• When the muscle contracts and there is movement at the joint, the tension in the muscle is constant while its length decreases.
• This is known as isotonic contraction.

• When the muscle contracts but now movement occurs, the tension of in the muscle increases drastically but the length of the muscle remains constant.
• This is called isometric contraction

In reality, most of the time, muscle contraction is a mixture of both isometric and isotonic contractions.