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Validation of a cross country ski simulator as an ergometer
Ten trained male cross-country ski athletes were studied during maximal, incremental exercise testing on Quinton treadmill (TM) and calibrated “Nordictrack” Cross Country Ski Simulator (X-C) at equated workloads. Each subject was tested to determine if Physiological differences existed in VO2 (ml./kg.min.), HR (beats/min.), and Respiratory Exchange Ration (R). The design consisted of five continuous states of submaximal, incremental work, culminating in a maximal effort on both modes. Pearson’s correlation coefficient between mechanical workloads on the two modes was 0.997 (P<.05) between modes (TM=194, X-C=189). This HR difference was not considered to be of practical significance. Two-way ANOVA with repeated measures for both stages and mode on the five submaximal stages revealed significant difference in both HR and VO2 (P<.05). This finding suggested an error in the calculation of work performed on the X-C simulator by subjects’ upper extremities and other ancillary muscles used in trunk support. A regression equation was development based on the relationship between TM VO2 responses and TM work per stage. This equation was then used to predict X-C work from VO2 responses. Five subjects previously used in data collection underwent further TM testing to determine the reliability of the regression equation. Mechanical workloads for the five submaximal stages on the X-C ski simulator were then adjusted to correspond to the work performed on TM. Two-way ANOVA with repeated measures was used to compare VO2 differences between the TM and X-C ski simulator and submaximal stages of work adjusted by the regression equation. This analysis revealed no significant differences in VO2 or HR between modes. To verify X-C work predicted by the regression equation, a metabolic component method, which consisted of the summation of metabolic work performed at RMR with work performed by the upper and lower extremities, and trunk extensors as recommended in the A.C.S.M. Guidelines for Exercise Testing and Prescription was used as a second predictor of mechanical work on the X-C ski simulator. Repeated measure ANOVA revealed no significant differences between original TM work, work predicted by the regression equation, and work predicted by the metabolic component method. It was concluded that there were no remarkable physiological differences between modes, when equivalent work was performed at five submaximal stages, or at maximum exercise. This study and its findings demonstrate, for the first time, a method for measuring mechanical work on the X-C ski simulator and the effectiveness of the X-C ski simulator as an ergometer. Future research is being planned with an expanded sample, to test the validity of the metabolic work calculation and to validate the regression equation on an independent sample of subjects.