Introducing a psychological postural threat alters gait and balance parameters among young participants but not among most older participants

The fear of falling can be manipulated by introducing a postural threat (e.g., an elevated support surface) during stance and gait. Under these conditions, balance parameters are altered in both young and elderly individuals. This study aimed to dissociate the physical and psychological aspects of the threat and show the impact of a verbal warning cue of imminent perturbation during gait among young and elderly healthy participants. Ten young subjects (29.4 +/- 3.9 years) and ten subjects aged over 65 years (72.9 +/- 3.5) participated in the study. Spatiotemporal and balance parameters were quantified during eight consecutive gait cycles using a motion analysis system and an instrumented treadmill. These parameters were compared twice in the control trial and before/after a verbal warning cue of imminent perturbation during gait ("postural threat") in perturbation trials and between groups using repeated measure ANOVAs. Results: The verbal cue yielded reduced step length (p = 0.008), increased step width (p = 0.049), advanced relative position of the center of mass (p = 0.016), increased stabilizing force (p = 0.003), and decreased destabilizing force (p = 0.002). This warning effect was not observed in the older participant group analyses but was found for three participants based on individual data analyses. The warning effect in younger participants was not specific to impending perturbation conditions. Most gait and balance parameters were altered in the older group (p < 0.05) versus the younger group in each condition, regardless of the warning cue. A psychological threat affects gait and balance similarly to a physical threat among young participants but not among most older participants.