A comparison of critical speed and critical power in runners using Stryd running power

Purpose Although running traditionally relies on critical speed (CS) as an indicator of critical intensity, portable inertial measurement units (IMUs) offer a potential solution for estimating running mechanical power to assess critical power (CP) in runners. The purpose of this study was to determine whether CS and CP differ when assessed using the Stryd device, a portable IMU, and if two running bouts are sufficient to determine CS and CP. Methods On an outdoor running track, ten trained runners ( , 59.0 [4.2] ml·kg -1 ·min -1 ) performed three running time-trials (TT) between 1200 and 4400m on separate days. CS and CP were derived from two-parameter hyperbolic speed-time and power-time models, respectively, using two (CS 2TT CP 2TT ) and three (CS 3TT CP 3TT ) time trials. Subsequently, runners performed constant intensity running for 800m at their calculated CS 3TT and CP 3TT . Results Running at the calculated CS 3TT speed (3.88 [0.44] m·s -1 ) elicited an average Stryd running power (271 [28] W) not different from the calculated CP 3TT (270 [28]; p=0.940; d=0.02), with excellent agreement between the two values (ICC=0.980). The CS 2TT (3.97 [0.42] m·s -1 ) was not significantly higher than CS 3TT (3.89 [0.44] m·s -1 ; p=0.178; d=0.46); however, CP 2TT (278 [29] W) was significantly greater than CP 3TT (p=0.041; d=0.75). Conclusion The running intensities at CS and CP were similar, supporting the use of running power (Stryd) as a metric of aerobic fitness and exercise prescription, and two trials provided a reasonable, albeit higher, estimate of CS and CP.