The diaphragm: Contractile properties and fatigue

Abstract

The diaphragm is a striated skeletal muscle controlled by voluntary and automatic neural pathways. Its primary function is the act of breathing, specifically the inspiratory phase. The diaphragm responds to neural drive and work load much like nonrespiratory striated skeletal muscles, and its functional characteristics are primarily determined by its contractile properties. However, diaphragmatic contraction is modified by particular constraints imposed by respiratory system mechanics and control mechanisms. For example, Fenn noted that the diaphragm contracts rhythmically aginst elastic and resistive forces, and that with each relaxation the diaphragm returns to a relatively constant resting position, determined by the balance of lung and chest wall recoil forces. Limb muscles also contract rhythmically during locomotion, but they must overcome predominantly inertial forces, and they have no special resting position. The most prominent influence on the diaphragm is the fact that, like the heart, it must contract in repetitive rhythmic fashion for life.