What is a good indicator of determining if you are exercising at the most beneficial intensity level?

Target heart rate.

Explanation:

Target heart rate is a term that refers to the minimum amount of heartbeats per given amount of time that is needed in order to reach the level of exertion that is necessary for fitness.

It is different for different people because it is calculated by subtracting one's age from 220. For instance, to get the average number of maximum heartbeats per minute during an exercise, an individual of 30 years will subtract 30 from 220 to get a maximum heart rate of 190. This is therefore the maximum number of times that the person's heart should beat per minute.

Target heart rate is important because it helps people to get the most benefit from their exercise routine.

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