Running power output allows for controlling variables that have been previously overlooked by relying solely on speed, such as surface, gradient and weight. The ability to measure this external load variable now enables the analysis of concepts that have predominantly been studied in cycling, such as the Critical Power (CP), in the context of running. This study aims to predict the CP target at which trained athletes run a half-marathon and determine whether races of this distance can serve as a valid alternative to update the CP record. A group of nine trained athletes performed the 9/3-minute Stryd CP test and participated in a half-marathon race in two separate testing sessions conducted in the field. The average power during a half-marathon race is a valid alternative method for determining the CP in trained athletes, as evidenced by the agreement (95% CI: -0.11 to 0.37 W/kg) and trivial systematic bias (0.13 W/kg) between methods. The linear regression model half-marathon power = 0.97 + 0.75·CP (W/kg) showed low standard error of estimate (0.29 W/kg) and significant large association between methods (r = 0.88; p = 0.002). Coaches and athletes should be aware that the CP target for a half-marathon race is 97.3% of the CP determined by the 9/3-minute Stryd CP test.

• The study demonstrates that the average power during a half-marathon race can be a valid alternative method for determining Critical Power (CP) in trained athletes.

• There is agreement and a negligible systematic bias between the 9/3-minute Stryd CP test and average power during the half-marathon race, indicating the validity of the alternative method.

• A linear regression model shows a significant association between the methods and a low standard error of estimate, supporting the accuracy of the CP determination using the alternative method.

• Coaches and athletes can utilize the 9/3-minute Stryd CP test to predict the target CP at which a half-marathon can be run, estimated to be approximately 97.3%.