A pill to make exercise obsolete

It was late summer, and the gray towers of the Salk Institute, in San Diego, shaded seamlessly into ocean fog. The austere, marble-paved central courtyard was silent and deserted. The south lawn, a peaceful retreat often used for Tai Chi and yoga classes, was likewise devoid of life, but through vents built into its concrete border one could detect a slight ammoniac whiff from more than two thousand cages of laboratory rodents below. In a teak-lined office overlooking the ocean, the biologist Ron Evans introduced me to two specimens: Couch Potato Mouse and Lance Armstrong Mouse.

Couch Potato Mouse had been raised to serve as a proxy for the average American. Its daily exercise was limited to an occasional waddle toward a bowl brimming with pellets of laboratory standard “Western Diet,” which consists almost entirely of fat and sugar and is said to taste like cookie dough. The mouse was lethargic, lolling in a fresh layer of bedding, rolls of fat visible beneath thinning, greasy-looking fur. Lance Armstrong Mouse had been raised under exactly the same conditions, yet, despite its poor diet and lack of exercise, it was lean and taut, its eyes and coat shiny as it snuffled around its cage. The secret to its healthy appearance and youthful energy, Evans explained, lay in a daily dose of GW501516: a drug that confers the beneficial effects of exercise without the need to move a muscle.

Exercise has its discomforts, after all: as we sat down to talk, Evans, a trim sixtysomething in a striped polo shirt, removed a knee brace from a coffee table, making room for a mug of peppermint tea; he was trying to soothe his stomach, having picked up a bug while hiking in the Andes. Evans began experimenting with 516, as the drug is commonly known, in 2007. He hoped that it might offer clues about how the genes that control human metabolism are switched on and off, a question that has occupied him for most of his career.

Mice love to run, Evans told me, and when he puts an exercise wheel in their cage they typically log several miles a night. These nocturnal drills are not simply a way of dealing with the stress of laboratory life, as scientists from Leiden University, in the Netherlands, demonstrated in a charming experiment conducted a few years ago. They left a small cagelike structure containing a training wheel in a quiet corner of an urban park, under the surveillance of a motion-activated night-vision camera. The resulting footage showed that the wheel was in near-constant use by wild mice. Despite the fact that their daily activities—foraging for food, searching for mates, avoiding predators—provided a more than adequate workout, the mice voluntarily chose to run, spending up to eighteen minutes at a time on the wheel, and returning for repeat sessions. (Several frogs and slugs also made use of the amenity, possibly by accident.)