Supercompensation
works for women - but better for men
Most
athletes are aware of the concept of 'supercompensation',
whereby muscle glycogen stores and endurance
performance are boosted in response to a regime of
exercise tapering and carbohydrate loading. But do
women benefit to the same extent as men?
Studies
of these regimes to date have mostly been performed
on men. And those which have included women have
tended to produce negative or marginal results. But
now a small but important Canadian trial has
demonstrated that well-trained women do boost their
muscle glycogen stores and their endurance
performance in response to carbo-loading and
exercise tapering - albeit to a lesser extent than
men.
The
study involved six female athletes - three
triathletes, two cyclists and a runner - who had
their endurance and their muscle glycogen content
tested after two different week-long dietary regimes
combined with exercise tapering. On days 1-6 of each
trial the women followed an exercise-tapering
programme, with 90 minutes of exercise (either
cycling or running at their normal intensity) on day
one, 45 minutes on days two and three, 20-30 minutes
on days four and five, and rest on day six.
For
the dietary aspect of the experiment, the women were
randomly assigned to one of two regimes: a 7-day
moderate-carbohydrate (MD) diet, with about 48% of
total daily energy derived from carbohydrate or a
3-day MD diet followed by four days of a
high-carbohydrate diet (HCD), in which about 78% of
total daily energy came from carbohydrate.
On
the seventh day all the women cycled to voluntary
exhaustion at about 80% of their VO2 max. Glycogen
content was measured by biopsy of their vastus
lateralis leg muscles before and after this exercise
bout. In a subsequent week-long trial the women
switched dietary regimes so that all six followed
both types of diet.
In
terms of performance, the women were able to cycle
for about nine minutes longer after the HCD than the
MD (an average of 115.31 minutes compared with
106.35). In terms of muscle glycogen, pre-exercise
glycogen content was on average 13% higher after HCD
than after MD. However, post-exercise muscle
glycogen contents were not significantly different
suggesting greater net utilisation by muscles after
HCD.
Why
did these results differ from those of previous
studies involving women? One key difference is that
the female athletes in previous studies were tested
during the follicular (early) phase of their
menstrual cycles, when circulating reproductive
hormones are low. Other research has suggested that
glycogen synthesis may be increased during the
luteal (late) stage of the cycle, when hormone
levels are much higher. And the current study,
carried out exclusively during the luteal phase of
the women's cycles, seems to bear out that
conclusion.
The
researchers conclude that 'the women were able to
supercompensate glycogen - but not to the same
magnitude as generally reported in men'. The women's
performance and muscle glycogen increases (8% and
13% respectively) were much smaller than those
previously reported in men (20% and 40%).
One
reason for this disparity may be the simple fact
that women eat less than men. The researchers point
out that it may be difficult for women whose
habitual calorie intakes are less than 2,400
kcal/day - which was true of all the women in the
trial - to achieve higher carbohydrate-intake
values. By contrast, male athletes are known to
consume more than 3,000 and often more than 5,000
kcal/day during carbo-loading.
Supercompensation
may also be influenced by gender differences related
to the uptake and storage of glucose. But the team
concludes that: 'Little information presently exists
to explain this gender difference in the ability to
store muscle glycogen.'
Journal
of Applied Physiology 88:2151-2158, 2000
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