As it does, the triceps relaxes, acting as the antagonist. When the ski pole is planted in the snow, the arm moves down and backwards. In this movement, the triceps becomes the agonist and the biceps is the antagonist. 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.