Practice-related improvements in posture control differ between young and older adults exposed to continuous, variable amplitude oscillations of the support surface.

Healthy older adults were repeatedly exposed to continuous, variable amplitude oscillations of the support surface to determine (1) whether age affects the capacity for postural motor learning under continuous perturbation conditions with limited predictability and (2) whether practice leads to modifications in the control strategy used to maintain balance in older adults. During training, a translating platform underwent 45-s trials of constant frequency (0.5 Hz) and seemingly random amplitude oscillations (range +- 2 to 15 cm). The middle 15 s of each trial contained the same sequence of oscillation amplitudes. This repeated middle segment was the same as the repeated segment used in Van Ooteghem et al. (Exp Brain Res 187(4): 603-611, 2008) and was therefore used for analyses. To examine learning, participants performed a retention test following a 24-h delay. Kinematic data were used to derive spatial and temporal measures of whole body centre of mass (COM), trunk, thigh, and shank segment orientation, and ankle and knee angle from performance during the repeated middle segment. Results showed that with training, older adults maintained the capacity to learn adaptive postural responses in the form of improved temporal control of the COM and minimization of trunk instability a a rate comparable to young adults. With practice, however older adults maintained a more rigid, 'platform-fixed' control strategy which differed from young adults who shifted towards 'gravity-fixed' control and decreased COM motion. This study provides important insight into the ability of older adults to demonstrate longer-term improvements in postural regulation.