In many patients with muscle weakness, exercise is limited, and therefore, maximum oxygen consumption is reduced because of weakness of the leg muscles rather than cardiorespi-ratory factors. The limited available data suggest that the relation of workload to oxygen consumption is normal, as also are indices of submaximal exercise performance (42).
Formal testing allows confirmation and quantification of exercise incapacity and may aid elucidation of its mechanism.
Exercise is limited by weakness of nonrespiratory muscles in many patients with neuromuscular disease. Exercise testing is poorly standardized in this patient population.
Exercise testing may help determine the main factor(s) limiting exercise capacity, especially if related or coexistent cardiac or pulmonary disease is present or suspected.
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