John D. Lloyd, PhD, CPE
Board Certified Ergonomist
32824 Michigan Avenue
San Antonio, Florida 33576
Tel: 813-624-8986
Email: DrJohnLloyd@Tampabay.RR.com
Clinical Biomechanics of Wheelchair Transfers and Repositioning tasks in SCI
Introduction: Persons with spinal cord injury (SCI) perform activities of daily living, including mobility, repositioning and everyday transfer tasks, without the use of their lower extremities. As such, biomechanical loading of the upper extremity dramatically increases incidence of musculoskeletal disorders adding to their disability and diminishing independence thereby dramatically affecting their quality of life.
Methods: Ten male veterans with paraplegia were recruited to perform everyday transfer and repositioning tasks in a laboratory environment. Assessed transfer tasks included: wheelchair to bed (horizontal), wheelchair to commode (downhill) and wheelchair to vehicle (uphill) transfers in a laboratory. Pressure relief and trapeze bar repositioning tasks were also evaluated.
Figure 1: Wheelchair to Commode Transfer Task
VICON motion tracking technology was employed to record human motion. Dynamic external forces were recorded using calibrated force-sensing resistors, which were mounted in the palmar surface of gloves. Electromyography data was captured for bilateral anterior deltoid, pectoralis major, latissimus dorsi, bicep and tricep muscle groups.
Human motion, force and EMG data were recorded simultaneously at 120 Hz using the VICON system for parallel analysis.
Results and Discussion: Findings from this study graphically illustrate the complex biomechanical processes at the shoulders elbows and wrists during execution of these demanding everyday transfer tasks. Joint forces and moments are computed as a function of joint kinematics as well as externally applied loads.
Figure 2: VICON Model Representation of Transfer Task
Figure 3: Shoulder Force
Figure 4: EMG – Left Anterior Deltoid
Conclusions: Understanding of the biomechanical demands acting on key joints of the upper extremities lends to the development of engineering and/or methodological interventions to minimize the risk of developing chronic shoulder disorders. By reducing secondary disabilities, persons with SCI can maintain their independence and quality of life.
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