The effect of excessive medio-lateral trunk movements on ankle plantar flexor work during gait in healthy individuals

Abstract

The ankle plantar flexion muscles are the main contributors to the propulsion of the body during gait. Deficits in these muscles, such as reduced muscle strength, often lead to impaired walking. A characteristic widely observed in gaits arising from various pathologies is an increase in medio-lateral trunk movements. However, this is not yet identified as a compensation strategy for ankle plantar flexor weakness. A previous analysis showed a decrease in positive work generated at the ankle joint in healthy individuals walking with excessive trunk sway compared to normal walking at the same speed. This suggests that excessive trunk sway could be used to compensate for a reduction in propulsive power generated at the ankle joint. This study investigates the relationship between excessive trunk movements in the frontal plane and propulsive power generated at the ankle joint by examining the contributions of individuals muscles to the total power generation during gait. The first aim of this study is to evaluate the validity of the previous results. The second aim is to uncover the underlying biomechanical compensatory mechanisms of walking with excessive medio-lateral trunk movements. A data set consisting of marker data and ground reaction force data of healthy individuals walking with and without excessive medio-lateral trunk movements is analysed in this study. Three-dimensional muscle-actuated simulations of the recorded gaits were generated in OpenSim. A residual reduction algorithm was applied to make the kinematic outcomes more dynamically consistent with the experimentally measured ground reaction forces and moments. This is in contrast to the previous analysis, in which the residuals were not reduced. The power and work generated by the total system and the individual segments, joints and muscles were derived from the simulations. An increase in positive work at the lumbar joint was found, but no differences in positive work at the hip, knee and/ or ankle joints were found over the gait cycle. The lumbar bending muscles turned out to be responsible for the increase in positive work at the lumbar joint. In conclusion, we did not find medio-lateral trunk sway to be a compensatory mechanism for ankle plantar flexor weakness. Therefore, more research is needed to understand why trunk sway is commonly observed in patients with reduced plantar flexion muscle strength. The results of our study contrast those of the previous analysis. Our findings suggest that the discrepancy between the outcomes is caused by high residual forces and moments in the previous analysis. Hence, by revealing the discrepancy between the results of this study and the results of the previous analysis, this study highlights the importance of the validation of results before drawing conclusions.