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 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 inertial measurement unit, and if 2 running bouts are sufficient to determine CS and CP. Methods: On an outdoor running track, 10 trained runners ( V ˙ O 2 max , 59.0 [4.2] mL·kg⁻¹·min⁻¹) performed 3 running time trials (TT) between 1200 and 4400 m on separate days. CS and CP were derived from 2-parameter hyperbolic speed–time and power–time models, respectively, using 2 (CS_2TT and CP_2TT) and 3 (CS_3TT and CP_3TT) TTs. Subsequently, runners performed constant-intensity running for 800 m 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 =.940; d = 0.02), with excellent agreement between the 2 values (intraclass correlation coefficient =.980). The CS_2TT (3.97 [0.42] m·s⁻¹) was not higher than CS_3TT (3.89 [0.44] m·s⁻¹; P =.178; d = 0.46); however, CP_2TT (278 [29] W) was greater than CP_3TT (P =.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 2 trials provided a reasonable, albeit higher, estimate of CS and CP. [ABSTRACT FROM AUTHOR]