Running Ends at the Table, Not on the Track

Walk along any riverside path or park trail at dusk and you will find it crowded with runners. Running has become one of the most accessible sports in the world. It asks for no court, no team and no membership, only a pair of shoes. When the air turns cool in autumn, the roads fill with people chasing better health and a stronger body. Yet from a physician’s point of view, one imbalance stands out. Everyone studies how to run farther and faster, while almost no one gives the same thought to what the body needs once the running stops. A run does not end when the distance is covered. The real work of recovery begins the moment you stop.

Our understanding of how the body stores energy changed in the middle of the nineteenth century. In 1857 the French physiologist Claude Bernard found that blood sugar is not sustained by food alone. Observing that sugar continued to flow from the liver of a fasted animal, he uncovered the mechanism by which the body keeps glucose in reserve, stored in the liver and muscle as glycogen. We hold roughly 100 grams in the liver and three to four times that amount in muscle. Together this comes to about 500 grams, or some 2,000 calories. Liver glycogen works as a safeguard that holds blood sugar steady. Muscle glycogen is the fuel that drives the legs directly.

Because that tank has a fixed capacity, glycogen runs down faster the longer the distance. Even well trained runners often meet the wall somewhere around mile 18 to 20, when the legs turn to stone and the engine seems to cut out. This is a physiological limit, not a failure of will. A 155-pound runner covering 30 kilometers, a shade under 19 miles, burns roughly 2,100 calories, since running costs about 1 calorie per kilogram of body weight per kilometer. That figure is almost exactly the body’s entire glycogen reserve. Once stored carbohydrate is gone the body turns to fat, but fat is metabolized slowly and cannot deliver power on demand. The moment when the mind is willing and the body is not comes from this bottleneck in the fuel supply.

The signs come in two forms. Legs that no longer respond mean muscle glycogen has run out. A clouded head and slowed judgement mean liver glycogen has fallen and blood sugar with it, since the brain has little else to burn. Dizziness or trembling hands point to the latter. Pushing on in that state raises the risk of injury.

Timing decides how well glycogen is restored. Straight after hard exercise, muscle takes up sugar far more readily than usual, and the window is widest in the first thirty to sixty minutes. Left alone, glycogen rebuilds at around 5% an hour and needs the better part of a day to refill. Taking in carbohydrate soon after finishing can nearly double that early rate. Glucose and fructose are absorbed through different routes in the gut, so foods containing both, including ordinary table sugar, are taken up more quickly. Cutting back on sugar is sound advice for daily life. After hard exercise the situation is different, because what you eat then goes first to rebuilding what the run emptied.

Three rules make recovery reliable.

First, do not stay empty for hours. Going without food after a long run wastes the best chance to clear fatigue and repair. Nothing elaborate is needed. Bread, a rice ball, a banana or any simple carbohydrate will do. If you have to train hard again within the day, aim for about 1 gram of carbohydrate per kilogram of body weight, roughly 70 grams for a 155-pound runner.

Second, pair carbohydrate with protein in a ratio of roughly three or four to one. Carbohydrate refills glycogen while protein repairs the small tears in muscle fibre. Rice with meat, milk with fruit, a sandwich with egg all fit. Chocolate milk is a standby recovery drink for the same reason.

Third, replace sodium along with the water you lost. A liter of sweat carries between 500 and 1,500 milligrams of sodium. Drinking large amounts of plain water while badly dehydrated dilutes blood sodium and can bring on the headache and nausea of hyponatremia. On days of heavy sweating take electrolytes with your fluid. After an easy thirty minute jog, an ordinary meal and water are enough.

The hunger and the craving for something sweet that arrive after a run are not weakness of character. They are the body asking, precisely, for what it spent. There is no reason to meet that request with guilt. Replace what you used, rest properly, and only then is the session truly complete. Run well, eat well, sleep well. That is what lets you run again tomorrow.