Effects of Treadmill Exercise Protocol with Constant and Ascending Grade on Levelling-Off O₂ Uptake and VO₂max

Abstract

In order to investigate the effect of an exercise protocol on the levelling-off O₂ uptake and VO₂max values, ten male subjects aged 28 ± 5 yrs, height 1.8 ± 0.05 m, body mass 76 ± 6 kg performed two treadmill exercise protocols: 1) constant grade (CG) of 5 %, with increasing running speed starting at 6 km · h^-1 and increments of 2 km h^-1 every 3 minutes. 2) ascending grade (AC) 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 concentration (La) and heart rate (HR) were measured. In CG a levelling-off phenomenon of VO₂ in all cases was observed. Aerobic capacity expressed as VO₂max in CG was 46.2 ± 6.0 ml min^-1 kg^-1. In contrast, VO₂max was 35 % higher in AC (62.6 ± 7.2 ml min^-1 · kg^-1). The behaviour of VO₂ indicates a lower efficiency with increasing work load in AC as compared to CG. Regarding maximum performance it can be concluded that VO₂ in CC seems to be limited by a mechanical or neuromuscular constraint on the depth of breathing, which is confirmed by a distinct flattening of V_T. The levelling-off of the VO₂ in CG, something which is not observed in AC, can be explained plausibly this way.

Key words

Treadmill ergometry - ascending treadmill protocol - spiroergometry