Accuracy of the VO2peak prediction equation in firefighters

Abstract

Background: A leading contributing factor to firefighter injury and death is lack of fitness. Therefore, the Fire Service Joint Labor Management Wellness-Fitness Initiative (WFI) was established that includes a focus on providing fitness assessments to all fire service personnel. The current fitness assessment includes a submaximal exercise test protocol and associated prediction equation to predict individual VO2peak as a measure of fitness. There is limited information on the accuracy, precision, and sources of error of this prediction equation. This study replicated previous research by validating the accuracy of the WFI VO2peak prediction equation for a group of firefighters and further examining potential sources of error for an individual firefighters' assessment.

Methods: The sample consisted of 22 firefighters who completed a maximal exercise test protocol similar to the WFI submaximal protocol, but the test was terminated when firefighters reached a maximal level of exertion (i.e., measured VO2peak). We then calculated the predicted VO2peak based on the WFI prediction equation along with individual firefighters' body mass index (BMI) and 85% of maximum heart rate. The data were analyzed using paired samples t-tests in SPSS v. 21.0.

Results: The difference between predicted and measured VO2peak was -0.77 ± 8.35 mL•kg(-1)•min(-1). However, there was a weak, statistically non-significant association between measured VO2peak and predicted VO2peak (R(2) = 0.09, F(1,21) = 2.05, p = 0.17). The intraclass correlation coefficient (ICC = 0.215, p > 0.05) and Pearson (r = 0.31, p = 0.17) and Spearman (ρ = 0.28, p = 0.21) correlation coefficients were small. The standard error of the estimate (SEE) was 8.5 mL•kg(-1)•min(-1). Further, both age and baseline fitness level were associated with increased inaccuracy of the prediction equation.

Conclusions: We provide data on the inaccuracy and sources of error for the WFI VO2peak prediction equation for predicting fitness level in individual firefighters, despite apparently accurate predictions for a group of firefighters. These results suggest that the WFI prediction equation may need to be reevaluated as a means of precisely determining fitness for individual firefighters, which may affect employment status, duty assignment, and overall life safety of the firefighter.

Keywords: Aerobic capacity; Evaluation; Firefighter; Fitness; Validation.

Figure 1

Scatterplot along with line of best fit and 95% confidence limits for the association between measured and predicted VO _2peak .

Figure 2

Bland-Altman plot of the difference between measured and predicted VO_2peak as a function of the mean of measured and predicted VO_2peak in the entire sample. The lines represent average ±2SDS.