Medical & Biological Engineering & Computing

, Volume 46, Issue 3, pp 213–221

Stability of the human upright stance depending on the frequency of external disturbances

  • Akimasa Ishida
  • Tadashi Masuda
  • Hidenori Inaoka
  • Yutaka Fukuoka
Original Article

DOI: 10.1007/s11517-007-0269-8

Cite this article as:
Ishida, A., Masuda, T., Inaoka, H. et al. Med Biol Eng Comput (2008) 46: 213. doi:10.1007/s11517-007-0269-8

Abstract

During an upright stance of humans, it is usually assumed that a stiffer ankle joint contributes to stabilize the stance. To show that under certain conditions a stiffer ankle joint can reduce the stability, the frequency responses of the moment and the angle of the ankle joint against external disturbances caused by random horizontal translations of the support surface were evaluated in ten healthy adult subjects by varying the difficulty of the task at four levels. When it was difficult to keep the upright stance, the subject tended to make the ankle joint stiffer. The transfer function relating the external disturbance moment to the ankle joint moment showed a larger gain in the high frequency range (>0.3 Hz) compared with the gains obtained under easier conditions. A simulation analysis based on a simple inverted pendulum model also reproduced this tendency. These results indicate that the stiffer ankle joint and the resulting higher ankle moment for high frequency external disturbances enhance the possibility that the center of pressure exceeds the limit arising from the size of the feet and can make the upright stance unstable.

Keywords

Upright stanceJoint impedanceExternal disturbanceTransfer functionFrequency response

Copyright information

© International Federation for Medical and Biological Engineering 2007

Authors and Affiliations

  • Akimasa Ishida
    • 1
  • Tadashi Masuda
    • 2
  • Hidenori Inaoka
    • 3
  • Yutaka Fukuoka
    • 2
  1. 1.Institute of Biomaterials and Biomedical EngineeringTokyo Medical and Dental UniversityTokyoJapan
  2. 2.School of Biomedical ScienceTokyo Medical and Dental UniversityTokyoJapan
  3. 3.School of Allied Health SciencesKitasato UniversitySagamiharaJapan