Body weight supported treadmill training (BWSTT) is a rehabilitation method that can help individuals with incomplete spinal cord injuries (SCIs) regain the ability to walk. In BWSTT patients are supported by a harness above a treadmill while therapists provide manual assistance to help approximate normal gait. Training parameters, such as treadmill speed and percentage of body weight support (BWS) are chosen by therapists based on visual inspection of “what looks right” while the patient is on the treadmill. It is believed that the forces and motions associated with normal walking should be provided to the patient during training in order for BWSTT to be effective. Despite the need to replicate normal gait characteristics, objective techniques for selecting treadmill speed and BWS, have not been established. As a first step toward addressing this challenge, the purpose of this research was to determine the effects of changing treadmill speed and BWS on lower extremity joint kinematics and kinetics in healthy individuals.
We collected kinematic and kinetic gait data from ten healthy subjects as they walked on an instrumented treadmill at three treadmill speeds (Self-Selected (SS), 0.5xSS, and 1.5xSS) and four levels of BWS (0%, 30%, 50%, and 70% of weight supported). Subject specific computer models were used to determine the duration of stance, joint angles, joint moments and ground reaction forces produced during walking at each combination of treadmill speed and BWS.
All kinematic and kinetic variables of interest were significantly affected by changing treadmill speed and changing BWS. All variables other than the peak ankle plantarflexion angle were also significantly affected by the interaction effect of treadmill speed and BWS. The results from the 0% BWS, SS-speed condition were treated as the baseline condition; results from all other conditions were compared back to this case. Changing treadmill speed and BWS caused 28 out of 44 peak joint angles, and 60 out of 66 peak joint moments to be significantly different compared to those produced during the baseline condition. Additionally, 30 out of 33 peak vertical and anterior-posterior ground reaction forces were significantly different compared to the baseline condition.
This research is the first step towards helping therapists make more informed decisions when choosing training parameters during BWSTT. These results suggest that it is possible to achieve some normal kinematics in the BWSTT environment, however joint moments and ground reaction forces will almost always deviate from those produced during normal walking. Because of this, visual inspection of patient kinematics during training may not be the most appropriate method for choosing training parameters such as treadmill speed and BWS. Understanding how treadmill speed and BWS affect lower extremity biomechanics could lead to the development of training parameters which target specific muscle groups or areas of weakness throughout the rehabilitation process. This study has laid the groundwork for further research involving patients with SCIs which may provide therapists with objective information to choose training parameters during BWSTT that will help patients learn how to walk better, faster.