The practice of increasing carbohydrate intake before racing is a longstanding tradition in endurance sports. It began when athletes discovered that their endurance seemed to improve when they loaded up on carbs in the days preceding a longer race. Its popularity exploded in the 1960s, when a Swedish exercise scientist named Gunvar Ahlborg discovered that carbo loading worked by greatly increasing muscle glycogen stores, which are the limiting fuel supply for athletes in races.
In the 50 years since Ahlborg’s discovery, much more work on carbo loading has been done. This work has served to define the limits to the effectiveness and applicability of the practice. Key findings include the following:
– Tapering, or reduced training, itself boosts muscle glycogen stores substantially without increased carbohydrate intake.
– Carbo loading has no effect on performance in races lasting less than 90 minutes.
– Carbo loading does not enhance endurance performance when adequate carbohydrate is consumed during the race.
Does this mean you shouldn’t bother with carbo loading? Not necessary. It definitely helps in some circumstances, and it can’t hurt if you use a less extreme carbo loading protocol (eating 10 grams of carbs per kilogram of carbohydrate two days before racing without a preceding “glycogen depletion” period). So you might as well do it before your most important long events.