Validation of the firefighter WFI treadmill protocol for predicting VO2 max

Abstract

Background: The Wellness-Fitness Initiative submaximal treadmill exercise test (WFI-TM) is recommended by the US National Fire Protection Agency to assess aerobic capacity (VO. 2 max) in firefighters. However, predicting VO. 2 max from submaximal tests can result in errors leading to erroneous conclusions about fitness. Aims: To investigate the level of agreement between VO. 2 max predicted from the WFI-TM against its direct measurement using exhaled gas analysis. Methods: The WFI-TM was performed to volitional fatigue. Differences between estimated VO2 max (derived from the WFI-TM equation) and direct measurement (exhaled gas analysis) were compared by paired t-test and agreement was determined using Pearson Product-Moment correlation and Bland-Altman analysis. Statistical significance was set at P < 0.05. Results: Fifty-nine men performed the WFI-TM. Mean (standard deviation) values for estimated and measured VO2 max were 44.6 (3.4) and 43.6 (7.9) ml/kg/min, respectively (P < 0.01). The mean bias by which WFI-TM overestimated VO2 max was 0.9ml/kg/min with a 95% prediction interval of ±13.1. Prediction errors for 22% of subjects were within ±5%; 36% had errors greater than or equal to ±15% and 7% had greater than ±30% errors. The correlation between predicted and measured VO2 max was r = 0.55 (standard error of the estimate = 2.8ml/kg/min). Conclusions: WFI-TM predicts VO. 2 max with 11% error. There is a tendency to overestimate aerobic capacity in less fit individuals and to underestimate it in more fit individuals leading to a clustering of values around 42ml/kg/min, a criterion used by some fire departments to assess fitness for duty.