Maximal oxygen uptake: "old" and "new" arguments for a cardiovascular limitation.

The research performed over the last 100 yr in regard to oxygen transport during exercise is reviewed. Special focus is on major shifts in views held on which link may limit maximal oxygen uptake of an individual exercising with a large fraction of the muscle mass. Initially the pump capacity of the heart was proposed as the critical factor, a view basically unchallenged until results on the plasticity of muscle came about in the 1960-70s. The capillary bed of the muscle and its mitochondrial volumes can be enhanced with training. These adaptations were then suggested to be prerequisites for maximal oxygen uptake to become elevated. The pendulum is slowly swinging back again toward heart and lungs setting the upper limit for the oxygen transport. It appears to be in the range of 80-90 ml.kg-1.min-1 or 150-200 ml.kg-1 muscle.min-1, which can easily be consumed by a fraction of the muscle mass intensely contracting.