Abstract des Autors

We examined the effect of metabolic acidosis, induced by dynamic exercise, on ventilation, lactate concentration and EMG activity. Seven subjects performed two consecutive incremental exercise tests until volitional exhaustion. The two tests were indentical and were separated by a 7-min period of light exercise. During the tests, ventilation, mixed expired oxygen and carbon dioxide, arterialized venous blood and EMG activity from the vastus lateralis was sampled. The results showed that the ventilation and EMG measurements followed a similar time course during both tests, although ventilation during the initial 6 min of the second test was significantly greater than the values recorded during the first test. In addition, throughout the first test lactate concentration increased with time, and pH, bicarbonate concentration and partial pressurre of carbon dioxide decreased. In contrast, during the second test, lactate concentration decreased, and pH and bicarbonate concentration increased; during a period of time when ventilation and EMG activity were increasing. These findings have led us to conclude that changes in ventilation and EMG activity observed during incremental exercise are not related to changes in blood lactate concentration. It is suggested that the changes in ventilatiton are mediated by an increase in neural activity orginating from the subthalamic motor region or exercising limbs, induced in response to the need to progreesively recruit fast twitch muscle fibres as exercise work rate is increased.