Perturbations In Older Adults Research Articles

Reduced adaptability to balance perturbations in older adults with probable cognitive impairment after a severe fall.

Falls in older individuals often result from unexpected balance disturbances during walking, necessitating the analysis of recovery strategies for effective falls prevention. This becomes particularly crucial for individuals with cognitive impairment, who face a higher fall risk compared to cognitively healthy adults. Hence, our study aimed to compare the recovery response to standardized walking perturbations on a treadmill between older adults with cognitive impairment and cognitively healthy older adults. 36 individuals with a recent history of a severe fall, leading to an emergency department visit without subsequent admission, were stratified into two groups (with and without probable cognitive impairment) based on scores of the Montreal Cognitive Assessment. Recovery performance was quantified using force plate data from a perturbation treadmill (M-Gait, Motek Medical B.V., Amsterdam, the Netherlands), specifically evaluating the number of steps needed to restore step length and width to pre perturbation baseline across two trials of nine different perturbations. Individuals with cognitive impairment (n = 18, mean age: 74.7) required significantly (p = 0.045, Cohen's d = 0.69) more steps to recover total steps after perturbations compared to cognitively healthy individuals (n = 18, mean age: 69.7). While step width recovery was similar between the groups, those with probable cognitive impairment required significantly more steps to recover their step length (p = 0.039, Cohen's d = 0.72). Thus, our findings indicate that older adults with probable cognitive impairment manifest inferior gait adaptability, especially in adapting step length, potentially underscoring a critical aspect for effective falls prevention in this population.

Spatiotemporal modulation of a common set of muscle synergies during unpredictable and predictable gait perturbations in older adults.

Muscle synergies as functional low-dimensional building blocks of the neuromotor system regulate the activation patterns of muscle groups in a modular structure during locomotion. The purpose of the current study was to explore how older adults organize locomotor muscle synergies to counteract unpredictable and predictable gait perturbations during the perturbed steps and the recovery steps. Sixty-three healthy older adults (71.2±5.2 years) participated in the study. Mediolateral and anteroposterior unpredictable and predictable perturbations during walking were introduced using a treadmill. Muscle synergies were extracted from the electromyographic activity of 13 lower limb muscles using Gaussian non-negative matrix factorization. The four basic synergies responsible for unperturbed walking (weight acceptance, propulsion, early swing and late swing) were preserved in all applied gait perturbations, yet their temporal recruitment and muscle contribution in each synergy were modified (P<0.05). These modifications were observed for up to four recovery steps and were more pronounced (P<0.05) following unpredictable perturbations. The recruitment of the four basic walking synergies in the perturbed and recovery gait cycles indicates a robust neuromotor control of locomotion by using activation patterns of a few and well-known muscle synergies with specific adjustments within the synergies. The selection of pre-existing muscle synergies while adjusting the time of their recruitment during challenging locomotor conditions may improve the effectiveness to deal with perturbations and promote the transfer of adaptation between different kinds of perturbations.

Compensatory latency time delays during consecutive perturbations in older adults with and without kinesiophobia

BackgroundFear of movement has been related to lower limb activation patterns in older adults. However, insight into consecutive perturbations on stepping strategy while considering fall-related confidence is unknown. Research questionAre there latency time delays following three consecutive slip perturbations between subjects with and without kinesiophobia when considering limb dominance and fall efficacy differences? MethodsThere were 15 older adults with kinesiophobia and 15 age- and body mass index (BMI)-matched control subjects. The subjects stood on the platform during three consecutive perturbations (250, 300, and 400 msec excursions), which were produced by a Bertec device. The subjects completed questionnaires to evaluate the psychological features of their fall-related fear (Tampa Scale for Kinesiophobia: TSK) as well as the modified fall efficacy scale (FES). The latency times (msec) measured the time it took for a subject to respond to a translation. ResultsOverall, the results of the FES demonstrated a moderate negative association with the TSK (r = −0.52, p = 0.004). There was a significant group difference for the FES (t = 2.78, p = 0.01). The FES demonstrated significant positive correlation coefficients (ranging from 0.40 to 0.51) and significant negative correlation coefficients (ranging from −0.41 to −0.61), except for the slow perturbations. The groups demonstrated a significant interaction on consecutive latency times and limb side (F = 5.84, p = 0.02). The latency time during the fast perturbations on the dominant limb (F = 5.53, p = 0.02) was significantly shorter in the kinesiophobia group. SignificanceThe control group demonstrated confidence during fall-related activities, but the latency times were significantly different between groups when considering the dominant limb following repeated slip perturbations. The kinesiophobia group demonstrated shorter latency times on the dominant limb to protect against potential fall-risks from perturbations. The group interactions on limb side and consecutive perturbations need to be considered with fall-related confidence and improved standing balance in older adults with kinesiophobia.

Reduced adaptability to balance perturbations in older adults with probable cognitive impairment after a severe fall.

Falls in older individuals often result from unexpected balance disturbances during walking, necessitating the analysis of recovery strategies for effective falls prevention. This becomes particularly crucial for individuals with cognitive impairment, who face a higher fall risk compared to cognitively healthy adults. Hence, our study aimed to compare the recovery response to standardized walking perturbations on a treadmill between older adults with cognitive impairment and cognitively healthy older adults. 36 individuals with a recent history of a severe fall, leading to an emergency department visit without subsequent admission, were stratified into two groups (with and without probable cognitive impairment) based on scores of the Montreal Cognitive Assessment. Recovery performance was quantified using force plate data from a perturbation treadmill (M-Gait, Motek Medical B.V., Amsterdam, the Netherlands), specifically evaluating the number of steps needed to restore step length and width to pre perturbation baseline across two trials of nine different perturbations. Individuals with cognitive impairment (n = 18, mean age: 74.7) required significantly (p = 0.045, Cohen's d = 0.69) more steps to recover total steps after perturbations compared to cognitively healthy individuals (n = 18, mean age: 69.7). While step width recovery was similar between the groups, those with probable cognitive impairment required significantly more steps to recover their step length (p = 0.039, Cohen's d = 0.72). Thus, our findings indicate that older adults with probable cognitive impairment manifest inferior gait adaptability, especially in adapting step length, potentially underscoring a critical aspect for effective falls prevention in this population.

Hearing Aid Amplification Improves Postural Control for Older Adults With Hearing Loss When Other Sensory Cues Are Impoverished.

Recent studies suggest that sound amplification via hearing aids can improve postural control in adults with hearing impairments. Unfortunately, only a few studies used well-defined posturography measures to assess balance in adults with hearing loss with and without their hearing aids. Of these, only two examined postural control specifically in the elderly with hearing loss. The present study examined the impact of hearing aid use on postural control during various sensory perturbations in older adults with age-related hearing loss. Thirty individuals with age-related hearing impairments and using hearing aids bilaterally were tested. Participants were asked to perform a modified clinical sensory integration in balance test on a force platform with and without hearing aids. The experiment was conducted in the presence of a broadband noise ranging from 0.1 to 4 kHz presented through a loudspeaker. As expected, hearing aid use had a beneficial impact on postural control, but only when visual and somatosensory inputs were both reduced. Data also suggest that hearing aid use decreases the dependence on somatosensory input for maintaining postural control. This finding can be of particular importance in older adults considering the reduction of tactile and proprioceptive sensitivity and acuity often associated with aging. These results provide an additional argument for encouraging early hearing aid fitting for people with hearing loss.

The effect of cognitive tasks on reactive stepping in young and older adults

BackgroundDivided attention is commonly required in daily life, and to prevent falls, balance must be recovered when a person experiences unexpected perturbations. Previous studies have shown that additional cognitive tasks in postural responses negatively affect automatic postural responses. However, the effect of dual-tasking on reactive stepping performance is still not clearly understood. This study investigated the effect of dual-tasking on reactive stepping induced by a large perturbation in older adults and characterized the effect of dual-tasking by comparison with young adults. Research questionHow does the effect of dual-tasking on reactive stepping performance differ between young and older adults? MethodsTwenty-nine older adults and twenty-two young adults were prospectively exposed to external perturbations to induce forward reactive steps. Perturbations were delivered under simple front fixed gaze (single-task condition) and modified Stroop task (dual-task condition). Measures of the time to foot-off and reach stability, step length, velocity, and number of steps were based on force plate data for both the single- and dual-task conditions. ResultsYoung and older adults showed a delay in foot-off time during the dual-task condition compared with that during the single-task condition. The reach stability time, step length, and number of steps were worse in the dual-task condition than in the single-task condition for older adults, but not for young adults. The deficits in reactive stepping performance during dual-tasking could reflect the reactive balance capacity in real life. SignificanceThe findings of this study highlight the increased risk of falls with age.

Beta cortical oscillatory activities and their relationship to postural control in a standing balance demanding test: influence of aging.

Age-related changes in the cortical control of standing balance may provide a modifiable mechanism underlying falls in older adults. Thus, this study examined the cortical response to sensory and mechanical perturbations in older adults while standing and examined the relationship between cortical activation and postural control. A cohort of community dwelling young (18-30 years, N = 10) and older adults (65-85 years, N = 11) performed the sensory organization test (SOT), motor control test (MCT), and adaptation test (ADT) while high-density electroencephalography (EEG) and center of pressure (COP) data were recorded in this cross-sectional study. Linear mixed models examined cohort differences for cortical activities, using relative beta power, and postural control performance, while Spearman correlations were used to investigate the relationship between relative beta power and COP indices in each test. Under sensory manipulation, older adults demonstrated significantly higher relative beta power at all postural control-related cortical areas (p < 0.01), while under rapid mechanical perturbations, older adults demonstrated significantly higher relative beta power at central areas (p < 0.05). As task difficulty increased, young adults had increased relative beta band power while older adults demonstrated decreased relative beta power (p < 0.01). During sensory manipulation with mild mechanical perturbations, specifically in eyes open conditions, higher relative beta power at the parietal area in young adults was associated with worse postural control performance (p < 0.001). Under rapid mechanical perturbations, specifically in novel conditions, higher relative beta power at the central area in older adults was associated with longer movement latency (p < 0.05). However, poor reliability measures of cortical activity assessments were found during MCT and ADT, which limits the ability to interpret the reported results. Cortical areas are increasingly recruited to maintain upright postural control, even though cortical resources may be limited, in older adults. Considering the limitation regarding mechanical perturbation reliability, future studies should include a larger number of repeated mechanical perturbation trials.

Neuromuscular mechanisms of motor adaptation to repeated gait-slip perturbations in older adults

Individuals can rapidly develop adaptive skills for fall prevention after their exposure to the repeated-slip paradigm. However, the changes in neuromuscular control contributing to such motor adaptation remain unclear. This study investigated changes in neuromuscular control across different stages of slip-adaptation by examining muscle synergies during slip training. Electromyography signals during 24 repeated slip trials in gait were collected for 30 healthy older adults. Muscle synergies in no-adaptation (novel slip), early-adaptation (slip 6 to 8), and late-adaptation trials (slip 22 to 24) were extracted. The similarity between the recruited muscle synergies in these different phases was subsequently analyzed. Results showed that participants made significant improvements in their balance outcomes from novel slips to adapted slips. Correspondingly, there was a significant increase in the muscle synergy numbers from no-adaptation slips to the adapted slips. The participants retained the majority of muscle synergies (5 out of 7) used in novel slips post adaptation. A few new patterns (n = 8) of muscle synergies presented in the early-adaptation stage to compensate for motor errors due to external perturbation. In the late-adaptation stage, only 2 out of these 8 new synergies were retained. Our findings indicated that the central nervous system could generate new muscle synergies through fractionating or modifying the pre-existing synergies in the early-adaptation phase, and these synergies produce motor strategies that could effectively assist in recovery from the slip perturbation. During the late-adaptation phase, the redundant synergies generated in the early-adaptation phase get eliminated as the adaptation process progresses with repeated exposure to the slips, which further consolidates the slip adaptation. Our findings improved the understanding of the key muscle synergies involved in preventing backward balance loss and how neuromuscular responses adapt through repeated slip training, which might be helpful to design synergy-based interventions for fall prevention.

Quantitative Electroencephalography and Surface Electromyography Correlations upon Predictable and Unpredictable Perturbation in Older Adults.

Background: Quantitative Electroencephalography (qEEG) is a non-invasive method used to quantify electrical activity over the cortex. QEEG provides an accurate temporal resolution of the brain activity, making it a useful tool for assessing cortical function during challenging tasks.Objective: This study aimed to investigate postural adjustments in older adults in response to an external perturbation.Material and Methods: In this observational study, nineteen healthy older adults were involved. A 32-channel qEEG was employed to track alterations in beta power on the electrodes over the two sensory-motor areas. Integrated electromyographic activity (IntEMG) of the leg muscles was evaluated in response to perturbations under predictable and unpredictable conditions.Results: The results indicated higher beta power during late-phase in the Cz electrode in both conditions. IntEMG was significantly greater in the tibialis anterior muscle during both conditions in the CPA epoch. In predictable condition, a positive correlation was found between the beta power over C4 (r = 0.560, p = 0.013) and C3 (r = 0.458, p = 0.048) electrodes and tibialis anterior muscle amplitude, and between beta power in C4 and gastrocnemius amplitude (r = 0.525, p = 0.021). In unpredictable condition, there was a positive correlation between beta power over the C4 and the tibialis anterior amplitude (r = 0.580, p = 0.009) and also it over the C3 and the tibialis anterior amplitude (r = 0.452, p = 0.049).Conclusion: Our findings demonstrate that sensorimotor processing occurs in the brain during response to perturbation. Furthermore, cortical activity appeared to be greatest during the recruitment of the muscles upon late-phase in older adults.

Postural control in response to unilateral and bilateral external perturbations in older adults

BackgroundBalance is an important determinant of physical function and falls risk. The ability to withstand external perturbations is important when walking on icy or uneven surfaces, whether the perturbations are bilateral or unilateral. Research questionThis study sought to determine the effect of unilateral and bilateral standing perturbations on leg muscle activity in healthy older adults. MethodsParticipants experienced unilateral and bilateral standing perturbations of the treadmill. Surface electromyography (EMG) from lower limb muscles was recorded unilaterally. EMG onset latency and root mean square (RMS) amplitude of the muscle bursts were calculated. ResultsOlder adults demonstrated a combined ankle/hip strategy, along with pre-activation and co-contraction of muscles in response to unilateral and bilateral stance perturbations. As well, older adults demonstrated higher levels of EMG, but no difference in the latency of burst onset, in bilateral than unilateral perturbation types. SignificanceWhen the stance limb was perturbed in the bilateral condition, the older adults responded with a Gastrocs EMG burst nearly 100% of the maximum EMG. The high level of EMG used, especially in the Gastrocs, during the bilateral perturbations may reduce the safety factor for falls in older adults. Older adults responded to the different perturbation demands by modulating EMG amplitude as opposed to the onset timing of EMG.

Cortical Engagement Metrics During Reactive Balance Are Associated With Distinct Aspects of Balance Behavior in Older Adults.

Heightened reliance on the cerebral cortex for postural stability with aging is well-known, yet the cortical mechanisms for balance control, particularly in relation to balance function, remain unclear. Here we aimed to investigate motor cortical activity in relation to the level of balance challenge presented during reactive balance recovery and identify circuit-specific interactions between motor cortex and prefrontal or somatosensory regions in relation to metrics of balance function that predict fall risk. Using electroencephalography, we assessed motor cortical beta power, and beta coherence during balance reactions to perturbations in older adults. We found that individuals with greater motor cortical beta power evoked following standing balance perturbations demonstrated lower general clinical balance function. Individual older adults demonstrated a wide range of cortical responses during balance reactions at the same perturbation magnitude, showing no group-level change in prefrontal- or somatosensory-motor coherence in response to perturbations. However, older adults with the highest prefrontal-motor coherence during the post-perturbation, but not pre-perturbation, period showed greater cognitive dual-task interference (DTI) and elicited stepping reactions at lower perturbation magnitudes. Our results support motor cortical beta activity as a potential biomarker for individual level of balance challenge and implicate prefrontal-motor cortical networks in distinct aspects of balance control involving response inhibition of reactive stepping in older adults. Cortical network activity during balance may provide a neural target for precision-medicine efforts aimed at fall prevention with aging.

Age-Related Differences in Arm and Trunk Responses to First and Repeated Exposure to Laterally Induced Imbalances.

The objective of this study was to examine age-related differences in arm and trunk responses during first and repeated step induced balance perturbations. Young and older adults received 10 trials of unpredictable lateral platform translations. Outcomes included maximum arm and trunk displacement within 1 s of perturbation and at first foot lift off (FFLO), arm and neck muscle activity as recorded using electromyography (EMG), initial step type, balance confidence, and percentage of harness-assisted trials. Compared to young adults, older adults demonstrated greater arm and trunk angular displacements during the first trial, which were present at FFLO and negatively associated with balance confidence. Unlike young adults, recovery steps in older adults were directed towards the fall with a narrowed base of support. Over repeated trials, rapid habituation of first-trial responses of bilateral arm and trunk displacement and EMG amplitude was demonstrated in young adults, but was absent or limited in older adults. Older adults also relied more on harness assistance during balance recovery. Exaggerated arm and trunk responses to sudden lateral balance perturbations in older adults appear to influence step type and balance recovery. Associations of these persistently amplified movements with an increased reliance on harness assistance suggest that training to reduce these deficits could have positive effects in older adults with and without neurological disorders.

Transfer and retention effects of gait training with anterior-posterior perturbations to postural responses after medio-lateral gait perturbations in older adults

BackgroundGait perturbations, occurring in any direction in daily life, may result in a fall. In fall prevention, gait perturbation training is a promising approach. Treadmill perturbations in anterior-posterior direction can easily be applied by accelerations or decelerations of the belt, but it is unknown whether training effects transfer to reactive recovery in medio-lateral direction. We aimed to evaluate the transfer and retention effects of gait training with treadmill perturbations in anterior-posterior direction to medio-lateral reactive recovery. Methods30 community dwelling older adults (>65 years) participated in this study. They were randomly assigned to a treadmill training session either with 16 anterior-posterior perturbations or with treadmill walking. The assessments contained a walking trial with 4 anterior-posterior and 4 medio-lateral perturbations. Deviations in trunk velocity from unperturbed walking were summed over the first three strides after perturbation as a measure of recovery. FindingsAn exposure to gait perturbations during the baseline assessment led to significant improvement of recovery responses. For anterior-posterior perturbations, both groups showed better recovery immediately and 1-week post-intervention, and no group x time interaction was found.. For medio-lateral perturbations, both groups showed better recovery immediately and 1-week post-intervention, and again no group × time interaction. InterpretationBaseline assessment with perturbations in anterior-posterior and medio-lateral directions caused significant improvements that were retained. Short-term training can be effective in dynamic stabilization of one's trunk, but our findings do not exclude that multi-directional perturbations may be needed.

Single and multiple step balance recovery responses can be different at first step lift-off following lateral waist-pull perturbations in older adults

An inability to recover lateral balance with a single step is predictive of future falls in older adults. This study investigated if balance stability at first step lift-off (FSLO) would be different between multiple and single stepping responses to lateral perturbations. 54 healthy older adults received left and right waist-pulls at 5 different intensities (levels 1–5). Crossover stepping responses at and above intensity level 3 that induced both single and multiple steps were analyzed. Whole-body center of mass (COM) and center of pressure (COP) positions in the medio-lateral direction with respect to the base of support were calculated. An inverted pendulum model was used to define the lateral stability boundary, which was also adjusted using the COP position at FSLO (functional boundary). No significant differences were detected in the COP positions between the responses at FSLO (p≥0.075), indicating no difference in the functional boundaries between the responses. Significantly smaller stability margins were observed at first step landing for multiple steps at all levels (p≤0.024), while stability margins were also significantly smaller at FSLO for level 3 and 4 (p≤0.048). These findings indicate that although reduced stability at first foot contact would be associated with taking additional steps, stepping responses could also be attributable to the COM motion state as early as first step lift-off, preceding foot contact. Perturbation-based training interventions aimed at improving the reactive control of stability would reduce initial balance instability at first step lift-off and possibly the consequent need for multiple steps in response to balance perturbations.

Aging effect on muscle synergies in stepping forth during a forward perturbation.

We explored changes in muscle interactions during healthy aging as a window into neural control strategies of postural preparation to action/perturbation. In particular, we quantified the strength of multi-muscle synergies stabilizing the center of pressure (COP) displacement during the preparation for making a step associated with support surface translations. Young and elderly subjects were required to make a step in response to support surface perturbations. Surface muscle activity of 11 leg and trunk muscles was analyzed to identify sets of 4 muscle modes (M-modes). Linear combinations of M-modes and their relationship to changes in the COP displacement in the anterior-posterior direction were then determined. Uncontrolled manifold analysis was performed to determine variance components in the M-mode space and indices of M-mode synergy stabilizing COP displacement. Prior to the step initiation, the older subjects showed strong synergies that stabilized COP displacement to forward perturbation of the support surface. However, the synergy indices were significantly lower than those of the young subjects during preparation for making a step. The timings of early postural adjustment (EPA) and anticipatory postural adjustment (APA) were consistently earlier in the young subjects as compared to the older subjects. For both groups, the timing of EPA did not change across tasks, while APA showed delayed timing in response to the support surface translations. We infer that changes in the indices of synergies with age may present challenges for the control of postural preparation to external perturbation in older adults. They may lead to excessive muscle co-contractions and low stability of COP displacement. The results reported here could have clinical relevance when identifying the risk of making a step, which has been linked to an increased risk of falls among the elderly.

Effect of higher muscle coactivation on standing postural response to perturbation in older adults.

Although several studies have reported that muscle coactivation during postural control increases with age, the effect of higher muscle coactivation on standing postural response to perturbation is unknown. To investigate whether higher muscle coactivation affects standing postural response to perturbation in older adults. Thirty-four community-dwelling older participants were randomly assigned either to the coactivation group (CG), where muscle coactivation was increased intentionally, or to the non-coactivation group (NCG). The participants were instructed to stand on a force plate that moved forward or backward. Electromyography data were collected from the lower leg muscles. We requested the participants in the CG to increase the activity of their tibialis anterior, and to maintain this posture during the tasks. We moved the force plate with a constant amplitude and velocity, and measured kinematic data with a camera during the tasks. During forward transfer, the knee extension and hip flexion decreased in the CG after perturbation compared to NCG, and the trunk extension angle increased. The center of pressure (COP) displacement decreased around the peak of the movement in the CG compared to NCG. During backward transfer, ankle dorsal and knee flexion changed after perturbation in the CG compared to NCG. Our study found that higher muscle coactivation inhibits lower limb and COP movement as well as increases trunk tilt and the risk for falls during forward perturbations. Postural control with higher coactivation appears to be inefficient for maintaining balance during the backward sway of posture.

Exercise to Improve Mobility in Healthy Aging.

Biological aging inevitably affects every individual, no matter what their color of skin, country of origin, level of education, and socio-economic status is. Intuitively, we associate aging with old age. However, aging encompasses more than senescence. In fact, the process begins at conception and continues throughout the lifespan, with marked physiological and performance changes occurring for some reason after age 60 years. Aging is a process or group of processes occurring in living organisms that with the passage of time leads to a loss of adaptability, functional impairment, and eventually death [1]. Healthy aging is a desirable path that is worth pursuing for every individual. Factors that determine healthy or successful aging are avoiding disease (e.g., obesity), engagement with life (e.g., social activities), maintaining high cognitive and physical function through, for instance, proper diet, and sufficient physical activity [1]. The American College of Sports Medicine and the American Heart Association have provided recommendations on the types and amounts of physical activity needed to improve and maintain health in older adults [2]. With this purpose in mind, seniors are advised to perform physical activity at a moderate intensity that results in aerobic metabolism for a minimum of 30 min on 5 days each week or vigorous-intensity aerobic activity for a minimum of 20 min on 3 days each week. To maintain the flexibility necessary for regular physical activity and daily life, older adults should perform activities that maintain or increase flexibility on at least 2 days each week for at least 10 min each day. To reduce the risk of injury due to falls, community-dwelling older adults at substantial risk of falls should perform exercises that maintain or improve balance. In addition, at least twice each week older adults should perform muscle-strengthening activities using the major muscles of the body to maintain or increase muscular strength and endurance [2]. The German Research Foundation provided support for a series of workshops that took place in Potsdam, Freiburg, and Kassel between October 2013 and September 2014 (MU 3327/2-1). International experts discussed current knowledge of how age affects motor performance throughout the lifespan and how exercise interventions could improve motor performance in older adults, delay the onset and progression of mobility disability, and promote healthy aging. To complement already existing physical activity guidelines, this themed issue of Sports Medicine contains systematic literature reviews and meta-analyses that provide evidence-based overviews of current knowledge concerning the efficacy of exercise interventions with a focus on seniors. Four of seven papers focus on the intervention effects of strength training using unstable surfaces, resistance training, power training, coordination training, and balance training on measures of balance, strength, power, and mobility in cohorts across the lifespan with a focus on older adults (Behm et al., Borde et al., Hortobagyi et al., Lesinski et al). Two papers describe the dose-response relationships following resistance and balance training in older adults (Borde et al., Lesinski et al.). This is new and important evidence-based information for practitioners and therapists seeking to design and implement effective exercise programs to counteract dynapenia, sarcopenia, and mobility disability in seniors. Further, two papers analyze how task difficulty affects responses to balance perturbations in older adults (Bohm et al.) and cognitive-motor dual tasking across the lifespan (Ruffieux et al.), with a perspective on intervention design. Finally, Muehlbauer et al. examine the relationship between measures of balance and leg strength/power across the lifespan in an effort to provide information that facilitates better-informed exercise prescription. The consistent message from this wealth of up-to-date information is that spontaneous physical activity and systematic exercise delivered in a variety of forms can increase motor performance independent of age, slow the progression of mobility disability, and most likely improve health in old age. As part of their efforts to promote healthy aging, practitioners, healthcare professionals, and policy makers can use this new knowledge to recommend and urge seniors to become and remain physically active.

Center of pressure control for balance maintenance during lateral waist-pull perturbations in older adults

When balance is disturbed, location of the center of pressure (COP) contributes to a person’s ability to recover from a perturbation. This study investigated COP control prior to first step lift-off (FSLO) during lateral perturbations in older non-fallers and fallers. 38 non-fallers and 16 fallers received lateral waist-pulls at 5 different intensities. Crossover stepping responses at the intensity level where the largest number of subjects responded with crossover steps were analyzed. Whole-body center of mass (COM) and COP positions in the medio-lateral (ML) direction with respect to the base of support (BOS), and COP velocity were calculated. An inverted pendulum model was used to define the BOS stability boundary at FSLO, which was also adjusted using the COP position at FSLO (functional boundary). No significant differences were found in the COP velocities between fallers and non-fallers (p>.093). However, the COP positions for fallers were located significantly more medial at FSLO (p≤.01), resulting in a significantly reduced functional boundary. Although the stability margins, measures of stability based on the BOS, were significantly larger than zero for fallers (p≤.004), they were not significantly different from zero for the functional boundary, i.e., reaching the functional stability limit. Fallers had reduced functional limits of stability in the ML direction, which would predispose them to more precarious stability conditions than non-fallers. This could be a cause for taking more steps than non-fallers for balance recovery as we observed. The functional boundary estimation may be a more sensitive marker of balance instability than the BOS boundary.

EMG and kinematic responses to unexpected slips after slip training in virtual reality.

The objective of the study was to design a virtual reality (VR) training to induce perturbation in older adults similar to a slip and examine the effect of the training on kinematic and muscular responses in older adults. Twenty-four older adults were involved in a laboratory study and randomly assigned to two groups (VR training and control). Both groups went through three sessions including baseline slip, training, and transfer of training on slippery surface. The training group experienced 12 simulated slips using a visual perturbation induced by tilting a VR scene while walking on the treadmill and the control group completed normal walking during the training session. Kinematic, kinetic, and electromyography data were collected during all the sessions. Results demonstrated the proactive adjustments such as increased trunk flexion at heel contact after training. Reactive adjustments included reduced time to peak activations of knee flexors, reduced knee coactivation, reduced time to trunk flexion, and reduced trunk angular velocity after training. In conclusion, the study findings indicate that the VR training was able to generate a perturbation in older adults that evoked recovery reactions and such motor skill can be transferred to the actual slip trials.

Leg preference associated with protective stepping responses in older adults

BackgroundAsymmetries in dynamic balance stability have been previously observed. The goal of this study was to determine whether leg preference influenced the stepping response to a waist-pull perturbation in older adult fallers and non-fallers. Methods39 healthy, community-dwelling, older adult (>65years) volunteers participated. Participants were grouped into non-faller and faller cohorts based on fall history in the 12months prior to the study. Participants received 60 lateral waist-pull perturbations of varying magnitude towards their preferred and non-preferred sides during quiet standing. Outcome measures included balance tolerance limit, number of recovery steps taken and type of recovery step taken for perturbations to each side. FindingsNo significant differences in balance tolerance limit (P≥0.102) or number of recovery steps taken (η2partial≤0.027; P≥0.442) were observed between perturbations towards the preferred and non-preferred legs. However, non-faller participants more frequently responded with a medial step when pulled towards their non-preferred side and cross-over steps when pulled towards their preferred side (P=0.015). InterpretationLeg preference may influence the protective stepping response to standing balance perturbations in older adults at risk for falls, particularly with the type of recovery responses used. Such asymmetries in balance stability recovery may represent a contributing factor for falls among older individuals and should be considered for rehabilitation interventions aimed at improving balance stability and reducing fall risk.