During the London Olympics, and beyond, many endurance athletes will attempt to increase their muscle glycogen stores by carbohydrate loading. This is because, despite its importance, glycogen is a fuel present only in small amounts in skeletal muscles and can be rapidly depleted during prolonged intense aerobic exercise, thus causing fatigue.
Unfortunately, many athletes aiming to increase their glycogen stores find this aspect of their preparation challenging. It is thus important to remind them that nearly a decade ago my colleagues and I developed some carbohydrate loading regimens to make this task easier.
Close to the end of the 1960s, a team of scientists from Northern Europe introduced a carbohydrate loading regimen that resulted in a near two-fold increase in muscle glycogen stores.
This regimen involved a glycogen-depleting bout of exercise followed by three days of a carbohydrate-poor diet. Another bout of exercise was then performed to deplete once more the stores of muscle glycogen.
For the next three days the athletes were asked to eat a carbohydrate-rich diet and to avoid any strenuous physical activity.
As one would expect, despite its benefits, this regimen was difficult to tolerate and highly impractical, particularly for athletes wishing to train during the carbohydrate-deprivation phase of this regimen.
It is in part for this reason that nearly 30 years ago, Sherman and colleagues introduced an improved carbohydrate-loading regimen that resulted in comparable increases in muscle glycogen levels, but without the disadvantages associated with the classical regimen.
These investigators found that the accumulation of high levels of muscle glycogen is possible without any glycogen-depletion phase.
All that is required is for athletes to taper their training over several days and rest on the day before competition while ingesting a carbohydrate-rich diet for three days prior to competing.
Unfortunately, even this three-day carbohydrate loading regimen was difficult to adhere to given the large amounts of carbohydrate that needed to be ingested over several consecutive days.
For this reason, nearly a decade ago my colleagues and I at UWA undertook to develop an improved carbohydrate-loading regimen that allows the attainment of maximal muscle glycogen levels within a shorter time period.
Since the rates of muscle glycogen synthesis are generally higher during recovery from a short bout of high intensity exercise than during recovery from prolonged exercise of moderate intensity, we examined whether combining a short bout of high intensity exercise with a one day high-carbohydrate intake could provide a faster way to carbohydrate load.
To this end, we asked a group of participants to cycle for 150 seconds at 130% of their maximal aerobic capacity followed by a 30-second all-out sprint. For the next 24 hours, we fed them the equivalent of 10 grams of carbohydrate-rich food per kilo of body mass.
To our surprise, after only 24 hours their muscle glycogen stores increased to levels comparable to or higher than those reported in previous studies on carbohydrate loading.
One limitation with this regimen is that many endurance athletes may not wish to perform three minutes of intense exercise on the day before competing. Ideally, it would be better if they could accumulate as much glycogen within one day but without a glycogen-depleting exercise bout.
Sherman and colleagues had shown it was possible without a glycogen-depleting period of exercise to store maximal amounts of muscle glycogen if a carbohydrate-rich diet was adopted for three days while tapering exercise-training.
We examined whether this approach could work in endurance-trained athletes fed the equivalent of 10 g of carbohydrate-rich food per kilo of body mass while remaining physically inactive for a whole day.
We found that muscle glycogen stores reach maximal levels within only one day of starting this regimen, with no added benefits by extending the high-carbohydrate intake period for up to three days.
In other words, all that is required of our endurance athletes who trained regularly and want to carbohydrate load before competing is simply to interrupt their training for one day and eat the equivalent of 10 grams of carbohydrate-rich food (e.g. pasta, bread, rice, potatoes) per kilo of body mass during that day.
Simply, the best
To the best of our knowledge, no better carbohydrate loading regimen has been published since then, but many athletes still rely on earlier regimens.
Our carbohydrate loading protocol sounds simple, and it is simple – but it works.