the commonly used formula is one of “220 minus age”. While this is a ballpark, it works pretty good as a starting point.
Let’s use an example with a client who is 60 years old. Based on this formula, his maximum heart rate is 160 (220 – 60). This would be a heart rate that the person really could not sustain without running out of gas in a very short time. So we tend to assign exercise intensities as a percentage of this maximum heart rate.
Let’s say, this person is really deconditioned and just starting to exercise. You ask him to exercise at an intensity of 60% to 70 % of his maximum heart rate. 60% of his maximum heart rate of 160 is 96 beats per minute 70 % is 112 beats per minute. In real life you would be close to the client and watch him as he exercises to see how this intensity works. If he gets out of breath very quickly, you adjust the range down.
If the client is already in good shape, you go with a higher exercise intensity. Your textbook gives you examples of you to do this. You always need to monitor the exertion, though. As I said earlier, this 220 – age formula is only a ballpark. Some people are simple born with a higher or lower maximum heart rate.
I hope this helped.