The short answer is that this helps prevent the tendency to adapt or habituate. Living organisms are experts at adapting to things. Exercise is an excellent example of this. When we start a new exercise program muscles, and other systems like the heart and lungs, adapt to it, which allows us to perform better. To optimize our response to exercise, we need to perform it, and allow time to recover from it. By doing something intermittently, instead of continuously, we typically get more benefits and continue to get benefits over long periods of time.
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