Coming theses from other universities

Background and aims

To address the increasing number of falls among the older population, this thesis sought to increase the understanding of the postural control among older adults. The specific aims was to explore: i) how muscular co-contractions affect postural control outcome for a novel surface perturbation task, and which sensorimotor variables that explain the level of co-contractions; ii) which sensorimotor variables and postural control strategies explain the ability to adapt to repeated surface perturbations; iii) the relationships of specific cognitive functions and parameters of postural control tasks; iv) the feasibility and potential effects of a tablet-based intervention for balance and cognitive functions.

Methods and results

In Study I and II, 45 adults (27 women) with a mean age of 75.5 years performed extensive sensorimotor testing and a repeated surface perturbation test while electromyography and kinematics were recorded. In Study I, a binominal regression analysis found that higher levels of agonist-antagonist co-contractions in response to a novel surface perturbation was associated with unsuccessful postural control. An OPLS – analysis found that higher levels of co-contractions were associated with female sex, poorer leg muscle strength, and slower processing speed. Co-contractions prior the perturbation did not explain task success, nor was it explained by sensorimotor variables.

In study II, an OPLS – Discriminative Analysis found that the inability to successfully adapt to three repeated surface perturbations was associated with higher age, poorer physical functioning, slower processing speed and poorer leg muscle strength. Postural control strategies that explained this were: less dorsiflexed ankles prior the third perturbation and more co-contractions of the lower legs in response to the third perturbation. Wilcoxon signed rank test found that the successful participants changed their starting position between trails by flexing their legs, whereas the unsuccessful did not.

In Study III, forty-six older adults (30 women) with a mean age of 74.5 years tested cognitive measures of global cognition, executive functions, and reaction time as well as discrete variables of walking, dual-task walking and postural sway in quiet stance. OPLS models found that longer step length and faster gait speed were related to faster processing speed and less intraindividual variability in a choice reaction test. Moreover, longer step length was also related to less fall-related concerns and less severe fall-related injuries, while faster gait speed was also related to female sex and poorer global cognition. Lower dual-task cost for gait speed was explained by faster processing speed and better inhibitory ability. Postural sway in quiet stance, step time or gait variability were not explained by cognitive functions.

In Study IV, twenty participants (10 women) with subjective cognitive decline participated in an eight-week tablet-based intervention. One group performed balance training three times a week and walked three times a week for at least 30 minutes. The second group additionally performed cognitive training three times a week. Recruitment via social media and senior organizations was considered successful. Adherence to the balance program was better in the group that only did the balance training and walking program. The balance training was well perceived but thought to be too easy. The cognitive training was well perceived but quite challenging, but adherence was high. No adverse events were reported. Assessments of fall-related concerns, cognitive functions and postural control indicated that the group that only performed balance training and walks got worse dual-task walking performance, whereas the group that also performed cognitive training improved their dual-task walking performance.

Conclusions                                                                                                 

For a novel surface perturbation, high co-contraction reactions are associated with poorer postural control outcome, whereas physical capacity, cognitive functions and flexibility in postural strategies dictate if older adults can adapt to repeated postural challenges. Different cognitive processes explain discrete parameters of simple postural control tasks. To improve cognitive functions and postural control, a tablet-based intervention could be feasible, but should be flexible to accommodate different personal requirements, interactive to promote motivation and challenging enough to elicit positive adaptations.