Author(s): NUUTTILA, O., MALINEN, T., SIEVÄNEN, H., VASANKARI, T., KYRÖLÄINEN H., Institution: THE UKK INSTITUTE FOR HEALTH PROMOTION RESEARCH, Country: FINLAND, Abstract-ID: 2535

INTRODUCTION:
Maximal oxygen uptake (VO2max) and metabolic thresholds provide valuable information about an individual’s cardiorespiratory fitness that can also be used for personalized exercise intensity prescription. The gold-standard assessments of these outcomes require maximal exercise testing with direct pulmonary gas exchange measurements and/or blood lactate sampling. Several prediction equations have been developed for estimating VO2max from feasible submaximal tests, but estimation methods for metabolic thresholds are more limited. This study evaluated: 1) whether a 6 minute walking test (6MWT) can be used to validly estimate VO2max and ventilatory thresholds (VTs) in a cross-sectional setting, and 2) whether estimated changes in VO2max and VTs align with respective measured changes after a 9 week training intervention.
METHODS:
Thirty healthy, untrained females (41 ± 7 years) completed an incremental treadmill test to determine VO2max and VO2 at VT1 and VT2 before and after the training period. The 6MWT was performed during the same week on a separate visit. Stepwise linear regression was used to identify predictors for VT1, VT2, and VO2max, and to generate prediction equations. The accuracy of these equations was assessed using the coefficient of determination (R²) and standard error of estimate (SEE), and they were further compared with five previously published 6MWT-derived VO2max prediction equations. Pearson correlation coefficient was used to examine associations between measured and estimated changes. In addition, receiver operating characteristics (ROC) analysis was used to test the sensitivity of the 6MWT to detect meaningful improvements in VTs or VO2max (>1 metabolic equivalent).
RESULTS:
Formulated prediction equations estimated VT1 (R² = 0.57, SEE = 3.3 ml/kg/min), VT2 (R² = 0.78, SEE = 2.2 ml/kg/min), and VO2max (R² = 0.69, SEE = 3.0 ml/kg/min) with moderate accuracy. Previously published VO2max models showed R² values of 0.27–0.61 and SEE of 3.7–6.1 ml/kg/min. Correlations between estimated and measured pre–post changes varied from weak to small (r = 0.02–0.29). ROC analysis indicated significant discrimination (p < 0.05) for meaningful improvements using the formulated VO2max and VT₁ equations. These equations required information on body mass index, percentage of estimated heart rate reserve used, and walking distance.
CONCLUSION:
VO2max and VTs can be predicted with moderate accuracy from the 6MWT in a cross-sectional setting. Detecting small longitudinal changes remains challenging, but meaningful improvements appear detectable when heart rate is included in the prediction equation. When using the 6MWT as an indicator of cardiorespiratory fitness adaptations, it is important to recognize the limitations of VO2max prediction equations that do not incorporate measures of internal load.