DOES PEAK INSPIRATORY FLOW CONTRIBUTE TO SETTING V(O-2MAX)

Symmorphosis predicts that animal design is optimized in such a way th at structure 'satisfies but does not exceed' functional requirements. To provide one test of this hypothesis, we examined peak inspiratory f low and its relation to maximum oxygen uptake in humans. We measured m aximal forced (peak) inspiratory flow (VImax) and maximum oxygen uptak e (V-o2max) via cycle ergometry in well trained (V-o2max>65 ml O-2.kg( -1).min(-1)) and untrained (V(o2)max<45 ml O-2.kg(-1).min(-1)) male su bjects. Tests of VImax and peak oxygen uptake (V-o2peak) were made whi le the subjects were breathing through inspiratory orifices differing in area. VImax varied as an identical function of orifice diameter in both groups of subjects. However, V-o2peak was more sensitive to decre asing orifice diameter in trained endurance athletes than it was in un trained individuals. The diameter of the largest orifice that caused a reduction in oxygen uptake was over two times larger for trained than for untrained subjects, corresponding to about a four-fold difference in resistance at any flow rate. These results suggest that the struct ures setting VImax (airway resistance and inspiratory muscle strength) are not matched to oxygen demand (V-o2max) in humans. While these str uctures seem to be 'over-built' and hence do not likely contribute to setting the limits to aerobic performance in most humans, they may be among the primary limiting factors in the most elite endurance athelet s.