Start about 36 to 48 hours before a long-distance race to allow muscles to store extra glycogen while you reduce training load. Research dating back to work by Bengt Saltin and Eric Hultman at the Karolinska Institute established the physiological basis for glycogen supercompensation, and contemporary guidance from Louise Burke at Australian Catholic University and the Australian Institute of Sport translates that physiology into practical plans for marathoners. The key components are reducing training intensity and increasing carbohydrate intake so that muscle glycogen levels peak at the start line.
How it works
During prolonged exercise the body relies increasingly on glycogen for steady power output. When training volume is lowered in the days before a race the muscles stop drawing down glycogen, and a higher carbohydrate intake shifts the balance toward storage rather than use. This process is the reason athletes achieve supercompensated glycogen stores that support sustained pace in the later stages of a marathon. The underlying mechanism is well described in exercise physiology literature and underpins modern sports nutrition recommendations.
Practical timing and amounts
Begin the taper and higher-carbohydrate phase roughly two days before competition. Most sports nutrition experts recommend an intake in the range of about 8 to 10 grams of carbohydrate per kilogram of bodyweight per day during the 36 to 48 hours before the event, combined with a substantial reduction in training volume so the body can store glycogen. These targets are intended to maximize muscle glycogen without causing digestive distress. The Australian Institute of Sport and nutrition scientists such as Louise Burke at Australian Catholic University emphasize tailoring intake to body size, previous experience with high-carbohydrate days, and the usual race pace.
Consequences and practical considerations extend beyond simple numbers. A successful pre-race strategy reduces the risk of "hitting the wall" by preserving carbohydrate availability for the later miles. However, high carbohydrate intake can increase body water due to glycogen-associated water, which may feel like slight weight gain on the scale but is not harmful. Gastrointestinal symptoms are a common complication, so athletes should practice their pre-race meals in training to find foods that are both culturally familiar and well tolerated. Cultural dietary patterns influence the choice of carbohydrate sources, with rice, bread, tubers, or pasta each serving as valid options depending on regional cuisines.
Environmental and individual nuances matter. Heat and humidity increase carbohydrate utilization during racing, making effective glycogen loading even more valuable for athletes competing in warm climates. At altitude reduced appetite and altered digestion can complicate efforts to reach carbohydrate targets, so incremental planning is important. Ultimately, individual variability matters: shorter runners or those with very fast predicted times may need slightly different approaches than recreational marathoners. Work with a qualified sports dietitian or a coach experienced with endurance fueling to adapt timing and composition based on prior trial runs and personal response.