Recovery from a trip in young and older adults : mechanics and control of the support limb

Falls and fall-related injuries are the cause of serious medical and social problems, especially in the growing elderly population. Tripping over an obstacle is one of the major causes for falls in the elderly. This thesis was aimed to obtain insight in the requirements for a successful recovery reaction after tripping and to understand why older people sometimes fail to meet these requirements and fall. Young and older subjects were tripped over an obstacle during walking over an experimental setup, while wearing a safety harness. The kinematics, dynamics and muscle activity during their balance recovery reactions were measured and compared. A rapid and strong push-off reaction by the support limb appeared to be important for successful balance recovery. Older adults, especially older fallers, were less able to recovery their balance due to a lower rate of change of moment generation in all support limb joints and a lower peak ankle moment. In addition to changes in muscle and tendon properties, a lower rate of muscle activation can reduce the rate of force generation, which can hamper the recovery mechanism and lead to a fall. These results suggest that muscle strength may be a limiting factor in preventing a fall. Strength training, combined with training on a functional level, is indicated in older people with low physical capacities to reduce the risk of falling after a trip.Dieen, J.H. van [Promotor]Bobbert, M.F. [Copromotor

Control of support limb muscles in recovery after tripping in young and older subjects

Older people fall more often after tripping than young people due to a slower development of mechanical responses. This might be due to age-related changes in muscle properties, but also to changes in motor control. The purpose of the present study was to determine whether (a) timing and sequencing of muscle activation and (b) the magnitude and rate of development of muscle activation in recovery after a trip differs between young and older subjects. We focused on the support limb, as it contributes to recovery after tripping by counteracting the forward angular momentum. Ten young (25 years) and seven older (68 years) men and women walked over a platform and were tripped several times at different points in the gait cycle. Kinematics and EMG of the support limb muscles were measured. After tripping, rapid EMG responses (60-80 ms) were observed in hamstring and triceps surae muscles in both young and older subjects. A slightly increased delay (11 ms) was found only in the soleus muscle of the older subjects. The muscle activity patterns (timing and sequencing) were similar in young and older subjects, but the magnitude and rate of development of muscle activity were significantly lower in older subjects. Especially the lower rate of development of muscle activation in the support limb of older subjects is likely to reduce the rate of force generation, which can contribute to inadequate recovery responses and falls. © Springer-Verlag 2004

Estimating fall risk with inertial sensors using gait stability measures that do not require step detection

Falls have major consequences both at societal (health-care and economy) and individual (physical and psychological) levels. Questionnaires to assess fall risk are commonly used in the clinic, but their predictive value is limited. Objective methods, suitable for clinical application, are hence needed to obtain a quantitative assessment of individual fall risk. Falls in older adults often occur during walking and trunk position is known to play a critical role in balance control. Therefore, analysis of trunk kinematics during gait could present a viable approach to the development of such methods. In this study, nonlinear measures such as harmonic ratio (HR), index of harmonicity (IH), multiscale entropy (MSE) and recurrence quantification analysis (RQA) of trunk accelerations were calculated. These measures are not dependent on step detection, a potentially critical source of error. The aim of the present study was to investigate the association between the aforementioned measures and fall history in a large sample of subjects (42 fallers and 89 non-fallers) aged 50 or older. Univariate associations with fall history were found for MSE and RQA parameters in the AP direction; the best classification results were obtained for MSE with scale factor τ = 2 and for maximum length of diagonals in RQA (72.5% and 71% correct classifications, respectively). MSE and RQA were found to be positively associated with fall history and could hence represent useful tools in the identification of subjects for fall prevention programs. © 2013 Elsevier B.V

Two-stage muscle activity responses in decisions about leg movement adjustments during trip recovery

Item does not contain fulltextStudies on neural decision making mostly investigated fast corrective adjustments of arm movements. However, fast leg movement corrections deserve attention as well, since they are often required to avoid falling after balance perturbations. The present study aimed at elucidating the mechanisms behind fast corrections of tripping responses by analyzing the concomitant leg muscle activity changes. This was investigated in seven young adults who were tripped in between normal walking trials and took a recovery step by elevating the tripped leg over the obstacle. In some trials, a forbidden landing zone (FZ) was presented behind the obstacle, at the subjects' preferred foot landing position, forcing a step correction. Muscle activity of the tripped leg gastrocnemius medialis (iGM), tibialis anterior (iTA), rectus femoris (iRF), and biceps femoris (iBF) muscles was compared between normal trips presented before any FZ appearance, trips with a FZ, and normal trips presented in between trips with a FZ ("catch" trials). When faced with a real or expected (catch trials) FZ, subjects shortened their recovery steps. The underlying changes in muscle activity consisted of two stages. The first stage involved reduced iGM activity, occurring at a latency shorter than voluntary reaction, followed by reduced iTA and increased iBF and iGM activities occurring at longer latencies. The fast response was not related to step shortening, but longer latency responses clearly were functional. We suggest that the initial response possibly acts as a "pause," allowing the nervous system to integrate the necessary information and prepare the subsequent, functional movement adjustment

Can explicit visual feedback of postural sway efface the effects of sensory manipulations on mediolateral balance performance?

Explicit visual feedback on postural sway is often used in balance assessment and training. However, up-weighting of visual information may mask impairments of other sensory systems. We therefore aimed to determine whether the effects of somatosensory, vestibular, and proprioceptive manipulations on mediolateral balance are reduced by explicit visual feedback on mediolateral sway of the body center of mass and by the presence of visual information. We manipulated sensory inputs of the somatosensory system by transcutaneous electric nerve stimulation on the feet soles (TENS) of the vestibular system by galvanic vestibular stimulation (GVS) and of the proprioceptive system by muscle-tendon vibration (VMS) of hip abductors. The effects of these manipulations on mediolateral sway were compared with a control condition without manipulation under three visual conditions: explicit feedback of sway of the body center of mass (FB), eyes open (EO), and eyes closed (EC). Mediolateral sway was quantified as the sum of energies in the power spectrum and as the energy at the dominant frequencies in each of the manipulation signals. Repeated-measures ANOVAs were used to test effects of each of the sensory manipulations, of visual conditions and their interaction. Overall, sensory manipulations increased body sway compared with the control conditions. Absence of normal visual information had no effect on sway, while explicit feedback reduced sway. Furthermore, interactions of visual information and sensory manipulation were found at specific dominant frequencies for GVS and VMS, with explicit feedback reducing the effects of the manipulations but not effacing these

Assessing physical activity in older adults: Required days of trunk accelerometer measurements for reliable estimation

We investigated the reliability of physical activity monitoring based on trunk accelerometry in older adults and assessed the number of measured days required to reliably assess physical activity. Seventy-nine older adults (mean age 79.1 ± 7.9) wore an accelerometer at the lower back during two nonconsecutive weeks. The duration of locomotion, lying, sitting, standing and shuffling, movement intensity, the number of locomotion bouts and transitions to standing, and the median and maximum duration of locomotion were determined per day. Using data of week 2 as reference, intraclass correlations and smallest detectable differences were calculated over an increasing number of consecutive days from week 1. Reliability was good to excellent when whole weeks were assessed. Our results indicate that a minimum of two days of observation are required to obtain an ICC ≥ 0.7 for most activities, except for lying and median duration of locomotion bouts, which required up to five days

Mediolateral balance and gait stability in older adults.

Early detection of balance impairment is crucial to identify individuals who may benefit from interventions aimed to prevent falls, which is a major problem in aging societies. Since mediolateral balance deteriorates with aging, we proposed a mediolateral balance assessment (MELBA) tool that uses a CoM-tracking task of predictable sinusoidal and unpredictable multisine targets. This method has shown to be reliable and sensitive to aging effect, however, it is not known whether it can predict performance on common daily-life tasks such as walking. This study aimed to determine whether MELBA is an ecologically valid tool by correlating its outputs with a measure of mediolateral gait stability known to be predictive of falls.Nineteen community-dwelling older adults (72±5 years) tracked predictable and unpredictable target displacements at increasing frequencies with their CoM by shifting their weight sideward. Response delay (phase-shift) and amplitude difference (gain) between the CoM and target in the frequency domain were used to quantify performance. To assess gait stability, the local divergence exponent was calculated using mediolateral accelerations with an inertial sensor when walking on a treadmill (LD

Physical performance and physical activity in older adults: associated but separate domains of physical function in old age.

Background: Physical Function Is A Crucial Factor In The Prevention And Treatment Of Health Conditions In Older Adults And Is Usually Measured Objectively With Physical Performance Tests And/or Physical Activity Monitoring. Objective: To Examine Whether 1) Physical Performance (PP) And Physical Activity (PA) Constitute Separate Domains Of Physical Function; 2) Differentiation Of PA Classes Is More Informative Than Overall PA. Design: Cross-Sectional Study To Explore The Relationships Within And Among PP And PA Measures. Methods In 49 Older Participants (83±7 Years; M±SD), Performance-based Tests Were Conducted And PA Was Measured For One Week. Activity Monitor Data Were Reduced In Terms Of Duration, Periods, And Mean Duration Of Periods Of Lying, Sitting, Standing And Locomotion. The Relation Between And Within PP Scores And PA Outcomes Were Analysed Using Rank Order Correlation And Factor Analysis. Results: Factor Structure After Varimax Rotation Revealed Two Orthogonal Factors Explaining 78% Of The Variance In The Data: One Comprising All PA Variables And One Comprising All PP Variables. PP Scores Correlated Moderately With PA In Daily Life. Differentiation Of Activity Types And Quantification Of Their Duration, Intensity And Frequency Of Occurrence Provided Stronger Associations With PP, As Compared To A Single Measure Of Acceleration Expressing Overall PA. Limitations: For Independent Validation, The Conclusions About The Validity Of The Presented Conceptual Framework And Its Clinical Implications Need To Be Confirmed In Other Studies. Conclusions: PP And PA Represent Associated But Separate Domains Of Physical Function, Suggesting That An Improvement Of PP Does Not Automatically Imply An Increase Of PA, I.e. A Change To A More Active Lifestyle. Differentiation Of Activity Classes In The Analysis Of PA Provides More Insights Into PA And Its Association With PP Than Using A Single Overall Measure Of Acceleration

Characteristics of daily life gait in fall and non fall-prone stroke survivors and controls

BACKGROUND: Falls in stroke survivors can lead to serious injuries and medical costs. Fall risk in older adults can be predicted based on gait characteristics measured in daily life. Given the different gait patterns that stroke survivors exhibit it is unclear whether a similar fall-prediction model could be used in this group. Therefore the main purpose of this study was to examine whether fall-prediction models that have been used in older adults can also be used in a population of stroke survivors, or if modifications are needed, either in the cut-off values of such models, or in the gait characteristics of interest. METHODS: This study investigated gait characteristics by assessing accelerations of the lower back measured during seven consecutive days in 31 non fall-prone stroke survivors, 25 fall-prone stroke survivors, 20 neurologically intact fall-prone older adults and 30 non fall-prone older adults. We created a binary logistic regression model to assess the ability of predicting falls for each gait characteristic. We included health status and the interaction between health status (stroke survivors versus older adults) and gait characteristic in the model. RESULTS: We found four significant interactions between gait characteristics and health status. Furthermore we found another four gait characteristics that had similar predictive capacity in both stroke survivors and older adults. CONCLUSION: The interactions between gait characteristics and health status indicate that gait characteristics are differently associated with fall history between stroke survivors and older adults. Thus specific models are needed to predict fall risk in stroke survivors