There are three types of movements associated with muscle movement. These are static, concentric, and eccentric. Static action is a non-moving position of a joint. The length of the muscle does not change. When a cross-country skier is tucked in a downhill body position, they are in a static muscle state.
Concentric action is a shortening of the muscle.
Eccentric action lengthens the muscle. When these actions occur together, it is referred to as dynamic action. In Olympic cross-country skiing, eccentric muscle action is used immediately before concentric action. This increases the force of the muscle actions. An Olympic skier must perfect this movement to get greater forward acceleration and speed.