Regular exercise can make your heart stronger and more efficient.

"Well, we want that target heart rate range. And that means we're working hard enough that our heart is getting beneficial activity and beneficial exercise."

Dr. Ed Laskowski, co-director of Mayo Clinic Sports Medicine, says you should get about 30 minutes of moderate activity at least five days a week.

"And moderate is something that you're — you're breathing kind of hard, but you can still hold a conversation."

That should get your heart rate up to the target range, and studies show that the level of exertion we feel correlates quite well with our heart rate.

"We're getting good blood flow. We're training our heart muscle to work more efficiently, and … actually strengthening it. So if we … don't do that — if we're doing something too light — we won't get as much of the beneficial effect."

Dr. Laskowski says the actual numbers aren't as important as the effects.

"As long as we feel we're working moderately hard and … we're getting some good activity, we're doing good things for ourself."

For the Mayo Clinic News Network, I'm Ian Roth.