If you are a very fit adult, with a history of hard cardiovascular training, the odds are good that your resting heart rate is under 50 bpm. Although heart rates vary widely, a low resting heart rate is one fairly good indicator of cardiovascular fitness. We have no solid evidence that lower is better, though many of the top endurance athletes have resting heart rates in the low 30's, and some have had mid-20's, supposedly. (I'm thinking urban legend on some of these numbers, but....)
During my first stress test, done at age 40 at my wife's insistence, my cardiologist used Borg's ekg as a template for the "perfect" rhythm. Of course, that was in the dark ages of medicine, and today the "youngest science" is approaching pubescence so we must know more, eh?
I thought it was a good argument for the benefits of tennis anyway.
If you are over the age of 18, please post your resting heart rate. Your resting heart rate, by my definition, is your pulse taken in bed in the morning shortly after waking from a night's sleep. If you are under 18, you are likely to have significantly higher heart rates. Females also tend to have higher heart rates than males.
My resting heart rate this a.m. was 44 beats per minute. That is a bit high for me but I had 2.5 hours of hard tennis yesterday. On the other hand, I'm 63. In my late 20's my RHR was in the low 30's.
-Robert