Three dimensional analysis of ground reaction force during level walking correlates with sacrum displacement.

Objective: We determined the association between sacrum displacement and ground reaction force (GRF) during walking on a level surface and identify the sub-phase of gait cycle most affected by GRF. The kinematic parameters of angular displacement of sacrum bone in three directions were measured and a correlation was derived to integrate the effect of GRF to sacrum displacement. Furthermore, gender variation in the sacrum bone configuration that induces the GRF to shift in one direction was determined. Methods: Forty healthy university students were evaluated for a normal gait pattern using the Qualysys motion capture system or a motion analysis system (MAS). The synchronization between MAS and force plate was done through computer software for the three-dimensional analysis (3D) of the force and angular displacement. Results: A positive correlation in the vertical direction was observed in the early and late phases of the stance phase in females. In males, a positive correlation was demonstrated in the middle and late phase of the stance phase. However, a positive correlation in the anteroposterior direction during the middle part of the stance phase was found only among the male group. Conclusion: Incorporation of strength training exercises help to increase the rotator muscle strength of the trunk and lower extremities in both genders. In the male group, flexors and extensors of the trunk and lower extremities in the middle part need to be focused during strength training, especially for athletes. This would be useful in decreasing the incidence of sports injuries.