Over 55 years of critical power: Fact or artifact?

This report aims to generate an evidence-based debate of the Critical Power (CP), or its analogous Critical Speed (CS), concept. Race times of top Spanish runners were utilized to calculate CS based on three (1500-m to 5000-m; CS_1.5-5km ) and four (1500-m to 10000-m; CS_1.5-10km ) distance performances. Male running world records from 1000 to 5000-m (CS_1-5km ), 1000 to 10,000-m (CS_1-10km ), 1000-m to half marathon (CS_{1km-half marathon} ), and 1000-m to marathon (CS_1km-marathon ) distance races were also utilized for CS calculations. CS_1.5-5km (19.62 km h^-1 ) and CS_1.5-10km (18.68 km h^-1 ) were different (p < 0.01), but both approached the average race speed of the longest distance chosen in the model, and were remarkably homogeneous among subjects (97% ±1% and 98% ±1%, respectively). Similar results were obtained using the world records. CS values progressively declined, until reaching a CS_1km-marathon value of 20.77 km h^-1 (10% lower than CS_1-5km ). Each CS value approached the average speed of the longest distance chosen in the model (96.4%-99.8%). A power function better fitted the speed-time relationship compared with the standardized hyperbolic function. However, the horizontal asymptote of a power function is zero. This better approaches the classical definition of CP: the power output that can be maintained almost indefinitely without exhaustion. Beyond any sophisticated mathematical calculation, CS corresponds to 95%-99% of the average speed of the longest distance chosen as an exercise trial. CP could be considered a mathematical artifact rather than an important endurance performance marker. In such a case, the consideration of CP as a physiological "gold-standard" should be reevaluated.