Development of a method to determine abnormal joint torque coupling patterns during walking in chronic hemiparetic stroke

Abnormal joint torque coupling between (sub)maximal isometric hip extension and hip adduction torques was found in individuals with chronic hemiparetic stroke in a previous study, however, it is unclear how this coupling affects dynamic tasks like walking. Especially during stance phase of gait, in which hip extension and abduction torques need to be generated simultaneously, this abnormal hip extension/adduction coupling might lead to instability. Therefore, the aim of this study was to develop a method to quantify joint torque coupling patterns in stroke patients by modulating hip extension torques during walking.
We developed a method to increase or decrease hip extension torques during walking in the sagittal plane and measure the effect on hip abduction/adduction torques. A motor which was placed behind a treadmill was attached to the pelvis of the subject and a constant force was applied in anteroposterior direction while the subject was walking. Each subject participated in three to five trials of two minutes and in each trial a different force was applied in either forward or backward direction. For each trial, joint angles and joint torques were calculated based on kinematic data and ground reaction forces.
Preliminary results of one healthy participant and one stroke patient indicate that hip extension torques during stance phase of walking could be modulated by applying forces in anteroposterior direction to the pelvis. In addition to this, changes of hip abduction torques during stance phase were found. For example, applying a force in backward direction led to a larger hip extension torque and less hip abduction torque compared to normal walking in both participants. In contrast to this, applying a force in forward direction resulted in less hip extension torque and larger hip abduction torque.
Based on these preliminary findings, we conclude that applying a force in anteroposterior direction to the pelvis during walking might be used to modulate hip extension torques and measure joint torque coupling in the abduction/adduction degree of freedom during walking. After further optimizing our protocol, additional experiments will be performed in individuals with stroke and healthy participants. Results of these future experiments are expected to provide insight into the effect of abnormal joint torque coupling patterns on walking stability following stroke and may lead to the development of new more subject specific therapies.