Objective: The objective was to assess the reliability of the crossover point (COP) and maximal fat oxidation (LIPOXmax) points in sedentary young men. Methods: Maximal oxygen intake was assessed in 12 sedentary subjects (aged 20.5. ±. 1.0 years), using a progressive maximal cycle ergometer test. They performed in random sequence, two submaximal graded exercise tests (E1 and E2), based on the measured maximal aerobic power (MAP) to test the reliability. The tests were separated by 4-day interval. Blood lactate, heart rate, respiratory parameters, the COP and the LIPOXmax points were measured during these submaximal exercises. Results: We found no significant differences between E1 and E2 with respect to COP, LIPOXmax, and the corresponding heart rates. Coefficients of variation for COP and LIPOXmax values between E1 and E2 were low, falling well within the 10% criterion of absolute reliability. ICC measures of relative reliability were 0.96 for COP and 0.97 for LIPOXmax. The mean differences (bias). ±. the 95% limits of agreement were 0.006. ±. 0.066, -1.3. ±. 12.15. W and 0.6. ±. 7.1. W for the non-protein respiratory quotient (RER), COP and LIPOXmax, respectively. The smallest worthwhile changes for COP and LIPOXmax were 3.5 and 3.0%, respectively. The ventilatory threshold was significantly correlated to COP (r. = 0.88, P<. 0.001) and to LIPOXmax (r. = 0.85, P<. 0.001). Conclusion: With appropriate care in establishing individualized submaximal protocol based on measured MAP, COP and LIPOXmax values have a good relative and absolute reliability in sedentary subjects, when they are retested over a 4-day interval. Moreover, during cycle ergometry, both of these indices are strongly correlated with the individual's ventilatory threshold.
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