Background: Postural control is dependent on the central nervous system’s accurate interpretation of sensory information to formulate and execute adequate motor actions. Research has shown that cognitive functions are associated with both postural control and fall risk, but specific associations are not established. The aim of this study was to explore how specific components of everyday postural control tasks are associated with both general and specific cognitive functions.

Methods: Forty-six community-dwelling older adults reported their age, sex, physical activity level, falls and fall-related concerns. The following cognitive aspects were assessed: global cognition, executive functions, processing speed and intraindividual variability. Postural control was quantified by measuring postural sway in quiet stance, walking at a self-selected pace, and walking while performing a concurrent arithmetical task. Separate orthogonal projections of latent structures models were generated for each postural control outcome using descriptive and cognitive variables as explanatory variables.

Results: Longer step length and faster gait speed were related to faster processing speed and less intraindividual variability in the 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 the executive function inhibition and faster processing speed. Postural sway in quiet stance was not explained by cognitive functions.

Conclusions: Cognitive functions explained gait speed and step length during normal walking, as well as the decrease of gait speed while performing a concurrent cognitive task. The results suggest that different cognitive processes are important for different postural control aspects. Postural sway in quiet stance, step time and gait variability seem to depend more on physical and automatic processes rather than higher cognitive functions among physically active older people. The relationships between cognitive functions and postural control likely vary depending on the specific tasks and the characteristics of different populations.

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.

Background: As a strategy to maintain postural control, the stiffening strategy (agonist-antagonist co-contractions) is often considered dysfunctional and associated with poor physical capacity. The aim was to investigate whether increased stiffening is associated with unsuccessful postural control during an unpredictable surface perturbation, and which sensory and motor variables that explain postural stiffening.

Methods: A sample of 34 older adults, 75.8 ± 3.8 years, was subjected to an unpredicted surface perturbation with the postural task to keep a feet-in-place strategy. The participants also completed a thorough sensory- and motor test protocol. During the surface perturbation, electromyography was measured from tibialis anterior and gastrocnemius to further calculate a co-contraction index during the feed-forward and feedback period. A binary logistic regression was done with the nominal variable, if the participant succeeded in the postural task or not, set as dependent variable and the co-contraction indexes set as independent variables. Further, the variables from the sensory and motor testing were set as independent variables in two separate Orthogonal Projections of Latent Structures (OPLS)-models, one with the feed-forward- and the other with the feedback co-contraction index as dependent variable.

Results: Higher levels of ankle joint stiffening during the feedback, but not the feed-forward period was associated with postural task failure. Feedback stiffening was explained by having slow non-postural reaction times, poor leg muscle strength and being female whereas feed-forward stiffening was not explained by sensory and motor variables.

Conclusions: When subjected to an unpredicted surface perturbation, individuals with higher feedback stiffening had poorer postural control outcome, which was explained by poorer physical capacity. The level of feed-forward stiffening prior the perturbation was not associated with postural control outcome nor the investigated sensory and motor variables. The intricate causal relationships between physical capacity, stiffening and postural task success remains subject for future research.

Objectives

To investigate the accuracy of visual assessments made by physical therapists of lumbo-pelvic movements during the squat and deadlift and how much movement is considered injurious.

Design

Quantitative Cross-sectional.

Participants

14 powerlifters, 10 Olympic weightlifters and six physical therapists.

Setting

The lifters were recorded simultaneously by video and an inertial measurement unit (IMU) system while performing squats and deadlifts. The physical therapists assessed the videos and rated whether specific lumbo-pelvic movements were visible during the lifts and whether the movement amplitude was considered injurious.

Main outcome measures

The nominal visual assessments, if there was a movement and if it was considered injurious, were compared to the degrees of movement attained from the IMU system.

Results

During the squat, a posterior pelvic tilt of ≥34° was required to visually detect the movement. For other lumbo-pelvic movements, there was no significant difference in the amount of movement between those who were assessed as moving or not moving their lumbo-pelvic area, nor was there a difference in movement amplitude between those who were assessed as having an increased risk of injury or not.

Conclusions

Physical therapists did not consistently detect lumbo-pelvic movements during squats and deadlifts when performed by competitive lifters.

As we age there are natural physiological deteriorations that decrease the accuracy and flexibility of the postural control system, which increases the risk of falling. Studies have found that there are individual differences in the ability to learn to manage repeated postural threats. The aim of this study was to investigate which factors explain why some individuals are less proficient at adapting to recurrent postural perturbations. Thirty-five community dwelling older adults performed substantial sensory and motor testing and answered surveys regarding fall-related concerns and cognitive function. They were also subjected to three identical surface perturbations where both kinematics and electromyography was captured. Those that were able to adapt to the third perturbation were assigned to the group “Non-fallers” whereas those that fell during all perturbations were assigned to the group “Fallers”. The group designation dichotomized the sample in a hierarchical orthogonal projection of latent structures— the discriminant analysis model. We found that those who fell were older, had poorer physical performance, poorer strength and longer reaction times. The Fallers’ postural control strategies were more reliant on the stiffening strategy along with a more extended posture and they were less skillful at making appropriate feedforward adaptations prior to the third perturbation.