Short periods of rest are as crucial as exercise to keep you fitter and faster, say researchers.
Stirling University sports scientists believe taking it easy now and again not only allows the muscles to recover, it also makes the body fitter faster.
Their study was of keen cyclists but they think that men and women who are simply trying to get a bit fitter could also benefit from building periods of rest into their exercise programme.
In the study, 12 cyclists were split into two groups. One did bursts of high intensity exercise, interspersed with short rest periods, three times a week.
In each session, they pedalled hard, but below sprint pace, for four minutes, then stopped for two minutes, before repeating the pattern five times.
The second group rode continuously for an hour at a slightly easier pace, three times a week.
After four weeks, the two groups swopped programmes.
Tests showed that the first programme, which involved a mixture of tough training and taking it easy, to be the most beneficial, leading to twice as big an improvement in power and performance.
"It is a case of training smarter. We found in these cyclists that if you can make the hard sessions harder and the easy sessions easier, then you will likely see better progress," the Daily Mail quoted researcher Stuart Galloway as saying.
The researchers suggest that while high intensity is still important, it's the combination with low intensity which has the biggest impact.
It is thought that muscles find it harder to recover from long periods of exercise, than from short bursts, even if they are physically tougher.
According to co-author Dr Angus Hunter, muscles may be fatigued more quickly when you work at high intensity but they recover more quickly too, which could leave people feeling less tired in between exercise sessions.
The study has been published in the Journal of Applied Physiology.