Relative and absolute reliability of the crossover and maximum fat oxidation points during treadmill running

Objective: was to investigate the relative and absolute reliability of cross over (COP) and maximal lipid oxidation (LIPOX_max) points during treadmill running in sedentary healthy subjects. Subjects and methods: Twelve sedentary subjects (aged 20.5±1.0years) performed in random sequence two submaximal graded exercise tests to test the criterion standard for reliability of metabolic tests on treadmill over a time interval of four days. Maximal oxygen intake and maximal aerobic velocity (MAS) were assessed, using a progressive maximal exercise test on a treadmill (Cosmed T170, Germany). Subjects performed two submaximal graded exercise tests (T1 and T2), based on the measured maximal aerobic speed (MAS). Respiratory parameters, the COP and the LIPOX_max points, and the maximal fat oxidation rate (MFO) were measured during these submaximal protocols. Results: We found no significant differences between T1 and T2 with respect to COP, LIPOX_max and the MFO. Intra-class correlation (ICC) measures of relative reliability were 0.91 for COP, 0.84 for LIPOX_max and 0.803 for MFO. Coefficients of variation (CV) for COP and MFO values between T1 and T2 were low, falling well within the 10% criterion of absolute reliability (CV_COP=9.0%, CV_MFO=2.6%). However, LIPOX_max showed greater variability (CV= 15.2%). The standard error of measurement±minimal detectable change (SEM±MDC) values were 0.89±2.08mL.min^-1.kg^-1, 1.79±4.17mL.min^-1.kg^-1 and 23.74±65.80mg.min^-1 for COP, LIPOX_max and MFO, respectively. The mean differences (bias)±95% limits of agreement (LOA) were 0.4±5.9mL.min^-1.kg^-1, -0.4±8.8mL.min^-1.kg^-1 and 10.3±104.05mg.min^-1 for COP, LIPOX_max and MFO, respectively. Conclusion: Our data shows that COP, LIPOX_max, and MFO measurements on a treadmill, over a time interval of four days, are reproducible. These metabolic measurements could be used in sedentary subject to calibrate training intensity.