It sounds too good to be true. Cash in that gym membership. Pack away those running shoes. Scientists are testing drugs that they claim will produce the benefits of exercise in muscles without the hard work.
The researchers have shown that four weeks after administering one drug to mice, the animals were able to run 44% farther than untreated mice, despite not exercising. The finding raises the possibility of treatments for muscle-wasting conditions in humans, but also recreational "gym pills" that confer a performance gain without the pain.
Couch potatoes should not get too comfortable though. Despite nearly a decade of scientific research on stimulating muscle endurance in rodents, efforts to achieve the same results in humans have so far ended in failure. "There's been very little success," said Prof Paul Greenhaff, an expert in muscle metabolism at the University of Nottingham. "It's not really having the large impact that you would expect to see from the animal work."
The US research team used two drugs to stimulate different elements of muscle metabolism involved in endurance. In one experiment they used an experimental drug to stimulate PPAR delta, a gene involved in muscle metabolism. On its own this did not improve the animals' exercise performance, but when the scientists combined it with an exercise regimen that involved a daily 50-minute run on a treadmill they saw a 77% improvement in endurance compared with mice that had the same exercise regimen, but were not given the drug.
The combination of drug and exercise increased the proportion of "slow twitch" muscle fibres by 38%. These are the fibres involved in endurance rather than strength.
In a separate study, the team used a compound called AICAR to stimulate another gene involved in muscle metabolism, AMPK. After four weeks without exercise, the mice were able to run 23% longer and 44% farther than untreated mice. "That's as much improvement as we get with regular exercise," said Dr Vihang Narkar at the Salk Institute in La Jolla, California. The results are reported in the journal Cell.
Narkar said the team hoped to replicate the results in people. "The ability of these drugs to improve muscle performance can be potentially exploited in treating muscle-wasting or weakening diseases," he said. But he added that boosting endurance would also be attractive to athletes such as marathon runners who wanted to cheat their way to success.
"We have developed tests (early stage) to measure the levels of these compounds in blood and urine. These tests are being developed in collaboration with the World Anti-Doping Agency [the body that polices doping in sport] in response to concerns regarding doping," he said.
However, Greenhaff said that worrying about abuse by athletes was premature because despite nearly a decade of research the same effects on performance have not been replicated in people. "It is just taking it way out of the realms of reality ... The observations themselves are very interesting – don't get me wrong. But in the context it is being spun, ie human athletics and mimicking exercise, it is really a million miles away," he said. "There are AICAR human studies ... and you don't see these effects. If it's that hot, where are the human data?"
Prof David Cowan, director of the Drug Control Centre at King's College London, whose laboratory is accredited by the World Anti-Doping Agency, said WADA was keeping an eye on the research. But he added: "It is a big step from mouse to man."