Your heart is the fuel pump that works every second of your life to supply oxygen and energy to every cell in your body. Your heart is an incredible, non-fatiguing muscle that contracts about 108,000 times a day in unfit people. In addition to being an essential, life-sustaining organ, your heart is an internal computer that provides meaningful information regarding exercise intensity and cardiovascular adaptations.
For example, an average, nonexercising adult has a resting heart rate of about 75 beats per minute. Each heart beat represents a contraction of the heart muscle that sends oxygen-rich blood throughout the body. Your resting heart rate is the slowest rate at which your heart muscle contracts.
If you were running for your life, your heart rate would increase. This is called your maximum heart rate, and is generally estimated by subtracting your age from 220. So, if you are 20 years old, your maximum heart rate is about 200 beats per minute; if you are 40 years old, your maximum heart rate is about 180 beats per minute. As you may have noted, your maximum heart rate decreases by about one beat per year throughout life. This is one reason why our aerobic ability declines with age.
There is a zone within our heart rate range (between resting and maximum heart rate) that corresponds to the most effective exercise intensity for improving our cardiovascular fitness. This optimal training zone is from 60 to 90 percent of your maximum heart rate, with 75 percent of maximum considered ideal for most purposes. This means that a 60-year-old would have a maximum heart rate of 160 beats per minute (220 – 60 = 160), and a training heart rate around 120 beats per minute (160 x .75 = 120). Typically, you try to exercise between 10 heart beats below to 10 heart beats above your training heart rate, which in this case would be from 110 to 130 beats per minute.
As your cardiovascular system becomes better conditioned, your heart becomes capable of pumping more blood each time it contracts, and therefore does not need to beat as frequently to supply your body’s oxygen requirements. One indicator of your improved aerobic capacity is a lower heart rate during your standard exercise session. This reveals beneficial adaptations in your cardiovascular system, and a need to increase your exercise intensity (e.g. from 3.0 to 3.5 miles per hour on the treadmill) to stimulate further aerobic improvements.
Another indicator of your enhanced cardiovascular fitness is your resting heart rate. As our hearts become stronger through endurance exercise, they pump more oxygen-rich blood in every contraction, so they beat at a slower rate. After a year or two of training, your resting heart rate could decrease by as much as 20 beats per minute. So instead of contracting 75 times a minute (108,000 beats/day), it may contract only 55 times a minute (79,200 beats/day). Remarkably, your better-conditioned heart saves about 30,000 contractions a day at rest. The slower heart rate gives your heart muscle more rest between contractions, gives your heart chambers more time to fill with blood between contractions, and gives your heart tissue more time to receive its own oxygen supply between contractions.
In addition to showing improvements in heart function and aerobic fitness, your resting heart rate provides excellent feedback about your recovery from exercise and related conditions. For example, let’s say that your resting heart rate first thing in the morning is typically 60 beats per minute. If, on a given day, it is considerably higher than normal (e.g., 68 beats per minute), this is an indication that your cardiovascular system is under some type of stress. While this may be related to psychological factors or illness, the typical physiological stressors include too much exercise (over-training) and too little rest (not enough recovery time between training sessions or insufficient sleep). Whatever the cause, when your resting heart rate is elevated more than a few beats per minute, you should postpone or reduce your exercise activity until it returns to normal.
Checking your heart rate when you wake up is an excellent habit for adjusting your training program to your physiological condition and to reduce the risk of over-training. Generally, a 10-second pulse count (multiplied by 6) is sufficient during exercise, but I recommend a full minute count to most accurately assess your resting heart rate in the morning.
Wayne L. Westcott, Ph.D., is senior fitness executive at the South Shore YMCA in Quincy, Mass., adjunct instructor of exercise science at Quincy College, and author of 22 books.
author: Wayne Westcott