1. Six healthy male subjects followed a programme of endurance training for 36 weeks. At 12 week intervals each underwent an incremental exercise test to maximum on a treadmill. Minute ventilation, cardiac frequency, expired and end-tidal concentrations of oxygen and carbon dioxide, oxygen uptake and carbon dioxide output were measured continuously during each test.

2. Anaerobic threshold (AT) was determined non-invasively as the onset of sustained increases in each of the ventilatory equivalent for oxygen, expired and end-tidal concentrations of oxygen followed by an increase in ventilatory equivalent for carbon dioxide after a brief delay due to isocapnic buffering. A new computerized cumulative-sum method was employed.

3. Significant increases in maximum oxygen uptake (Vo2 max.) of 13.6%, AT (32.3%) and % AT/Vo2 max. (17.0%) and a significant decrease (10.2%) in cardiac frequency at an oxygen uptake of 1.0 litres/min (fc1.0) were observed at the completion of the training programme.

4. The time courses of the changes for each of AT, Vo2 max. and fc1.0 were not identical during the training. Compared with Vo2 max. the disproportionate increases in AT occurred earlier and were usually completed within 12 weeks. Vo2 max. increased for the first 24 weeks of training, but showed no further increase over the final 12 weeks. fc1.0 decreased through the whole training period.

5. The improved AT after training is more likely to be related to improved peripheral utilization of oxygen than to an improved oxygen delivery to muscles.

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