Metabolic and cardio-respiratory responses of four asthmatic and four non-asthmatic athletes to two hours of treadmill running at 70 percent of maximal oxygen uptake are compared. The asthmatic group had pre-exercise airflow obstruction, as indicated by the lower forced expiratory volume in one second (FEV1) even after medication (2.90 +/- 0.661) compared to the non-asthmatic group (4.09 +/- 1.331). Changes in blood lactate, glucose and catecholamine concentrations as a result of the two hour run were similar for the two groups. However, the pattern of breathing was different. The asthmatics had a slower breathing frequency but a similar tidal volume to the non-asthmatics. Both groups had an increase in the ventilation rate over the two hour run. For the non-asthmatic group, this increase in ventilation was achieved by an increase in the breathing frequency (p less than 0.01), whereas tidal volume was reduced (p less than 0.05). The increase in the ventilation rate over the two hour run for the asthmatic group was brought about by a small increase in breathing frequency (p less than 0.05), whereas tidal volume was not changed. This maintenance of the tidal volume by the asthmatic athletes during endurance running may compensate for the airflow obstruction, and so allow successful participation in endurance running.
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