The principal difference between isometric and isotonic exercises is the a. use of free weights and weight machines b. rate of calories burned during exercise c. change in muscle length during exercise d. type of muscles exercised

 Isometric exercise involve muscle contraction without a change in the length of the muscle, while isotonic exercises involve muscle contraction with a change in the length of the muscle.

The principal difference between isometric and isotonic exercises is the change in muscle length during exercise. Correct C

c) it can produce three-dimensional images.