High Test-Retest Reliability but Questionable Validity: Assessing a Step-Ramp-Step Protocol to Estimate Critical Power and W’ in Trained Triathletes

Purpose: This study aimed to assess: 1) the concurrent validity between critical power (CP) and the corrected power output at the respiratory compensation point (PO RCP ) and between W’ and the quantity of energy depleted above PO RCP (W’ mod-SRS ) in a modified Step-Ramp-Step (mod-SRS) protocol; 2) the test-retest reliability of endurance variables derived from a mod-SRS protocol. Methods: Twelve trained male triathletes (31 ± 6 yr, 67.9 ± 7.1 mL.min -1 .kg -1 ) performed i) a SRS protocol, ii) 4 to 5 severe-intensity Constant-Work Rate (CWR) trials, iii) two mod-SRS protocols (test/re-test) and iv) a heavy-intensity CWR trial. CP and W’ were computed using a “best individual fit” approach. PO RCP was corrected appropriately while W’ mod-SRS was computed as the energy depleted above PO RCP . Test-retest reliability was assessed with the intraclass correlation coefficient (ICC), the standard error of measurement (SEM) and the coefficient of variation (CV%). Results: CP was higher than PO RCP in both trials (bias = 19 ± 19 W and 17 ± 20 W, p = 0.019 and 0.045). W’ and W’ mod-SRS were similar between trials (bias = -2.8 ± 7.9 kJ and -5.4 ± 8.8 kJ, p = 0.735 and 0.173). Test-retest reliability was moderate for W’ mod-SRS (ICC = 0.66, SEM = 3.0 kJ, CV = 11.6%) and high for V̇O 2peak , GET, RCP and their associated PO values (ICCs = 0.85-0.95, SEMs = 68-184 mL.min -1 and 7-8W, CVs = 2.1-3.7%). Conclusions: The mod-SRS protocol reliably measures V̇O 2peak , GET and RCP. Corrected PO RCP systematically underestimated CP, which consequently impacts computation of W’ using a mod-SRS protocol. The design of the protocol may allow a more complete depletion of energy available above RCP while still eliciting V̇O 2peak .