title: Effect of higher muscle coactivation on standing postural response to perturbation in older adults.
abstract: BACKGROUND
  Although several studies have reported that muscle coactivation during postural control increases with age, the effect of higher muscle coactivation on standing postural response to perturbation is unknown.
  
  
  OBJECTIVE
  To investigate whether higher muscle coactivation affects standing postural response to perturbation in older adults.
  
  
  METHODS
  Thirty-four community-dwelling older participants were randomly assigned either to the coactivation group (CG), where muscle coactivation was increased intentionally, or to the non-coactivation group (NCG). The participants were instructed to stand on a force plate that moved forward or backward. Electromyography data were collected from the lower leg muscles. We requested the participants in the CG to increase the activity of their tibialis anterior, and to maintain this posture during the tasks. We moved the force plate with a constant amplitude and velocity, and measured kinematic data with a camera during the tasks.
  
  
  RESULTS
  During forward transfer, the knee extension and hip flexion decreased in the CG after perturbation compared to NCG, and the trunk extension angle increased. The center of pressure (COP) displacement decreased around the peak of the movement in the CG compared to NCG. During backward transfer, ankle dorsal and knee flexion changed after perturbation in the CG compared to NCG.
  
  
  CONCLUSIONS
  Our study found that higher muscle coactivation inhibits lower limb and COP movement as well as increases trunk tilt and the risk for falls during forward perturbations. Postural control with higher coactivation appears to be inefficient for maintaining balance during the backward sway of posture.
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan. nagai-k@huhs.ac.jp.|Department of Rehabilitation, Graduate School of Health Sciences, Hyogo University of Health Sciences, 1-3-6 Minatojima, Chuo-ku, Kobe, 650-8530, Japan. nagai-k@huhs.ac.jp.
authors.forename: Koutatsu
authors.initials: K
authors.lastname: Nagai
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Okita
authors.affiliation: School of Comprehensive Rehabilitation, Osaka Prefecture University, Osaka, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Ogaya
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Tadao
authors.initials: T
authors.lastname: Tsuboyama
mesh_terms: D000058:Accidental Falls / Q000517:prevention & control*; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001696:Biomechanical Phenomena; D004576:Electromyography / Q000379:methods; D005260:Female; D015577:Geriatric Assessment / Q000379:methods; D006801:Humans; D035002:Lower Extremity / Q000502:physiology / Q000503:physiopathology; D008297:Male; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D013647:Task Performance and Analysis
keywords: Coactivation; Muscle; Older adults; Perturbation; Postural control