What makes circuit training so good?

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Explanation: Circuit training is a high volume but low resistance weight workout with 2-3 minute rest intervals involving cardio, and is focused on improving muscle tone and definition while also improving cardiovascular fitness. It is a popular way of working out, especially if you are looking for variety in your workouts.

answer; genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes;