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(Stroke. 2008;39:139.)
© 2008 American Heart Association, Inc.

Original Contributions

Evidence of Abnormal Lower-Limb Torque Coupling After Stroke

An Isometric Study

Theresa Hayes Cruz, MS Yasin Y. Dhaher, PhD

From the Department of Biomedical Engineering (T.H.C., Y.Y.D.), Northwestern University, Chicago, Ill; Sensory Motor Performance Program (T.H.C., Y.Y.D.) Rehabilitation Institute of Chicago, Chicago, IL; Department of Physical Medicine and Rehabilitation (Y.Y.D.), Northwestern University, Chicago, Ill.

Correspondence to Yasin Dhaher, PhD, Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Room 1406, Chicago, IL 60611. E-mail y-dhaher{at}northwestern.edu

Background and Purpose— Although stroke survivors often display abnormal joint torque patterns, studies of torque-coupling in the lower limb are lacking, despite their potential impact on gait abnormalities.

Methods— Twenty-two chronic ambulating stroke subjects and 11 age-matched control subjects produced isometric hip torques in the frontal and sagittal planes with the hemiparetic leg (or randomly selected leg for the control group) in postures that resemble stages of gait. The involuntary knee torques were also recorded although no feedback or instructions were given.

Results— In the toe-off and midswing postures, the stroke group had a significant torque bias toward extension and adduction, whereas the control group had a symmetric torque space. The stroke group also produced significantly smaller torques than the control group in the flexion and abduction/flexion directions. Finally, the stroke group displayed abnormal coupling of knee extension with hip adduction, unique to the toe-off position.

Conclusions— Whereas gait abnormalities after stroke have been attributed to a number of factors, including sagittal plane strength impairments at the hip, knee, and ankle, our findings indicate that neuromechanical changes after stroke may play a significant role in determining the nature of the movement abnormality. Specifically, abnormal hip adduction and knee extension torque coupling was observed, in addition to direction-specific hip torque weakness. Future studies are needed to delineate the differential contributions of each potential factor to gait abnormalities. Understanding the underlying neuromechanical changes after stroke may aid the development of rehabilitation strategies.

Supplemental Materials and Methods