University of Virginia Health System

Gait and Motion Laboratory

Gait and Motion Laboratory Work
The UVa Gait and Motion Laboratory is devoted to advancing the physiological and biomechanical understanding of gait and other common activities, so as to both prevent and treat disease, impairment and disability. Although the laboratory is under the auspices of the School of Medicine's Department of Physical Medicine and Rehabilitation, students, faculty, and staff from throughout UVa including the Departments of Aerospace and Mechanical Engineering and Electrical Engineering in the School of Engineering, the Center for Complementary and Alternative Medicine in the School of Nursing and the Sports Medicine Program in the Curry School of Education collaborate together in the laboratory on a variety of projects. The laboratory contains standard state-of-the-art equipment including a ten camera motion analysis system, a 16-channel dynamic electromyographic apparatus, and a portable oxygen consumption measuring unit. Additionally it contains the only force-plate instrumented treadmill in the world that allows capture of ground reaction force measurement in all three planes during walking or running in an individual with virtually any particular gait pattern, e.g. extremely slow or fast gait, step-to gait, cross-over gait, etc.

Work to Date
We have gained an altogether new understanding of the role of different gait parameters on the body's center of mass displacement and discovered a new "determinant of gait," replacing a 50-year-old doctrine of the important physiologic functions during gait. We developed a new model to understand what gait functions are particularly critical to minimizing the energy cost of walking and proved this model with measured gait kinematics. The model, combined with new insights from the study of a variety of gait disorders, led to the development of a novel strategy for dynamically controlled partial body weight support gait training. A prototype "smart" gait training system based on this work, in collaboration with multiple UVa departments and expertise, was constructed. The system relies upon specific algorithms and feedback control from kinematic and ground reaction force measurements. We have preliminarily tested the training system in people with gait disabilities in association with a variety of neurological and orthopedic diagnoses. The prototype is proving to induce superior kinematic and kinetic gait characteristics as compared to both baseline walking and any other standard partial body weight support system.

We have evaluated the effect of different types of shoe-wear on lower extremity joint torques. We discovered that women's high-heeled shoes significantly alter knee joint torques in a manner that predisposes to degenerative joint changes in the medial and patellofemoral compartments, the usual areas of osteoarthritis. This finding was published in the Lancet, representing the first biomechanical study ever published by a major, general medical journal. Also we demonstrated that these knee torques are equivalent between women and men when walking barefoot and that men's dress shoes and sneakers slightly increase these torques. We found that wide-based heeled women's dress shoes, not just "stilleto" types, alter these torques (also published in the Lancet) and that even orthopedic-type shoes with moderate heel height (1½") increase these torques. These findings are the first to implicate external biomechanical factors as a cause of knee osteoarthritis, and may explain why women have nearly twice the incidence of knee osteoarthritis compared to men. We have also recently found that current modern running shoes significantly increase these knee joint torques during running. The knowledge regarding women's footwear is being incorporated into several epidemiology studies, including the osteoarthritis arm of the Framingham Study, supervised by David T. Felson at Boston University. 

We have discovered an isolated, functionally limiting impairment in elderly people (impaired hip hyperextension range) that may be reversible with specific exercise.  We have found that reduced peak hip extension at the end of the stance period is the only age-related gait parameter change (from 60 different gait parameters studied), that cannot be explained merely by the fact that elderly subjects walk slower than young adults. We also found that reduced peak hip extension is the only gait parameter consistently further exaggerated in elderly people who recurrently fall compared to healthy elderly non-fallers, suggesting that hip tightness (into hyperextension) occurring with aging may be a particularly key impairment in the deterioration of walking function. We performed a preliminary randomized hip extension stretching exercise trial in elderly subjects, which demonstrated improvement in several age-related gait changes and we are currently performing a large National Institutes of Health (National Institute on Aging) funded randomized controlled stretching exercise trial in both healthy elderly and frail elderly subjects. We have also performed a preliminary study of the effect of Iyengar Yoga (that emphasizes hip extension stretching), which also demonstrated improvement in several age-related gait changes, including peak hip extension, step length and gait velocity. We are currently submitting an additional grant application to the National Institute on Aging for a large randomized controlled study of yoga. 

We are currently exploring the use of the smart gait training system as a regular exercise tool to maintain and improve walking in healthy elderly people with the goal to improve overall function as well as reduce the risk for falls. We are demonstrating that the system, using specific feedback algorithms that we have developed, encourages normal gait movement allowing greater stretch into hip extension and greater step length compared to walking overground while simultaneously minimizing the joint torques believed to be relevant to the development and progression of knee and hip osteoarthritis. The system we have developed is currently only a prototype, utilizing sophisticated kinematic and kinetic gait measures from motion cameras and a series of force-plate embedded treadmills.  Eventually, the system could be developed into an affordable, under $10,000 exercise device. Potentially, elderly people would use the system regularly as an exercise tool to safely reverse age-related gait difficulties and reduce the risk of falling.   

Laboratory Facilities
The Gait and Motion Laboratory at the Department of Physical Medicine and Rehabilitation encompasses 1400 square feet. It is equipped with:
    

A customized instrumented treadmill built by AMTI (Advanced Mechanical Technology, Inc.) that  includes three  treadmill/forceplates recording ground reaction forces. This instrumented treadmill is a unique piece of equipment that, in conjunction with the motion analysis system, allows for the computation of joint torques for extended time walking, and is driven by a dedicated computer synchronized with the motion analysis system computer. 
Two staggered force plates embedded in the floor (AMTI) which allow for the measurement of the ground reaction forces. These force platforms, in conjunction with the motion analysis system, allow for the estimation of joint torques.
A state-of-the-art motion analysis system (VICON 624, with 10 cameras featuring 1.3 megapixel CCDs) which allows for the highest possible resolution with today’s technology and is driven by a dedicated computer and software.

Treadmill Technical Approach 
There are a total of three separate treadmills.   The rear treadmill, is 24 inches wide by 54 inches long.  This is primarily used for running.  Two treadmills, each 12 inches wide by by 54 inches long, are mounted in front of the larger single treadmill.  These units are primarily used for walking when the patient or subject has a wide stance. One of the smaller units can be used in conjunction with the larger unit for walking when the patient or subject has more of an “in line” walk.  The front treadmills each have small diameter rear rollers very close to small diameter rollers on the front of the rear treadmill.  This allows the user to transition from one treadmill to the other with only a small perceptible change while wearing footwear.  All treadmills run at the same speed with respect to each other.  

Three force platforms, one under each belt,  are used to allow independent measurement of both feet on the treadmill.  The force measurement system is incorporated into this treadmill in a manner which eliminates many possible sources of measurement error.  Basically, each force plate consists of a top plate and a base plate connected by four strain elements.  In this system design each belt and driver system is entirely attached to the top plate, while the base plate will be attached to the “ground”.  This eliminates the measurement of any forces generated by the treadmill mechanism (for example, belt friction) and focuses on measuring the reaction forces of the foot with the ground.  These reaction forces and the weight of the treadmill [1] are the only forces measured by the force sensor. The base of this force platform is attached to the support frame of the treadmill.

AMTI strain gage amplifiers provide signal conditioning for the strain gages.   The output is six signals corresponding to the six components of force and moment.The entire treadmill including the drive mechanism and force measurement systems is 60 inches wide and 137 inches long.  It is 12.5 inches high in the non-inclined state. Cover plates are provided all around the treadmills and removable guard rails are provided. The treadmill is capable of simulating up to a 25% grade in either direction.  This is accomplished using pairs of double ended hydraulic pistons at each end of the treadmill.  When an uphill run is simulated, the treadmill end facing the subject is raised and when downhill running is intended, the end behind the subject is raised.

Force Sensing Treadmill Specifications
Treadmill Surface Size:
24” wide x 108”long consisting of three Units – One “Running” Unit 24” wide x 54” long  behind two “Walking” units – each 12” wide  by 54” long.
Treadmill Spacing:
The spacing between the rollers of the running unit and the walking units and the spacing between  the walking units is no greater than 4 mm.
Speed:
The treadmill is capable of running 0-12 MPH.
Grade:
The treadmill is capable of operating from 0 to 25% grade in both the uphill and downhill direction.
Load:
The treadmills can handle up to a 400 LB test subject while walking, running, or performing other related activities.
Force Measurement Capabilities:
The system is able to independently measure Fz, Fx, Fy, Mz, Mx, and My on each treadmill.  The system should provide signals adequate to determine the center of pressure (COP).  The load range for vertical forces applied to the treadmill should be 2000 lb. above the weight of the treadmill.
Calibration:
The force plates are installed in the treadmill using both a static and dynamic calibration.
Portability:
The treadmill is capable of wheel mounting to allow movement within the facility.
Safety Railings:
The treadmill has removable  front and side railings surrounding the running surface.  These can be easily installed or removed from the treadmill.
Power Requirements:
The treadmill is powered by 208/240 VAC three-phase electric power.