The submaximal heart rate assessments used during the HZE program are the 1-mile (1.6 km) walking test, talk test, biggest number test, step test, and chair test. The mathematical MHR formula has limitations and is less reliable than submaximal assessments.

Most methods used to determine MHR are valued or rated according to the ultimate use of the number obtained. Competitive athletes, for example, need very accurate numbers. The intention of the HZE program is to teach students the process for determining MHR. The numbers they get will be only estimates, and depending on the method used, the estimated MHR will vary. In the school setting, we are looking for a general all-sport maximum: a global fitness estimate, not a specific MHR for each sport activity.

MHR can be determined by exercising to a maximal intensity or by completing submaximal heart rate tests to estimate it. The most accurate method is a maximal test to near exhaustion, but this may not be practical in school settings and is difficult to do, particularly for the unfit. Thus, exercise scientists have developed a series of submaximal heart rate tests that can be used to predict MHR. These tests most often use a formula that predicts MHR based on age. The theory behind this formula for predicting MHR is that the maximal number of times our hearts can beat decreases as we age.

The original studies on MHR were conducted in the 1930s on fit young men and not fit older men. The results of those original studies are now being challenged. Several long-term studies of fit people indicate that MHR is related not to age, as many have believed for so long, but to lifestyle. For example, an active 30-year-old may have an MHR of 210 bpm. If, as that person ages, she simultaneously decreases physical activity and becomes sedentary, her MHR will likely decrease. If, however, she were to exercise at a moderate intensity regularly as she aged, her MHR would likely remain unchanged. Indeed, Dr. Dave Costill (1996) conducted studies that follow the same fit people over a period of 22 years. His findings show that MHR remained unchanged when his subjects exercised regularly at moderate intensity.

People who want to get fit may find that exercising at certain percentages of true or predicted MHR provides a variety of benefits, such as the following:

  • Enhanced fat burning: Burning more fat and more total calories by training in different heart zones.
  • Improved stamina: Going farther, faster, and longer because endurance fitness improves (called improved endurance capacity).
  • Increased efficiency: Going farther on each calorie burned.
  • Cardiovascular improvement: Transporting nutrients and oxygen throughout the body more efficiently.
  • Psychological power: Increased alertness, mental stamina, and self-esteem.

At lower exercise intensities (i.e., lower heart zones), these benefits result in lowered blood pressure, reduced stress, and stabilized body weight. As the intensity of a workout increases (i.e., higher heart zones), the benefits of exercising change.