engleski

maximal respiratory exchange ratio and test duration in runners

The respiratory exchange ratio registered at maximal exercise in graded exercise tests (RERmax) is used as a criterion for test interpretation, and confirmation that maximal oxygen uptake has been obtained. Several arbitrary ’cut-off’ values (i.e. 1.00, 1.10, 1.15) are used for acceptance or rejection of exercise tests. The steeper is the ramp slope (the work-rate increase per unit of time), the shorter is the duration of the incremental test, yielding greater rates of CO2 output and higher RERmax values. However, the relationship between RERmax and test duration has not been clearly defined. The aim of this study was to determine the relationship between RERmax and duration of all-out incremental treadmill tests, in runners competing in different running events. The sample consisted of 48 male runners: 25 sprinters, and 23 middle/long distance runners. All subjects performed three incremental treadmill tests to the limit of tolerance in random order, with increases in running speed: a) 1 km/h each ½ minute (T0.5), b) 1 km/h each minute (T1), and c) 2 km/h every four minutes (T2). In all trials, the starting running speed was 8 km/h, with a constant inclination of 1.5%. Gas exchange data were recorded breath-by-breath and analyzed (Quark b2, Cosmed). Regression analysis of pooled data was used to model the relationship between RERmax and the duration of the tests. Two-way ANOVA was used to determine differences in the measured variables between the tests and the groups. The average test durations were 7.6±1.0 min (T0.5), 13.0±2.1 min (T1) and 22.8±4.1 min. The mean VO2max values did not differ between protocols (p>0.10). With increasing duration of the test, a progressive decrease of maximal respiratory exchange ratio was found. The RERmax mean values were as follows: 1.23±0.10 (T0.5), 1.18±0.08 (T1) and 1.12±0.07 (T2), and the differences between tests were statistically highly significant (p<0.001). The regression analysis of pooled data showed an inverse linear relationship between RERmax and test duration (RERmax=1.272-0.0064min). For the same absolute test duration, a trend towards higher RERmax values in sprinters than in aerobically trained runners was present. CONCLUSIONS. In incremental treadmill tests of 5 to 30 minutes duration, performed to the limit of tolerance, runners of various predominantly anaerobic (100m-400m) and predominantly aerobic (800m-marathon) specific events show an inverse linear relationship between test duration and the respiratory exchange ratio at maximal exercise. For practical implications, the RERmax value used as a VO2max criterion in the interpretation of graded exercise testing should be protocol dependent.

running; respiratory exchange ratio; graded exercise test

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