Biomechanics of leaning and downward reaching tasks in young and older women

Stooping crouching or kneeling (SCK) difficulty is prevalent among older adults yet few studies have explored the mechanisms underlying downward reaching and pickup difficulty. During targeted movements tradeoffs are expected between the speed and accuracy of center of pressure (COP) movements as balance is maintained. Thus, this research focused on how age-related changes in COP control strategies affect the performance of tasks with a large range of truncal motion and momenta. It was hypothesized that while performing leaning and downward reaching movements, older women, compared to younger women, would exhibit slower but more frequent COP submovements in order to accomplish the task and regain the upright posture.;First, we investigated the limiting factors in downward reach and pick-up movements. Using an age-adjusted proportional odds model, increased SCK difficulty was found to be independently associated with balance confidence, leg joint limitations, and knee extension strength.;Secondly, we explored the age-related changes in COP control in healthy women. Despite being 27% slower, older women rely on nearly twice as many submovements to maintain a similar level of endpoint accuracy in volitional COP movements, particularly when moving posteriorly. Furthermore, older women used slower primary submovements that more often undershot their target, in comparison to young women, particularly as movement amplitude increased.;Lastly, healthy older women were found to lose their balance more often than young women in downward reaching tasks, but rely on similar COP control strategies when successful. Modeling results suggest that a simple forward dynamic model that accounts for changes in musculoskeletal factors may distinguish between healthy young and healthy older women with and without SCK difficulty.;We conclude that biomechanical factors can distinguish between older women with and without SCK difficulty. Given the significance of the rate of torque development in arresting downward reaching movements, changes in COP control may be effective tools in evaluating early signs of physical impairment. Undershooting primary submovements and increased secondary submovements are indicative of an increasingly conservative strategy used by older adults near the limits of the base of support that may explain their slower speeds during whole body movements to maintain balance.