Agreement analysis between critical power and intensity corresponding to 50% in cycling exercise

Abstract

The purpose of this study was to determine the level of agreement between critical power (CP) and intensity corresponding to 50% of the difference (50% ?) between oxygen uptake (VO₂) at lactate threshold (LT) and maximal oxygen uptake (VO_2max) in untrained subjects during cycling exercise. Fifteen healthy male subjects (age: 26.0 ± 3.5 years; body weight: 76.6 ± 10.4 kg; height: 178.2 ± 7.6 cm) volunteered to participate in the study. Each subject performed a series of tests to determine LT, VO₂LT, CP, VO₂CP, 50% ?, VO₂50% ?, and VO_2max. The values of LT, VO₂LT, CP, VO₂CP, 50% ?, VO₂50% ? and VO_2max were 109 ± 15 W, 1.84 ± 0.23 L.min^-1, 207 ± 17 W, 2.78 ± 0.27 L.min^-1, 206 ± 19 W, 2.77 ± 0.29 L.min^-1, and 3.71 ± 0.49 L.min^-1, respectively. No significant difference was found between CP and 50% ? (t = 0.16; p = 0.87) or between VO₂CP and VO₂50% ? (t = 0.12; p = 0.90). However, the bias ± 95% limits of agreement for comparison between CP and 50% ? and between VO₂CP and VO₂50% ? were 1 ± 27 W (0.3 ± 14.1%) and 0.01 ± 0.24 L.min^-1 (0.2 ± 8.9%), respectively. In summary, the mean CP and 50% ? values were not significantly different. However, considering the limits of agreement between the two intensities, CP estimated based on 50% ? might result in a remarkable error when the absolute variability of individual differences is taken into account