Researchers at the Salk Institute in San Diego have found two drugs that did wonders for the athletic endurance of “couch potato” mice. One drug, known as Aicar, increased the mice’s endurance on a treadmill by 44 percent after just four weeks of treatment. A second drug, GW1516, increased endurance by 75 percent, but had to be combined with exercise to have any effect.

The chemicals involved are already available, and athletes are already asking about whether they work on humans.

Dr. Richard N. Bergman, an expert on obesity and diabetes at the University of Southern California, worried that the drugs might prove to have serious side effects. However, he acknowledged that if they are safe, they could become widely used.

The drugs activate at least one of the chemical pathways triggered by resveratrol, a substance that also resulted in increased endurance in mice. Large doses of resveratrol can allow mice to run twice as far as usual on a treadmill before collapsing.