What if you could get a lot of the benefits of exercise, without moving a muscle? A class of naturally occurring proteins called Sestrins might be able to mimic such metabolic effects, a new study suggests, although so far the results have only been observed in mice and fruit flies.

An instant exercise pill for humans is still some way off then – don't give up your gym membership just yet – but the new findings could further research into helping the physically impaired and injured keep their bodies in healthy shape.

During experiments, a team led by researchers from the University of Michigan found that suppressing Sestrins in flies and mice had a negative impact on how effective their exercise was; but by increasing Sestrin levels, the test subjects got some of the benefits of exercise without actually doing any.

"Sestrin upregulation mimics both molecular and physiological effects of exercise, suggesting that it could be a major effector of exercise metabolism," write the researchers in their published paper.

The team started with Drosophila flies, fashioning a makeshift insect treadmill in the lab. They compared the running and flying of flies (bred to lack the ability to make Sestrin) against flies bred to overexpress the proteins, and also looked at a normal group of flies.

This normal control group of flies showed improved endurance and better flying ability after three weeks of training – but the same improvements weren't seen in the flies that had their Sestrin production inhibited.

In the flies with Sestrin overexpression, the researchers observed their capabilities went beyond the control group, even when they weren't doing any exercise.

The effects seem to go beyond endurance too: another experiment on mice showed that animals without Sestrin didn't get the same boost in aerobic capacity, respiration, and fat burning usually associated with exercise.

In a related study on mice, produced in collaboration with some of the same researchers, the overexpression of Sestrin was shown to also help combat muscle atrophy – so Sestrin treatments could potentially be used to protect broken limbs inside casts, for example.

These findings could also be helpful in care for the elderly, the researchers point out, enabling older people who aren't as mobile as they used to be to still get some of the same benefits as they would from hitting the gym twice a week.

Of course, there's no evidence yet that any of these effects can be replicated in humans, though it has been well established that our muscles produce more Sestrin during exercise, so there is enough here to warrant future research.

It's also encouraging that the same effects were noted in both flies and mice during the study, making it perhaps more likely that the muscles of other animals – including humans possibly – might work the same way too. If so, more research will be needed to find out for sure.

"We propose that Sestrin can coordinate these biological activities by turning on or off different metabolic pathways," says physiologist Jun Hee Lee from the University of Michigan.

"This kind of combined effect is important for producing exercise's effects."

The research has been published in Nature Communications.