Ph.D Thesis

Ph.D StudentFischer Arielle
SubjectThe Effects of Body Weight Unloading on the Biomechanical
Parameters of Healthy Subjects during Overground
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. Alon Wolf


Background: The task of daily walking involves several biomechanical demands placed on lower joints which may often be modified by controlling loads during gait. Thus, treadmill walking with a body weight unloading (BWU) system to reduce body weight and consequently lower joint loads, has become a common method of gait rehabilitation for patients with neurological and musculoskeletal disorders. However, the unique effects of BWU on gait rehabilitation were confounded by the walking modality- treadmill which did not replicate daily walking. Once conducted overground, gait research on the effects of BWU was facing another challenge namely, controlling healthy subjects’ gait speed variability, easily controlled on treadmills but hard to control overground when subjects had to pull the BWU system to which they were attached. In this research, the novel mechanical device designed allowed to pull the BWU system at a constant speed thus enabling the research participants to maintain a comfortable speed when walking overground attached to the system. In so doing, this study could assess the unique effects of BWU on the gait biomechanical parameters of (1) normal weight subjects and (2) overweight subjects during overground walking, a condition that approximates daily walking.

Methods: This study included two stages: the first fifteen healthy normal weight (18.5≤BMI<24.9kg/m2) male subjects and the second ten overweight male subjects (25≤BMI<29.9kg/m2). The research participants were instructed to walk overground under a control (no vest), and three 0%, 15%, and 30% BWU experimental conditions performed with the Biodex system connected to an electric winch that pulled the system at a constant speed of 4km/h. Kinematic, kinetic and muscle activation (EMG) data were simultaneously recorded with a Vicon Nexus motion tracking system.

Results: A reduction of 0%, 15% and 30% BWU does not significantly change the spatiotemporal parameters of healthy and overweight subjects during overground walking. Furthermore, for both subject groups the reduction of body weight by 0% to 30% resulted in a significant decrease in lower joint kinematics, kinetics and muscle activation patterns and an increased lateral shift in COP. Additionally, despite changes in the peak kinematic and kinetic measures, the kinematic, kinetic and EMG curvature patterns of overground gait remained similar under the three BWU experimental conditions.

Discussion: The present study leads us to conclude that up to 30% BWU and consequent joint load reductions neither modify the spatiotemporal parameters or curvature patterns suggesting that overground gait corrections with partial BWU may transfer to daily walking. Overground gait rehabilitation with BWU stands out as a promising method to retrain gait deficits resulting from neurological and musculoskeletal impairments by giving clinical subjects the confidence and body weight support to achieve forward propulsion. As lower joints regain their functional activity with respect to balance, range of motion and locomotor patterns, the patients’ body weight may be gradually increased until they resume overground walking without any body weight support. The potential applications of BWU on gait rehabilitation extend beyond clinical subjects with neurological or musculoskeletal impairments to young athletes who engage in strenuous sports and subjects with obesity.