Current Interests

Elastic Locomotion
Walking and running gaits have traditionally been treated as distinct paradigms of movement. Walking is usually simplified to the motion of an inverted pendulum and running simplified as a spring mass. However, humans can walk and run with a single mechanical system, and neither robots nor human studies have yielded a single model that passively generates multiple gaits.

Our elastic locomotion model is made up of a point mass at the pelvis, two axially-compliant legs, and a torsion spring acting between the legs. After adding leg compliance to our simple model, we found that the motion of both legs for an entire step can be generated completely passively. A variety of human-like gaits may be produced with one simple model , without enforcing ground reaction force patterns or prescribing motions. Since no active control is used to generate these gaits, motions are produced simply by the interaction of leg stiffness, inertia, and gravity.

posted by Shawn O'Connor at 2:43 PM 0 comments
Inertial Measurement of Human Walking

This study uses small, portable inertial measurement units to measure human motion.

Currently, accurate measurements of human kinematic motion data, particularly for data to be used for clinical purposes, are generally only available using lab based equipment, typically a camera and marker setup. These systems can be very accurate, but they have a limited workspace and can only be used to measure laboratory based movement tasks. Some measurements are difficult to make in laboratory situations. When measuring human walking, for example, the subject may be told to walk at a comfortable speed. This so-called self-selected gait has debatable relevance to the subject's lifestyle, which can be measured by self reported "activity levels". It would be ideal to instrument a person with non-obtrusive sensors to be worn all day, collecting kinematic data on the subject which can be later analyzed for metrics of activity levels (walking speed, total number of steps per day). More importantly, the data can yield important clinical measurements such as step width and step width variability of a subject, which are often used to quantify a person's risk of falling.

This study looks at using inertial measurement units to measure the kinematics of human motion. Inertial measurement units require proper filtering techniques to yield usable data. We plan to exploit knowledge of the dynamics of walking using a kalman filter to perform model based state estimation.

posted by John Rebula at 1:20 PM 0 comments
Visual Control of Walking Balance

Falling is a serious health risk for the elderly and other populations with neuromuscular deficits. Problems with balance are a frequent reason why people fall and many falls occur while walking.

We are using a virtual reality environment to study how vision is used for making foot placement corrections related to walking balance. Specifically, our goal is to test model-based predictions of how physical requirements for maintaining balance and quality of visual information affect how components of vision are utilized. The visual surround can be suddenly perturbed to induce balance corrections and/or continuously oscillated to make the visual information less reliable. The findings of these studies will lend insight into how vision is used and integrated for walking control and may lead to improvements in our understanding of how to treat and assist patients with sensory loss or deficits.

posted by Shawn O'Connor at 1:52 PM 1 comments
Elastic Preload Energy Storage in Prosthetic Feet

Presently, amputees expend more metabolic energy than intact individuals during walking -- unilateral transtibial: 20-30% more; transfemoral & bilateral: 30-100% more (Collins 2008, Herbert 1994). Commonly prescribed Dynamic Elastic Response (DER) feet flex under walking loads, allowing mechanical energy to be stored in carbon fiber construction and returned later during the gait cycle.

During the preload phase of walking, just prior to push-off when negative work is typically performed about the ankle, DER feet flex and store energy in the carbon fiber toe plates. Even with this assistive mechanical design, DER feet have not been shown to reduce metabolic energy cost (ml O2/kg-m) or rate of expenditure (ml O2/kg-min) during walking compared to Solid-Ankle Cushioned Heel (SACH) feet (Torburn 1995). A better understanding of how the body utilizes elastic energy-storing components may assist in development of next-generation prostheses and orthoses.

Project members: Karl Zelik, Peter Adamczyk, Steve Collins, Art Kuo

External links:
Karl's prosthesis page

posted by The HBCL at 8:47 AM 0 comments
The Role of the Arms in Human Walking

People tend to swing their arms when they walk. We use simulations and human subject experiments to help figure out why.

Project members: Steve Collins, Peter Adamczyk, Art Kuo

posted by Steve Collins at 6:23 AM 0 comments
Instrumented Split-Belt Treadmill

Instrumented treadmills enable the collection of force data for many continuous steps in a laboratory setting. We custom built a split-belt instrumented treadmill, then calibrated it in order to increase the accuracy of force and center of pressure measurements for each individual leg during gait. The design was based on Joel Banks' Masters thesis work at the University of Texas, Austin.

Project members: Peter Adamczyk, Steve Collins, Greg Sawicki, Dan Ferris, and Art Kuo
posted by Steve Collins at 6:35 AM 0 comments
Balance During Gait - Lateral Foot Placement

Balance is an important aspect of gait. Improving our understanding of the neural control involved in balance may help prevent falls in elderly individuals and help to develop rehabilitation techniques for persons with disabilities. Simple dynamic walking models, such as the one described by Kuo (1999), suggest that during gait fore-aft motions may be passively stable, while lateral motions may require feedback control for stabilization. We use human subject experiments to test model-based hypotheses pertaining to the control utilized by humans during walking.

Project members: Steve Collins, Catherine Bauby, Art Kuo

Publications: Bauby and Kuo, (2001); Collins and Kuo, (2007)

posted by Steve Collins at 6:33 AM 0 comments


Selected Papers
Adamczyk, P. G., Collins, S. H., and Kuo, A. D. (2006) The advantages of a rolling foot in human walking. Journal of Experimental Biology, 209:3953-3963. [DOI:10.1242/jeb.02455] (pdf)

Huang, F. C., Gillespie, R. B., and Kuo, A. D. (2006) Human adaptation to interaction forces in visuo-motor coordination. IEEE Transactions on Neural Systems and Rehabilitation Engineering, 14: 390-397 [DOI:10.1109/TNSRE.2006.881533] (pdf)

Kuo, A. D. (2005) Harvesting energy by improving the economy of human walking. Science, 309(5741): 1686-1687. [DOI: 10.1126/science.1118058] (pdf)

Kuo, A. D. (2005) An optimal state estimation model of sensory integration in human postural balance. Journal of Neural Engineering, 2: S235-S249. (pdf)

Collins, S. H., Ruina, A. L., Tedrake, R., and Wisse, M. (2005) Efficient bipedal robots based on passive-dynamic walkers. Science, 209:3953-3963. (pdf)

Kuo, A. D., Donelan, J. M., and Ruina, A. (2005) Energetic consequences of walking like an inverted pendulum: Step-to-step transitions. Exercise and Sport Sciences Reviews, 33: 88-97. (pdf)

Doke, J., Donelan, J. M., and Kuo, A. D. (2005) Mechanics and energetics of swinging the human leg. Journal of Experimental Biology, 208: 439-445. (pdf)

Donelan, J. M., Shipman, D. W., Kram, R., and Kuo, A. D. (2004) Mechanical and metabolic requirements for active lateral stabilization in human walking. Journal of Biomechanics, 37: 827-835. (pdf)

Park, S., Horak, F. B., and Kuo, A. D. (2004) Postural feedback responses scale with biomechanical constraints in human standing. Experimental Brain Research, 154: 417-427. (pdf)

Gard, S. A., Miff, S. C., and Kuo, A. D. (2004) Comparison of kinematic and kinetic methods for computing the vertical motion of the body center of mass during walking. Human Movement Science, 22: 597-610. (pdf)

Dean, J.D., Alexander, N. B., and Kuo, A. D. (2004) Age-related changes in maximal hip strength and movement speed. Journal of Gerontology: Medical Sciences, 59A: 286-292. (pdf)

Donelan, J. M., Kram, R., and Kuo, A. D. (2002) Mechanical work for step-to-step transitions is a major determinant of the metabolic cost of human walking. Journal of Experimental Biology, 205: 3717-3727. (pdf)

Kuo, A. D. (2002) The relative roles of feedforward and feedback in the control of rhythmic movements, Motor Control, 6: 129-145. (pdf)

Donelan, J. M., Kram, R., and Kuo, A. D. (2002) Simultaneous positive and negative external mechanical work in human walking, Journal of Biomechanics, 35: 117-124. (pdf)

Kuo, A. D. (2002) Energetics of actively powered locomotion using the simplest walking model, Journal of Biomechanical Engineering, 124: 113-120. (pdf)

Speers, R. A., Kuo, A. D. (2002) Contributions of altered sensation and feedback responses to changes in coordination of postural control due to aging, Gait and Posture, 16: 20-30. (pdf)

Donelan, J. M., Kram, R., and Kuo, A. D. (2001) Mechanical and metabolic determinants of the preferred step width in human walking. Proceedings of the Royal Society of London, Series B, 268: 1985-1992. (pdf)

Kuo, A. D. (2001) A simple model predicts the step length-speed relationship in human walking, Journal of Biomechanical Engineering, 123: 264-269. (pdf)

Bauby, C. E., and Kuo, A. D. (2000) Active control of lateral balance in human walking, Journal of Biomechanics, 33: 1433-1440. (pdf)

Kuo, A. D. (1999) Stabilization of lateral motion in passive dynamic walking, International Journal of Robotics Research, 18(9): 917-930. (pdf)

Speers, R. A., Shepard, N. T., Kuo, A. D. (1999) EquiTest modification with shank and hip angle measurements: differences with age among normal subjects, J. Vestibular Research, 9 (6): 435-444. (pdf)

Zhang, X.D., Chaffin, D. B., Kuo, A. D. (1998) Optimization-based differential kinematic modeling exhibits a velocity-control strategy for dynamic posture determination in seated reaching movements, J. Biomechanics, 31: 1035-1042. (pdf)

Speers, R. A., Paloski, W. H., Kuo, A. D. (1998) Multivariate changes in coordination of postural control following spaceflight, J. Biomechanics, 31: 883-889. (pdf)

Kuo, A. D., Speers, R. A., Peterka, R. J., and Horak, F. B. (1998) Effect of altered sensory conditions on multivariate descriptors of human postural sway, Experimental Brain Research, 122: 185-195. (pdf)

Kuo, A. D. (1998) A least squares estimation approach to improving the precision of inverse dynamics computations, J. Biomechanical Engineering, 120(1): 148-159. (pdf)

Kuo, A. D. (1995) An optimal control model for analyzing human postural balance, IEEE Transactions on Biomedical Engineering, 42: 87-101. (pdf)

Kuo, A. D. (1994) A mechanical analysis of force distribution between redundant, multiple degree-of-freedom actuators in the human: implications for central nervous system control. Human Movement Sciences, 13: 635-663. (pdf)

Kuo, A. D. and Zajac, F. E. (1993) Human standing posture: multijoint movement strategies based on biomechanical constraints, Progress in Brain Research, 97: 349-358. (pdf)

Kuo, A. D. and Zajac, F. E. (1993) A biomechanical analysis of muscle strength as a limiting factor in standing posture, Journal of Biomechanics, 26 (suppl. 1): 137-150. (pdf)

Kuo, A. D. and Carter, D. R. (1991) Computational methods for analyzing the structure of cancellous bone, Journal of Orthopaedic Research, 9: 918-931. (pdf)
posted by The HBCL at 11:19 AM
Book Chapters
Kuo, A. D. (2001) The action of two-joint muscles: The legacy of W. P. Lombard. In: Classics in Movement Science, M. L. Latash & V. M. Zatsiorsky, eds. Human Kinetics, Champaign, IL. Ch. 10, pp. 289-316. (pdf)

Horak, F. B. and Kuo, A. D. (2000) Postural adaptation for altered environments, tasks, and intentions. In: Biomechanics and Neural Control of Movement, J. Winters & P. Crago, eds. Springer-Verlag, New York. Ch. 19, pp. 267-281.
posted by Steve Collins at 5:42 AM 0 comments
Gordon, K. E., Ferris, D. P., and Kuo, A. D. (2003) Reducing vertical center of mass movement during human walking doesn't necessarily reduce metabolic cost. In: Proc. 27th Annual Meeting of the American Society of Biomechanics, Toledo, Ohio. #53. (Poster) (pdf)
posted by Steve Collins at 5:48 AM 0 comments