Which type of exercise involves muscle lengthening and shortening through a range of motion with variable speed?

Isotonic exercise is characterized by muscle contractions that involve both lengthening and shortening of the muscle through a range of motion. This type of exercise can be performed at variable speeds, which allows for a more dynamic movement that can closely replicate normal activities and sports. Isotonic exercises include activities like free weight lifting, where the muscles contract (shortening) while lifting the weight and then lengthening as the weight is lowered.

This method of exercising is particularly beneficial for improving strength, endurance, and overall functional fitness because it can engage multiple muscle groups at once and allows for the application of various loads. It also enhances the ability of muscles to perform in real-life situations, where movements are not always done at a fixed pace or with constant resistance.

In contrast, isometric exercises involve muscle tension without any change in length or movement, while isokinetic exercises require a constant speed of movement but typically involve specialized equipment to provide variable resistance. Static exercises do not involve movement at all. Thus, the key aspect of isotonic exercise—its capacity to encompass a range of motion with variable speed—clearly distinguishes it as the correct answer.