RESPIRATORY MUSCLE FUNCTION IN TRAINED AND UNTRAINED ADOLESCENTS DURING SHORT-TERM HIGH-INTENSITY EXERCISE

The breathing pattern and respiratory muscle function were investigate d in ten trained and ten untrained adolescents (aged 15-16 years) whil e undergoing an incremental intensity exercise test on a cycle ergomet er up to 80% maximal oxygen consumption (VO2max), maintained to exhaus tion. Before and after exercise, maximal inspiratory (P(Imax)) and exp iratory (P(Emax)) pressures were measured at residual volume and total lung capacity, respectively. During exercise, the breathing pattern [ tidal volume (V(T)), respiratory frequency (f(R)), ventilation] and th e relative contribution of ribcage and abdomen to V(T) were assessed u sing inductance plethysmography. Electromyographic activities of trans versus abdominis (EMG(tr)) and diaphragm (EMG(di)) Muscles were record ed and analysed during exercise. There was a difference in the change in the pattern of breathing between the trained and the untrained grou p; f(R) increased significantly (P<0.05) at 40% VO2max for the untrain ed group. Before exercise there was no difference in the maximal respi ratory pressures. Up to 60% and 80% VO2max, transversus abdominis and diaphragm muscle activity increased significantly in the trained adole scents. However in this group, no evidence of respiratory muscle fatig ue appeared: P(Imax), P(Emax) and the frequency spectrum of EMG(tr) an d EMG(di) were not altered by exercise up to exhaustion. In the untrai ned group, who had high ventilatory responses, expiratory muscle funct ion was unchanged at the end of the exercise, but signs of inspiratory muscle fatigue appeared in that P(Imax) was significantly decreased a fter exercise.