Introduction: Older adults show increased postural sway and a greater risk of falls when completing activities with high cognitive demands. While dual-task approaches have clarified an association between cognitive processes and postural control, it is unclear how manual ability, which is also required for the successful completion of cognitively demanding tasks (such as putting a key into a lock), affects this relationship.Method: Kinematic technology was used to explore the relationship between postural sway and manual control in healthy younger and older adults. Participants (n=82) remained standing to complete a visual-motor tracking task on a tablet computer. Root mean square tracking error measured manual performance, and a balance board measured deviations in centre of pressure as a marker of postural sway.Results: Older adults displayed poorer manual accuracy and increased postural sway across all testing conditions.Conclusions: Cognitive capacity can interact with multiple task demands, and in turn affect postural sway in older adults. Improving our understanding of factors that influence postural control will assist falls-prevention efforts and inform clinical practice.

Manual dexterity and postural control develop throughout childhood, leading to changes in the synergistic relationships between head, hand and posture. But the postural developments that support complex manual task performance (i.e. beyond pointing and grasping) have not been examined in depth. We report two experiments in which we recorded head and posture data whilst participants simultaneously performed a visuomotor task. In Experiment 1, we explored the extent to which postural stability is affected by concurrently performing a visual and manual task whilst standing (a visual vs. manual-tracking task) in four age groups: 5-6 years (n = 8), 8-9 years (n = 10), 10-11 years (n = 7) and 19-21 years (n = 9). For visual tracking, the children's but not adult's postural movement increased relative to baseline with a larger effect for faster moving targets. In manual tracking, we found greater postural movement in children compared to adults. These data suggest predictive postural compensation mechanisms develop during childhood to improve stability whilst performing visuomotor tasks. Experiment 2 examined the extent to which posture is influenced by manual activity in three age groups of children [5-6 years (n = 14), 7-8 years (n = 25), and 9-10 years (n = 24)] when they were seated, given that many important tasks (e.g. handwriting) are learned and performed whilst seated. We found that postural stability varied in a principled manner as a function of task demands. Children exhibited increased stability when tracing a complex shape (which required less predictive postural adjustment) and decreased stability in an aiming task (which required movements that were more likely to perturb posture). These experiments shed light on the task-dependant relationships that exist between postural control mechanisms and the development of specific types of manual control.

Visual information plays an important role in maintaining posture. The role of vision changes over the lifespan with children relying more on haptic information as they mature (Wann et al., 1998). The role of vision in the maintenance of posture is not well understood in older populations but it is possible that neuromuscular degeneration increases the reliance upon vision. Our poor understanding is particularly worrying because falls have been reported as the primary cause of premature death in older persons (Sattin, 1992). Standing balance is a reasonable predictor of increased risk of falling (Jarnlo, 2003, Winter et al., 1990). Nonetheless, many falls occur when someone is engaged in a visuomotor task (e.g. putting a key in a lock) rather than simply standing upright. A high-profile study has also suggested that contemplating the past or the future can influence postural stability (Macrae et al., 2010). We explored these factors whilst measuring postural stability in young (16–26 years) and older (70–87 years) adults using a novel kinematic measuring device. First, we measured standing posture whilst participants tracked a moving target with a handheld stylus presented on a touch-screen laptop. The target moved at three speeds with stylus position recorded at 120 Hz to provide accurate performance metrics. Second, we measured posture when participants reflected on future or past events. The results for tracking showed that error increased with higher target speeds and this led to greater postural sway. The speed manipulation interacted with age so the high speed target had a particularly large impact on postural stability within the older population. In contrast, the manipulation of past versus future contemplation had no effect on posture. These findings suggest that a full evaluation of postural stability should measure the impact of visuomotor tasks when establishing the risk of falls in an older population.