ABSTRACT
Exercise intolerance can be defined as the inability of a subject to sustain a required work rate sufficiently long for the successful completion of the task, because the oxygen demand exceeds the maximal oxygen conductance capability of the oxygen transport chain. In fact, at maximum exercise, muscle respiration increases by a factor of 30-80, and the cardiovascular and ventilatory systems must respond appropriately to achieve the increased cellular respiration required to generate the highenergy phosphate needed for muscle contraction.
