As a cancer survivor, you know that exercise is one of the key factors in lowering your risk of cancer recurrence. But how do you know if you’re exercising enough -- or hard enough? That part is trickier. And that’s where your heart rate comes in.

Your heart rate indicates how quickly your heart is pumping blood – in other words, how hard it’s working. Knowing your heart rate can help you determine if you need to back off to make...