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Marathon runners can feel like they are 'hitting the wall' when the brain runs low on sugar. Daniel Leal-Olivas/AFP/Getty

Metabolism

Athletic endurance enhanced by metabolic shift

Mice whose muscles use less sugar ‘hit the wall’ later.

Stimulating a protein that modifies muscle metabolism could keep the brain refreshed and delay the onset of ‘hitting the wall’ — the sudden and extreme fatigue felt by long-distance athletes such as marathon runners.

Michael Downes and Ronald Evans at the Salk Institute for Biological Studies in La Jolla, California, and their colleagues studied how the muscles of mice burn energy after the animals received daily treadmill training for four weeks. The animals shifted their metabolism so that the muscles used more fatty acids and less glucose, a switch that was controlled by a protein called PPARδ. The researchers saw a similar effect in mice that were not exercise-trained and were treated with a drug that activates PPARδ; these animals could run for about 100 minutes longer than untreated ones.

The drop in glucose use by the muscles leaves more available for the brain, which can only metabolize the sugar.