Is the difficulty presented by a certain force, and is key for fitness because it makes

the activity harder on your muscles.

Intensity

Resistance

Acceleration

Velocity

Resistance

Explanation:

Resistance is the opposite force that acts against the work done. Resistance in muscle exercise refers to the exercise in which the muscle moves against the resistance provided by the gravity and external force like the dumbbells, bars and weight.  

This external exercise puts the Resistance on the muscle and when the muscle tries to move against the resistance puts pressure on the muscle and the exercise becomes hard. As a result of this, the endurance and strength of the muscle increases and nowadays is used as fitness exercise in the gym and professional bodybuilders.

Thus, Resistance is the correct answer.

answer; /// i believe the correct answer is (analogue);