Submaximal Testing to Estimate Aerobic Capacity Using a Matrix C5x Stepmill

The primary purpose of this study was to determine if the Matrix C5x stepmill's preprogrammed submaximal test is able to accurately predict maximal oxygen uptake. Sixteen participants completed a maximal treadmill test and a preprogrammed submaximal test on a Matrix C5x stepmill. Oxygen uptake was measured using a Cosmed K5 during both tests. Maximal oxygen uptake (VO_2max) was calculated from submaximal data using a multi-stage calculation and compared against measured VO_2max from the maximal test and estimated VO_2max from the submaximal stepmill test. METs were also measured during the submaximal test and compared to the METs estimated by the stepmill and METs calculated using submaximal stepping equations. Measured VO_2max (39.18 α 6.6 ml^.kg^-1.min^-1) was significantly higher (p < 0.001) than estimated VO_2max (28.06 α 3.2 ml^.kg^-1.min^-1) and calculated VO_2max (35.58 α 8.0 ml^.kg^-1.min^-1). Measured METs were significantly (p = 0.04) higher than estimated METs in all stages, and higher than calculated METs in stage 1 of the submaximal test. The C5x did not provide accurate estimations of METs or maximal oxygen uptake. Calculating maximal oxygen uptake from submaximal stepmill data may provide an alternative, although development of a new equation may be warranted.