Human postural control against external force perturbation applied to the high-back

Many studies have reported postural control against support surface translation. However, postural control mechanism against external force perturbation is not clear. Therefore, in this study we investigated the postural recovery against external force (1 similar to 4Kg) applied to the high-back in health young male subjects (24 +/- 4 years). Kinematic data and center of pressure of the reaction to an unexpected perturbation were analyzed. Experimental results showed that the hill-lifting strategy with ankle plantarflexion and knee hyperextension was used in all subjects, regardless of the force magnitude. Specifically, maximum ankle plantarflexion and hip flexion increased with the perturbation force magnitude, the heel vertical excursion and anterior COP excursion. The results of this study show that the postural control strategy for the external force perturbation is quite different from that for surface translation and needs further investigation.