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.
2. Stop and quickly count your pulse. If your heart rate hasn't reached the ideal range (see the chart opposite), start over and push yourself. After several minutes, do the ranking and pulse check again.
3. Once you hit the right pulse, remember the ranking. From then on you simply need to feel you've reached that reasonably strenuous seven, eight or whatever to put your heart rate in the aerobic range.
4. Check yourself every couple of weeks to make sure you haven't lost your feel.