Strengthening is where the muscles and other soft tissues are put under strain, and respond by increasing their loading capacity.
Strengthening is important for:
Initially strength training is aimed at assisting the healing process and improving muscular performance.
As rehabilitation develops the training begins to become more functional - eg a builder with a lower back injury would start with abdominal or core conditioning, then do squats and lifting later to better simulate the day-to-day functional activities.
There are a number of methods used to strengthen. Pilates-based core conditioning recognises that some muscle types are predominantly stability muscles and others moving muscles. A strong core improves the quality of limb movement and reduces loads to other parts of the body, thereby helping to prevent injury. These exercises are very subtle and do not necessarily require the use of any resistance.
Resistance can be added by using free weights, machine weights, resistance bands, cable pulleys, body weight exercise e.g. pull-ups and press-ups, and environmental resistance e.g. swimming. The type of exercise and instruction will depend on the muscle, its function, and your stage of rehabilitation.