HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Loram, I. D. Articles by Lakie, M. Search for Related Content PubMed PubMed Citation Articles by Loram, I. D. Articles by Lakie, M.

Human balancing of an inverted pendulum: is sway size controlled by ankle impedance?

Ian D. Loram, Sue M. Kelly * and Martin Lakie

1. Using the ankle musculature, subjects balanced a large inverted pendulum. The equilibrium of the pendulum is unstable and quasi-regular sway was observed like that in quiet standing. Two main questions were addressed. Can subjects systematically change sway size in response to instruction and availability of visual feedback? If so, do subjects decrease sway size by increasing ankle impedance or by some alternative mechanism?
2. The position of the pendulum, the torque generated at each ankle and the soleus and tibialis anterior EMG were recorded.
3. Results showed that subjects could significantly reduce the mean sway size of the pendulum by giving full attention to that goal. With visual feedback sway size could be minimised significantly more than without visual feedback. In changing sway size, the frequency of the sways was not changed.
4. Results also revealed that ankle impedance and muscle co-contraction were not significantly changed when the sway size was decreased. As the ankle impedance and sway frequency do not change when the sway size is decreased, this implies no change in ankle stiffness or viscosity.
5. Increasing ankle impedance, stiffness or viscosity are not the only methods by which sway size could be reduced. A reduction in torque noise or torque inaccuracy via a predictive process which provides active damping could reduce sway size without changing ankle impedance and is plausible given the data. Such a strategy involving motion recognition and generation of an accurate motor response may require higher levels of control than changing ankle impedance by altering reflex or feedforward gain.

This article has been cited by other articles:

				B. T. Zazulak, T. E. Hewett, N. P. Reeves, B. Goldberg, and J. Cholewicki The Effects of Core Proprioception on Knee Injury: A Prospective Biomechanical-Epidemiological Study Am. J. Sports Med., March 1, 2007; 35(3): 368 - 373. [Abstract] [Full Text] [PDF]

				E. Guigon, P. Baraduc, and M. Desmurget Computational Motor Control: Redundancy and Invariance J Neurophysiol, January 1, 2007; 97(1): 331 - 347. [Abstract] [Full Text] [PDF]

				M. Lakie and I. D. Loram Manually controlled human balancing using visual, vestibular and proprioceptive senses involves a common, low frequency neural process J. Physiol., November 15, 2006; 577(1): 403 - 416. [Abstract] [Full Text] [PDF]

				I. D. Loram, P. J. Gawthrop, and M. Lakie The frequency of human, manual adjustments in balancing an inverted pendulum is constrained by intrinsic physiological factors J. Physiol., November 15, 2006; 577(1): 417 - 432. [Abstract] [Full Text] [PDF]

				G. L. Onambele, M. V. Narici, and C. N. Maganaris Calf muscle-tendon properties and postural balance in old age J Appl Physiol, June 1, 2006; 100(6): 2048 - 2056. [Abstract] [Full Text] [PDF]

				I. D Loram, C. N Maganaris, and M. Lakie Human postural sway results from frequent, ballistic bias impulses by soleus and gastrocnemius J. Physiol., April 1, 2005; 564(1): 295 - 311. [Abstract] [Full Text] [PDF]

				I. D. Loram, C. N. Maganaris, and M. Lakie Paradoxical muscle movement in human standing J. Physiol., May 1, 2004; 556(3): 683 - 689. [Abstract] [Full Text] [PDF]

				I. D. Loram and M. Lakie Human balancing of an inverted pendulum: position control by small, ballistic-like, throw and catch movements J. Physiol., May 1, 2002; 540(3): 1111 - 1124. [Abstract] [Full Text] [PDF]