Contributions of muscles to terminal-swing knee motions vary with walking speed

Allison S. Arnold, Michael H. Schwartz, Darryl G. Thelen, Scott L. Delp

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


Many children with cerebral palsy walk with diminished knee extension during terminal swing, at speeds much slower than unimpaired children. Treatment of these gait abnormalities is challenging because the factors that extend the knee during normal walking, over a range of speeds, are not well understood. This study analyzed a series of three-dimensional, muscle-driven dynamic simulations to determine whether the relative contributions of individual muscles and other factors to angular motions of the swing-limb knee vary with walking speed. Simulations were developed that reproduced the measured gait dynamics of seven unimpaired children walking at self-selected, fast, slow, and very slow speeds (7 subjects×4 speeds=28 simulations). In mid-swing, muscles on the stance limb made the largest net contribution to extension of the swing-limb knee at all speeds examined. The stance-limb hip abductors, in particular, accelerated the pelvis upward, inducing reaction forces at the swing-limb hip that powerfully extended the knee. Velocity-related forces (i.e., Coriolis and centrifugal forces) also contributed to knee extension in mid-swing, though these contributions were diminished at slower speeds. In terminal swing, the hip flexors and other muscles on the swing-limb decelerated knee extension at the subjects' self-selected, slow, and very slow speeds, but had only a minimal net effect on knee motions at the fastest speeds. Muscles on the stance limb helped brake knee extension at the subjects' fastest speeds, but induced a net knee extension acceleration at the slowest speeds. These data-which show that the contributions of muscular and velocity-related forces to terminal-swing knee motions vary systematically with walking speed-emphasize the need for speed-matched control subjects when attempting to determine the causes of a patient's abnormal gait.

Original languageEnglish (US)
Pages (from-to)3660-3671
Number of pages12
JournalJournal of Biomechanics
Issue number16
StatePublished - 2007

Bibliographical note

Funding Information:
The authors gratefully thank Joyce Trost and Roy Wervey for assistance with data collection, and Felix Zajac, Frank Anderson, and Ilse Jonkers for helpful discussions related to simulation and interpretation of muscle function. This work was supported by the National Institutes of Health through the NIH Roadmap for Medical Research U54 GM072970, NIH RO1 HD33929, and NIH R01 HD046814.


  • Cerebral palsy
  • Dynamic simulation
  • Gait
  • Muscle function
  • Swing phase


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