EFFECTS OF TREADMILL EXERCISE PROTOCOL WITH CONSTANT AND ASCENDING GRADE ON LEVELING-OFF O-2 UPTAKE AND VO(2)MAX

In order to investigate the effect of an exercise protocol on the leve lling-off O-2 uptake and VO(2)max values, ten male subjects aged 28+/- 5 yrs, height 1.8+/-0.05 m, body mass 76+/-6 kg performed two treadmil l exercise protocols: 1) constant grade (CG) of 5 %, with increasing r unning speed starting at 6 km . h(-1) and increments of 2 km . h(-1) e very 3 minutes. 2) ascending grade (AG) starting at 0 % and increments of 5 % every 3 minutes, with constant running speed of 5 km . h(-1). During each protocol oxygen uptake (VO2), pulmonary ventilation (VE), tidal volume (V-T), and breathing rate (BR) as well as blood lactate c oncentration (La) and heart rate (HR) were measured. In CG a levelling -off phenomenon of VO2 in all cases was observed. Aerobic capacity exp ressed as VO(2)max in CG was 46.2+/-6.0 ml . min(-1). kg(-1). In contr ast, VO(2)max was 35 % higher in AG (62.6+/-7.2 ml . min(-1). kg(-1)). The behaviour of VO2 indicates a lower efficiency with increasing wor k load in AG as compared to CG. Regarding maximum performance it can b e concluded that VO2 in CG seems to be limited by a mechanical or neur omuscular constraint on the depth of breathing, which is confirmed by a distinct flattening of V-T. The levelling-off of the VO2 in CG, some thing which is not observed in AG, can be explained plausibly this way .