Balance control under different passive contributions of the ankle extensors

Quiet standing on inclined surfaces

Shun Sasagawa, Junichi Ushiyama, Kei Masani, Motoki Kouzaki, Hiroaki Kanehisa

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

Human bipedal stance is often modeled as a single inverted pendulum that pivots at the ankle joints in the sagittal plane. Because the center of body mass is usually maintained in front of the ankle joints, ankle extensor torque is continuously required to prevent the body from falling. During quiet standing, both passive and active mechanisms contribute to generate the ankle extensor torque counteracting gravity. This study aimed to investigate the active stabilization mechanism in more detail. Eight healthy subjects were requested to stand quietly on three different surfaces of 1) toes-up, 2) level, and 3) toes-down. Surface electromyogram (EMG) was recorded from the medial head of the gastrocnemius (MG), soleus (SOL), and tibialis anterior muscles. Inclination angle of the body was simultaneously measured. As a result, we found that EMG activities of MG and SOL were lowest during the toes-up standing and highest during the toes-down, indicating that increased (decreased) passive contribution required less (more) extensor torque generated by active muscle contraction. Frequency domain analysis also revealed that sway-related modulation of the ankle extensor activity (0.12-4.03 Hz) was unchanged among the three foot inclinations. On the other hand, isometric contraction strength of these muscles increased as the slope declined (toes-up < level < toes-down). These results support the idea that by regulating the isometric contraction strength, the CNS maintains a constant level of muscle tone and resultant ankle stiffness irrespective of the passive contribution. Such control scheme would be crucial when we consider the low bandwidth of the intermittent controller.

Original languageEnglish
Pages (from-to)537-544
Number of pages8
JournalExperimental Brain Research
Volume196
Issue number4
DOIs
Publication statusPublished - 2009 Jul

Fingerprint

Toes
Ankle
Torque
Isometric Contraction
Ankle Joint
Electromyography
Accidental Falls
Muscles
Gravitation
Muscle Strength
Muscle Contraction
Healthy Volunteers

Keywords

  • Ankle extensors
  • EMG
  • Inverted pendulum
  • Posture
  • Quiet standing

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Balance control under different passive contributions of the ankle extensors : Quiet standing on inclined surfaces. / Sasagawa, Shun; Ushiyama, Junichi; Masani, Kei; Kouzaki, Motoki; Kanehisa, Hiroaki.

In: Experimental Brain Research, Vol. 196, No. 4, 07.2009, p. 537-544.

Research output: Contribution to journalArticle

Sasagawa, Shun ; Ushiyama, Junichi ; Masani, Kei ; Kouzaki, Motoki ; Kanehisa, Hiroaki. / Balance control under different passive contributions of the ankle extensors : Quiet standing on inclined surfaces. In: Experimental Brain Research. 2009 ; Vol. 196, No. 4. pp. 537-544.
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