Critical Power : CP
BikeThe power theoretically sustainable indefinitely without depleting anaerobic capacity, slightly below FTP and derived from a two-parameter mathematical model.
The Critical Power model (Monod & Scherrer, 1965, adapted by Poole & Jones) defines two parameters: CP (critical power) and W' (anaerobic work capacity in joules). Any power above CP draws from W', which depletes in a few minutes. FTP (20-min test) slightly overestimates CP by about 5-10%. A more precise CP test chains two maximal efforts at different durations (e.g., 3 min + 15 min) then fits the model. In Ironman, riding is below CP : the risk of depleting W' on the bike is low with correct pacing, but a hard climb or sudden surge can draw from it and degrade the run.
In TriPaced:
In TriPaced, FTP (CP proxy) calibrates bike power zones. The CP model is not yet exposed in the UI, but the planner accounts for the fact that in Ironman the core bike effort must stay below FTP threshold to preserve W', noted in the Race A sheet guidelines.
Source Jones A.M. et al., 2019 : The Critical Power Concept - Applications to Sports Performance (Med Sci Sports Exerc)