The
Pill may be the most effective contraceptive and the
best way to manipulate your cycle for important
events, but are you aware of its physiological
effects and their impact on performance?
By
Andrew Harrison
for peak
performance
The
oral contraceptive pill (OCP) is the form of
contraception most widely used by women in general
and sportswomen in particular. Undoubtedly, the main
reason for its popularity with both groups is its
high effectiveness in preventing pregnancy.
Female
athletes may also choose the Pill on the basis of
other perceived benefits, including bone health, the
ability to manipulate the menstrual cycle and
control of premenstrual symptoms.
However,
the impact of the Pill goes further than that, and
the purpose of this article is to make sportswomen
and their coaches fully aware of its physiological
effects, both positive and negative, and their
impact on performance and health?
An
OCP is made up of hormones which can be combined in
four different ways, defined by the ratio of
oestrogen to progesterone:
-
The
monophasic pill has a low oestrogen content and
the dose of both hormones remains constant
throughout the cycle, allowing for easy
manipulation of cycles when competing and
travelling;
-
The
triphasic pill provides three different dosages
of hormones during the cycle. Because it
contains less total progesterone (and therefore
a lower overall dose of hormones) than the
monophasic pill, it is thought to mimic the
‘natural’ cycle more closely than other
types of OCP. It is recommended for women who
experience side effects, such as weight gain,
when using the monophasic pill. However, the
varying dosages employed throughout the cycle
make cycle manipulation more difficult;
-
The
biphasic pill maintains a constant oestrogen
dose throughout the cycle, with a change in
progesterone mid-cycle. It offers no particular
advantage over the other two preparations and is
not often prescribed;
-
The
‘minipill’ contains progesterone only and is
recommended for new mothers and those who are
sensitive to the oestrogen component of other
pills. Its main drawback is that it has a higher
failure rate than the other formulations.
The
manner and extent to which these combinations affect
athletic performance is far from clear. Some
investigators have reported reductions in VO2max
associated with the use of the OCP.
A
recent Canadian trial, involving 14 female athletes
with average VO2max values of over 50 ml/kg/min,
demonstrated a mean reduction in aerobic capacity of
4.7% following two months of OCP usage.
Similarly,
another research group reported a 5% reduction in
VO2max in a group of élite subjects after two
months on OCPs. Other performance variables
measured, including maximum heart rate and endurance
at 90% VO2max, were not affected by OCP usage. And
both sets of researchers concluded that the observed
reductions in VO2max were reversible following
cessation of medication, typically within 4-6 weeks.
However,
other researchers have observed no negative impact
of the OCP on performance. One recent study found no
differences in exercsie performance between an OCP
and control group despite differences in blood
lactate and temperature. In another, a low-dose OCP
taken over a single cycle was found to have no
effect on breathing rate, VO2max during a treadmill
assessment, or an endurance running test. These
findings have been echoed by numerous other studies
investigating the effect of the OCP on aerobic and
anaerobic variables.
Even
if the OCP does lead to a slight drop in VO2max, it
is unclear whether this would translate to a
fall-off in performance. And against this
possibility should be balanced the known
supplementary benefits of the OCP. For example, a
reduction in pre-menstrual symptoms, which is a
confirmed effect of OCP usage, might well outweigh a
slight drop in VO2max during training or
competition.
Another
benefit of OCPs is that they reduce menstrual blood
loss by up to 50%, so also reducing the risk of iron
deficiency anaemia posed by heavy menstrual loss
combined with inadequate dietary iron intake.
Increased stroke volume, blood volume and cardiac
output have also been reported with OCP usage,
potentially increasing oxygen delivery to the
muscles.
How
the Pill impacts on body weight and muscle strength
The
issue of weight gain is of great concern to athletes
and often of even greater concern to their coaches.
This is particularly the case in power:weight
ratio-dependent sports such as distance running,
light weight rowing and gymnastics.
Individual
responses to the hormones in the OCP may include
some weight gain as a result of either fluid
retention or, possibly, appetite stimulation.
Nevertheless, contrary to popular belief, most
population studies indicate no overall effect on
body weight while taking the OCP. This is
particularly the case with the newer low-dose pills.
Few
studies have investigated the effects of OCP on
muscle strength in female athletes, and those which
have been carried out have found no significant
differences in the strength of various muscle groups
with OCP usage. Fluctuations in muscle strength have
been noted during a normal menstrual cycle, and
these appear to relate to changes in levels of
oestradiol, the major female sex hormone produced by
the ovaries. Increased strength has been reported
late in the follicular (pre-ovulatory) phase of the
cycle, corresponding to increases in oestradiol
before ovulation, with reduced strength reported in
the luteal (pre-menstrual) phase, possibly due to
increases in deep muscle tissue.
The
point about OCP usage is that it appears to
eliminate these natural fluctuations in muscle
strength.
Adverse
effects on risk factors for cardiovascular disease
have been highlighted with higher dose OCPs.
However, researchers have hypothesised that exercsie
itself may counteract these potentially negative
effects.
Substrate
utilisation during exercsie has also been studied in
relation to the Pill. In one study, a group of women
on OCPs was shown to have lower blood glucose levels
and lower carbohydrate usage during prolonged
submaximal exercise than a control group. Another
trial documented an increase in free fatty acids
with exercise in association with these lower blood
glucose levels. This trial also found an increase in
the growth hormone response to exercise, possibly as
a result of direct stimulation by the oestrogen
component of the Pill.
Such
findings suggest that the OCP may facilitate
carbohydrate sparing during prolonged exercise, thus
delaying time to exhaustion. An alternative
interpretation, however, is that the increase in
free fatty acid utilisation is a compensatory
response to a decreased glucose release, suggesting
that, even with increased free fatty acid
availability, endurance performance might be
negatively affected.
In
summary, the pros and cons of OCP use for female
athletes and sportswomen may be set out as follows,
with the benefits appearing to outweigh the costs:
Advantages
-
Highly
effective, convenient and reversible;
-
Provides
a source of oestrogen for athletes without
periods, decreasing their risk of stress fractures
and osteoporosis;
-
May
decrease menstrual blood loss, which reduces the
risk of iron-deficiency anaemia;
-
Reduces
painful period cramps;
-
May
decrease premenstrual symptoms (eg mood swings,
nausea, headaches) which could have a negative
impact on training and competition;
-
Can
be used to manipulate the menstrual cycle for
important events and travel;
-
Associated
with a decreased risk of cancers of the ovary and
uterus;
-
No
known long-term effect on fertility.
Disadvantages
-
Possibility
of breakthrough bleeding, fluid retention, weight
gain, breast tenderness and headaches (although
these usually settle within a few months and can
be controlled by changing to a different OCP);
-
No
protection from sexually transmitted diseases;
-
Associated
with a small increased risk of breast cancer in
women using OCPs for more than 10 years without
having children;
-
Possibility
of decreased VO2max/endurance performance.
The
conflicting results found in the scientific literature are
often difficult to interpret, given the known differences in
such variables as Pill dosages and formulation, menstrual
history, duration of OCP use, age at which subjects were
exposed to OCP, and outcome measurements. Nevertheless,
there are individual variations in response to OCP use and
these should be taken into account and monitored. Female
athletes should be counselled about the range of potential
benefits and disadvantages in order to make informed
decisions based on their individual circumstances.
BACK |