Eccentric Contraction

When we think of a muscle contracting normally, we think of the muscle shortening as it generates force. During normal activity, though, muscles are often active while they are lengthening. Classic examples of this are walking, when the quadriceps (knee extensors) are active just after heel strike while the knee flexes, or setting an object down gently (the arm flexors must be active to control the fall of the object). This is referred to as an eccentric contraction and is characterised by two main features. First, the absolute tensions are very high relative to the muscle's maximum tetanic tension generating capacity, meaning you can set down a much heavier object than you can lift. Second, the absolute tension is relatively independent of lengthening velocity.