Validity of oxygen uptake cut-off criteria in plateau identification during horizontal treadmill running

When determining achievement of maximal oxygen uptake (V̇O2max) during treadmill running using speed increments, the V̇O2 cut-off criteria applied during plateau identification is often not justified, not protocol specific, or not related to actual change in V̇O2 (ΔV̇O2) with speed increment, which can influence plateau achievement rates between studies. The purpose of this study was to compare plateau incidence using an individualised plateau criteria approach based on a "percentage" ΔV̇O2 compared to using previously established criteria of ΔV̇O2≤2.1 mL∙kg-1∙min-1 not developed on running speed.

Fifty-four males completed a ramp horizontal treadmill test with 0.5 or 1.0 km∙h-1 per minute (km∙h-1∙min-1) speed increments to measure V̇O2max. Average Δ V̇O2 for the each 1-minute speed increment was determined and used to develop individualised cut-off criteria deemed to be a plateau: a final ΔV̇O2 of less than 50% of the average change elicited between consecutive speed increments during the test (V̇O2≤50%); plateau incidence using this was compared to ΔV̇O2≤2.1 mL∙kg-1∙min-1 (V̇O2≤2.1).

Mean ΔV̇O2 was 1.74±0.59 and 3.09±0.59 mL∙kg-1∙min-1 for 0.5 and 1.0 km∙h-1∙min-1increments respectively. V̇O2 cut-off criteria were met by 48%/65% (1.0 km∙h-1∙min-1) (P=0.234) and 53%/100% (0.5 km∙h-1∙min-1) (P=0.003) for V̇O2≤50% and V̇O2≤2.1 respectively.

Use of V̇O2≤2.1 resulted in distortedly high plateau achievement, particularly for smaller speed increments where the V̇O2-speed relationship was actually less than V̇O2≤2.1 making its use inappropriate. Use of V̇O2≤50% may be a suitable alternative, but as a plateau was not consistently demonstrated, application of cut-off criteria should not be a requirement in deciding whether one's achieved V̇O2max.