Obstacle negotiation kinematics: age-dependent effects of postural threat.

This study investigated whether obstacle negotiation kinematics among younger (YA) and older adults (OA) are influenced by postural threat. Obstacle negotiation kinematics among YA and OA were examined under four conditions of postural threat. Seventeen older and 15 YA negotiated a fixed virtual obstacle while walking at a self-determined velocity along a 7.2 m walkway. Postural threat was manipulated by varying the width (0.60 vs. 0.15 m) and height (0.00 vs. 0.60 m) of the walkway. Increasing postural threat resulted in elevated levels of physiological arousal and altered crossing kinematics for all subjects. Specifically, crossing step length, lead limb velocity, trail limb velocity, and whole body center of mass (COM) velocity decreased and lead limb crossing height increased in the condition of greatest postural threat compared with the condition of least postural threat. Although both YA and OA altered obstacle negotiation kinematics under conditions of postural threat, the changes observed among older adults were considerably different from those of YA. In particular, OA demonstrated more marked reductions in the crossing velocity of the lead limb, trail limb, and COM than YA between the condition of least postural threat and the condition of greatest postural threat. The results of this study reveal that postural threat influences negotiation kinematics among YA and OA and illustrate that age-dependent differences exist for obstacle negotiation kinematics when postural threat increases. These findings may imply a beneficial effect of fear of falling on reducing fall probability among healthy OA.