Joint kinematics and ground reaction forces in overground versus treadmill graded running

Background: Treadmills are often used to assess running biomechanics, however the validity of applying results from treadmill graded running to overground graded running is currently unknown. Research question: The purpose of this study was to investigate whether treadmill and overground graded running have comparable kinematics and ground reaction force parameters. Methods: Eleven healthy male adults ran overground and on an instrumented treadmill as motion capture and force platform data were collected for the following conditions: downhill running at a slope of -8 degrees at 10, 13 and 16 km.h(-1) ; level running at 10 and 13 km.h(-1) ; uphill running at a slope of at +8 degrees, 10 and 13 km.h(-1). Sagittal joint angles at heel strike, mid-stance, and toe-off were computed for the ankle, knee and hip. Ground reaction force parameters including peak average and instantaneous normal loading rate, peak impact and active normal force, peak tangential (braking and propulsive) forces, and normal and tangential impulses were also calculated. Results: Joint kinematics and ground reaction forces for level running were generally similar between overground and treadmill conditions. The following variables were significantly higher during overground uphill running (mean difference +/- SD): average normal loading rate (14.4 +/- 7.1 BW.s(-1)), normal impulse (0.04 +/- 0.02 BW.s), propulsive impulse (0.04 +/- 0.02 BW.s), and vertical center of mass excursion (0.092 +/- 0.031 m). The following variables were significantly higher during overground downhill running (mean difference +/- SD): ankle plantarflexion at toe-off (-5.39 +/- 6.19 degrees) and vertical center of mass excursion (0.046 +/- 0.039 m). Significance: These findings suggest that subtle differences in kinematics and ground reaction forces exist between overground and treadmill graded running. These differences aside, we believe that overground kinematics and ground reaction forces in graded running are reasonably replicated on a treadmill.