Most gym equipment has a built in heart rate monitor, so here’s how to get the most from it. Your optimum training zone is between 70 and 90% of your maximum heart rate (MHR). To find it subtract your age in years from 220 to get your MHR, then multiply this figure by, say, 0.8 (to work out 80% of your MHR). So if you are 45 subtracting 45 from 220 gives you an MHR of 175. Multiplying this by 0.8 will tell you that to work in a training zone at 80% of your maximum heart rate you need to achieve a maximum of 140 beats per minute during your workout to efficiently burn fat.