Examining the influence of mental stress on balance perturbation responses in older adults

Abstract

BACKGROUND\nReach-to-grasp responses following balance perturbations are important to fall prevention but are often ineffective in older adults. The ability to shift attention from an ongoing cognitive task to balance related processes has been shown to influence reach-to-grasp effectiveness in older adults. However, the added influence of stress and anxiety - known to negatively affect attention shifting ability - has not yet been explored in relation to recovery from balance perturbations. Given that fear and anxiety over falling is a key fall risk factor, an understanding of how such a negative mental state may affect postural reactions is important. This study aimed to investigate the effect of varied induced emotional states on reach-to-grasp balance responses in older adults.\n\n\nMETHODS\nHealthy older adults (mean age 70.5\xa0±\xa05.38\xa0years) stood laterally between 2 handrails with contact sensors. A safety harness with an integrated loadcell was worn to prevent falls and measure the amount of harness assistance (expressed as percent body weight). With instructions to grasp one rail to restore balance, participants balance was laterally disturbed using surface translations under three randomized conditions: no cognitive task, neutral (verb generation) task, and mental stress task with negative prompts (paced auditory serial addition). The primary outcome was frequency of protective grasps. Secondary outcomes included frequency of harness assistance during trials with grasp errors as well as wrist movement time, trajectory distance, and peak velocity.\n\n\nRESULTS\nPerceived level of distress was highest for the mental stress task compared to no task (p\xa0<\xa00.001) and neutral task conditions (p\xa0=\xa00.008). The mental stress task resulted in the lowest percentage of protective grasps (p\xa0<\xa00.001) in response to balance perturbations. Closer examination of trials that resulted in grasp errors (i.e., collisions or overshoots), revealed increased harness assistance and reduced peak velocity of wrist movement (p\xa0<\xa00.001) under the mental stress condition compared to grasp errors that occurred under the no task or neutral task condition.\n\n\nDISCUSSION AND CONCLUSION\nDistressing mental thoughts immediately prior to a balance perturbation lead to reduced effectiveness in reach-to-grasp balance responses compared to no or neutral cognitive tasks and should be considered as a possible fall risk factor.