Deciphering the limits to human maximal exercise performance

It has remained unknown during centuries what is the main factor limiting maximal exercise capacity in humans. During the past century evidence has accumulated suggesting that maximal exercise capacity in humans is limited by the maximal amount of O2 that can be delivered to the active muscles.

A rather important step in this direction was the finding that blood flow may reach maximal values around 2-4 l kg-1 min-1 in the quadriceps muscle during maximal knee extension exercise. Since the mean muscle mass of the quadriceps muscle is about 2.5 kg, it was suggested that this magnitude of perfusion would overwhelm the pumping capacity of the heart (which lies close to 25 l.min-1 in normal young humans) if a similar level of hyperaemia could be elicited during whole body exercise in the majority of active muscles.

By studying elite athletic humans with highly trained arm and legs muscles (cross-country skiers), Dr Jose A. Calbet and a team of Scandinavian colleagues led by Professor Bengt Saltin present, in the forthcoming issue of The Journal of Physiology, conclusive evidence showing that during maximal exercise in the upright position the combined maximal arm and leg blood flows surpass the maximal pumping capacity of the heart.

The latter means that to avoid hypotension during maximal exercise in the upright position, humans must restrain the voracity for blood flow of active muscles. This finding may facilitate the comprehension of several pathologic conditions characterised by reduced exercise tolerance and may guide some new therapeutic approaches.

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