When skeletal muscles are trained by adding physical stress to them, this is called 1. progressive resistance training 2. muscle endurance3. isometric exercise training4. isotonic exercise training?

Progressive resistance training

Explanation:

Progressive resistance training is a type of exercise in which the person exercise their muscles against some kind of resistance in order to increase the strength of the muscles.

The exercise is usually conducted two or three times in a week. The intensity of the exercise increases from moderate to high.

Machines, heavy bands and free wights are used in order to improve the physical function of the body.

Hence, the correct answer is option A

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frequency is the answer