Whether you're interested in running a marathon or staving off the chronic diseases of ageing, to reap the rewards of your efforts getting into the zone is essential.

Experts say knowing and staying within your heart rate training zone is an easy way to pace the intensity of your workout.

"Exercisers need to get to at least a moderate level of physical activity in order to reap the benefits," says Dr Adrian Hutber of the American College of Sports Medicine. "Your goal is to get to a stage where you're fit enough to exercise within your heart rate training zone."

Your heart rate training zone, or target heart rate, is based on your maximum heart rate (MHR), which is roughly calculated as 220 minus your age.

"It's not exact but it doesn't need to be," Hutber says. "It's a really good indicator."

For moderate-intensity physical activity, a person's target heart rate should be 50 to 70 percent of MHR, according to the Centers for Disease Control and Prevention.

"Science tells us you need at least 150 hours of moderate-level physical activity per week to be healthy, says Hutber, quoting US government guidelines.