Abstract

Background: A plateau in oxygen consumption (o₂) is the primary means of confirming that maximal oxygen uptake (o₂max) is attained during incremental exercise to fatigue. However, it is still unresolved what causes expression of a plateau in o₂ at the end of incremental exercise.

Objectives: To elucidate incidence and identify determinants of the o₂ plateau in subjects of varying fitness.

Methods: Thirty subjects (mean (SD) age and o₂max 26.9 (9.8) years and 3.4 (0.8) litre/min respectively) were separated into three groups: endurance trained (ET; n  =  9), recreationally active (Rec; n  =  11), and strength/sprint trained (STR; n  =  10). During three separate visits, subjects completed incremental treadmill exercise during which breath by breath gas exchange data were obtained. Body composition was measured using a three site skinfolds model. Force production of the knee extensors and flexors was assessed using isokinetic dynamometry.

Results:o₂max was significantly higher (p<0.05) in the ET group vs STR and Rec. The change in o₂ (Δo₂) at o₂max was not different (p>0.05) in the ET group (33.0 (27.3) ml/min) compared with the Rec group (30.3 (24.1) ml/min) and the STR group (44.4 (23.8) ml/min). No correlations (p>0.05) were evident between Δo₂ at o₂max and o₂max (r  =  0.05), fat-free mass (r  =  0.12), and muscular strength (r  =  −0.12).

Conclusions: The incidence of a plateau in o₂ at o₂max (from correlation data) is not due to factors related to training status or physical fitness of subjects, but is altered by analysis and interpretation of gas exchange data.