Lifespan changes in postural control

Validation of the Equidyn protocol for evaluation of dynamic balance in older adults through a smartphone application

BACKGROUND

Different tasks and proxy measurements have been employed to evaluate dynamic balance in older individuals. However, due to inherent limitations, results from most evaluations could hardly be taken as valid measurements of dynamic balance.

RESEARCH QUESTION

Is the Equidyn smartphone application-based protocol valid and sensitive for assessment of dynamic balance in older adults?

METHODS

Dynamic balance was evaluated in 52 physically active individuals, age range 60-80 years (M = 69.36). The dynamic tasks were one-leg sway either in the mediolateral (ML) or anteroposterior (AP) direction while supported on the contralateral leg, and cyclic sit-to-stand with a narrow support base. These tasks were performed under standardized movement amplitude and rhythm. Outcomes were correlated with unipedal quiet standing. A smartphone was attached to the trunk backside, and a custom-made application (Equidyn) was employed to provide guidance throughout evaluation, timed beeps to pace the movements, and three-dimensional trunk acceleration measurement for balance evaluation.

RESULTS

Our data showed (a) that both ML and AP leg sway tasks were sensitive to aging and to direction of leg sway movements; (b) referenced to quiet unipedal stance, moderate/strong correlations for the ML/AP leg sway tasks and moderate correlations for the sit-to-stand task; and (c) moderate/strong correlations between the ML and AP leg sway tasks, and moderate correlations between the sit-to-stand and the two unipedal dynamic tasks in the ML acceleration direction.

SIGNIFICANCE

The current results support the conclusion that the Equidyn protocol is a sensitive and valid tool to evaluate dynamic balance in healthy older individuals. The protocol tasks standardized in amplitude and rhythm favor their reproducibility and trunk acceleration data interpretation. As the whole assessment is made through a smartphone application, this dynamic balance evaluation could be made in a low-cost simple way both in the laboratory and clinical settings.

Multitasking across the lifespan in different task contexts

We assessed lifespan development of multitasking in a sample of 187 individuals aged 8-82 years. Participants performed a visuo-spatial working memory (VSWM) task together with either postural control or reaction time (RT) tasks. Using criterion-referenced testing we individually adjusted difficulty levels for the VSWM task to control for single-task differences. Age-differences in single-task performances followed U-shaped patterns with young adults outperforming children and older adults. Multitasking manipulations yielded robust performance decrements in VSWM, postural control and RT tasks. Presumably due to our adjustment of VSWM challenges, costs in this task were small and similar across age groups suggesting that age-differential costs found in earlier studies largely reflected differences already present during single-task performance. Age-differences in multitasking costs for concurrent tasks depended on specific combinations. For VSWM and RT task combinations increases in RT were the smallest for children but pronounced in adults highlighting the role of cognitive control processes. Stabilogram diffusion analysis of postural control demonstrated that long-term control mechanisms were affected by concurrent VSWM demands. This interference was pronounced in older adults supporting concepts of compensation or increased cognitive involvement in sensorimotor processes at older age. Our study demonstrates how a lifespan approach can delineate the explanatory scope of models of human multitasking.

A sensorimotor enhanced neuromusculoskeletal model for simulating postural control of upright standing

The human's upright standing is a complex control process that is not yet fully understood. Postural control models can provide insights into the body's internal control processes of balance behavior. Using physiologically plausible models can also help explaining pathophysiological motion behavior. In this paper, we introduce a neuromusculoskeletal postural control model using sensor feedback consisting of somatosensory, vestibular and visual information. The sagittal plane model was restricted to effectively six degrees of freedom and consisted of nine muscles per leg. Physiologically plausible neural delays were considered for balance control. We applied forward dynamic simulations and a single shooting approach to generate healthy reactive balance behavior during quiet and perturbed upright standing. Control parameters were optimized to minimize muscle effort. We showed that our model is capable of fulfilling the applied tasks successfully. We observed joint angles and ranges of motion in physiologically plausible ranges and comparable to experimental data. This model represents the starting point for subsequent simulations of pathophysiological postural control behavior.

Symmetric unipedal balance in quiet stance and dynamic tasks in older individuals

Previous evidence of increased difference of muscular strength between the dominant and non-dominant legs in older adults suggests the possibility of dissimilar balance control between the legs (between-leg asymmetry) associated with aging. In the current investigation, we evaluated between-leg asymmetries in older adults when performing quiet and dynamic balance tasks. Fifty-two physically active and healthy older adults within the age range of 60 to 80 years were recruited. Participants performed balance tasks in unipedal stance, including quiet standing and cyclic sway (rhythmic oscillation) of the non-supporting leg in the anteroposterior or mediolateral directions, producing foot displacements with amplitudes of 20 cm paced in 1 Hz through a metronome. Body balance was evaluated through trunk accelerometry, by using the sensors embedded into a smartphone fixed at the height of the 10th-12th thoracic spines. Analysis revealed lack of significant differences in balance control between the legs either when comparing the right versus left or the preferred versus non-preferred legs, regardless of whether they were performing quiet stance or dynamic tasks. Further examination of the data showed high between-leg correlation coefficients (rs range: 0.71-0.84) across all tasks. Then, our results indicated symmetric and associated between-leg balance control in the examined older adults.

Effects of Sensory Input Interactions on Components of Nonlinear Dynamics of Postural Sway in Aging

Postural control involves complex nonlinear dynamics influenced by the interaction and adaptation of different sensory inputs. However, it is not how these inputs interact with one another due to the complex complications associated with aging, particularly concerning the nonlinear dynamics of postural sway. This study aimed to examine how different sensory inputs, surface conditions, and aging factors to influence postural control mechanisms between young and older by investigating the nonlinear dynamics of postural control using the stabilogram diffusion analysis (SDA) and entropy methods. SDA parameters were much greater on foam surfaces than on firm surfaces for both groups in eyes-open and eyes-closed conditions (p ≤ 0.05). For older subjects, there were significant differences in entropy values between firm and foam surfaces (p ≤ 0.05) but no significant difference between eyes conditions (p > 0.05). For both SDA and entropy parameters, surface and age interaction potentially revealed significant differences between young and older subjects (p ≤ 0.05) than eyes and age interaction. The present study provided insight into uncovering the complex relationships between sensory inputs, surface conditions, age, and their potential interaction effects on postural control mechanisms that could mitigate falls and alleviate the fear of falling, particularly in older populations.

External mechanical perturbations challenge postural stability in dogs

This study aimed to explore the effect of external mechanical perturbations on postural stability (PS) in dogs using the body center of pressure (COP). Thirteen sound adult dogs were included in this study. PS was tested during quiet standing on a pressure measurement plate. The conditions included a standard standing measurement and external mechanical perturbations conducted using six settings on a motorized training platform with different intensities of speed and amplitude. Measurement conditions were compared using linear mixed-effects models, followed by multiple comparisons using Sidak's alpha correction procedure. Compared with the standing measurement, external mechanical perturbations resulted in a significant increase in almost all COP parameters, indicating a challenge for the PS. Furthermore, an increase in amplitude had a greater effect than an increase in speed, whereas the combination of the highest intensities of amplitude and speed was not well tolerated by the dogs. The mediolateral COP displacement was significantly greater than the craniocaudal COP displacement during standing measurement and conditions with a small amplitude, whereas no significant difference was observed during settings with an increased amplitude. To the best of our knowledge, this is the first study to demonstrate the effects of a balance training device in dogs. Therefore, the intensity of the training programs on motorized platforms or similar devices can be controlled by the wobbling amplitude of the platform.