How long does it take to achieve steady state for an accurate assessment of resting \( \dot{\text{V}}{\text{O}}_{2} \) in healthy men?

The time necessary to obtain a steady state for an accurate and reliable assessment of resting \( \dot{V}{\text{O}}_{2} \) remains unclear and was the purpose of this study. Thirty healthy men, aged 17–28 years, visited the laboratory twice for the assessment of resting \( \dot{V}{\text{O}}_{2} \), which was assessed as follows: (a) 24 h abstention from physical exercise, alcohol, soft drinks and caffeine, (b) fasting for at least 8 h, (c) an acclimation period of 10 min, and (d) 60 min assessment in a supine position. Resting \( \dot{V}{\text{O}}_{2} \) significantly changed during the 60 min (F = 37.4, P < 0.001), exhibiting a monoexponential decrease before reaching an asymptote. Post hoc pairwise comparisons showed that significant differences existed between consecutive means until the 30 min time point, after which there were no significant differences. The \( \dot{V}{\text{O}}_{2} \) response across trials exhibited high test–retest reliability, with within-subject coefficients of variations at each time point ranging from 2.8 to 7.0 % and intraclass correlation coefficients ranging from 0.90 to 0.99. The reliability was higher from the 25 min time point onwards. Based on these findings, the following recommendations are made to promote accurate assessment of resting \( \dot{V}{\text{O}}_{2} \): (a) initiate the resting \( \dot{V}{\text{O}}_{2} \) measurement with 10 min of acclimation to the assessment apparatus, (b) determine resting \( \dot{V}{\text{O}}_{2} \) for a minimum of 30 min, until an apparent \( \dot{V}{\text{O}}_{2} \) steady state has been achieved; and (c) determine resting \( \dot{V}{\text{O}}_{2} \) for a further 5 min, with the average of this last 5 min of data being regarding as the resting \( \dot{V}{\text{O}}_{2} \).