Cardiovascular System Science: Investigating Heart Rate Recovery Time
Summary
Introduction
As Valentine’s Day approaches, we’re increasingly confronted with stylized images of the heart. Real hearts serve very important functions – a person’s heart beats to supply blood to their entire body, and the heart has to work harder when they exercise. Have you ever wondered how quickly your heart beats when you exercise, or how long it takes to recover back to its normal rate after you’re done exercising? In this science activity, you’ll get to do some exercises to explore your own heart rate recovery time.
Background
Your heart is constantly beating – even before birth! – to keep blood circulating through your body. For a person to keep their heart healthy, it’s important to exercise regularly. The American Heart Association recommends that a person does exercise that is vigorous enough to raise their heart rate to their target heart zone for at least 30 minutes on most days, or about 150 minutes a week in total. (A person’s target heart rate zone is 50% to 85% of their maximum heart rate, which is 220 beats per minute [bpm] minus their age.)
After getting some exercise, a person’s heart needs time to recover, or go back down to its normal, resting heart rate. How long it takes for the heart to return to its resting heart rate is referred to as the heart rate recovery time. In general, people who regularly exercise, and therefore are likely to have healthier hearts, have faster heart rate recovery times than people who do not regularly exercise.
Materials
- Pen or pencil
- Scrap piece of paper
- Clock or stopwatch that shows seconds
- Simple and fun exercise equipment, such as jump rope, hula-hoop, stepping stool, etc. Alternatively, you can do exercise that does not require equipment, such as jogging.
- A chair
- Calculator
Preparation
- Practice finding your pulse. You can do this by using the first two fingers on one hand to feel the radial pulse on the opposite hand’s wrist. The radial pulse is found on the “thumb side” of the wrist, just below the hand. You will need to be able to find your pulse quickly, so practice finding it until it is easy to do.
- You can alternatively use your carotid pulse, but make sure you know how to take it safely by pressing on your neck only very lightly.
- Prepare a scrap piece of paper so that you can quickly write down your testing results when doing the activity. You will be measuring your resting heart rate, your heart rate immediately after doing a short exercise, and then every minute for the next five minutes. After that, you will measure your heart rate every two minutes. You will continue to measure your heart rate until it returns to your resting heart rate.
Instructions
- Measure your resting heart rate. To do this, take your pulse (when you have been resting) and multiply the number of beats you count in ten seconds by six. This will give you your resting heart rate in beats per minute (bpm). What is your resting heart rate? Write it down on your prepared scrap piece of paper.
- Choose a vigorous activity you’d like to briefly do. This could be jumping rope, stepping on and off a low stool, hula-hooping, jogging, etc. Then, engage in that activity for about two minutes.
- Immediately after the end of the exercise period, sit and rest on the chair and quickly measure and record your heart rate. What is your heart right after exercising? Write down what time it is (including seconds) or start a stopwatch.
- While you continue to sit and rest, measure and write down your heart rate every minute for the next five minutes. How does your heart rate change as you continue to rest after you stopped exercising?
- If your heart rate has not reached your resting heart rate, continue to sit and rest but only measure and write down your heart rate every two minutes. Continue measuring it until it returns to your resting heart rate. How does your heart rate continue to change over time?
- What was your heart rate recovery time, or the amount of time it takes your heart to return to its resting heart rate after exercising? How did your heart rate change over time after you stopped exercising?
Extra: Graph your results. How did your heart rate change over the course of this activity?
Extra: Try repeating this activity but compare a group of athletes to a group of non-athletes. How does the heart rate recovery time of people who are physically fit compare to people who do not regularly exercise?
Extra: Do this activity again but this time include volunteers of different ages. Does heart rate recovery time increase with age? Be sure that the volunteers you recruit can safely do the exercise!
Extra: Design an activity to compare the heart rate recovery time of people who smoke to people who don’t. Do smokers have increased heart rate recovery times compared to non-smokers?
Observations and Results
Did your heart rate quickly drop when you started resting, and then start to level out as it approached your resting heart rate? Did it reach your resting heart rate after one to seven or more minutes when you stopped exercising?
Immediately after exercising, your heart rate was likely in the upper end of its target heart rate zone. As soon as you started resting, your heart rate should have quickly decreased. Specifically, one minute after you started resting, your heart rate likely rapidly dropped, and then continued to drop, but much more slowly, as it approached your resting heart rate over the following minutes. It may have taken about one to seven or more minutes for your heart rate to go back down to your resting heart rate (after you stopped exercising). Generally, the faster a person’s heart rate recovers, or reaches their resting heart rate, the better shape they are in. Specifically, in 1999 a study was published in The New England Journal of Medicine that found that if a person’s heart rate decreases by 12 bpm or less within the first minute after exercising, it is considered abnormal and can be indicative of heart problems and a predictor of mortality. (See the link in the “More to explore” section, below, for entire study.)
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Additional Resources
- American Heart Association Recommendations for Physical Activity in Adults, from the American Heart Association
- Improve Heart Health by Knowing Your Recovery Heart Rate, from Hannah Kitzmiller, Enhanced Medical Care
- Heart-Rate Recovery Immediately After Exercise as a Predictor of Mortality, from Christopher R. Cole, et al., The New England Journal of Medicine
- Fun, Science Activities for You and Your Family, from Science Buddies
- Heart Rate Recovery Times, from Science Buddies
