title: Identification of the contribution of the ankle and hip joints to multi-segmental balance control.
abstract: BACKGROUND
  Human stance involves multiple segments, including the legs and trunk, and requires coordinated actions of both. A novel method was developed that reliably estimates the contribution of the left and right leg (i.e., the ankle and hip joints) to the balance control of individual subjects.
  
  
  METHODS
  The method was evaluated using simulations of a double-inverted pendulum model and the applicability was demonstrated with an experiment with seven healthy and one Parkinsonian participant. Model simulations indicated that two perturbations are required to reliably estimate the dynamics of a double-inverted pendulum balance control system. In the experiment, two multisine perturbation signals were applied simultaneously. The balance control system dynamic behaviour of the participants was estimated by Frequency Response Functions (FRFs), which relate ankle and hip joint angles to joint torques, using a multivariate closed-loop system identification technique.
  
  
  RESULTS
  In the model simulations, the FRFs were reliably estimated, also in the presence of realistic levels of noise. In the experiment, the participants responded consistently to the perturbations, indicated by low noise-to-signal ratios of the ankle angle (0.24), hip angle (0.28), ankle torque (0.07), and hip torque (0.33). The developed method could detect that the Parkinson patient controlled his balance asymmetrically, that is, the right ankle and hip joints produced more corrective torque.
  
  
  CONCLUSIONS
  The method allows for a reliable estimate of the multisegmental feedback mechanism that stabilizes stance, of individual participants and of separate legs.
authors: Laboratory for Biomechanical Engineering, MIRA institute for biomechanical technology and technical medicine, University of Twente, Faculty of Engineering Technology, PO Box 217, Enschede, AE 7500, The Netherlands. t.a.boonstra@gmail.com
authors: Tjitske Anke
authors: TA
authors: Boonstra
authors: Alfred C
authors: AC
authors: Schouten
authors: Herman
authors: H
authors: van der Kooij
mesh_terms: D000368:Aged; D000843:Ankle Joint / Q000502:physiology*; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D004856:Postural Balance / Q000502:physiology*