Breaking up an exercise session by adding a rest period in between may boost a workout's fat-burning efficiency, researchers report.
When men exercised for two 30-minute stretches, taking a 20-minute rest break in between, they burned more fat than when they exercised for a single 60-minute session, and then rested afterward, Dr Kazushige Goto of the University of Tokyo and colleagues found.
Current recommendations on exercise for preventing or treating obesity emphasise longer exercise sessions, the researchers note in Journal of Applied Physiology.
But there is evidence that following one exercise session with another workout may increase fat metabolism, they add. The researchers had seven healthy men complete one long workout and then two shorter workouts on exercise bicycles, measuring several different indicators of fat metabolism. All exercised at 60 per cent of their maximum level of exertion.
When the men performed the two shorter exercise sessions, their blood levels of free fatty acids and other substances rose during the rest period, indicating greater fat metabolism.
Levels of these substances also were higher during an hour-long rest period after the two-part exercise session.
Greater fat metabolism was recorded during each of the rest periods in the two-part session than during the rest period following the single, longer workout. The men also showed lower levels of insulin and blood glucose during the second phase of the two-part exercise session.
While the proportion of total calories burned did not differ between the two workouts, fat represented nearly 77 per cent of the calories burned in the recovery period after the two-part exercise session, compared with about 56 per cent of calories burned in the recovery period after the single exercise session.
Although a single bout of prolonged exercise is often performed in response to a physician's advice to exercise more, exercising with rest periods may be more effective, especially for overweight people, the study concludes.