I have a friend who is totally crazy about running. He clocks at least 40 miles per week. I, on the other hand, do well to get in 20 miles per week. Neither of us has a weight problem, so I’m wondering if there is some health reason for me to push it more.

A recent study looked at one specific indicator of good heart health–heart rate variability (HRV). The greater the HRV, the better. The researchers did not find any major differences between the endurance-trained exercisers and those who exercised at a moderate level similar to yours. There was a definite difference between the men who were classified as sedentary when compared to these other two groups. The sedentary men had less heart rate variability and higher resting pulses.