Fitness: Post-Exercise Pulse Measurements Give Low Values
It's common practice to have students and athletes take their heart rate after a bout of exercise. Whether running a track interval or performing an aerobics routine, this method is frequently used to monitor the intensity of exercise.
In groups, common procedure is to wait until everyone has located their pulse (often 15 seconds or so) then to time six, 10 or 15 seconds while everyone counts their own pulse. Students multiply by the appropriate number to arrive at a beats-per-minute value.
However, research has shown that this procedure underestimates exercise heart rates because of the time lag between the cessation of exercise and the fact that heart rates drop very quickly after exercise ends. This is particularly true for trained athletes.
Study and Method
A study at the University of Texas at Austin investigated manual heart rate measurement methods compared to actual heart rates as measured by an ECG. The subjects exercised (with sessions at 70% or 85% of their max heart rate), waited 15 seconds, counted their pulse for 15 seconds and multiplied by four to get their beats per minute count.
They were simultaneously hooked up to an ECG, which measured their actual heart rates during the last 10 seconds of exercise, then in the first 15 seconds after exercise, and finally, 15 seconds after that. Manual and ECG results were compared.
Findings
The study revealed several things:
• Any measurement method taking place after exercise underestimated the heart rate actually experienced during the final 10 seconds of the exercise session.
• Even the ECG, taken immediately after exercise, yielded a heart rate that was 7-9 beats per minute lower than the during-exercise rate. This is because heart rates drop dramatically once exercise ends -- especially for trained athletes.
• The longer the wait before taking the pulse, the less accurate the measurement.
• Manual methods for measuring pulse rates were fairly accurate, although the radial (wrist) method was less accurate at higher heart rates (10 bpm too low).
Editor's Conclusion
1. The best way to measure exercise heart rate is by measuring it during exercise. Using a heart rate monitor is best.
Taking a Radial Pulse2. You can measure manually, post-exercise, as long as you add a correction factor (see below). Measuring at the carotid pulse is the generally the most accurate, as long as you don't press too hard (which can stimulate the carotid sinus reflex and lower the heart rate).
3. The sooner you can take the measurement, the more accurate it will be.
4. A six-second or 10-second measuring period will probably be more accurate than a 15-second period (they take less time).
Correction Factor if Counting Pulse Rates Post-Exercise
If heart rate is measured manually or with a heart rate monitor:
• Add 10 beats per minute if measured within 10 seconds.
• Add 20 beats per minute if measured after 15 seconds.
These are ballpark numbers, but you can't expect field measurements to be exact anyway. To get a practical read on levels of exertion, it's best to combine heart rate estimates with your observation of the athletes' condition and their feedback on perceived exertion.
Reference: Allison DeVan, Barbara Lacy, Miriam Cortez-Cooper, Hirofumi Tanaka, "Post-exercise palpation of pulse rates: its applicability to habitual exercisers." Scandinavian Journal of Medicine & Science in Sports, 15:177-181, 2005. http://www.blackwellpublishing.com/journal.asp?ref=0905-7188&;site=1
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