The physical inactivity of the critically ill patient is an abnormal state that compromises muscle function to an extent that the immobile skeletal muscle may not simply be a bystander in the disease process.Skeletal muscle seems to maintain a system of defense against inflammation through heat shock proteins and the production of myokines. It contributes in a bidirectional role in systemic inflammatory signaling and the modulation of the inflammatory response. Skeletal muscle is a major contributor to whole-body glucose and protein metabolism, exemplified by its role in nutrient provision for the immune system and other rapidly dividing tissues through glutamine production.