Isolation exercises are useful when you resume fitness training after a long break. They can help you strengthen a part of your body that may have been weakened by illness, surgery or an injury. It is often difficult to engage in complex exercises when a part of you body is still weak. Isolation exercises allow you to gradually build-up muscular mass in the affected area. They also prove useful when you need to strengthen an area of your body that may not be getting adequate stimulation from multi-joint exercises. However, isolation exercises are not without their pitfalls.

You don't burn as many calories as you would with multi-joint exercises. This is because only one muscle group is targeted during the training which makes it harder to burn excess body fat. Isolation exercises also don't significantly help to elevate your resting metabolic rate (RMR). This hampers effective fat-burn which may frustrate a weight loss program. Focus on a single muscle group doesn't help to improve muscular balance which increases the risk of injury. This can lead to an unbalanced physique. It also hampers normal biomechanical functions of the body. Leg extensions are a good example of isolation exercises. Although they work your quadriceps, with time they can lead to knee joint instability.