Isotonic contractions are those which cause the muscle to change length as it contracts and causes movement of a body part. There are two types of Isotonic contraction:
Concentric – Concentric contractions are those which cause the muscle to shorten as it contracts.
Eccentric – Eccentric contractions are the opposite of concentric and occur when the muscle lengthens as it contracts.
For example, when doing a biceps curl it is an isotonic movement.
Isometric contractions occur when there is no change in the length of the contracting muscle.
For example, this occurs when carrying an object in front of you as the weight of the object is pulling your arms down but your muscles are contracting to hold the object at the same level. Another example is when you grip something , such as a tennis racket. There is no movement in the joints of the hand, but the muscles are contracting to provide a force sufficient enough to keep a steady hold on the racket.
Isokinetic contractions are similar to isotonic in that the muscle changes length during the contraction, where they differ is that Isokinetic contractions produce movements of a constant speed.
For example, breast stroke in swimming, where the water provides a constant, even resistance to the movement of adduction.