Relative vo2 max (i.e., normalized to body weight can vary widely in adults depending upon their age, health and training status. For example, VO2 max can be less than 20 ml kg 1 min 1 in patients with severe cardiovascular and pulmonary disease, and more than 80 ml kg -1 min 1 in world-class distance runners and cross-country skiers (Table 13.1). The extremely high VO2 max values possessed by elite male and fe- male endurance athletes are the genetic gift of a large cardiovascular capacity and high percentage of slow muscle fibers (5). Indeed, studies have concluded that heritability of VO2 max in the untrained state is approximately 50% (12, 13)