RELIABILITY OF OXYGEN CONSUMPTION AND HEART RATE AS FUNCTIONS OF POWER DEMAND WHILE ROLLER SKIING

T.J. Reinking, B.W. Reinking, & D.P. Heil Montana State University, Bozeman, MT A recent study investigated Nordic skiers’ anaerobic capacities by calculating the accumulated oxygen (VO2) deficit from a maximal roller ski test. The calculation of VO2 deficit required a submaximal graded exercise test (GXT) to assess the relationship between the calculated external power demand (PD) and the skier’s oxygen consumption (VO2). However, the reliability of the protocol used to establish this relationship has not been tested. PURPOSE: To investigate the test-retest reliability of using a roller ski GXT for determining the relationship between physiological markers (VO2 and heart rate) and external power demand. METHODS: Seven male collegiate Nordic ski racers (Mean±SD, Range: 21±1, 19-22 years; 181.5±10.5, 174-198.1 cm; 77.0±13.2, 61.2-100.5 kg) completed two roller skiing GXTs on two separate days with 24-96 hours between trials. Subject heart rate (HR) and VO2 were measured continuously and averages from the last 2 minutes of each 4-minute stage were considered steady-state values. PD was calculated as the sum of rolling resistance from the roller ski wheels on the treadmill and gravitational resistance from treadmill grade. PD was then plotted against steady-state VO2 and HR values. Slope and intercept terms were generated for each variable as a function of the skier’s power output using standard linear regression. Reliability of the slope and intercept terms were evaluated using a two-factor, repeated-measures ANOVA (α=0.05), an intraclass correlation coefficient (ICC) and the standard error of measurement (SEM); the latter two of which were computed for both 2-trial and 1-trial reliability. RESULTS: There were no significant differences between trials for all variables (P=0.69-0.98). ICC values were moderate to high for both 2-trial (0.76-0.95) and 1-trial (0.62-0.91) assessments. Highest ICC values were from VO2 slope and HR slope. Similarly, the SEM was low for both 1-trial and 2-trial VO2 (±0.01 for both) and HR slopes (±0.03 and ±0.02, respectively). HR intercept showed moderate reliability (2-trial ICC=0.86, SEM=±5.06; 1-trial ICC=0.75, SEM=±6.69), and VO2 intercept was slightly less reliable (2-trial ICC=0.77, SEM=±1.75; 1-trial ICC=0.62, SEM=±2.23) CONCLUSIONS: The HR and VO2 slope parameters were both considered more reliable than the corresponding intercept parameters, though all variables showed moderate to high test-retest reliability. This analysis suggests that one roller ski GXT sufficiently approximates the VO2 and HR slope relationships