Exercise Limitation in Health and Disease

Classic studies of the factors that limit exercise revealed that exercise capacity is reduced at high altitudes1 and in persons with cardiopulmonary disorders.2 Because animal muscle deprived of oxygen rapidly fatigues and produces lactic acid,3 these findings suggested that inadequate oxygen delivery limits exercise. Maximal oxygen consumption (V̇O2max) became the primary measure of exercise capacity, and mechanisms related to the delivery of oxygen to the muscles were considered the main factors determining exercise capacity. These principles dominate the conventional interpretation of clinical exercise tests.4,5 PhysiologyNormal Exercise PerformanceExercise can be categorized as follows: short-term maximal exercise, . . .