Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance

by Alex Hutchinson

The cliché of the pasta-fueled marathoner can be traced back to the work of Swedish scientists Jonas Bergström and Eric Hultman in 1960s. Bergström pioneered the use of needle biopsies, a technique that allowed researchers to slice out small pieces of muscle from their long-suffering research volunteers—or, as was the habit in Scandinavian labs at the time, from their own muscles.11 In one notable study, Bergström and Hultman sat on opposite sides of a stationary bike, each pedaling with one leg while the other leg rested, until they were both too exhausted to continue. Self-inflicted muscle biopsies before and after cycling showed that levels of glycogen, the form in which carbohydrate is stored in muscles, had dropped to zero in the exercised leg. Running out of this specific muscle fuel, in other words, seemed to coincide with exhaustion. Over the next three days, the two men ate a high-carbohydrate diet and performed regular biopsies. Glycogen levels stayed roughly constant in their rested legs, but in the exercised legs, levels shot up to twice their initial value—a supercompensation effect that launched the idea of “carbohydrate loading” before long-distance races.