Measured Heart Rates

Heart rates are generally expressed as a number of beats per minute (bpm) and, if accurately taken, can precisely assess exercise intensity. You can monitor your heart rate either manually or electronically. In general, you will take your heart rate immediately upon completion of a lap. As soon as exertion ceases, your heart rate begins to drop. The better your aerobic conditioning, the faster it drops. You want to take your heart rate before it drops significantly. An electronic heart-rate monitor (HRM) is the much-preferred method of taking your heart rate. It is immediate and very accurate, and it requires little conscious thought and no refined skill.

A manual (or palpated) heart rate (taken by placing your fingers on an artery in your neck or wrist and then counting the beats) is much less accurate than an electronic reading for two reasons: Counting is difficult because the beats are rapid, you are tired, and your breathing is labored; and because your heart rate is dropping while you find and count your pulse, even an accurate count will be lower than the actual immediate heart rate. Only care and repetition can help with the former. We try to minimize the latter error by keeping the counting period short—0.10 of a minute, or 6 seconds—then multiplying by 10. But even a short count results in a calculated heart rate that is anywhere from 10 to 30 beats per minute lower than your actual heart rate. To offset this phenomenon, you can add 2 to the count before multiplying by 10. Even with this adjustment, the result is, at best, an estimate of your exercise heart rate rather than an accurate measurement.

How to Take a Manual Heart Rate

 

Use two fingers to locate your carotid artery, which is just below the hinge point of your jaw—an inch or so below your earlobe—and feel your pulse. Use the smallest amount of pressure that allows you to feel the beats. Some people can more easily find their pulse on the inside surface of their wrist, closer to the thumb than the pinkie. For 6 seconds, count the number of beats you feel. As you watch a clock, count one on the first beat after any convenient mark on the clock, then continue counting beats until the sixth second ticks by. If a beat falls on the 6-second mark, include it in your count. (For example, you finish swimming a particular distance, and when you look up, the second hand is on the 37-second mark. You locate your pulse by the 39-second mark. You begin counting on the first beat you feel after the 40-second mark. Start with one. Count all beats up to and including the 46-second mark.) Let’s say you count 14 beats and you add your adjustment of 2 to get 16. Multiply that number by 10, and you have your estimated IHR of 160. If you are new to taking your heart rate in this manner, it will take some trial and error to get good at it. It is easier to find your pulse after physical exertion than when you are at rest, because the beats are stronger and are thus easier to feel.

    You can become more accurate at manually taking your heart rates by borrowing a heart-rate monitor and doing some testing. You’ll need a buddy to help you. While wearing the monitor, swim several different distances at various intensities. Immediately upon completing each swim, your buddy reads your monitor (but does not tell you the result just yet) as you take your heart rate manually. Compare your reading with the reading your buddy took. Repeated experimentation like this can help you determine whether 2 is the correct adjustment for you. You may find that an adjustment of 1 or 3 (or more) gets you closer to the electronic readings. It is good to revisit this exercise every few months, because as your conditioning improves, your adjustment may change. 
    If you do not have access to a heart-rate monitor or if you are unable to consistently match your manual readings to electronic readings, then you should not take your heart rate manually to gauge exercise intensity. Either buy and use your own monitor or else use the RPE method described earlier in this chapter. RPE is also the preferred method to assess intensity among people who take medications that affect heart rate or pulse. Comparing heart rates taken manually during workouts to benchmarks calculated from electronic readings will likely yield unreliable results. If you choose to go the manual route, you should use manual heart rates both during workouts and for the calculations you’ll be doing soon. 
    You will often see the acronym IHR in the following chapters. IHR is your heart rate taken immediately after completing a period of exertion. When you use an HRM, simply glance at it as soon as possible after touching the wall. The first number you see is your IHR. If you are taking your heart rate manually, use the method detailed in the How to Take a Manual Heart Rate sidebar.