A run, swim or bike ride that merely feels strenuous may not always boost your heart rate into the "aerobic zone." Aerobic exercise lowers blood pressure, improves cholesterol profiles, burns body fat and reduces the risk of heart attack. It's worthwhile, in other words, to find out just how hard your heart is really working.
No set of sensations -- breathing hard or breaking into a sweat -- signifies a suitably beneficial workout for everybody in every setting. But with practice you can learn to connect your perceived exertion to your heart rate. There are four simple steps for getting yourself in sync.
1. While exercising, rank the difficulty of your exertion on any scale you like -- one to 10 is fine. Or Borg's six through 20 if you prefer.