title: Elderly Fallers Enhance Dynamic Stability Through Anticipatory Postural Adjustments during a Choice Stepping Reaction Time.
abstract: In the case of disequilibrium, the capacity to step quickly is critical to avoid falling in elderly. This capacity can be simply assessed through the choice stepping reaction time test (CSRT), where elderly fallers (F) take longer to step than elderly non-fallers (NF). However, the reasons why elderly F elongate their stepping time remain unclear. The purpose of this study is to assess the characteristics of anticipated postural adjustments (APA) that elderly F develop in a stepping context and their consequences on the dynamic stability. Forty-four community-dwelling elderly subjects (20 F and 24 NF) performed a CSRT where kinematics and ground reaction forces were collected. Variables were analyzed using two-way repeated measures ANOVAs. Results for F compared to NF showed that stepping time is elongated, due to a longer APA phase. During APA, they seem to use two distinct balance strategies, depending on the axis: in the anteroposterior direction, we measured a smaller backward movement and slower peak velocity of the center of pressure (CoP); in the mediolateral direction, the CoP movement was similar in amplitude and peak velocity between groups but lasted longer. The biomechanical consequence of both strategies was an increased margin of stability (MoS) at foot-off, in the respective direction. By elongating their APA, elderly F use a safer balance strategy that prioritizes dynamic stability conditions instead of the objective of the task. Such a choice in balance strategy probably comes from muscular limitations and/or a higher fear of falling and paradoxically indicates an increased risk of fall.
authors.affiliation: IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), Université de Lyon, Université Claude Bernard Lyon 1 Lyon, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Tisserand
authors.affiliation: IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), Université de Lyon, Université Claude Bernard Lyon 1 Lyon, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Robert
authors.affiliation: Laboratoire Interuniversitaire de Biologie de la Motricité (LIBM), Université de Lyon, Université Claude Bernard Lyon 1 Villeurbanne, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Chabaud
authors.affiliation: Service de Médecine Gériatrique, Centre Hospitalier Lyon Sud Pierre-Bénite, France.
authors.forename: Marc
authors.initials: M
authors.lastname: Bonnefoy
authors.affiliation: IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), Université de Lyon, Université Claude Bernard Lyon 1 Lyon, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Chèze
keywords: anticipatory postural adjustments; balance; dynamic stability; elderly; fall; step initiation