Skeletal muscle characteristics: relationships to cardiovascular risk factors.

Recent studies have reported that skeletal muscle characteristics are altered in hypertension, insulin resistance, and android obesity. These conditions represent cardiovascular risk factors that are often "clustered" together, and have begun to be recognized as part of a metabolic/cardiovascular syndrome. This paper reviews the evidence correlating skeletal muscle characteristics to cardiovascular risk factors, and outlines the proposed mechanisms for the relationships. Muscle characteristics (e.g., fiber type, capillary density, oxidative capacity, insulin binding, GLUT 4 levels, and glucose uptake) are discussed. Although aerobic training does not appear to alter the ratio of Type I/II fibers, it favorably affects other skeletal muscle characteristics that are mechanistically linked to cardiovascular risk factors. These muscle adaptations are important in understanding how exercise training helps to prevent cardiovascular disease.