Can you enjoy the benefits of exercise without the pain of exertion? The answer may one day be yes — just take a pill that tricks the muscles into thinking they have been working out furiously. 

Researchers at the Salk Institute report they have found two drugs that do 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, supercharged the mice to a 75 percent increase in endurance, but had to be combined with exercise to have any effect. 

“It’s a little bit like a free lunch without the calories,” said Dr. Ronald M. Evans, leader of the Salk group. 

The results, Dr. Evans said, seem reasonably likely to apply to people, who control muscle tone with the same underlying genes as do mice. And if the drugs work and prove to be safe, they could be useful in a wide range of settings. 

They should help people who are too frail to exercise and those with health problems such as diabetes that are improved with exercise, he said. 

But such muscle-enhancing drugs would also have obvious appeal to athletes seeking to gain an edge in performance. With funds from the Howard Hughes Medical Institute, Dr. Evans has devised test to detect whether an athlete has taken the drugs, and has made it available to the World Anti-Doping Agency, which prepares a list of forbidden substances for the International Olympic Committee. 

Officials at the anti-doping agency confirmed that they were collaborating with Dr. Evans on testing procedures but could not say when they would start using them. 

Experts not involved in the study agreed that the drugs held promise for treating disease. Dr. Johan Auwerx, a specialist in metabolic diseases at the University Louis Pasteur in Strasbourg, France, said the result with the Aicar drug “looks pretty good’ and could be very helpful in the treatment of diabetes and obesity. “The fact you can mimic exercise is a big advantage because diet and exercise are the pillars of diabetes treatment,” he said. 

Dr. Richard N. Bergman, an expert on obesity and diabetes at the University of Southern California, said the drugs could become widely used if they prove safe. “It is possible that the couch potato segment of the population might find this to be a good regimen, and of course that is a large number of people,” he said. 

The idea of a workout in a pill seems almost too good to be true, but Dr. Evans has impressive research credentials, including winning the Lasker award, which often presages a Nobel prize. He is an expert on how hormones work in cells, and on a powerful gene-controlling protein called PPAR-delta which instructs fat cells to burn off fat. 

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