The physiological foundation of exercise prescription: target heart rate calculation, heart rate reserve method, and individualized intensity monitoring

Heart rate is the frequency of the heart's periodic mechanical activity, that is, the number of times the heart beats per minute. Heart rate reflects exercise intensity and is the most commonly used and simple indicator for assessing exercise intensity, training level, physical function, and post-exercise recovery. Target heart rate, also known as the desired heart rate, refers to the intensity at which the heart is expected to reach and maintain a certain level during exercise. It is generally a heart rate range, expressed in beats per minute; it can also be expressed in beats per 10 seconds. During exercise, too low an intensity results in ineffective or poor training; too high an intensity may cause injury. To achieve better exercise results, exercise must be performed at an appropriate intensity. There are many methods for determining the target heart rate; currently, two commonly used calculation formulas are employed.

The first method is the maximum heart rate method, where a person's maximum heart rate is 220 minus their age. The lower limit of the target heart rate is typically set at 50% of the maximum heart rate, and the upper limit at 60%. For example, a 20-year-old's maximum heart rate is 200 beats per minute, and their target heart rate range is 100 to 120 beats per minute. The second method is the heart rate reserve method, where heart rate reserve is the maximum heart rate minus the resting heart rate. The lower limit of the target heart rate is equal to heart rate reserve multiplied by 20% plus the resting heart rate, and the upper limit is equal to heart rate reserve multiplied by 40% plus the resting heart rate.

For example, a 20-year-old with a resting heart rate of 72 beats per minute has a heart rate reserve (HRR) of 128. This calculates to a lower limit of 97.6 beats per minute and an upper limit of 123.2 beats per minute. Therefore, the target heart rate calculated using the HRR method is between 98 and 123 beats per minute. The target heart rate calculated using the HRR method takes into account the individual's resting heart rate and is more individualized than the result calculated using the maximum heart rate method. Therefore, the HRR method is more recommended for calculating target heart rate. An accurate target heart rate range should be determined through specialized testing at a professional institution using specialized testing methods.

Research shows that the target heart rate for obese patients exercising to lose weight is generally between 20% and 40% of their resting heart rate plus their heart rate reserve. This target heart rate can vary at different stages of exercise for weight loss, requiring repeated testing to determine the optimal range. Knowing the target heart rate allows for targeted exercise, maximizing weight loss results. Furthermore, the exerciser's physical capacity and workload are also considered when determining the target heart rate. Therefore, determining the target heart rate is a crucial measure for ensuring safety during exercise for weight loss.

Obese patients often have underlying factors for or pre-existing chronic diseases. Clearly, their exercise capacity is lower than that of healthy individuals of the same age and sex. Using the same exercise intensity as healthy individuals not only fails to achieve optimal weight loss but may also significantly increase the risks associated with exercise due to the presence of chronic diseases. Obese patients can control the intensity of their exercise during weight loss by adjusting their target heart rate, thus ensuring safe and effective weight loss. It is important to note that determining the target heart rate requires specialized institutions and professionals to ensure its validity.

Heart rate reflects not only intensity but also cardiac function. Generally, obese patients who lack physical activity tend to have a faster resting heart rate, indicating poorer cardiac contraction and ejection capacity, and a smaller stroke volume. In severely obese patients, fat accumulation around the heart impairs ventricular diastolic function, preventing the ventricles from fully filling and further reducing stroke volume. Therefore, obese patients with a faster resting heart rate can tolerate lower exercise intensity. Severely obese patients also experience a faster heart rate immediately after quantitative exercise, and during progressively increasing exercise stress tests, their heart rate rises more rapidly with increasing intensity.

During the exercise-based weight loss process, as time progresses and weight and body fat percentage decrease, the physiological burden on the body's circulatory system gradually lessens. Exercise can also improve cardiovascular function to a certain extent, slowing down the resting heart rate and the heart rate during quantitative exercise. Therefore, the intensity of exercise for weight loss should be adjusted promptly. Maintaining the original exercise intensity (target heart rate) may result in excessive exercise and reduce weight loss effectiveness. Generally, an exercise load test can be conducted again after two weeks of exercise to re-determine the target heart rate. The chosen exercise for weight loss should facilitate relative stability of exercise intensity during the exercise process, and the intensity should be easy to control.