For those who find getting up for early morning runs or spin classes a bitter pill to swallow, researchers have some good news.

American scientists have discovered two drugs that dramatically improve endurance in laboratory mice.

One pill showed benefits when taken in conjunction with performing regular exercise and another pill actually showed benefits in sedentary mice.

The research was conducted by scientists at the Salk Institute for Biological Studies in La Jolla, Calif. Their findings are published in the advance online edition of the journal Cell.

The research team was led by Ronald M. Evans, a professor and biologist at Salk Institute for Biological Studies at the Salk Institute.

"We have exercise in a pill," said Evans. "With no exercise, you can take a drug and chemically mimic it."

Previous research by Evans and his team showed that if they activated a gene expression called PPAR delta in mice, the critters turned into tireless marathoners. They also developed a resistance to weight gain, even when fed a high-fat diet.

Evans and his team have now invented a pill that mimics how exercise stimulates PPAR delta, which occurs when two signalling pathways in the body work together to increase endurance.

This new drug, known as GW1516 and currently only available for scientific research, had no effect on PPAR delta in sedentary mice. However, when given to mice that ran for up to 50 minutes on a treadmill, it did turn on PPAR delta.

The active mice who took the drug had a 77 per cent improvement in their endurance compared to mice who only exercised. As well, the drug increased the number of so-called non-fatiguing muscle fibres in the mice by 38 per cent.

Evans and his team also developed a second drug that mimics how exercise triggers a chemical reaction that provides muscles with energy.

When the researchers gave this drug, known as AICAR, to sedentary mice, the rodents could run 44 per cent longer than mice who did not take AICAR. The effects were noticed after only four weeks.

The researchers said that such drugs are appealing for distance runners and other endurance athletes. As well, they could offer benefits to those who have health problems that range from muscle-wasting diseases to obesity to metabolic deficiencies.

However, the researchers have already developed blood and urine tests for GW1516 and AICAR and are collaborating on developing other tests with the World Anti-Doping Association.