Task-dependence of ankle stretch reflex

D. Ludvig*, M. Baker, I. Cathers, R. E. Kearney

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review

3 Scopus citations


An investigation was undertaken to determine whether ankle stretch reflexes vary with the task performed by a subject. We measured reflex gain in three subjects while they performed position-matching and torque-matching tasks. In the position-matching task, subjects were required to hold their foot at a desired position while a hydraulic actuator, configured to act like a compliant spring, applied random torque perturbations to their ankle. In the torque-matching task, subjects were required to maintain a desired torque while their foot position was perturbed randomly by the actuator which behaved as a very stiff position control servo. Care was taken to ensure that the movements resulting from the perturbations were similar in both tasks. A nonlinear identification procedure was used to identify the reflex and intrinsic stiffness. Reflex stiffness was greater in the position-matching task than in the torque-matching task in all three subjects. In contrast, intrinsic stiffness was task-independent. Thus, subjects appeared to modulate their reflexes in a way appropriate to the task, supporting the hypothesis that the nervous system has the ability to modulate the stretch reflex characteristics to meet the needs of the task.

Original languageEnglish (US)
Pages (from-to)1487-1490
Number of pages4
JournalAnnual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings
StatePublished - 2003
EventA New Beginning for Human Health: Proceddings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society - Cancun, Mexico
Duration: Sep 17 2003Sep 21 2003


  • Ankle stiffness
  • Impedance control
  • Intrinsic
  • Stretch reflex
  • Task
  • Torque

ASJC Scopus subject areas

  • Signal Processing
  • Biomedical Engineering
  • Computer Vision and Pattern Recognition
  • Health Informatics


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