Runners need to move 15 per cent faster on a treadmill to burn the same number of calories as jogging outdoors, research reveals.
Researchers from Milan University analysed the difference between running outdoors or on a treadmill in 15 physically fit males with an average age of 21.
The participants sprinted for 30 seconds followed by 30 seconds of recovery for a total of 15 minutes both outdoors and on a treadmill.
Oxygen use and exercise intensity were measured after both types of running. The findings were published in the journal of Applied Physiology, Nutrition and Metabolism.
Results revealed that when on a treadmill, runners use significantly lower amounts of oxygen, suggesting less effort is required.
The study authors wrote: 'A 15 per cent increase in running velocity during a high intermittent intensity treadmill training session is the optimal solution to reach the same physiological responses as an outdoor training session.'
Although the study did not speculate why treadmill running appears to be less strenuous, previous research suggests the moving belt of a treadmill propels joggers forward, causing them to move faster.
Exercising indoors also means gym-goers do not have to contend with steep hills or wind resistance.