between 50 and 70 per cent of your maximum heart rate. When you exercise at this low intensity, your body draws energy from fat. As your heart rate goes up, more energy comes from carbs. So it seems logical that to lose fat you should keep your heart

or so higher. "In the opening stages of a marathon, the heart rate of both men and women should climb to the plateau of about 140bpm, working at about 70 per cent of your maximum effort, a guide we use for testing new athletes' fitness," says Pedlar

says.Dr Jaques advises women to keep their heart rate at or below 140 beats per minute (bpm) while exercising. Experiments on pregnant dogs suggest that running at an intensity greater than 70 per cent VO2max (the point of maximum oxygen capacity

50 and 70 per cent of your maximum heart rate. When you exercise at this low intensity, your body draws energy from fat. As your heart rate goes up, more energy comes from carbs. So it seems logical that to lose fat you should keep your heart rate low

. The last physiological variable to adapt is your sweat rate, which takes eight to 14 days to reach maximum efficiency. Other, faster responders include increased plasma volume, decreased sodium concentration in the blood, decreased heart rate while running