we have just seen, carbohydrate reserves, which primarily take the form of
muscle glycogen stores, are very limited (350 to 500 g in an average athlete).
During normal exercise, the body consumes at least 130 g of glycogen per hour
(520 kcal), which translates into a theoretical autonomy (without
replenishment) of 2 to 3 hours. However, muscle glycogen stores are rarely
fully stocked except in rest or pre-race periods, and you must also bear in
mind that consumption can be much higher (up to 230 g/hour, or 900 kcal). In
these situations, even the nourishment provided by sports drinks and gels is
not enough, as the body’s capacity to absorb sugars during periods of intense
exertion is limited to 1 g/kg of body weight/hour (in other words, 60/70 g/h).
You will need to draw on other sources of energy, principally lipids (fats),
high-performance fuels which the body contains in abundance.
body’s fat stores consist of 300 g of intramuscular fat and an average of 10 to
12 kg in reserve tissue (adipose tissue). Fat is a practically inexhaustible
resource (representing a reserve of nearly 100,000 kcal!) which is also very efficient
(1 g of fat provides 9 kcal, double the calories that 1 g of carbs can supply).
Fats can supply up to 50-60% of the energy a body consumes. Thus, in situations
of comparable intensity, an athlete who knows how to tap into his fat reserves
better than his rivals will have a substantial advantage in terms of endurance
the body is not able to process fats as quickly as it does carbohydrates (as
the former must be converted), which explains why fats are not the body’s first
choice when trying to fuel itself in situations of urgent, immediate,
high-intensity exertion. Yet you can train your body to do two things: speed up
the processing of fats, and delay reaching the point of intensity after which
fat stores can no longer supply energy. This adaptation effect kicks in when an
athlete regularly stimulates lipolysis (the breakdown of fats). Nutritional
conditioning facilitates this adaptation by limiting all foods and habits that
counteract lipolysis: excessive ingestion of high GI (sugary) foods, snacking
between meals, and eating or drinking too much sugar during training sessions.
Another indirect benefit is that you will shed excess body fat, thereby
reducing the amount of energy you burn during a workout (as you will have less
weight to move). This strategy will help you to enter a virtuous circle.
(sugars, sugared products, sugary drinks, refined grains, etc.) in your normal
diet, outside the metabolic windows.*
(both sweet and salty snacks).
(choose hypotonic beverages instead), and cut back on high-sugar energy
bars and gels in average-intensity training sessions of under two hours (this
practice also enhances the muscle groups’ glycogen storage capacity, as it
stimulates a process known as gluconeogenesis**).
this is a brief “window of opportunity” after a workout in which the
human body is capable of rapid regeneration.
gluconeogenesis or GNG is a metabolic pathway that synthesises glucose from
non-carbohydrate precursors (fats and proteins).
David Padare is a dietician nutritionist specialized in preferred disciplines such as endurance sports and outdoor running, trail running, cycling, triathlon, swimming….