An example of using motion analysis to assess functional activity: walking up a ramp, wearing an orthosis.

Hank White, MSPT; Jennifer Jenkins, PT; Donna Oeffinger, MS; Sam Augsburger, MSME; Joel N. Heuring, RO; Lance Hoag, CO; David Turley, CO; Mike Johnson, RTO; Matthew Mattox, RTO; Chester Tylkowksi, MD; Janet Walker, MD; Shriners Hospital for Children, Lexington, Kentucky, USA


Three dimensional motion analysis data studying human movement has been published for over a half a century. The majority of research to date has been on human gait analysis conducted by orthopedists, physical therapists and engineers. Physiatrists, neurologists, occupational therapists and communication disorder therapists often assess and treat clients with movement disorders. Typically, these movement abnormalities are qualitatively described. Application of three-dimensional motion analysis and other systems (electromyography, dynamic pressure) are promising tools to quantify evaluations and treatment outcomes for many diverse populations.

Mulder, Nienhuis and Pauwels (1998) performed a review of the literature for the types of tasks employed in the assessment of gait. They found that the majority of published studies between 1982 andl995 assessed walking on level surfaces and identified a gap between the walking impairments studied in motion laboratories and the disabilities of gait seen in rehabilitation. Although walking has been studied at length, it is usually clients on level surfaces without distractions with little study of walking under other conditions.

The enabling-disabling process

The Institute of Medicine (IOM) presents the enabling-disabling process that is different from other models of disability. There are three parts to the IOM model: the person, their environment, and the person's level of disability. In this model, disability is a function of the individual's interaction with the environment and not within the individual (Brandt, 1997). The environment in this model is represented as a flexible mat that the person stands on. The more support the environment provides, the less the person sinks into the mat and the less disability is experienced. The environment is the person's physical and psychosocial environments.

Through simulations of the environment in which people move, motion analysis laboratories can assess the effects of positive and negative physical transitional factors (such as height of different surfaces [bath tubs, toilets, bed], slope of ramps, stair height, amount of light in a room) on functional limitation. For example, assessing the effects of bed height on a person's ability to transfer into and out of the bed may reveal a relationship of limb length and surface height. The client's home environment could then be modified to improve the environment and reduce his/her level of disability. This type of research can also provide tangible evidence to support the premise that environmental changes can reduce disability. More objective documentation of the subtle differences in a patient's body response to wearing an orthosis may lead to increased funding by public and private resources for home modifications.


Kinetics is the study of the forces upon the motions of material objects and is based on the principles of the three laws of force by Sir Isaac Newton. The ground reaction force (GRF) is based on Newton's third law: For every action there is an equal and opposite reaction. The GRF is the upward force applied by the ground to the foot equal and opposite to the force applied to the ground by the foot (Whittle, 1996).To measure these forces a person must sit, stand or step on a forceplate. These force-plate measures the ground reaction force as the person moves on the forceplate (Craik, 1995). From this information, estimations of the forces generated through each joint can be made. These forces are a combination of the passive (segment mass, ligaments, bone, joint capsule) and active (muscle contraction) forces of the body's response to the ground reaction force. Kinetics can also provide information about the center of pressure for someone sitting or standing. The friction coefficient between someone's foot and the surface they stand on can also be a form of kinetic data.

Bracing with different types of ankle foot orthoses (AFOs) is a common treatment of people with ankle impairments. It is often difficult to obtain subjects with similar levels of impairment. Ground reaction ankle foot orthoses (GRAFO) are often prescribed to decrease ankle dorsiflexion and in turn decreases knee flexion during walking. Walking up a ramp is similar in that it causes the ankle to be in more dorsiflexion. A study was performed to document the changes noted in knee and ankle motions and joint moments for four able-bodied individuals wearing GRAFOs.


Four healthy adult males without impairments were enrolled as subjects. Subjects walked up a 5 percent grade ramp. The ramp was constructed of an aluminum frame with a plywood walking surface. The ramps dimensions were 21' long, progressing from 1" in height to 12", and was 4' wide. Two "cutout" boxes were constructed in the middle of the ramp so ground reaction forces could be measured through the ramp and the AMTI forceplates.

Walking up ramp. At top of ramp. Walking down ramp.

Subjects wore a GRAFO on the right side, and shoes on both feet. Data were collected under two conditions: l)shoes only and 2)right side GRAFO and shoes. Each GRAFO consisted of a proximal tibial shell from below the tibial tubercle upward to the distal patellar tip, a solid ankle, and a full-length toe plate. The most proximal portion of the anterior shell was at the level of the patellar tendon. Polypropylene from 1/4 inch to 5/16 inch thick was used since subject body weights ranged from 155 lb. to 235 lb. The GRAFO was preset in 5-degrees of plantar flexion. All 4 braces were fabricated by the same orthotist.

A full body gait analysis including kinematic, kinetic, and temporal-spatial data was performed. Data were collected using a Motion Analysis Corporation HiRes Expert Vision System including eight HiRes Falcon cameras and two AMTI forceplates. Subjects walked up a ramp at a self-selected pace until three clean forceplates strikes for the stated conditions were achieved. OrthoTrak software (Motion Analysis Corporation, Santa Rosa, CA) was used to reduce and plot kinematic data and kinetic data. The markers were not removed from the shoes between each condition to decrease the error of ankle marker placement on the shoes. Each subject was allowed 10-15 minutes of time to accommodate to wearing the orthosis.

A push stick with a force transducer was used to apply varying point loads at different angles on the "cutout" sections of the forceplates to assess the accuracy of the force data calculated through the ramp and the forceplates. Two methods of measurement were within + 2 New-ions. Therefore no modifications to OrthoTrak software were required.

A point-to-point paired t-test was performed to test for differences between conditions with significance set at p < 0.05.


A statistically significant (p<0.05) decrease in stance phase knee flexion and ankle dorsiflexion motions and corresponding moments were noted when healthy subjects walked up the ramp when comparing the braced condition to the non-braced condition.

If someone is walking with a "crouch" gait, there is an increase in stance phase knee flexion, and typically a corresponding increase in the knee extensor moment during stance. For these healthy subjects wearing a GRAFO, a statistically significant (p= 0.05) decrease in stance phase knee flexion and corresponding statistically significant (p= 0.05) increase in stance phase knee flexor moment was noted (Graphs 1 & 2).

During the stance phase of gait a statistically significant (p= 0.05) decrease in ankle dorsiflexion of the braced side, with corresponding statistically significant (p= 0.05) increase in stance phase ankle plantar flexor moment was noted (Graphs 3 & 4).



Little research quantifying the effects of orthoses has been published. Clinically, GRA-FOs do not always work. We would encourage having subjects with very good responses or very poor responses to GRAFO to be assessed in motion laboratories. As more information about the knee and ankle moments is obtained we maybe able to learn why this orthosis helps some clients but not others.

Motion analysis laboratories have been used to document many different movements. The majority of publications to date continue to focus on human walking. Presently, motion analysis systems are being utilized more for entertainment (movies, video games, golf swing

analysis) than in the area of patient care. Amateur and professional athletes used motion analysis in hopes of improving their game. The potential of motion analysis has not been realized in the study of human movements in rehabilitation.

Through collaborative efforts, perhaps motion laboratories could provide new information to the clinical care and rehabilitation of clients. This can lead to improved patient care. By providing objective documentation of outcomes due to the interventions provided, increased funding by public and private resources may be obtained. Most motion analysis laboratories employ knowledgeable engineers, physical therapists, kinesiologists, physicians and technicians, who enjoy the challenges of a new situation. With appropriate technical and financial support, the use of a motion analysis laboratory is virtually unlimited in its potential to study all human motions.

The limitations of this study are that our subjects were without impairment and it is questionable if walking up a ramp simulates "crouch" gait. However, if a more detailed understanding of a movement and the forces that cause a movement to occur can be obtained, then potentially, treatments can be augmented.



Brandt, E. P., A (Ed.). (1997).


Enabling America: assessing the role of rehabilitation science and engineering. Washington: National Academy Press.


Craik, R., and Oatis, C. (1995).


Gait analysis: theory and application. St. Louis: Mosby.


Mulder, T., Nienhuis, B., & Pauwels, J. (1998).


Clinical gait analysis in a rehabilitation context: some controversial issues. Clin Rehabil, 72(2), 99-106.


Whittle, M. (1996).


Gait analysis: an introduction. Second edition. Oxford: Butterworth-Heinemann.





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