Abstract
To investigate the agreement between critical power (CP) and functional threshold power (FTP), 17 trained cyclists and triathletes (mean ± SD: age 31 ± 9 years, body mass 80 ± 10 kg, maximal aerobic power 350 ± 56 W, peak oxygen consumption 51 ± 10 mL⋅min–1⋅kg–1) performed a maximal incremental ramp test, a single-visit CP test and a 20-min time trial (TT) test in randomized order on three different days. CP was determined using a time-trial (TT) protocol of three durations (12, 7, and 3 min) interspersed by 30 min passive rest. FTP was calculated as 95% of 20-min mean power achieved during the TT. Differences between means were examined using magnitude-based inferences and a paired-samples t-test. Effect sizes are reported as Cohen’s d. Agreement between CP and FTP was assessed using the 95% limits of agreement (LoA) method and Pearson correlation coefficient. There was a 91.7% probability that CP (256 ± 50 W) was higher than FTP (249 ± 44 W). Indeed, CP was significantly higher compared to FTP (P = 0.041) which was associated with a trivial effect size (d = 0.04). The mean bias between CP and FTP was 7 ± 13 W and LoA were −19 to 33 W. Even though strong correlations exist between CP and FTP (r = 0.969; P < 0.001), the chance of meaningful differences in terms of performance (1% smallest worthwhile change), were greater than 90%. With relatively large ranges for LoA between variables, these values generally should not be used interchangeably. Caution should consequently be exercised when choosing between FTP and CP for the purposes of performance analysis.
Highlights
Sport scientists, athletes, and coaches intuitively understand that as exercise intensity increases, a point is reached where a maximal metabolic steady state occurs, beyond which perceptions of effort and physiological perturbations progress more rapidly
functional threshold power (FTP) was calculated as 95% of the 20 min maximal measured PO (20MMP) obtained during the time trial (TT) (Allen and Coggan, 2010; Denham et al, 2017; Borszcz et al, 2018; Valenzuela et al, 2018)
Significant main effects and a large effect size were found between critical power (CP), FTP, and 20MMP (F2,32 = 13.029; P < 0.001; η2p = 0.45)
Summary
Athletes, and coaches intuitively understand that as exercise intensity increases, a point is reached where a maximal metabolic steady state occurs, beyond which perceptions of effort and physiological perturbations progress more rapidly (for review see: Jones et al, 2019) These perceptions of physical discomfort are associated with mechanisms of peripheral fatigue which lead to task failure (Hureau et al, 2018). During laboratory testing this threshold is usually identified using lactate landmarks (e.g., lactate turning point, maximal lactate steady state or Critical Power and FTP ventilatory thresholds). We chose a test protocol for CP assessment that is not different from the traditional constant-work rate approach (Triska et al, 2017; Karsten et al, 2018) and a widely used and recommended 20 min TT for FTP (Denham et al, 2017; Borszcz et al, 2018; Valenzuela et al, 2018), in a cohort of moderately trained cyclists
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