Evaluating the FitMáx questionnaire for fitness-to-dive assessments in a military population

This study evaluated the validity of the FitMáx questionnaire for estimating VO₂peak in 157 Dutch Navy divers and recompression personnel, a population characterised by high physical fitness and occupational demands. While self-reported questionnaires offer a logistically feasible alternative to resource-intensive direct testing, their accuracy in fitness-to-dive assessments remains unclear. Participants completed the FitMáx questionnaire prior to cycle ergometry with direct VO₂peak measurement. Results showed a moderate correlation (r = 0.631, P < 0.001) between mean estimated VO₂max (43.7, SD 5.34 mL·kg^-1·min^-1) and mean measured VO₂peak (45.4, SD 6.52 mL·kg^-1·min^-1), with the questionnaire systematically underestimating fitness by 1.8 mL·kg^-1·min^-1, with a 95% confidence interval of agreement limit of ± 10.9 mL·kg^-1·min^-1, and a moderate intraclass correlation coefficient of 0.748 (P < 0.001). False-positive and false-negative rates were 8.9% and 10.8%, respectively, raising concerns about reliability for pass/fail decisions. Participants reported difficulties answering questions unrelated to their routine activities, potentially contributing to the observed variability. Given these limitations, including the homogeneous, highly fit sample and the inability to differentiate between subgroups, the Royal Netherlands Navy Diving Medical Center has not adopted the FitMáx for fitness-to-dive evaluations. While questionnaires may streamline large-scale assessments, direct exercise testing remains valuable for precise, individualised risk stratification in occupational diving.