Biomechanics of skateboarding: kinetics of the Ollie.

Seven top amateur or professional skateboarders (BW=713 N+/-83 N) performed Ollie maneuvers onto and off an elevated wooden platform (45.7 cm high). We recorded ground reaction force (GRF) data for three Ollie Up (OU) and Ollie Down (OD) trials per participant. The vertical GRF (VGRF) during the OU has a characteristic propulsive peak (M=2.22 body weight [BW]+/-0.22) resulting from rapidly rotating the tail of the board into the ground to propel the skater and board up and forward. The anterior-posterior (A-P) GRF also shows a pronounced peak (M=0.05+/-0.01 BW) corresponding with this propulsive VGRF peak. The initial phase of landing in the OD shows an impact peak in VGRF rising during the first 30 to 80 ms to a mean of 4.74+/-0.46 BW. These impact peaks are higher than expected given the relatively short drop of 45.7 cm and crouched body position. But we observed that our participants intentionally affected a firm landing to stabilize the landing position; and the Ollie off the platform raised the center of mass, also contributing to higher forces.