Several types of muscle actions exist. For example, it is possible for skeletal muscle to generate force without a large amount of muscle shortening. This can occur when an individual attempts to perform a “curl” with a dumbbell weight that he or she cannot move
(see Fig. 8.14(a)). What happens here is that muscle tension increases, but the dumbbell does not move, and therefore neither does the body part that applies the force. This kind of muscle force development is called an isometric action and is referred to as a static exercise. Isometric actions are common in the postural muscles of the body, which act to maintain a static body position during periods of standing or sitting.