Ironman
triathlon: ironman triathlon gender differences
High energy intakes
during an Ironman Triathlon help males athletes to
faster finishing times but have the opposite effect
in females. That is the surprise finding of study
investigating energy balance in 10 male and eight
female participants in the 1997 New Zealand Ironman
Triathlon, comprising a 3.8k swim, 180k cycle ride
and 42.2k marathon run.
Few
studies have described energy balance in these
situations, and the researchers’ aims were to
examine gender differences in the following
variables during the Ironman:
-
Total
energy, food and fluid, macronutrient and sodium
intake;
-
Energy
expenditure for each stage of the event;
-
Energy
balance for the event;
-
Relationships
between energy and carbohydrate intake, energy
balance and finishing times.
Their
theory was that athletes would be in substantial
negative energy balance (EB) after completing the
Ironman and that carbohydrate ingestion would be
related to improved performance in both male and
female competitors.
They
were certainly right in their first supposition:
mean energy expenditure (EE) was significantly
greater than mean energy intake (EI), with a
substantial mean energy deficit after the event of
5,123 and 5,973kcal for women and men
respectively.
‘These
results reveal,’ comment the researchers, ‘that
subjects obtained a high proportion (59%) of their
energy from endogenous fuel stores.’
They
also illustrate ‘the importance of consuming a
high [carbohydrate] diet prior to ultradistance
events to maximise endogenous fuel stores’.
But
the researchers were surprised to find themselves
wrong in their second hypothesis – that energy
intake would be positively correlated with
performance for both men and women.
Energy intake during the Ironman was monitored by
the athletes themselves and passed on to the
research team during in-race interviews followed up
by telephone interviews a few days later.
Mean
total energy intake during the cycle and run
portions of the event was 3,115 kcal for women and
3,940 for men, with all subjects consuming
significantly more energy during the cycle section
than the run. Women obtained significantly more
energy from food than fluid during the cycle and run
sections – a finding that did not apply to the
men. However, the women consumed significantly more
water than men and (non-significantly) less sports
drink and Coca Cola.
But
the most interesting differences between the sexes
was this: for women, total energy intake and energy
consumed during the cycle section showed significant
positive relationship with finishing time: in other
words, the more they ate, the slower their
times.
For
men, the opposite tended to be true, with a
significant inverse relationship between relative
carbohydrate intake during the run and finishing
time: in other words, the more carbohydrate they ate
while running, the faster their times.
Acknowledging
that the finding about women is difficult to
explain, the researchers offer the following
possible explanations:
-
The
longer average finishing time for women in this
study may have provided more opportunity for
energy consumption: in other words the energy
consumption was an effect rather than a cause of
the slower times;
-
Difficulties
associated with digesting and absorbing large
amounts of energy and carbs, particularly in the
form of solid food, may have contributed to
longer finishing times among the women;
-
Females
may be less reliant than men on energy from
carbohydrates because of an enhanced ability to
mobilise lipid stores.
The
researchers conclude that increasing carbohydrate
ingestion during the run portion may be a useful
strategy for improving Ironman performance in male
triathletes.
[originally
published in the International Journal of Sport
Nutrition and Exercise Metabolism, 2002, 12, 47-6
]
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