Types of muscle contraction - isotonic concentric and eccentric
There are two main types of muscle contraction:
- Isotonic contractions 鈥 these occur when a muscle contracts and changes length and there are two types:
- Isotonic concentric contraction 鈥 this involves the muscle shortening. The origin and insertion of the muscle move closer together and the muscle becomes fatter.
- Isotonic eccentric contraction 鈥 this involves the muscle lengthening whilst it is under tension. The origin and the insertion move further away from each other. An eccentric contraction provides the control of a movement on the downward phase and it works to resist the force of gravity.
Left: Concentric contraction - the biceps are contracting concentrically to move the weights upwards; Right: Eccentric contraction - the biceps are contracting eccentrically to lower the weights against resistance
- Isometric contraction 鈥 this involves a muscle producing tension but staying the same length. This occurs when the body is fixed in one position.
Here, the muscles are contracting isometrically to hold this gymnast in the crucifix position and are not changing length. When the isometric contractions end, isotonic contraction will occur.
