Evidence of biomechanical functional symmetry in the presence of lower extremity structural asymmetry during running
Creators: name: McBride, Margaret E.
Publisher: name: University of British Columbia
Year: 2010

description: The biomechanical analysis of human gait is typically characterized by the generation of large volumes of collected data. In an attempt to simplify the analysis of results, researchers have made the pragmatic decision to record force and cinematographical data from only one side of the body and assume symmetry between the left and right sides. This study was devised to address two topics related to the issue of assumed biomechanical symmetry in the study of human gait mechanics. The initial objective was to determine if the assumption of symmetry in kinematic and kinetic variables remained valid in a group of runners diagnosed with a leg length differential. It was postulated that lower extremity structural asymmetry in the form of leg length inequality would be manifested as functional asymmetry in biomechanical parameters. The second objective of this study was to determine if runners with a leg length inequality were characterized by common systematic patterns of asymmetry in kinematic and kinetic variables. If universal compensation strategies were identified, they may eventually be linked to etiological factors involved in the development of overuse injuries in runners with a difference in leg length. A group of ten asymptomatic male runners served as subjects in this study. Subjects were assigned to one of two experimental conditions based upon bilateral anthropometric determination of leg length. Leg length assessment was comprised of bilateral measurements of the distance from the anterior superior iliac spine to the lateral and medial malleoli as well as the distance from the greater trochanter to the floor. The five runners in the structurally symmetrical group were characterized by a leg length differential of less than 3 mm while the five runners in the structurally asymmetrical group demonstrated a leg length inequality of greater than 10 mm. Subjects were required to run barefoot at 4.88 m/s over a flush-mounted Kistler force platform imbedded in a straight 20 meter runway. After sufficient practice, six trials were collected from both the left and right legs. The three components of the ground reaction force were collected while a Locam 16 mm camera recorded each trial in the sagittal plane at 150 frames per second. Filtered kinematic and ground reaction force data were used as input into a mathematical model designed to estimate the joint forces and muscle moments occurring at each lower extremity joint during the stance phase of running. Bilateral comparisons were made on the range of motion at the hip, knee and ankle joints, mean vertical force peaks and net anterior-posterior impulses. Analysis of the internal kinetic variables included the mean vertical joint reaction force and the mean muscle moment of force for each joint averaged to every 20% of the total stance duration. Results for each runner were assessed for functional equality using a symmetry index. For each variable analyzed, this calculation provided the mean absolute difference between the left and right legs for members of the structurally symmetrical group and between the long and short legs for the structurally asymmetrical runners. Comparison of group results revealed functional equality in the majority of biomechanical measures analyzed. Analysis of individual results revealed that regardless of structural status, some runners demonstrated functional equality while others were characterized by functional asymmetry. The second portion of the study attempted to determine if runners with a leg length inequality were characterized by universal patterns of asymmetry in kinematic and kinetic variables which could eventually be linked to the etiology of overuse injuries. As the structurally asymmetrical group demonstrated functional equality in the majority of variables measured, it was not possible to detect common patterns of compensation utilized by all runners with a leg length differential. Based upon these results, the following conclusions were made: 1. Regardless of structural status, functional symmetry remained a valid assumption in the majority of biomechanical variables measured in this study. 2. Structural asymmetry in the form of a leg length differential is not necessarily manifested as asymmetry in the biomechanical measures analyzed in this study. 3. No universal compensation strategy was utilized by all subjects presenting with a leg length differential. 4. Pooling data concealed bilateral asymmetries which existed in individual profiles.