title: A unified approach for revealing multiple balance recovery strategies.
abstract: In human balance recovery, different strategies have been proposed with generally overlooked knee motions but extensive focus on the ankle, hip, and step strategies. It is not well understood whether maintaining balance is regulated at the lower "muscular-articular" level of coordinating segment joints or at a higher level of controlling whole body dynamics. Whether balance control is to minimize joint degrees of freedom (DOF) or utilize all the available DOF also remains unclear. This study aimed to use a realistic musculoskeletal human model to identify multiple balance recovery strategies with a single optimization criterion. Movements were driven by neural excitations (which activated muscle force generation) and were assumed to be symmetric. Balance recoveries were simulated with forward-inclined straight body postures as the initial conditions. When the position of the toes was fixed, balance was regained with virtually straight knees and mixed ankle/hip strategies. Under a severely perturbed condition, use of the forward hop strategy after releasing the fixed-toes constraint indicated spontaneous recruitment or suppression of DOF, which mimicked functions of optimally computed CNS commands in humans. The results also indicated that increase/decrease in the number of DOF depends on the imposed perturbation intensity and movement constraints.
authors.affiliation: Institute of Physical Education, Health, and Leisure Studies, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Kuangyou B
authors.initials: KB
authors.lastname: Cheng
authors.affiliation: Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan. Electronic address: simpson.ycg@gmail.com.
authors.forename: Chih-Kuo
authors.initials: CK
authors.lastname: Yeh
mesh_terms: D000843:Ankle Joint / Q000502:physiology; D003198:Computer Simulation; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D009048:Motor Skills / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*
keywords: Degree of freedom; Movement coordination; Musculoskeletal model; Optimal simulation; Postural control