Comparison of Step Rate and Tibial Acceleration During Treadmill and Real-world Running

OBJECTIVE: To compare step rate and tibial acceleration during an 8-km run performed outdoors versus on a treadmill. DESIGN: Repeated-measures observational study. METHODS: Healthy adult runners (females: 9, males: 19) ran 8 km at a self-selected speed outdoors and on a treadmill. A chest-mounted inertial measurement unit (IMU) was used to measure step rate, whereas a tibial-mounted IMU collected tibial acceleration. Linear mixed-effects models adjusted for speed were used to assess step rate and peak vertical (PV) and peak resultant (PRES) tibial accelerations between conditions and across the 8 km, as well as their interactions. RESULTS: There was a significant interaction between distance and location (Est [95% CI] = 0.71 [0.38 to 1.05], P<.001) for step rate, with an increase in step rate observed over distance outdoors. There was also a significant interaction between distance and location for PV (−0.13 [−0.25 to −0.00], P = .047) and PRES (−0.16 [−0.31 to −0.00], P = .047) tibial accelerations, with both increasing over distance during treadmill running. Overall, PV (3.34 [2.85 to 3.83], P<.001) and PRES (5.05 [4.45 to 5.65], P<.001) tibial accelerations were significantly greater when running outdoors than when running on a treadmill. CONCLUSION: Treadmill and overground assessments of step rate were relatively comparable. Tibial acceleration may not be interchangeable with gait analysis in the field. JOSPT Open 2025;3(1):77-84. Epub 5 November 2024. doi:10.2519/josptopen.2024.0055