When a person sustains an injury from playing sports, an accident or any other reason, he or she may need to undergo physical therapy to restore normal movement to the body. Part of this approach involves the use of therapeutic exercise to help the patient regain balance, strength, flexibility, and range of motion and alleviate pain.

The physical therapist will evaluate the patient's condition by conducting an assessment of his or her ability to move, and taking a medical history. This information will be used to formulate a specific course of exercises which become progressively more challenging as the patient improves. Once the pain is overcome, the focus will be on restoring the body's strength, endurance, and flexibility.

Physical therapy exercises are classified according to the nature of the movement involved and the impact it has on the muscles and joints. Passive exercises help restore normal movement in joints and require little to no work from the muscles as the force is applied to them, either manually or from a continuous passive motion unit or similar mechanical device. In contrast, active exercise calls for muscular involvement, with or without assistance, in a manner which improves joint movement and neuromuscular control.

There are other type of activities designed to build endurance and strength in damaged muscles. Once the patient has progressed to the point where he or she can safely carry out range-of-motion and flexibility exercises, it's time to begin strength and endurance training. Gradually increasing resistance is added steadily so the body can respond by naturally gaining strength in the tendon, ligaments, muscles, and bones.

Strength exercises are classified as static or dynamic. A static activity does not require movement of the joint, the tension and resistance are equal, and the muscle fibers remain the same length throughout the movement. The angle is the key aspect which makes the difference in this case, so patients are advised to vary the angle of each set, making sure they hold it for several seconds each time, as this is what builds strength.

Dynamic exercises differs in that it does involve movement of the joints and muscles, in particular concentric and eccentric movement, which refers to a repeated shortening and lengthening of the muscle fibers that produces force and develops strength. This type of exercise can be grouped into isotonic, isokinetic, variable-resistance, and manual movements.

Variable-resistance and manual resistance exercises work based on the principle that the muscles produce a limited force when the joints are positioned in extremes of the range of motion. The main difference is that the latter involves the therapist manually applying resistance, and the former relies on the use of a machine that accounts for proper joint alignment and applies resistance relative to force. With isotonic movement, the muscles are lengthened by external force which imposes a change on the joint's angle, this is seen with many weight machines, ankle weights, and free weights.

Isokinetic exercises are carried out with a fixed speed and equal muscle force and resistance. Machines to generate this type of movement deliver force to match the user's level of muscle resistance and often have adjustable settings in terms of concentric and eccentric actions with varying velocities.