The extent to which healthy older adults rely on anticipatory control following simulated slip exposure.

As the recovery from gait perturbations is coordinatively complex and error-prone, people often adopt anticipatory strategies when the perturbation is expected. These anticipatory strategies act as a first line of defence against potential balance loss. Since age-related changes in the sensory and neuromotor systems could make the recovery from external perturbations more difficult, it is important to understand how older adults implement anticipatory strategies. Therefore, we exposed healthy young (N = 10, 22 ± 1.05 yrs.) and older adults (N = 10, 64.2 ± 6.07 yrs.) to simulated slips on a treadmill with consistent properties and assessed if the reliance on anticipatory control differed between groups. Results showed that for the unperturbed steps in between perturbations, step length decreased and the backward (BW) margin of stability (MOS) increased (i.e., enhanced dynamic stability against backward loss of balance) in the leg that triggered the slip, while step lengths increased and BW MOS decreased in the contralateral leg. This induced step length and BW MOS asymmetry was significantly larger for older adults. When exposed to a series of predictable slips, healthy older adults thus rely more heavily on anticipatory control to proactively accommodate the expected backward loss of balance.

Natural ageing primarily affects the initial response to a sustained walking perturbation but not the ability to adapt over time.

The ability to flexibly respond and adapt the walking pattern over time to unexpected gait perturbations is pivotal for safe and efficient locomotion. However, these abilities might be affected by age due to age-related changes in sensorimotor functioning. In this cross-sectional lifespan study, we used a split-belt paradigm to determine how age affects the initial response (i.e., flexibility)-and the ability to adapt after prolonged exposure-to a sustained gait perturbation. Healthy adults (N = 75) of different ages (12-13 per decade) were included and walked on a split-belt treadmill, in which a sustained gait perturbation was imposed by increasing one of the belt speeds. Linear regression models, with the evoked spatiotemporal gait asymmetry during the early perturbation and late adaptation, were performed to determine the effects of age on the flexibility and adaptability to split-belt walking. Results showed that the flexibility to respond to an unexpected perturbation decreased across the lifespan, as evidenced by a greater step length asymmetry (SLA) during the early perturbation phase. Despite this reduced flexibility in step lengths, late adaptation levels in SLA were comparable across different ages. With increasing age, however, subjects needed more steps to reach a stable level in SLA. Finally, when the belts were set to symmetrical speeds again, the magnitude of SLA (i.e., the aftereffects) increased with age. Collectively, these findings suggest that natural ageing comes with a decrease in gait flexibility, while the ability to adapt to split-belt walking was not affected by age-only how adaptation was achieved.

Do gait and muscle activation patterns change at middle-age during split-belt adaptation?

Advancing age affects gait adaptability, but it is unclear if such adaptations to split-belt perturbations are already affected at middle-age. Changes in neuromuscular control, that already start at middle-age, may underlie the age-related changes in gait adaptation. Thus, we examined the effects of age on adaptations in gait and muscle activation patterns during split-belt walking in healthy young and middle-aged adults. Young (23.3 ± 3.13 years) and middle-aged adults (55.3 ± 2.91 years) walked on an instrumented split-belt treadmill. Both age groups adapted similarly by reducing asymmetry in step length and double support time. Surface EMG was recorded from eight leg muscles bilaterally. Principal Component Analysis (PCA) was applied to the EMG data of all subjects, for the fast and slow leg separately, to identify muscle activation patterns. The principal components consisted of i.e. temporal projections that were analyzed with Statistical Parametric Mapping (SPM). The functional muscle groups, identified by PCA, increased activation during early adaptation and post-adaptation, and decreased activation over time similarly in both age groups. Extra activation peaks of the plantar- and dorsiflexors suggest a role in gait modulation during split-belt walking. Both young and middle-aged adults re-established gait symmetry and showed adaptation effects in the muscle activation patterns. Since the adaptation of muscle activation patterns parallels adaptation of gait symmetry, changes in muscle activation likely underlie the changes in step parameters during split-belt adaptation. In conclusion, split-belt adaptation, in terms of gait and muscle activation patterns, is still preserved at middle-age, suggesting that age-related differences occur later in the lifespan.

Assessing dynamic postural control during exergaming in older adults: A probabilistic approach.

Digital games controlled by body movements (exergames) have been proposed as a way to improve postural control among older adults. Exergames are meant to be played at home in an unsupervised way. However, only few studies have investigated the effect of unsupervised home-exergaming on postural control. Moreover, suitable methods to dynamically assess postural control during exergaming are still scarce. Dynamic postural control (DPC) assessment could be used to provide both meaningful feedback and automatic adjustment of exergame difficulty. These features could potentially foster unsupervised exergaming at home and improve the effectiveness of exergames as tools to improve balance control. The main aim of this study is to investigate the effect of six weeks of unsupervised home-exergaming on DPC as assessed by a recently developed probabilistic model. High probability values suggest 'deteriorated' postural control, whereas low probability values suggest 'good' postural control. In a pilot study, ten healthy older adults (average 77.9, SD 7.2 years) played an ice-skating exergame at home half an hour per day, three times a week during six weeks. The intervention effect on DPC was assessed using exergaming trials recorded by Kinect at baseline and every other week. Visualization of the results suggests that the probabilistic model is suitable for real-time DPC assessment. Moreover, linear mixed model analysis and parametric bootstrapping suggest a significant intervention effect on DPC. In conclusion, these results suggest that unsupervised exergaming for improving DPC among older adults is indeed feasible and that probabilistic models could be a new approach to assess DPC.

Exergames for unsupervised balance training at home: A pilot study in healthy older adults.

Exercise videogames (exergames) are gaining popularity as tools for improving balance ability in older adults, yet few exergames are suitable for home-based use. The purpose of the current pilot study was to examine the effects of a 6-week unsupervised home-based exergaming training program on balance performance. Ten community dwelling healthy older adults (age: 75.9 ± 7.2 years) played a newly developed ice skating exergame for six weeks at home. In the game, the speed and direction of a virtual ice skater on a frozen canal were controlled using lateral weight shifts, which were captured using Kinect. Sway characteristics during quiet standing in eyes open (EO), eyes closed (EC) and dual task (DT) conditions were assessed in time and frequency domain before, and after two, four and six weeks of training. Balance was also evaluated using the narrow ridge balance test (NRBT). Multilevel modeling was applied to examine changes in balance ability. Participants played 631 (± 124)min over the intervention period and no subjects dropped out. Balance in terms of sway characteristics improved on average by 17.4% (EO) and 23.3% (EC) after six weeks of training (p<0.05). Differences in rate of improvement (p<0.05) were observed between participants. No intervention effects were found for quiet standing in DT conditions and on the NRBT. In conclusion, the pilot study showed that unsupervised home-based exergaming is feasible in community dwelling older adults, but also that participants do not benefit equally from the program, thereby emphasizing the need for more personalized exergame training programs.

Pelvis-thorax coordination in the transverse plane during gait.

The coordination between horizontal pelvic and thoracic rotations during treadmill walking was studied in ten subjects. Previous studies have considered the relative phase using the mean to characterize coordination mode, and the S.D. as an index of its stability. However, to use S.D. of relative phase as a measure for coordinative stability, the underlying oscillations have to be phase-locked at a certain value. Random fluctuations around this value can then be viewed as stochastic perturbations of a stable fixed point, resulting in a unimodal distribution of relative phase. Using methods of circular statistics this study shows that these conditions were not met in pelvis-thorax coordination. Spectral analyses revealed that, as walking velocity increased, a triphasic component emerged in the pelvic rotations, while the thoracic rotations remained harmonic across all walking velocities. These findings refute the use of standard relative phase measures to capture pelvis-thorax coordination. An alternative measure is introduced, namely the difference between the continuous Fourier phases of the component oscillations as determined for the main frequency of the thorax oscillation. With this measure, pelvis-thorax coordination was found to evolve from in-phase coordination towards antiphase coordination as walking velocity increased. This method may be used to assess reliably the properties of pelvis-thorax coordination in both healthy and pathological gait patterns in the future.

Sensor technologies aiming at fall prevention in institutionalized old adults: a synthesis of current knowledge.

BACKGROUND: Falls are a serious health problem in old adults especially in nursing home residents and hospitalized patients. To prevent elderly from falling, sensors have been increasingly used in intramural care settings. However, there is no clear overview of the current used technologies and their results in fall prevention. OBJECTIVES: The present study reviews sensor systems that prevent falls in geriatric patients living in an intramural setting and describe fall rates, fall-related injuries, false alarms, and user experience associated with such systems. METHODS: We conducted a systematic search for studies that used sensor technologies with the aim to prevent falls in institutionalized geriatric patients. RESULTS: A total of 12 studies met the search criteria. Three randomized clinical trials reported no reductions in fall rate but three before-after studies reported significant reductions of 2.4-37 falls per 1000 patient days. Although there was up to 77% reduction in fall-related injuries and there was relatively low, 16%, rate of false alarms, the current data are inconsistent whether current sensor technologies are effective in reducing the number of falls in institutionalized geriatric patients. The occurrence of false alarms (16%) was too high to maintain full attention of the nursing staff. Additionally including the users opinion and demands in developing and introducing sensor systems into intramural care settings seems to be required to make an intervention successful. CONCLUSION: The evidence is inconsistent whether the current sensor systems can prevent falls and fall-related injuries in institutionalized elderly. Further research should focus more comprehensively on user requirements and effective ways using intelligent alarms.

Steady and transient coordination structures of walking and running.

We studied multisegmental coordination and stride characteristics in nine participants while walking and running on a treadmill. The study's main aim was to evaluate the coordination patterns of walking and running and their variance as a function of locomotion speed, with a specific focus on gait transitions and accompanying features like hysteresis and critical fluctuations. Stride characteristics changed systematically with speed in a gait-dependent fashion, but exhibited no hysteresis. Multisegmental coordination of walking and running was captured by four principal components, the first two of which were present in both gaits. Locomotion speed had subtle yet systematic differential effects on the relative phasing between the identified components in both walking and running and its variance, in particular in the immediate vicinity of gait transitions. Unlike the stride characteristics, the identified coordination patterns revealed clear evidence of both hysteresis and critical fluctuations around transition points. Overall, the results suggest that walking and running entail similar, albeit speed- and gait-dependent, coordination structures, and that gait transitions bear signatures of nonequilibrium phase transitions. Application of multivariate analyses of whole-body recordings appears crucial to detect these features in a reliable fashion.