the order of testing, that is, TDL followed by
TDH was completed in two subjects whereas TDH followed
by TDL was completed in three subjects.
The test retest reliability between trials at TDH was
determined by the coefficient of variation (CV). The CV for
the peak power test was 2.2% and the likely range 1.3–6.4
(%), and the CV for the 1000-m row was 1.5% which ranged
between 0.9 and 4.3 (%).
All exercise tests were performed on the Concept IIC
rowing ergometer. After 10 min of seated rest, subjects
completed a 10-s all-out row. Subjects were seated on the
ergometer, and feet were secured to the foot stretcher. After
two to three familiarization strokes and a 3-s countdown,
subjects were required to exert maximal effort for 10 s or
until peak power (W) was attained and performance (power
output) declined. Power output (W) was recorded each
stroke with the highest power output defined as the peak
value.
After 10 min of rest, subjects were seated on the rowing
ergometer and completed a 1000-m simulated row (anaer-
obic capacity test). Once the breathing apparatus and mouth-
piece were fitted and feet were secured in the foot stretcher,
subjects performed a few light strokes to ensure the comfort
of the breathing equipment. The nose-clip was attached and
the subject took hold of the ergometer handle in preparation
for the start of the exercise and remained stationary for 1
min while resting data were collected. Throughout the
1000-m ergometer test open spirometry techniques were
used to measure V
˙O
2
,V
˙CO
2
, and V
˙E (unreported data)
(MedGraphics CPX/D
TM
gas analysis system, MedGraphics
Corp. Minneapolis, MN). Heart rate was monitored contin-
uously using a Polar electro sports tester unit (Kempele,
Finland). Heart rate, stroke rate, and time (s) were recorded
at each 100-m interval. Blood samples were drawn at rest
and at several intervals postexercise (1.25, 2.5, 5, 7.5, and
10 min) for blood lactate measurements. At 5 min postex-
ercise, a venous blood sample was extracted for a postex-
ercise analysis of glucose and triglyceride concentrations.
Blood sampling. Before exercise venous blood sam-
ples were collected via a venipuncture of an antecubital vein
(Venoject 21G ⫻1.5 needle, Terumo Corporation, Bel-
gium) for evaluation of plasma 17

-estradiol, progesterone,
glucose, and triglyceride and immediately postexercise for
plasma glucose and triglyceride. Blood lactate concentration
was determined from capillary blood samples collected
from an arterialized earlobe (Finalgon
®
, Boehringer Mann-
heim) at rest and postexercise.
Hormone and metabolic analyses. Basal 17

-estra-
diol and progesterone concentrations were measured from a
5-mL venous blood sample collected in a plain-coated sil-
icon tube. The sample was refrigerated (4°C) until the
completion of the exercise session (1 h) when it was imme-
diately taken to the Chemical Pathology Department at the
Brisbane Mater Hospital for analysis. Hormones were ana-
lyzed by an automated immunoassay system (AIA-1200
TOSOH Medics Inc.) using commercially available immu-
noassay kits that have been validated for measurement in
human serum (TOSOH Medics Inc.). The intra- and inter-
assay coefficients of variation (CV) for estradiol ranged
from 2.25 to 7.17% and 2.9 to 9.8%, respectively, and
progesterone ranged from 6.5 to 9.2% and 4.5 to 9.1%,
respectively (TOSOH Medics Inc.). Pre- and postexercise
plasma glucose and triglyceride concentrations were deter-
mined from 4 mL of venous blood. The samples were
collected in lithium heparin-coated tubes, immediately cen-
trifuged, and the plasma stored at ⫺18°C until the analysis
was conducted (approximately 4 wk). Blood glucose and
triglyceride concentrations were analyzed using the Kodak
Ektachem DT60 model (Eastman Kodak Company) and DT
Vitros slides for glucose and triglycerides (Johnson & John-
son Clinical Diagnostics). Fifty microliters of capillary
blood was collected into a heparinized capillary tube and the
blood lactate concentrations analyzed using the YSI2700
Lactate Analyzer (Yellow Springs Instruments).
Statistical analysis. Data are reported as mean ⫾
SEM. All data were subject to descriptive statistics and
repeated measures analysis of variance (RMANOVA) using
SPSS for Windows version 8.0. A two-factor RMANOVA
(cycle, test day, cycle ⫻test day) were used to compare
hormonal and performance responses over time. Three-
factor RMANOVA (cycle, test day, pre/post, cycle ⫻test
day ⫻pre/post) were used to compare metabolic variables
pre- and postexercise and between testing days over time.
Significance was assumed when
␣
ⱕ0.05. The relationship
between test and retest was determined using the coefficient
of variation on the log transformation of raw data.
RESULTS
Longitudinal monitoring. There were slight variations
in body mass noted throughout the study; however, there
were no differences between cycle phase (TDH: 70.2 ⫾1.8
kg, TDL: 70.3 ⫾1.8 kg; P⫽0.4). Skinfold thickness (sum
of nine sites) was not significantly different between testing
days (TDH: 155.1 ⫾11.4 mm; TDL: 158.9 ⫾12.6 mm; P
⫽0.091) or across the three OC cycles (P⫽0.428). Train-
ing diaries confirmed that preexperimental training status
was consistent throughout the study. There was no signifi-
cant difference in preexperimental training distance rowed
between testing days (TDH: 17.3 ⫾0.9 km; TDL: 17.1 ⫾
0.8 km; P⫽0.869) or training time (TDH: 78.3 ⫾5.0 min;
TDL: 76.6 ⫾5.8 min; P⫽0.823).
The presence and severity of menstrual symptoms varied
considerably throughout the OC cycle. The highest preva-
lence of symptoms was reported from days 21–28 corre-
sponding to menstrual bleeding and the placebo pill. The
common symptoms reported at TDL were menstrual bleed-
ing, abdominal pain, and bloatedness, whereas headache and
tiredness were the most frequently reported symptoms at
TDH. Given the large interindividual variation in perception
of menstrual cycle symptoms, statistical analysis was not
carried out on these data.
Endogenous hormonal profile. Endogenous 17

-
estradiol and progesterone concentrations were not signifi-
ORAL CONTRACEPTIVES AND ANAEROBIC PERFORMANCE Medicine & Science in Sports & Exercise姞
133
cantly different between testing days (17

-estradiol: TDH,
60.3 ⫾10.1 pmol·L
⫺1
; TDL, 60.5 ⫾7.6 pmol·L
⫺1
;P⫽
0.99; progesterone: TDH, 1.10 ⫾0.21 nmol·L
⫺1
; TDL, 0.37
⫾0.14 nmol·L
⫺1
;P⫽0.20) or across the three OC pill
cycles tested.
Biochemical responses. A summary of the pre- and
postexercise blood chemistry at TDH and TDL are included
in Table 2. With TDL, the pre- and postexercise plasma
glucose concentrations were found to be significantly higher
(P⬍0.01), 37% and 8%, respectively, than during TDH.
The triglyceride concentrations increased in response to
exercise at both hormonal situations (Table 2, P⬍0.01).
The pre- and postexercise triglyceride concentrations at
TDH were significantly greater than (P⬍0.01) triglyceride
concentrations at TDL (31% and 8%, respectively). No
significant difference in triglyceride concentrations at TDH
and TDL between the OC cycles was shown (P⫽0.57).
Blood lactate concentrations at TDH and TDL are dis-
played in Table 2. Although blood lactate concentrations
significantly increased in response to anaerobic exercise
(P⫽0.00) at both time points, there was no significant
difference in concentrations between TDH and TDL
(P⫽0.16) or between OC cycles (P⫽0.45).
Anaerobic performance. The relationship between
peak power and hormone status is illustrated in Figure 2.
The average peak power was greater at TDL (448.73 ⫾5.80
W) compared with TDH (433.07 ⫾5.28 W). The
RMANOVA revealed a significant difference in peak power
scores between TDL and TDH (P⬍0.05), and results were
consistent across all OC cycles. During each OC pill cycle
tested the 1000-m simulated row times (Fig. 3) were faster
(P⬍0.05) at TDL (226.5 ⫾1.3 s) than TDH (230.6 ⫾
1.4 s).
DISCUSSION
This study found that OC administration consistently
suppressed circulating endogenous sex steroid hormone
concentrations in OC users to clinical deficiency levels (30).
The OC synthetically generated high or low hormone envi-
ronments similar to the normal menstrual cycle to enable
performance changes during the menstrual cycle to be stud-
ied, and therefore the only effects seen were from the
administration of the OC hormones.
Anaerobic performance was not constant during the
triphasic OC cycle with improved performances noted at
TDL (pill days 26–28) in each of the three OC cycles tested.
Increased performances during this time point were associ-
ated with significantly lower rest and postexercise triglyc-
eride concentrations, higher glucose concentrations, and a
tendency toward lower lactate concentrations after exercise
compared with TDH (pill days 16–18).
These results indicate that, provided the OC is taken as
directed, it could be used as an experimental model creating a
more controlled environment for this area of study. Orally
administered sex steroids act to indirectly reduce the natural
production of estrogens and progestogens allowing the men-
strual cycle to be manipulated by daily exogenous hormone
concentrations. This “synthetic”menstrual cycle as shown in
this study is less susceptible to inter- and intra-individual vari-
ations in basal hormone levels and menstrual cycle lengths.
The OC pill, therefore, represents an ideal research tool for
investigating daily acute ovarian steroid hormone changes and
their effect on performance. Decreased inter- and intra-indi-
FIGURE 2—Effect of high and low estrogen and progestogen concen-
trations on peak power output. Values are mean ⴞSEM. * Signifi-
cantly different from TDH (P<0.05).
FIGURE 3—Effect of high and low estrogen and progestogen concen-
trations on a 1000-m rowing time trial. Values are mean ⴞSEM.
* Significantly different from TDH (P<0.05).
TABLE 2. Pre- and postexercise biochemical assessment at TDH and TDL.
Variable TDH TDL
Glucose (mmol䡠L
⫺1
)
Pre 4.78 ⫾0.19 5.97 ⫾0.13*
Post 6.66 ⫾0.24† 7.25 ⫾0.14*†
Triglycerides (mmol䡠L
⫺1
)
Pre 1.26 ⫾0.05 0.87 ⫾0.02*
Post 1.55 ⫾0.08† 1.41 ⫾0.04*†
Blood lactate (mmol䡠L
⫺1
)
Pre 0.63 ⫾0.01 0.83 ⫾0.02
Post 13.14 ⫾0.46† 11.65 ⫾0.34†
Values are mean ⫾SEM.
* Statistical difference between concentrations at TDH and TDL.
† Statistical significance between pre- and postexercise concentrations (P
⬍0.05).
134
Official Journal of the American College of Sports Medicine http://www.acsm-msse.org
vidual variation in cycle length and endogenous hormone con-
centrations allows more accurate, reliable, and repeatable test-
ing sessions to be used. The OC therefore could be used to
rectify these common inconsistencies and limitations identified
by previous investigations (14,23,24).
There is no consensus in the literature whether anaerobic
performance is affected by changes in sex steroid concen-
trations typical throughout the normal menstrual cycle and
the synthetic menstrual cycle of the OC user. Results of the
current investigation found that both anaerobic power and
anaerobic capacity were increased at TDL, whereas circu-
lating concentrations of ethinyl estradiol and levonorgestrel
(E
2
and P
4
equivalents) are low.
Four earlier studies have reported menstrual cycle phase
differences in anaerobic performance. Consistent with the
findings of the current investigation are three studies
(5,9,34) that report improved anaerobic performances dur-
ing menstruation, menstrual phase or early follicular phase
(FP), time points consistent with TDL in the current inves-
tigation. Specifically, Brooks-Gunn et al. (5) compared
swimming (100-yard freestyle performance and 100-yard
preferred stroke) performances in six young adolescent
swimmers during menstruation, and mid-follicular and pre-
menstruation phases. Regardless of stroke, performance
times were fastest during the menstruation phase (during
menstrual flow), whereas the slowest performances were
associated with the premenstrual phase (4 d before onset of
menses). In contrast, one group (28) demonstrated higher
peak and mean power output during the mid-FP (days 7–9)
compared with the mid-luteal (days 13–17) and menstrua-
tion (days 1–2) phases in a modified Wingate protocol. In
addition, several studies (10,11,15,23,26,31) involving nor-
mally menstruating women have demonstrated no cycle
phase differences in anaerobic performance.
To our knowledge, only two studies (10,15) have inves-
tigated changes in anaerobic performance during an OC
cycle. Both studies found no differences in either anaerobic
endurance (10) or anaerobic power (15) throughout the OC
cycle or in comparison with normal menstrual cycle con-
trols. These earlier studies, however, investigated perfor-
mance changes throughout a single OC cycle unlike the
current investigation where performance changes through-
out three consecutive OC cycles were studied.
Most of the inconsistencies between studies are likely to
be the result of varied methods for determining menstrual
cycle phase, definition of different menstrual cycle phases,
and hence the choice of exercise testing days. In addition,
the sample sizes are small and have only measured perfor-
mance changes during a single menstrual or OC cycle.
Enhanced anaerobic performance in this study could be
the result of the secondary cellular effects of E
2
and P
4
equivalents on substrate utilization and buffering capacity.
High concentrations of E
2
and P
4
typical during the LP have
been reported to elicit a sparing of glycogen (4,6,23) both at
rest and during exercise with the concurrent inhibition of
gluconeogenesis and glycogenolysis (6,18). Thus, the de-
crease in plasma glucose and increase in plasma triglyceride
concentrations observed under high E
2
and P
4
equivalent
concentrations (TDH) could be due in part to a reduction in
glucose formation and increased storage of glycogen in the
liver and muscle tissues (1) and hence favored lipid metab-
olism. Lipid oxidation and utilization rates are reported to be
increased during the LP in comparison with the follicular
phase (15,16,18). Therefore, improved performance at TDH
when sex steroid concentrations are high could therefore
restrict carbohydrate metabolism and the availability of glu-
cose as substrate for the production of ATP. There is no
evidence in the literature to suggest that muscle phosphate
stores (ATP and CP) and utilization during exercise is
affected by menstrual cycle phase.
Enhanced anaerobic performance at TDL could also be
attributed to the secondary effects of progesterone on buff-
ering capacity. Progesterone acts as a competitive antagonist
at the aldosterone receptor site in the distal tubule of the
kidney (22,33). During the LP, high concentrations of pro-
gesterone result in water and electrolyte loss that stimulates
a concurrent increase in aldosterone concentration during
this phase. Therefore, the rapid reduction of circulating
progesterone concentrations on transition from the luteal to
FP results in excess aldosterone concentrations leading to
the commonly observed premenstrual increase in water and
electrolyte retention (14) during the normal menstrual cycle.
Fluid retention or bloatedness is also a common side effect
during OC usage (24) and was reported at TDL by subjects
in this study. Increased water and electrolyte stores have
been associated with improved plasma volume maintenance
(14), which could potentially promote improved buffering
capacity and cellular alkalosis. Improved buffering capacity,
thought to be a determinant of muscular fatigue, could
enhance anaerobic capabilities during the late LP and early
FP of the normal menstrual cycle and at TDL of the artificial
cycle created by the OC.
This study provided evidence that a triphasic OC pill
could alter anaerobic performances in female athletes. In
this study, rowing performances were improved at TDL,
that is, during the ingestion of the placebo or inert OC pill.
Although both anaerobic power and capacity were signifi-
cantly increased at TDL, the most significant finding lies
with a 3-s improvement in the 1000-m row time trial. Given
that 2000 m is the national and international distance for
most rowing events, this performance outcome could trans-
late to a 3- to 5-s difference in rowing performance at
different times of the OC cycle and the difference between
first and eighth place in a National or International final.
Given that OC pills are already being used by athletes to
manipulate the timing of menstrual bleeding in relation to
competition (3), the OC could be used by female athletes
engaged in anaerobic activities to ensure that the hormonal
milieu on the day of competition would foster an improve-
ment in performance and, in this case, would in some cases
correspond with menstrual bleeding.
In summary, this study found that anaerobic performance
is altered in cyclic patterns throughout the OC cycle with the
greatest performances observed under conditions of low E
2
and P
4
equivalents. Enhanced anaerobic performance could
be the result of the secondary cellular effects of sex steroids
ORAL CONTRACEPTIVES AND ANAEROBIC PERFORMANCE Medicine & Science in Sports & Exercise姞
135
on substrate choice and kidney function. The OC standard-
ized all performance and metabolic variables across each
OC cycle, shown by the lack of significant differences in
measured variables observed between OC cycles. Orally
administered sex steroids act to indirectly reduce the natural
production of estrogens and progestogens, allowing the
menstrual cycle to be manipulated by daily exogenous hor-
mone concentrations. The ability of the low-dose OC pill to
control the natural fluctuations in endogenous hormone con-
centration allows testing days to be more accurately pre-
dicted and decreases the inter- and intra-individual variabil-
ity of endogenous hormone concentrations within and
between menstrual cycles, providing more homogenous
subject group conditions. Provided the OC pill is taken as
directed, it will provide a consistent hormonal milieu from
cycle to cycle, therefore creating a more controlled envi-
ronment in which the acute effects of female sex steroids on
exercise performance can be studied.
The use of the Queensland Academy of Sport’s Performance
Enhancing Laboratory for the exercise tests and the assistance of
their staff are gratefully acknowledged.
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