Reliability and Validity of a Maximal Treadmill Test for Predicting Aerobic Fitness in Norwegian Prospective Soldiers.

Introduction: The Norwegian armed forces reintroduced physical fitness testing of prospective conscript soldiers in 2011. Since then, a customized maximal treadmill test (MILMAX) has been used to screen aerobic fitness in 15-20,000 young Norwegian men and women annually. The aim of the current study was to investigate reliability and validity of the MILMAX test.

Materials And Methods: Sixty-seven young Army recruits (including 11 women) participated in this method comparison study. The subjects completed the MILMAX test twice (test-retest), consisting of walking and running at increasing speed and inclination until voluntarily exhaustion. Performance was registered as exercise tolerance time (ETT). Later, the subjects performed a treadmill test of direct maximal oxygen uptake (V̇O2max). All tests were conducted within 15 days. The study protocol was submitted to the Regional Committee for Medical and Health Research Ethics for review, prior to study initiation. The Committee considered the study to be exempted from notification. The study was carried out according to the guidelines in the Declaration of Helsinki.

Results: There was no significant mean difference in MILMAX ETT between test and retest. Test-retest intraclass correlation coefficient was 0.95 (0.91, 0.97), while 95% limits of agreement was ± 60 seconds. Regression analyses showed that MILMAX ETT and gender explained 78% of the variance in directly measured V̇O2max, and a prediction equation with these two independent variables was generated. The Pearson correlation coefficient between predicted and directly measured V̇O2max was 0.89 (0.83, 0.93), while limits of agreement was ± 5.6 mL·kg-1·min-1.

Conclusions: The MILMAX is equally reliable and valid compared with well-known maximal indirect tests like the 2-mile run and the 20-m shuttle run test, and may serve as an alternative indoor test of aerobic fitness in the military, in other potentially physically strenuous occupations, or in healthy civilians.