Skeletal Muscle in the Stress-Induced Catabolic State

Abstract

Although the largest organ in the human body, skeletal muscle is often considered not to have any role of vital importance in the stress-induced catabolic state. This is true in the sence that muscular strength has no relevance in fighting infections or in improving oxygenation during critical illness. Nevertheless, skeletal muscle has two major roles for such patients: (1) to serve as a reservoire for amino acid substrates needed in other tissues during the stress-induced catabolic state and (2) to function as a limiting organ for mobilization during convalescence. This implies that the size of skeletal muscle tissue is a determinant for the size of the store of amino acid substrates available for mobilization during critical illness. This store may be a limiting factor for survival if critical illness is long-standing. Indirect evidence for this hypothesis is the well-documented fact that malnutrition, in general accompanied by muscle wasting, is associated with a poorer outcome after sepsis and surgical trauma. Furthermore, restitution of lean body mass following depletion is a very slow process. In younger individuals, restitution of body composition takes years, and among elderly people it is often not possible to achieve at all. Patients who have to be rehabilitated during the convalescence phase are heavily dependent upon their muscular reserves in this aspect. This means that remains of skeletal muscle tissue and in particular of muscle function are a determining factor for the duration as well as the outcome of convalescense. In addition, susceptibility to late complications is also related to the nutritional state, indirectly depending upon the muscle mass.