Balance recovery following pelvis perturbations during very slow walking

BACKGROUND AND AIM: Healthy humans have the ability to handle balance perturbations during walking very well. The ankle moment, as well as the foot placement location and timing are altered to counteract the perturbations and maintain balance.[1] Previously, healthy subjects have shown a strong linear relation between the body´s centre of mass (COM) velocity at heel contact (HC), and both the foot placement location and centre of pressure (COP) at subsequent toe off (TO) during laterally perturbed walking.[2] The walking speeds were 0.63 and 1.25 m/s.[2] In this study, it is questioned whether this relation also exist during very slow walking, because there will be more time during the double support phase to alter the balance recovery strategy. Therefore, we investigated the relation between the body´s COM velocity, and both the foot placement
location and COP during a very slow walking speed.

METHODS: Mediolateral (ML) pelvis perturbations were applied to 10 healthy subjects, during very slow (0.36 m/s) and normal (1.25 m/s) treadmill walking at TO of the right foot. An active optical motion capture system was used to record the body kinematics. Ground reaction forces were measured with the built-in force plates in the treadmill. The data was analysed to obtain COM velocities at HC right, foot placement location at HC right, COP locations at TO left and phase durations.

RESULTS: Figure 1 presents the durations of the double and single support phases for the different perturbation magnitudes. The ML perturbations significantly affected the double and single support durations during very slow walking, while these durations were not affected during normal walking. Additionally, the COM velocity at HC right showed to have a high predictive value for the foot placement of the leading foot during the normal walking speed, whereas this was considerable lower during the very slow walking speed. The predictive value of the COM velocity was present for the COP location at the subsequent TO for both the normal and very slow walking speed.

CONCLUSIONS: The results showed altered recovery strategies in the frontal plane during very slow walking compared to the normal walking speed. These differences were potentially caused by the longer double support phase duration, in which subjects used other strategies to control the distance between the COM and COP.

REFERENCES:[1] A. L. Hof, R. M. van Bockel, T. Schoppen, and K. Postema, "Control of lateral balance in walking. Experimental findings in normal subjects and above-knee amputees," Gait Posture, vol. 25, no. 2, pp. 250-258, 2007. [2] M. Vlutters, E. H. F. van Asseldonk, and H. van der Kooij, "Center of mass velocity-based predictions in balance recovery following pelvis perturbations during human walking," J. Exp. Biol., vol. 219, no. 10, pp. 1514-1523,2016.