A New Step Test-Derived Fitness Index to Predict Maximal Functional Capacity in Healthy Persons

Abstract

PURPOSE: This study addresses the need for an easily-administered fitness test, which is a valid and useful proxy for measuring maximal exercise capacity for health risk appraisal. METHODS: We validated a step-test-derived fitness index (the BODY iQ fitness index) by comparing it to measured maximal oxygen uptake (VO2max) derived from the Bruce treadmill test. Subjects included 38 men (36 + 1 yrs; BMI 24.6 + 0.4 kg/m2) and 26 women (36 + 2 yrs; BMI 22.8 + 0.5 kg/m2). The 14 min step test was comprised of 4 × 2 min workloads separated by three 2 min rest periods (25 cm starting at 20 steps/min up to 30 steps/min). The predicted peak workload (peakMETs) was calculated from individually-determined slope of the heart rate (HR)-workload relationship, and extrapolated to age-predicted maximal HR. PeakMETs, body fat %, gender, age and self-reported physical activity (max METhrs/wk) were entered into a regression analysis to predict maximal exercise capacity (VO2max). RESULTS: The test-re-test reliability coefficient for the peakMETs was r = 0.74 (p < 0.001), suggesting that the test is reliable. The final regression equation for predicting VO2max (from Bruce protocol) incorporated the following variables: BODY iQ Fitness Index (as a proxy for VO2max) = 47.6 - (age * 0.102) - (gender * 0.888) - (%body fat * 0.733) + (peakMETs * 0.795) + (max METhrs/wk * 0.155); where men = 1 and women = 2. This model explained more than 76% of the variance in estimated VO2max (SEE: 5.20). CONCLUSION: These data suggest that peakMETs derived from the HR response to a novel, intermittent step test has good test-retest reliability, and together with gender, age, fatness and reported physical activity levels explains more than 76% of the variance in estimated exercise capacity. It is proposed that the BODY iQ Fitness Index may be used as a useful proxy for maximal exercise capacity for purposes of health risk appraisal. Sponsored by BODY iQ.