Combined effects of breathing resistance and hyperoxia on aerobic work tolerance.

Effects of three curvilinear inspiratory resistances (R1, R2, R3) on the cardiorespiratory responses of seven well-trained men during incremental cycling tests to exhaustion were studied by comparison to the low resistance R0 (at 1 l/s, R0 = 0.2; R3 = 6.5 cmH2O-s/l). Submaximal VO2 and the gas exchange anaerobic threshold (AT) were not affected by increasing resistance. Although maximal work rates were not significantly changed, highly significant reductions were observed for VE (R0 = 166.3; R3 = 99.7 l/min BTPS), VO2 max (R0 = 4,26; R3 = 3.74 l/min), HR (R0 = 185; R3 = 176 beats/min), and endurance (R0 = 17.3; R3 = 15.5 min) suggesting that aerobic work tolerance was dependent on ventilatory capacity. In additional tests removal of R3 at exhaustion abruptly increased VE and VO2, and permitted work to continue. Ventilation and work tolerance were therefore limited by R3 before the legs fatigued. Breathing 35% O2 against R3 produced significant, although small, increases in AT, VO2 max, peak HR, and endurance while decreasing the hyperventilatory response to work above AT. Thus, aerobic work tolerance reduced with high inspiratory resistance was partly restored by moderate hyperoxia, apparently because the ventilatory limit was delayed.