Carbohydrate loading is a special practice that aims to maximize or “supercompensate” muscle glycogen stores up to twice the normal resting level (e.g., ~500–900 mmol/kg dry weight). The first protocol was devised in the late 1960s by Scandinavian exercise physiologists who found, using the muscle biopsy technique, that the size of pre-exercise muscle glycogen stores affected submaximal exercise capacity [41–43]. Several days of a low-carbohydrate diet resulted in depleted muscle glycogen stores and reduced endurance capacity compared with a mixed diet. However, high carbohydrate intake for several days caused a “supercompensation” of muscle glycogen stores and prolonged the cycling time to exhaustion. These pioneering studies produced the “classical” 7-day model of carbohydrate loading. This model consists of a 3- or 4-day “depletion” phase of hard training and low carbohydrate intake, followed by a 3- or 4-day “loading” phase of high carbohydrate intake and exercise taper (i.e., decreased amounts of training) [44]. Early field studies of prolonged running events showed that carbohydrate loading enhanced performance not by allowing the athlete to run faster but, rather, by prolonging the time that the athlete could maintain the race pace.