Itshak Melzer

Age-Related Changes of Postural Control: Effect of Cognitive Tasks

Background: Postural control and falls in the elderly constitute a major health problem. The interest in balance deficits is growing, as concern about the rising costs of health care increases. This issue is particularly relevant to the elderly population in which falls occur most frequently. Postural control in the elderly was studied using a cognitive approach. Objective: The purpose of this study was to study the characteristics of central processing of postural control while performing cognitive tasks. Methods: A dual-task procedure was developed to estimate the level of automaticity of a quiet upright standing task. The effect of a concurrent attention-demanding task (modified Stroop test) on the efficiency of balance control in the elderly was determined using force platform and electromyography measurements. Results: It was found that there is an increase in postural sway in old subjects compared with young subjects when performing single tasks and dual-task tests. The results of the study demonstrate that postural adjustments require cognitive processing; young and old subjects showed similar interference effects on postural steadiness (postural sway) caused by the concurrent attention-demanding task. The results are corroborated by the hypothesis that a dual task gives information on the restoration of automaticity of postural control in old age by a central reorganization process. When performing a dual task tested on a narrow base of support, the old subjects decreased their body sway, while the younger did not. According to electromyography measurements, the older subjects increased their muscle activity in the tibialis anterior and soleus muscles, using slow-twitch motor units compared with the younger subjects. Conclusions: Both alterations (cognitive and base of support) have a substantially greater effect on the elderly than on the young. The older subjects decreased their body sway by activating a cocontraction strategy of postural control around the ankle joint, probably because of the danger to their postural stability.

The Effect of a Cognitive Task on Voluntary Step Execution in Healthy Elderly and Young Individuals

Objectives: To investigate voluntary step behavior of healthy elderly individuals during single‐ and dual‐task conditions and to compare it with those of young subjects.

A retrospective analysis of balance control parameters in elderly fallers and non-fallers

BACKGROUND A cross-sectional retrospective study of parameters reflecting balance function in elderly fallers and non-fallers was conducted to better understand postural control mechanisms in individuals prone to falls. METHODS Ninety-nine old adults (65-91 years, mean age 78.4 (SD 5.7)) from two self-care residential facilities participated in the study. Foot center-of-pressure (CoP) displacement data were collected during narrow base upright stance eyes closed conditions and analyzed using summary statistics and Stabilogram-Diffusion Analysis (SDA) for mediolateral (ML) and anteroposterior (AP) directions. Subjects were instructed to minimize body sway. FINDINGS Twenty-nine of the subjects reported at least one fall and 69 subjects reported no falls in the past six months. The SDA showed significantly higher short-term diffusion coefficients and critical displacements in fallers in the ML but not the AP direction. Mean sway area and ML-CoP sway range were also larger in fallers. INTERPRETATION The greater ML critical displacement seen in fallers suggests that balance corrections on average occurred at higher sway amplitudes in this population. This is consistent with an ML decrease in the sensitivity of their postural control system. A higher short-term diffusion coefficient is consistent with increased muscle stiffness, a possible compensation for lost control sensitivity. Testing balance function under narrow stance conditions provides a modest increase in task difficulty that may help reveal pre-conditions of the balance control system that could increase the risk of falls.

Effects of Regular Walking on Postural Stability in the Elderly

Background: Both age and lack of physical activity may be responsible for poor health and poor balance control. Conversely, physical activity may modulate postural control in elderly people. Objective: An observational study was performed in older adults to explore whether walking on a regular basis might prove to be beneficial not only to the cardiovascular system but also to maintaining a good balance. Methods: Twenty-two healthy older subjects walking on a regular basis (DW group) and 121 healthy control older subjects who did not walk regularly (NW group) were studied. The subjects included in the study were free from major gait and postural disorders. An instrumented force platform was used to measure the time-varying displacements of the center of pressure under eight static conditions and postural limit tests. An isometric test was performed to evaluate lower limb muscle strength, and a static two-point discrimination test evaluated the innervation density of the slowly adapting receptors of the sole of the first toe. Results: The DW group had a significantly better (p < 0.05) postural stability under static conditions than the NW group. There were no significant differences in postural limit tests and in two-point discrimination between the groups. The DW group had significantly higher values of ankle plantar flexor and knee extensor strengths, while there were no significant differences in ankle dorsiflexors and knee flexors. None of the DW group reported experiencing a fall during the previous 6 months compared with 16% in the NW group who reported at least two falls during the last half year. Conclusions: Walking on a regular basis in old age may have the potential to modulate stability. It was found that healthy older subjects, who walked on a regular basis since their retirement, have better postural control, especially in their static balance, than those who do not. The laboratory results were accompanied by the important finding that although older subjects who walk on a regular basis walked much more than nonwalkers, they did not suffer from falls.

Association between ankle muscle strength and limit of stability in older adults

SIR—Loss of balance and falls in the elderly constitute a major problem associated with human suffering as well as high costs for society [1]. Falls might occur during various daily activities, such as tripping or tangling the feet, reaching movements or bending [2]. Many of these activities are constrained by limits of stability (LOS). LOS can be described as the maximum distance a person can intentionally displace his/her centre of gravity, and lean his/her body in a given direction without losing balance, stepping or grasping. Accordingly, ones LOS capacity is likely to be an important prerequisite for the successful planning and execution of movements such as using a step stool to reach into a high cabinet as well as bending over from standing position to pick up an object from the floor. Ageing is associated with decreased LOS [3–5], muscle strength [6] and foot sensation [7]. Investigators have reported significant correlations between postural stability, quadriceps, ankle dorsiflexion and hand-grip strength [8–11], tibialis anterior latency [8] and functional clinical balance testing [12] among older adults. However, the relationships between lower-limb muscle strength and falls are unclear. Several studies show minimal or no differences in strength between fallers and non-fallers [13, 14] while others show no strength–falls relationships [15]. Cutaneous mechanoreceptors at the soles of the feet contribute to postural stability when standing [16]. Those with reduced feet sensation have a higher risk of falling [17] and greater instability [18]. Reduced foot sensation may contribute to reduced LOS, since older adults might not properly detect when the centre of gravity approaches the LOS. To our knowledge, no one has studied how postural control during LOS relates to ankle strength and foot sensation among older adults. The aims of this study are to investigate how two specific tests of postural control, LOS and postural stability, relate to ankle muscle strength and foot sensation in older adults. Identification of sensorimotor factors associated with both types of balance control can help us to understand better the balance problems facing older adults. Given that LOS likely requires highly active muscular control and that postural stability requires careful sensory monitoring of stance, we hypothesised that ankle muscle strength (and not foot sensation) will be significantly correlated with LOS and that foot sensation (and not ankle muscle strength) will be significantly correlated with postural stability. Data from this study may lead to a better understanding of the mechanisms underlying falls that occur during reaching and bending movements.

Reliability of voluntary step execution behavior under single and dual task conditions

BackgroundThe current study investigated the repeatability (test-retest reliability) of ground reaction force parameters recorded during a voluntary step execution under single (motor task) and dual task (motor and cognitive task) conditions for healthy adults and elderly individuals as well as the number of trials required to produce repeatable results.MethodsTwenty-four healthy adults (21–63 years old) and 16 elderly adults (66–87 years) performed a voluntary rapid step execution following a tap on their heel while standing on a force platform under single and dual task conditions on three separate occasions. The first two tests were performed 30–60 minutes apart and the third test was performed a week later. Variables analyzed from the ground reaction force data included onset latency of step initiation (initiation phase), preparation and swing phases, foot-off and foot-contact times.ResultsIntraclass correlation coefficients (ICC(2,1)) were good to excellent across all parameters and test conditions for the pooled population and for elderly (0.74–0.92 and 0.62–0.88, respectively) except for the swing phase duration where lower values were seen (0.54–0.60 and 0.32–0.64 respectively). Values were similar under single and dual task conditions.ConclusionA voluntary step execution test, performed under single and dual task conditions especially foot-off and foot-contact times, is a reliable outcome measure that may be a useful tool to asses dynamic balance function for diagnostic purposes as well as clinical intervention trials.

The effect of plantar flexor muscle fatigue on postural control

OBJECTIVE Previous studies have demonstrated that ankle muscle fatigue alters postural sway. Our aim was to better understand postural control mechanisms during upright stance following plantar flexor fatigue. METHOD Ten healthy young volunteers, 25.7±2.2 years old, were recruited. Foot center-of-pressure (CoP) displacement data were collected during narrow base upright stance and eyes closed (i.e. blindfolded) conditions. Subjects were instructed to stand upright and as still as possible on a force platform under five test conditions: (1) non-fatigue standing on firm surface; (2) non-fatigue standing on foam; (3) ankle plantar flexor fatigue, standing on firm surface; (4) ankle plantar flexor fatigue, standing on foam; and (5) upper limb fatigue, standing on firm surface. An average of the ten 30-s trials in each of five test conditions was calculated to assess the mean differences between the trials. Traditional measures of postural stability and stabilogram-diffusion analysis (SDA) parameters were analyzed. RESULTS Traditional center of pressure parameters were affected by plantar flexor fatigue, especially in the AP direction. For the SDA parameters, plantar flexor fatigue caused significantly higher short-term diffusion coefficients, and critical displacement in both mediolateral (ML) and anteroposterior (AP) directions. Long-term postural sway was different only in the AP direction. CONCLUSIONS Localized plantar flexor fatigue caused impairment to postural control mainly in the Sagittal plane. The findings indicate that postural corrections, on average, occurred at a higher threshold of sway during plantar flexor fatigue compared to non-fatigue conditions.

A water-based training program that include perturbation exercises to improve stepping responses in older adults: study protocol for a randomized controlled cross-over trial

BackgroundGait and balance impairments may increase the risk of falls, the leading cause of accidental death in the elderly population. Fall-related injuries constitute a serious public health problem associated with high costs for society as well as human suffering. A rapid step is the most important protective postural strategy, acting to recover equilibrium and prevent a fall from initiating. It can arise from large perturbations, but also frequently as a consequence of volitional movements. We propose to use a novel water-based training program which includes specific perturbation exercises that will target the stepping responses that could potentially have a profound effect in reducing risk of falling. We describe the water-based balance training program and a study protocol to evaluate its efficacy (Trial registration number #NCT00708136).Methods/DesignThe proposed water-based training program involves use of unpredictable, multi-directional perturbations in a group setting to evoke compensatory and volitional stepping responses. Perturbations are made by pushing slightly the subjects and by water turbulence, in 24 training sessions conducted over 12 weeks. Concurrent cognitive tasks during movement tasks are included. Principles of physical training and exercise including awareness, continuity, motivation, overload, periodicity, progression and specificity were used in the development of this novel program. Specific goals are to increase the speed of stepping responses and improve the postural control mechanism and physical functioning. A prospective, randomized, cross-over trial with concealed allocation, assessor blinding and intention-to-treat analysis will be performed to evaluate the efficacy of the water-based training program. A total of 36 community-dwelling adults (age 65–88) with no recent history of instability or falling will be assigned to either the perturbation-based training or a control group (no training). Voluntary step reaction times and postural stability using stabiliogram diffusion analysis will be tested before and after the 12 weeks of training.DiscussionThis study will determine whether a water-based balance training program that includes perturbation exercises, in a group setting, can improve speed of voluntary stepping responses and improve balance control. Results will help guide the development of more cost-effective interventions that can prevent the occurrence of falls in the elderly.

Regular Exercise in the Elderly Is Effective to Preserve the Speed of Voluntary Stepping under Single-Task Condition but Not under Dual-Task Condition

Background: Stepping response may be considered the most important postural reaction to prevent a fall because it is the inability to respond effectively to a loss of balance that ultimately determines whether a fall occurs. However, very little has been studied on the effect of exercising on step execution behavior in the elderly. Objectives: To explore whether older persons who exercise regularly have faster voluntary stepping times than sedentary elderly persons. Additionally, we investigated the association between step execution behavior, self-reported physical function, and balance performance. Methods: Case-control study of 48 elderly adults aged 65–91 years who live independently in retirement homes. Participants were classified as 24 exercisers (reporting >2 exercise training activities/week) and 24 age- and gender-matched inactive elderly individuals (who do not exercise regularly). The Voluntary Step Execution Test was performed as a reaction time task while standing on a force platform under single-task and dual-task conditions. Step initiation phase, foot off time, foot contact time, preparatory, and swing phases were extracted from center of pressure and ground reaction force data. Self-reported function was examined using Late-Life Function and Disability Instrument; Berg Balance Test was also performed. Results: Exercisers had significantly faster voluntary step times in single-task condition (959 vs. 1,158 ms) but not during dual-task condition (1,170 vs. 1,303 ms). Exercisers had a significantly higher Berg Balance Test (53.7 ±3.6 vs. 49.8 ±5.3), consumed less medication (3.3 ±2.3 vs. 5.6 ±2.9), and their lower extremity function scores were higher (88.61 ±2.3 vs. 73.1 ±2.7) than those of inactive subjects. Conclusion: Exercising regularly protects from physical functioning loss in older persons and against a decrease in voluntary step execution times during single-task but not during dual-task conditions. Lack of specificity (dual-task exercises) during the training may be the cause of insignificant differences in dual-task stepping performance. Thus, adding dual-task training may improve dual-task performance in the elderly.

How to improve gait and balance function in elderly individuals—compliance with principles of training

Most balance training regimens for elderly individuals focus on self-controlled exercises, although automatic postural responses after a balance perturbation are not under direct volitional control. We critically review the literature on this topic, and notice that several studies fail to comply with basic principles of training and therefore show little improvement in function. Some present the view that physical function in the too frail and too fit cannot be improved, which we instead argue would be the effect of nonspecific training programs. We propose a concept for balance training that incorporates voluntary exercises as well as perturbation and dual-task exercises to improve balance control. The program is performed on five different levels where levels 1–4 exercises focus on the skill to maintain balance and level 5 adds perturbation exercises that focus on the skill to recover balance as well as dual task exercises providing a cognitive load during execution of a balance motor task. Functional requirements for muscle strength and power are directly incorporated into the program. The feasibility of the concept has been demonstrated on elderly fallers. A randomized control trial is underway to investigate the effects on healthy elderly individuals. Further intervention studies using this concept are encouraged.