Biomechanical behaviors of the human triceps surae during landing activities

The purpose of this study was to investigate biomechanical behaviors of human triceps surae in landing activities using a Hill-type muscle model. Ten healthy male subjects (23±3 yrs) performed five trials of drop landing from a height of 60 cm in each of four conditions: a normal landing (NL); a stiff landing that required the subject to perform a NL but with minimal knee flexion (SL); a SL but landing flat footed (SF); and a stiff landing while landing on the toes only (SC). Sagittal kinematic (120 Hz), ground reaction forces (GRF) and moments (1200 Hz) were recorded simultaneously. Using an inverse dynamics approach, ankle moment and triceps surae muscle forces were computed. In addition, the triceps surae muscle force and ankle moment were estimated using the Hill-type model. A one-way analysis of variance (ANOVA) was used to evaluate selected variables with the significant level set at P < 0.05. The mean peak GRF values for NL, SL, SF and SC were 38.0, 49.2, 35.5 and 58.6 N/kg, respectively. The mean VGRF of peak associated was found to be significantly different between each condition except NL and SC. The Hill model predicted the peak triceps surae forces at 54.6, 65.0, 40.7, and 62.1 N/kg for NL, SL, SF, and SC respectively. The mean peak plantar flexing moments for NL, SL, SF, and SC were 2.2, 4.0, 2.8, and 4.4 Nm/kg respectively while the estimated plantar flexing moment had values of 3.7, 4.6, 4.7 and 3.2 Nm/Kg for the same conditions. Greater discrepancy was observed between the experimental and estimated joint moment and muscle force for SF. The Hill model was considered to be a good predictor of the eccentric muscle force in the landing activity for NL, SL, and SC except for SF.