Aging of the somatosensory system: a translational perspective

Effects of aging and tactile stochastic resonance on postural performance and postural control in a sensory conflict task

Postural control in certain situations depends on functioning of tactile or proprioceptive receptors and their respective dynamic integration. Loss of sensory functioning can lead to increased risk of falls in challenging postural tasks, especially in older adults. Stochastic resonance, a concept describing better function of systems with addition of optimal levels of noise, has shown to be beneficial for balance performance in certain populations and simple postural tasks. In this study, we tested the effects of aging and a tactile stochastic resonance stimulus (TSRS) on balance of adults in a sensory conflict task. Nineteen older (71-84 years of age) and younger participants (22-29 years of age) stood on a force plate for repeated trials of 20 s duration, while foot sole stimulation was either turned on or off, and the visual surrounding was sway-referenced. Balance performance was evaluated by computing an Equilibrium Score (ES) and anterior-posterior sway path length (APPlength). For postural control evaluation, strategy scores and approximate entropy (ApEn) were computed. Repeated-measures ANOVA, Wilcoxon signed-rank tests, and Mann-Whitney U-tests were conducted for statistical analysis. Our results showed that balance performance differed between older and younger adults as indicated by ES (p = 0.01) and APPlength (0.01), and addition of vibration only improved performance in the older group significantly (p = 0.012). Strategy scores differed between both age groups, whereas vibration only affected the older group (p = 0.025). Our results indicate that aging affects specific postural outcomes and that TSRS is beneficial for older adults in a visual sensory conflict task, but more research is needed to investigate the effectiveness in individuals with more severe balance problems, for example, due to neuropathy.

H-index is important for postural control for people with impaired foot sole sensation

INTRODUCTION

People with Peripheral Neuropathy (PN), especially those with impaired sensory inputs through the small-afferent fiber (type II afferent fibers) reflex loop (SAF), might depend more on the large-afferent fiber (type I afferent fibers) reflex loop (LAF) for postural control.

PURPOSE

To examine whether the function of the LAF reflex loop, reflected by the H-reflex and ankle joint proprioception, influences postural control when the SAF reflex loop is impaired, as indicated by reduced foot sole cutaneous sensation.

METHODS

Thirteen participants (8 women, 5 men) diagnosed with PN and 12 age-matched controls (7 women, 5 men) completed the testing protocol. Measures of interest included the H-index, active (AAP) and passive (PAP) ankle proprioception, plantar pressure sensitivity (PPS), average sway velocity (VAVG) and area (A95) during 30 seconds eyes-closed standing, 6-minute walk distance (6MWD) and timed up-and-go duration (TUG).

RESULTS

Statistically significant group-dependent regression was observed between VAVG and H-index. Compared to the control group, the PN group demonstrated reduced PPS (2.0 ± 1.9 vs. 4.2 ± 1.2, P < .05) and H-index (63.6 ± 10.9 vs. 76.4 ± 16.0, P < .05), greater VAVG (3.5 ± 2.1 vs. 1.6 ± 0.6 cm/s, P < .05) and A95 (10.0 ± 10.1 vs. 2.5 ± 1.5 cm2, P < .05), shorter 6MWD (442.2 ± 93.0 vs. 525.3 ± 68.2 m, P < .05), and longer TUG (9.4 ± 1.6 vs. 6.5 ± 1.3 s, P < .05). Within the PN group, but not the control group, the H-index was correlated with VAVG (r = -.56, P < .05). Moreover, within the PN group only, PAP scores were correlated with 6MWD (r = -.68, P < .05) and TUG (r = -.59, P < .05) performance. No other statistically significant group difference, correlation or group-dependent regression was observed.

CONCLUSION

VAVG, 6MWD, and TUG correlated with LAF reflex loop function observed among those with impaired functioning of the SAF reflex loop. This observation suggests that the LAF reflex loop may be critical to the control of balance in those individuals suffering from small-fiber PN.

Use of Nerve Conduction Velocity to Assess Peripheral Nerve Health in Aging Mice

Nerve conduction velocity (NCV), the speed at which electrical signals propagate along peripheral nerves, is used in the clinic to evaluate nerve function in humans. A decline in peripheral nerve function is associated with a number of age-related pathologies. While several studies have shown that NCV declines with age in humans, there is little information on the effect of age on NCV in peripheral nerves in mice. In this study, we evaluated NCV in male and female C57Bl/6 mice ranging from 4 to 32 months of age. We observed a decline in NCV in both male and female mice after 20 months of age. Sex differences were detected in sensory NCV as well as the rate of decline during aging in motor nerves; female mice had slower sensory NCV and a slower age-related decline in motor nerves compared with male mice. We also tested the effect of dietary restriction on NCV in 30-month-old female mice. Dietary restriction prevented the age-related decline in sciatic NCV but not other nerves. Because NCV is clinically relevant to the assessment of nerve function, we recommend that NCV be used to evaluate healthspan in assessing genetic and pharmacological interventions that increase the life span of mice.

Age effects on mediolateral balance control

BACKGROUND

Age-related balance impairments, particularly in mediolateral direction (ML) may cause falls. Sufficiently sensitive and reliable ML balance tests are, however, lacking. This study is aimed to determine (1) the effect of age on and (2) the reliability of ML balance performance using Center of Mass (CoM) tracking.

METHODS

Balance performance of 19 young (26±3 years) and 19 older (72±5 years) adults on ML-CoM tracking tasks was compared. Subjects tracked predictable and unpredictable target displacements at increasing frequencies with their CoM by shifting their weight sideward. Phase-shift (response delay) and gain (amplitude difference) between the CoM and target in the frequency domain were used to quantify performance. Thirteen older and all young adults were reassessed to determine reliability of balance performance measures. In addition, all older adults performed a series of clinical balance tests and conventional posturography was done in a sub-sample.

RESULTS

Phase-shift and gain dropped below pre-determined thresholds (-90 degrees and 0.5) at lower frequencies in the older adults and were even lower below these frequencies than in young adults. Performance measures showed good to excellent reliability in both groups. All clinical scores were close to the maximum and no age effect was found using posturography. ML balance performance measures exhibited small but systematic between-session differences indicative of learning.

CONCLUSIONS

The ability to accurately perform ML-CoM tracking deteriorates with age. ML-CoM tracking tasks form a reliable tool to assess ML balance in young and older adults and are more sensitive to age-related impairment than posturography and clinical tests.

Sensory and motor peripheral nerve function and longitudinal changes in quadriceps strength

BACKGROUND

Poor peripheral nerve function is common in older adults and may be a risk factor for strength decline, although this has not been assessed longitudinally.

METHODS

We assessed whether sensorimotor peripheral nerve function predicts strength longitudinally in 1,830 participants (age = 76.3 ± 2.8, body mass index = 27.2 ± 4.6kg/m(2), strength = 96.3 ± 34.7 Nm, 51.0% female, 34.8% black) from the Health ABC study. Isokinetic quadriceps strength was measured semiannually over 6 years. Peroneal motor nerve conduction amplitude and velocity were recorded. Sensory nerve function was assessed with 10-g and 1.4-g monofilaments and average vibration detection threshold at the toe. Lower-extremity neuropathy symptoms were self-reported.

RESULTS

Worse vibration detection threshold predicted 2.4% lower strength in men and worse motor amplitude and two symptoms predicted 2.5% and 8.1% lower strength, respectively, in women. Initial 10-g monofilament insensitivity predicted 14.2% lower strength and faster strength decline in women and 6.6% lower strength in men (all p < .05).

CONCLUSION

Poor nerve function predicted lower strength and faster strength decline. Future work should examine interventions aimed at preventing declines in strength in older adults with impaired nerve function.

Postural response to vibration of triceps surae, but not quadriceps muscles, differs between people with and without knee osteoarthritis

Although proprioceptive impairments are reported in knee osteoarthritis (OA), there has been little investigation of the underlying causes. Muscle spindles make an important contribution to proprioception. This study investigated whether function of quadriceps, triceps surae, and tibialis anterior muscle spindles is altered in individuals with knee OA. Thirty individuals with knee OA (17 females, 66 ± 7 [mean ± SD] years) and 30 healthy asymptomatic controls (17 females, 65 ± 8 years) stood comfortably and blindfolded on a force plate. Mechanical vibration (60 Hz) was applied bilaterally over the quadriceps, triceps surae, or tibialis anterior muscles for the middle 15 s (Vibration) of a 45 s trial (preceded and followed by 15 s Baseline and Recovery periods). Two trials were recorded for each muscle site. Mean anterior-posterior displacement of centre of pressure was analysed. Although there were no differences between groups for trials with vibration applied to the quandriceps or tibialis anterior, participants with knee OA were initially perturbed more by triceps surae vibration and accommodated less to repeated exposure than controls. This indicates that people with knee OA have less potential to detect or compensate for disturbed input to triceps surae, possibly due to an inability to compensate using muscles spindles in the quadriceps muscle.

Comparison of a collagen membrane versus a fibrin sealant after a peroneal nerve section and repair: a functional and histological study

BACKGROUND

To date, fibrin sealant is considered to be one of the most effective substitutes to prevent post-operative fibrosis and to limit neuroma formation after nerve suture. Because fibrin sealant presents a number of drawbacks, more suitable techniques should be considered. The aim of this study was to functionally and histologically compare the efficiency of a fibrin sealant to a resorbable semi-permeable porcine type I collagen membrane after a peroneal nerve lesion and repair on rats.

METHODS

Rats were divided into four groups: (1) a SHAM group (n = 10) in which surgery was performed without damaging the nerve, (2) a LESION group (n = 15) in which the nerve was cut and immediately sutured without additional treatment, (3) a MEMBRANE group (n = 30) in which a collagen membrane was wrapped around the lesion site, and (4) a GLUE group (n = 30) in which the peroneal nerve was coated by fibrin sealant. Peroneal Functional Index (PFI), kinematic analysis of locomotion, muscular atrophy, axonal regrowth, and irritant ranking score (IRS) were performed during three months post-surgery.

RESULTS

Our results indicate that at the third month post-surgery, no difference in both the functional recovery and the histological measurement was observed between groups. However, no deleterious effect was observed following the use of the collagen membrane. Indeed, the porcine membrane was well-integrated into the host tissue, with no noticeable foreign body reaction at three months post-surgery.

CONCLUSION

Our preliminary results highlight the fact that the collagen membrane could be used as an alternative to fibrin sealant in peripheral nerve repair surgery. Indeed, animals in which the collagen membrane was used to wrap the lesion site exhibited similar functional and histological results as animals in which a fibrin sealant was used to coat the lesion. The greatest advantage of this membrane is that it could be used as a drug delivery device, regulated by its degradation rate.

Chronic physical activity preserves efficiency of proprioception in postural control in older women

The purpose of this study was to compare the effects of proprioceptive disruption on postural control for participants of different ages according to their physical and/or sport activity levels. Two groups of young and old participants who practiced chronic physical and/or sport activities (young active [n = 17; average age 20.5 +/- 1.1 yr] and old active [n = 17; average age 74.0 +/- 3.8 yr]) and two groups of young and old participants who did not practice physical and/or sport activities (young sedentary [n = 17; average age 20.0 +/- 1.3 yr] and old sedentary [n = 17; average age 74.7 +/- 6.3 yr]) participated in the study. They were compared in a bipedal quiet stance reference condition and a bilateral Achilles tendon vibration condition. Center of foot pressure displacements and frequency analysis were compared between the groups. The results indicated that when proprioceptive information was disrupted, the postural control disturbance was more important for the old sedentary group than for the other groups. There were no differences between the old active group and the young sedentary group. Postural control was less altered for the young active group than for the other groups. Aging decreases the efficiency of postural control regardless of the assessment conditions. Physical and sport activities may compensate for the disturbing effects of proprioceptive perturbation through a better use of sensory information whatever the age of the participants.

Aging and balance control in response to external perturbations: role of anticipatory and compensatory postural mechanisms

The ability to maintain balance deteriorates with increasing age. Anticipatory and compensatory postural adjustments (APAs and CPAs, respectively), both, are known to be affected in the elderly. We examined the effect of aging on the ability of older adults to utilize APAs and its effect on subsequent control of posture (CPAs). Ten elderly individuals were exposed to external predictable and unpredictable perturbations applied to the upper body in the sagittal plane. Body kinematics, electromyographic activity of 13 muscles, and ground reaction forces were analyzed during the anticipatory and compensatory phases of postural control. The elderly were capable of recognizing an upcoming predictable perturbation and activated muscles prior to it. However, the older adults used different muscle strategies and sequence of muscle recruitment than that reported in young adults. Additionally, when the perturbations were unpredictable, no APAs were seen which resulted in large CPAs and greater peak displacements of the center of pressure (COP) and center of mass (COM) following perturbations. As opposed to this, when the perturbations were predictable, APAs were seen in older adults resulting in significantly smaller CPAs. The presence and utilization of APAs in older adults also improved postural stability following the perturbation as seen by significantly smaller COP and COM peak displacements. Using APAs in older adults significantly reduces the need for large CPAs, resulting in greater postural stability following a perturbation. The results provide a foundation for investigating the role of training in improving the interplay between anticipatory and compensatory postural control in older adults.

Proprioception: where are we now? A commentary on clinical assessment, changes across the life course, functional implications and future interventions

Proprioception, the sense of where one is in space, is essential for effective interaction with the environment. A lack of or reduction in proprioceptive acuity has been directly correlated with falls and with reduced functional independence in older people. Proprioceptive losses have also been shown to negatively correlate with functional recovery post stroke and play a significant role in other conditions such as Parkinson's disease. However, despite its central importance to many geriatric syndromes, the clinical assessment of proprioception has remained remarkably static. We look at approaches to the clinical assessment of proprioception, changes in proprioception across the life course, functional implications of proprioception in health and disease and the potential for targeted interventions in the future such as joint taping, and proprioception-specific rehabilitation and footwear.

Site-specific differences in the association between plantar tactile perception and mobility function in older adults

Introduction: Impaired somatosensation is common in older adults and contributes to age-related loss of mobility function. However, little is known about whether somatosensation at different sites on the plantar surface of the foot are differentially related to mobility function. Such a finding may have important implications for clinical care of older adults and other at-risk populations, such as for optimizing interventions (e.g., footwear for augmenting somatosensory feedback) and for improving the efficiency of clinical assessment.

Materials and Methods: Tactile perception was evaluated with a 10 g monofilament at four sites on the plantar surface of each foot: great toe (GT), first metatarsal head (MT1), heel (H) and fifth metatarsal head (MT5). Mobility function was assessed with the Berg Balance Scale and walking speed.

Results: Sixty-one older adults participated. Tactile perception was significantly positively associated with Berg Balance Score (adjusted r = 0.30 − 0.75; p = 0.03 − < 0.001), with the strongest association found at the site of the MT1. Only at this site was tactile perception found to be significantly associated with usual walking speed (adjusted r = 0.51; p < 0.001) and maximal walking speed (adjusted r = 0.38, p = 0.004). Clinically mild somatosensory impairment at MT1, but not at other sites, was found to yield substantial deficits in both Berg Balance Score and walking speed.

Discussion: The present findings indicate that tactile perception at MT1 is more closely linked to mobility function than is tactile perception at GT, MT5 or H. These findings warrant further research to examine whether interventions (e.g., textured insoles) and assessments that preferentially or exclusively focus on the site of MT1 may be more effective for optimizing clinical care.

An overview of structure, mechanical properties, and treatment for age-related tendinopathy

Tendons transfer tensile loads from muscle to bone, which enable joint motions and stabilize joints. Tendons sustain large mechanical loads in vivo and as a result, tendons were frequently injured. Aging has been confirmed as a predisposing factor of tendinopathy and bad recovery quality following tendon repair. Current treatment methods are generally not effective and involve either symptomatic relief with non-steroidal antiinflammatory drugs and physical therapy or surgery when conservative treatments failed. The limitation in treatment options is due to our incomplete knowledge of age-related tendinopathy. Studies over the past decades have uncovered a number of important mechanical and cellular changes of aging tendon. However, the basis of aging as a major risk factor for tendon injury and impaired tendon healing remained poorly understood. The objectives of this review are to provide an overview of the current knowledge about the aging-associated changes of structure, mechanical properties and treatment in tendon and highlight causes and therapies for age-related tendinopathy.

Distribution of caveolin in the muscle spindles of human skeletal muscle

The aim of the present study was to demonstrate the location of the different members of the caveolin (cav) family in human muscle spindles. Twenty spindles of three human muscles (vastus medialis, ischiocavernosus, bulbospongiosus) from 12 cadavers were immunohistochemically stained for cav-1, cav-2, and cav-3, and the equatorial and polar regions evaluated. All layers of the outer and inner spindle capsule and all blood vessels within the spindle stained for cav-1 and cav-2. In the muscle spindle, intrafusal muscle fibres stained selectively for cav-3, but with a patchy appearance. Caveolinopathies may therefore also include changes in muscle spindle function.

Anti-phase action between the angular accelerations of trunk and leg is reduced in the elderly

Quiet standing posture in humans has often been modeled as a single inverted pendulum pivoting around the ankle joint. However, recent studies have suggested that anti-phase action between leg and trunk segments plays a significant role in stabilizing posture by reducing the acceleration of the center of mass (COM) of the body. The aim of this study is to test the hypothesis that anti-phase action is attenuated in the elderly compared to the young. The anterior-posterior movements of leg and trunk segments were measured using 4 laser displacement sensors from 22 healthy young subjects (age range, 20-35 years) and 38 healthy elderly subjects (age range, 57-80 years) standing quietly for 30s twice. To focus on the segmental action between trunk and legs, we applied constraints (i.e., wooden splints) on each segment. We found that the velocity and acceleration of the COM (standard deviation of the time series was evaluated) were significantly higher for the elderly subjects than for young subjects. The increase in the acceleration of the COM resulted not only from an increase in the angular acceleration of the segments but also from the reduction of their anti-phase relationship, as demonstrated by an index that quantifies the degree of cancelation between both segments. We conclude that the degree of anti-phase action between trunk and leg segments during quiet standing is smaller for elderly subjects than for young subjects, and that this change of the anti-phase action due to aging resulted in increased COM acceleration in the elderly subjects.

Aging causes a reorganization of cortical and spinal control of posture

Classical studies in animal preparations suggest a strong role for spinal control of posture. In humans it is now established that the cerebral cortex contributes to postural control of unperturbed and perturbed standing. The age-related degeneration and accompanying functional changes in the brain, reported so far mainly in conjunction with simple manual motor tasks, may also affect the mechanisms that control complex motor tasks involving posture. This review outlines the age-related structural and functional changes at spinal and cortical levels and provides a mechanistic analysis of how such changes may be linked to the behaviorally manifest postural deficits in old adults. The emerging picture is that the age-related reorganization in motor control during voluntary tasks, characterized by differential modulation of spinal reflexes, greater cortical activation and cortical disinhibition, is also present during postural tasks. We discuss the possibility that this reorganization underlies the increased coactivation and dual task interference reported in elderly. Finally, we propose a model for future studies to unravel the structure-function-behavior relations in postural control and aging.

Input-output characteristics of soleus homonymous Ia afferents and corticospinal pathways during upright standing differ between young and elderly adults

AIM

This study investigated the effects of ageing on the excitability of soleus homonymous Ia afferents and corticospinal pathways during bipedal upright standing.

METHODS

The input-output relations for the Hoffmann (H) reflex and motor-evoked potential (MEP) were computed for the soleus in response to electrical nerve stimulation and transcranial magnetic stimulation, respectively, in young (n = 16) and elderly (n = 16) adults. In subsets of subjects, the input-output relations were compared between normal and supported upright standing, and corticomotoneuronal excitability was assessed during upright standing with an H-reflex conditioning method. For the H-reflex and MEP threshold, maximal amplitude (Hmax , MEPmax ) and the slope of the input-output relation (Hslope , MEPslope ) were measured and normalized to the corresponding M-wave value.

RESULTS

In normal standing, the Hmax /Mmax [mean (SD); young: 48.3 (14.2)%; elderly: 17.3 (6.4)%] and Hslope /Mslope were significantly (P < 0.05) lower in elderly than in young adults, whereas the MEPmax /Mmax [young: 13.6 (7.5)%; elderly: 24.5 (12.8)%] and MEPslope /Mslope were greater in elderly adults (P < 0.05). The Hslope /Mslope and MEPslope /Mslope decreased and increased, respectively, from supported to normal standing for both age groups but more so in elderly adults. Furthermore, the conditioned H reflex was greater (P < 0.05) in elderly [175.1 (34.3)%] than in young adults [141.8 (29.8)%] during normal standing.

CONCLUSION

This is the first study that clearly indicates lower efficacy of Ia afferents to discharge spinal motor neurones accompanied by greater corticospinal excitability in elderly adults, suggesting an increased contribution of the descending drive in controlling soleus activity during upright standing with ageing.

Aging and limb alter the neuromuscular control of goal-directed movements

The purpose of this study was to determine whether the neuromuscular control of goal-directed movements is different for young and older adults with the upper and lower limbs. Twenty young (25.1 ± 3.9 years) and twenty older adults (71.5 ± 4.8 years) attempted to accurately match the displacement of their limb to a spatiotemporal target during ankle dorsiflexion or elbow flexion movements. We quantified neuromuscular control by examining the movement endpoint accuracy and variability, and the antagonistic muscle activity using surface electromyography (EMG). Our results indicate that older adults exhibit impaired endpoint accuracy with both limbs due to greater time variability. In addition, older adults exhibit greater EMG burst and lower EMG burst variability as well as lower coactivation of the antagonistic muscles. The impaired accuracy of older adults during upper limb movements was related to lower coactivation of the antagonistic muscles, whereas their impaired accuracy during lower limb movements was related to the amplified EMG bursts. The upper limb exhibited greater movement control than the lower limb, and different neuromuscular parameters were related to the accuracy and consistency for each limb. Greater endpoint error during upper limb movements was related to lower coactivation of the antagonistic muscles, whereas greater endpoint error during lower limb movements was related to the amplified EMG bursts. These findings indicate that the age-associated impairments in movement control are associated with altered activation of the involved antagonistic muscles. In addition, independent of age, the neuromuscular control of goal-directed movements is different for the upper and lower limbs.

Age-related differences in proprioceptive and visuo-proprioceptive function in relation to fine motor behaviour

Leversen et al. (PLoS One 7(6):e38830, 2012) emphasise the importance of understanding the principles of life-long development. In their study of motor control, they found a common tendency towards improved motor performance from childhood to adulthood and a subsequent deterioration. The aim of our study was to examine this issue further by investigating fine motor behaviour (tracing a model line) in 196 participants (age range 12-95 years old) in two sensory conditions-proprioceptive + visual (PV) and proprioceptive only-in both hands and in two types of movement, frontal and transversal. Regression analyses of line length and task performance speed in relation to age were conducted for the different test conditions. The best performance was found in middle age, and a quadratic function provided the best fit for most of the test conditions. The corresponding inflection points (the age at which graphical analysis showed a change in performance as a peak of maturation before decline due to ageing) showed earlier ages in the proprioceptive condition. For most types of movement analysed, performance speed was slower under the PV condition. Paired correlation analysis showed that the symmetry of precision performance between hands became stronger with age. The results provide information on age-dependent differences in proprioception based on fine motor performance. They may be of use in the design of preventive strategies for preserving proprioceptive function by reducing the risk of falls and accidents or diseases such as Parkinson's.

Aging in the olfactory system

With advancing age, the ability of humans to detect and discriminate odors declines. In light of the rapid progress in analyzing molecular and structural correlates of developing and adult olfactory systems, the paucity of information available on the aged olfactory system is startling. A rich literature documents the decline of olfactory acuity in aged humans, but the underlying cellular and molecular mechanisms are largely unknown. Using animal models, preliminary work is beginning to uncover differences between young and aged rodents that may help address the deficits seen in humans, but many questions remain unanswered. Recent studies of odorant receptor (OR) expression, synaptic organization, adult neurogenesis, and the contribution of cortical representation during aging suggest possible underlying mechanisms and new research directions.

Sensibilidad cutánea plantar y balance dinámico en adultos mayores saludables de la comunidad: estudio relacional

La somatosensación cutánea de los miembros inferiores es relevante para la preservación del balance, cuya interacción se compromete con el envejecimiento. El propósito de ésta investigación fue determinar el nivel de relación entre la sensación cutánea plantar y el balance dinámico en adultos mayores saludables. El diseño de estudio fue de corte transversal. La muestra fue conformada por 74 adultos mayores entre 60 y 75 años, incorporados desde un Centro de Salud de Talca, Chile. Se midió la discriminación táctil de dos puntos en: primer, segundo, tercer metatarsiano, borde lateral, arco plantar y talón de ambos pies. El balance dinámico fue valorado con el Biodex Balance System SD, registrando el Índice de Estabilidad General Bilateral, Antero Posterior y Medio Lateral. Para el análisis estadístico se utilizó el coeficiente de Pearson y la regresión lineal múltiple. Los resultados mostraron una correlación baja entre la discriminación de dos puntos del talón derecho con el Índice de Estabilidad General Bilateral (r=0,244; p=0,018) y con el Medio Lateral (r=0,267; p=0,011). El talón izquierdo se correlacionó con el Índice de Estabilidad General Bilateral (r=0,268; p=0,011) y el Medio Lateral (r=0,285; p=0,007). El análisis de correlación múltiple no mostró influencia de los factores antropométricos y de salud, tales como: edad, índice de masa corporal, número de medicamentos, enfermedades y caídas en la varianza de los índices de balance dinámico. En conclusión, la disminución de la sensación cutánea plantar de ambos talones se asoció levemente con mayores índices de balance dinámico total y medio lateral.

Previous physical activity and body balance in elderly people

The purpose of the research was to evaluate the efficiency of body balance regulation in the elderly and verify whether physical activity in adolescence could influence later physical efficiency. Research was carried out on 62 persons aged between 65 and 96 years of age. Fifty people declared that they undertook physical activity in adolescence, while 12 reported no activity. Stabilographic examinations were performed during trials with open and closed eyes on a horizontally situated platform tilted forward and backward. The centre-of-pressure (COP) path length, sway range area and centre-of-pressure velocity (COP velocity) were assessed. The safety margin when a person leans forward and backward was evaluated as well. On a horizontally situated platform, exclusion of visual control in most of the examined participants resulted in a significant increase in values of examined parameters. Tilting the platform caused in both groups an increase in values of all the parameters. These changes were more visible when a trial with eyes closed was performed and the group of active people obtained better results. These people were also able to use the support area more effectively when changing the position of the body. It was found that body balance disorder affects more often elderly people who were less active in adolescence and that with age visual balance control dominates the proprioceptive one. This means that physical activity directed towards, among other things, forming and improving the body balance regulation system is needed at an early age.

Cognitive demand does not influence the responsiveness of homonymous Ia afferents pathway during postural dual task in young and elderly adults

PURPOSE

This study was designed to investigate the influence of a cognitive task on the responsiveness of the homonymous Ia afferents pathway during upright standing in young and elderly adults.

METHODS

Twelve young and twelve elderly adults stood upright on a foam surface positioned over a force platform, and performed a colour-naming test (cognitive task) with two cognitive loads: congruent and incongruent colour conditions. The rate of correct response in naming colour (accuracy) and associated reaction time (RT) were recorded for the cognitive task. The excursion of the centre of pressure and surface electromyogramme (EMG) of leg muscles were measured. Modulation in the efficacy of homonymous Ia afferents to discharge spinal motor neurones was assessed by means of the Hoffmann (H) reflex method.

RESULTS

The accuracy and RT were similar in the congruent condition between young and elderly adults (p > 0.05), and increased for both age groups in the incongruent condition, but more so for elderly adults (p = 0.014). In contrast, the H reflex amplitude did not change with the cognitive load. The excursions of the centre of pressure in the sagittal plane and muscle EMG did not vary with colour conditions in both groups (p > 0.05).

CONCLUSION

This study indicates a lack of modulation in the efficacy of group Ia afferent to activate soleus motor neurones with the cognitive demand of a concurrent task during upright standing in young and elderly adults.

Manual physical therapy and perturbation exercises in knee osteoarthritis

Objectives:

Knee osteoarthritis (OA) causes disability among the elderly and is often associated with impaired balance and proprioception. Perturbation exercises may help improve these impairments. Although manual physical therapy is generally a well-tolerated treatment for knee OA, perturbation exercises have not been evaluated when used with a manual physical therapy approach. The purpose of this study was to observe tolerance to perturbation exercises and the effect of a manual physical therapy approach with perturbation exercises on patients with knee OA.

Methods:

This was a prospective observational cohort study of 15 patients with knee OA. The Western Ontario and McMaster Universities Arthritis Index (WOMAC), global rating of change (GROC), and 72-hour post-treatment tolerance were primary outcome measures. Patients received perturbation balance exercises along with a manual physical therapy approach, twice weekly for 4 weeks. Follow-up evaluation was done at 1, 3, and 6 months after beginning the program.

Results:

Mean total WOMAC score significantly improved (P = 0.001) after the 4-week program (total WOMAC: initial, 105; 4 weeks, 56; 3 months, 54; 6 months, 57). Mean improvements were similar to previously published trials of manual physical therapy without perturbation exercises. The GROC score showed a minimal clinically important difference (MCID)≥+3 in 13 patients (87%) at 4 weeks, 12 patients (80%) at 3 months, and 9 patients (60%) at 6 months. No patients reported exacerbation of symptoms within 72 hours following each treatment session.

Discussion:

A manual physical therapy approach that also included perturbation exercises was well tolerated and resulted in improved outcome scores in patients with knee OA.

Sensorimotor and postural control factors associated with driving safety in a community-dwelling older driver population

BACKGROUND

To establish whether sensorimotor function and balance are associated with on-road driving performance in older adults.

METHODS

The performance of 270 community-living adults aged 70-88 years recruited via the electoral roll was measured on a battery of peripheral sensation, strength, flexibility, reaction time, and balance tests and on a standardized measure of on-road driving performance.

RESULTS

Forty-seven participants (17.4%) were classified as unsafe based on their driving assessment. Unsafe driving was associated with reduced peripheral sensation, lower limb weakness, reduced neck range of motion, slow reaction time, and poor balance in univariate analyses. Multivariate logistic regression analysis identified poor vibration sensitivity, reduced quadriceps strength, and increased sway on a foam surface with eyes closed as significant and independent risk factors for unsafe driving. These variables classified participants into safe and unsafe drivers with a sensitivity of 74% and specificity of 70%.

CONCLUSIONS

A number of sensorimotor and balance measures were associated with driver safety and the multivariate model comprising measures of sensation, strength, and balance was highly predictive of unsafe driving in this sample. These findings highlight important determinants of driver safety and may assist in developing efficacious driver safety strategies for older drivers.

Eight forms of moving meditation for preventing falls in community-dwelling middle-aged and older adults

BACKGROUND

In numerous countries worldwide, fall prevention among older adults is a major public health issue. For older adults, regular participation in moderate physical activity or exercise lowers the risks of falls. However, scant information is available regarding the prevention strategies that the most at-risk groups may undertake. The purpose of this study is to examine the effects of a fall prevention strategy, eight forms of moving meditation (EFMM), on community-dwelling middle-aged and older adults in Taiwan.

METHODS

This was a quasi-experimental study; 84 participants were recruited from Taipei in Taiwan. For 12 weeks, participants in the experimental group performed 30-min EFMM 3 times per week. The measurements included a Functional Reach Test (FRT), Timed Get-up-and-Go Test (TGUG), and a One-Leg Stance Test (OLST) with eyes both opened and closed. All were conducted at the baseline and 12 weeks after intervention.

RESULTS

The participants who performed EFMM showed a significant and positive performance on FRT, TGUG, and OLST with eyes opened and eyes closed compared to those in the control group.

CONCLUSION

The results suggest that EFMM is an effective strategy for enhancing balance and functional mobility and preventing falls among community-dwelling middle-aged and older adults.

Using dynamic walking models to identify factors that contribute to increased risk of falling in older adults

Falls are common in older adults. The most common cause of falls is tripping while walking. Simulation studies demonstrated that older adults may be restricted by lower limb strength and movement speed to regain balance after a trip. This review examines how modeling approaches can be used to determine how different measures predict actual fall risk and what some of the causal mechanisms of fall risk are. Although increased gait variability predicts increased fall risk experimentally, it is not clear which variability measures could best be used, or what magnitude of change corresponded with increased fall risk. With a simulation study we showed that the increase in fall risk with a certain increase in gait variability was greatly influenced by the initial level of variability. Gait variability can therefore not easily be used to predict fall risk. We therefore explored other measures that may be related to fall risk and investigated the relationship between stability measures such as Floquet multipliers and local divergence exponents and actual fall risk in a dynamic walking model. We demonstrated that short-term local divergence exponents were a good early predictor for fall risk. Neuronal noise increases with age. It has however not been fully understood if increased neuronal noise would cause an increased fall risk. With our dynamic walking model we showed that increased neuronal noise caused increased fall risk. Although people who are at increased risk of falling reduce their walking speed it had been questioned whether this slower speed would actually cause a reduced fall risk. With our model we demonstrated that a reduced walking speed caused a reduction in fall risk. This may be due to the decreased kinematic variability as a result of the reduced signal-dependent noise of the smaller muscle forces that are required for slower. These insights may be used in the development of fall prevention programs in order to better identify those at increased risk of falling and to target those factors that influence fall risk most.

Effect of 14 days of bed rest in older adults on parameters of the body sway and on the local ankle function

This study explored the effects of a 14-day horizontal bed rest (BR) without countermeasures on postural sway, maximal voluntary torque and precision of voluntary torque matching. Sixteen subjects were tested before, immediately after and two weeks after BR. The increase in frequency and amplitude after BR was comparable for both sway subcomponents (rambling and trembling) in medial-lateral direction. But in anterior-posterior direction, rambling increased more in frequency (-7% vs. +31%, p < 0.05) while trembling increased more in amplitude (+35% vs. +84%, p < 0.05). The drop in maximal voluntary torque after BR was present for plantar flexion (p < 0.05) but not for dorsal flexion. After the BR, the subjects were less precise in the dorsal flexion torque matching task (p < 0.05). All the observed parameters, except the dorsal flexion torque matching error, returned back to the pre-BR values after the two weeks of re-conditioning. Results of this study indicate that body sway subcomponents responded differently to BR. Based on these findings, it was not possible to draw clear assumptions on the effects of neural and structural changes on body sway.

The effects of aging on the rambling and trembling components of postural sway: effects of motor and sensory challenges

The effects of healthy aging on postural sway and its rambling and trembling components were studied. Young and elderly subjects stood quietly for 1 min in different postures, and with eyes open and closed. We found that age-related changes in postural sway and its components were similar to those observed in young participants in challenging conditions. These changes may therefore be viewed as secondary to the increased subjective perception of the complexity of postural tasks. Contrary to our expectations, stronger effects of age were seen in characteristics of rambling, not trembling. The commonly accepted hypothesis that older persons rely on vision more was not supported by this study: we found no significant interaction effects of age and vision on any of the sway characteristics. It was concluded that the reported higher reliance on vision in older persons may be task-specific. The results are compatible with the ideas that much of the age-related changes in postural sway emerge at the level of exploring the limits of stability and using the drift-and-act strategy. Our results suggest that the dominant view on rambling and trembling as reflecting supraspinal and peripheral mechanisms, respectively, may be too simplistic.

Single stance stability and proprioceptive control in older adults living at home: gender and age differences

In developed countries, falls in older people represent a rising problem. As effective prevention should start before the risk becomes evident, an early predictor is needed. Single stance instability would appear as a major risk factor. Aims of the study were to describe single stance stability, its sensory components, and their correlation with age and gender. A random sample of 597 older adults (319 men, 278 women) living at home, aged 65–84, was studied. Stability tests were performed with an electronic postural station. The single stance test showed the impairment of single stance stability in older individuals (75–84 yrs). The significant decline of stability in the older subjects may be explained by the impairment of proprioceptive control together with the decrease in compensatory visual stabilization and emergency responses. Younger subjects (65–74 yrs) exhibited better, but still inadequate, proprioceptive control with compensatory visual stabilization. Gender differences appeared in older subjects: women were significantly less stable than men. The measurement of the sensory components of single stance stability could aid in the early detection of a decay in antigravity movements many years before the risk of falling becomes evident. Adequate proprioceptive control could mitigate the effects of all other risks of falling.

Does use of a virtual environment change reaching while standing in patients with traumatic brain injury?

Background

Although numerous virtual reality applications have been developed for sensorimotor retraining in neurologically impaired individuals, it is unclear whether the virtual environment (VE) changes motor performance, especially in patients with brain injuries. To address this question, the movement characteristics of forward arm reaches during standing were compared in physical and virtual environments, presented at different viewing angles.

Methods

Fifteen patients with traumatic brain injuries (TBI) and 15 sex- and age-matched healthy individuals performed virtual reaches in a computer-generated courtyard with a flower-topped hedge. The hedge was projected on a flat screen and viewed in 3D format in 1 of 3 angles: 10° above horizon (resembling a real-world viewing angle), 50° above horizon, or 90° above horizon (directly overhead). Participants were instructed to reach with their dominant hand avatar and to touch the farthest flower possible without losing their balance or stepping. Virtual reaches were compared with reaches-to-point to a target in an equivalent physical environment. A set of kinematic parameters was used.

Results

Reaches by patients with TBI were characterized by shorter distances, lower peak velocities, and smaller postural displacements than reaches by control individuals. All participants reached ~9% farther in the VE presented at a 50° angle than they did in the physical environment. Arm displacement in the more natural 10° angle VE was reduced by the same 9-10% compared to physical reaches. Virtual reaches had smaller velocity peaks and took longer than physical reaches.

Conclusion

The results suggest that visual perception in the VE differs from real-world perception and the performance of functional tasks (e.g., reaching while standing) can be changed in TBI patients, depending on the viewing angle. Accordingly, the viewing angle is a critical parameter that should be adjusted carefully to achieve maximal therapeutic effect during practice in the VE.

The effects of aging on visuomotor coordination and proprioceptive function in the upper limb

[Purpose] Sensorimotor processing, including motor performance, is altered during the process of normal aging. Previous studies have investigated tasks requiring complex visuomotor coordination and active joint reposition tests. Therefore, the purpose of this study was to investigate age-related changes in upper limb tasks, such as visuomotor coordination and proprioceptive acuity. [Subjects and Methods] We recruited 20 healthy elderly subjects and 20 healthy young subjects. We evaluated a tracking task for visuomotor function and a joint reposition test for integrity of proprioceptive sense in both hands of the elderly subjects, and compared the results with those of the healthy young subjects. [Results] The accuracy index scores for the tracking task were significantly lower in both the dominant and non-dominant hands of the elderly subjects than those of the young group. In addition, the reposition error score in the joint reposition test was significantly higher in the elderly group than in the young group. [Conclusion] Sensorimotor functions of both the dominant and non-dominant hands showed a decline in the elderly group. This finding suggests that sensorimotor function deteriorates with advancing age.

The embodied and relational nature of the mind: implications for clinical interventions in aging individuals and populations

Considerable research over the past decade has garnered support for the notion that the mind is both embodied and relational. Jointly, these terms imply that the brain, physical attributes of the self, and features of our interpersonal relationships and of the environments in which we live jointly regulate energy and information flow; they codetermine how we think, feel, and behave both individually and collectively. In addition to direct experience, evidence supports the view that stimuli embedded within past memories trigger multimodal simulations throughout the body and brain to literally recreate lived experience. In this paper, we review empirical support for the concept of an embodied and relational mind and then reflect on the implications of this perspective for clinical interventions in aging individuals and populations. Data suggest that environmental influences literally “get under the skin” with aging; that musculoskeletal and visceral sensations become more prominent in activities of the mind due to aging biological systems and chronic disease. We argue that conceiving the mind as embodied and relational will grow scientific inquiry in aging, transform how we think about the self-system and well-being, and lead us to rethink health promotion interventions aimed at aging individuals and populations.

The maximal width of the base of support (BSW): clinical applicability and reliability of a preferred-standing test for measuring the risk of falling

The aim of this study was to test the reliability and validity of a preferred-standing test for measuring the risk of falling. The preferred-standing position of elderly fallers and non-fallers and healthy young adults was measured. The maximal BSW was measured. The absolute and relative reliability and discriminant validity were assessed. The expanded timed get-up-and-go test (ETGUG), one-leg stance test (OS), tandem stance (TS), and falls efficacy scale international version (FES-I) were used to determine criterion validity. In total, 146 persons (102 females, 44 males; mean age 55±22 years, range 20-94) were recruited. Forty elderly community dwellers (8 fallers) and 26 young adults were tested twice to determine the test-retest reliability. The BSW showed acceptable test-retest reliability (Intraclass correlation coefficient, ICC2,1=0.77-0.83) and inter-rater reliability (ICC3,1=0.77-0.95) for all groups. The standard error of measurement (SEM) was between 0.77 and 1.87, and the smallest detectable change (SDC) was between 2.14cm and 5.19cm. The Bland-Altman plot revealed no systematic errors. There was significant difference between elderly fallers and non-fallers (F(1/75)=11.951; p=0.001. Spearman's rho coefficient values showed no correlation between the BSW and the ETGUG (-0.17, p=0.47), OLS (-0.04, p=0.65), TS (-0.11, p=0.21), and FES-I (-0.10; p=0.27). Only the BSW was a significant predictor for falling (odds ratio=0.736, p=0.007). The reliability and validity of the BSW protocol were acceptable overall. Prospective studies are warranted to evaluate the predictive value of the BSW for determining the risk of falling.

Somatosensation assessment using the NIH Toolbox

Touch sensation is one element of sensory function. As such, somatosensation is one of the sensory domains included in the NIH Toolbox, which is an assessment battery for measuring a range of human functions including emotional health, sensation, cognition, and motor function. We evaluated a variety of methods for inclusion in the NIH Toolbox main battery. In a convenience sample of 409 participants, we evaluated aspects of kinesthesia, pain, and tactile discrimination. We present results on these measures across the lifespan and discuss implications for future studies that use the NIH Toolbox and these measures.

Rapid repetitive passive movement promotes knee proprioception in the elderly

Joint proprioception plays an important role in the generation of coordinated movements, maintenance of normal body posture, body conditioning, motor learning, and relearning. Previous studies have demonstrated that proprioceptive function of the elderly can be enhanced via specific exercises; however, not all of the elderly can actively and safely participate in physical activities. The purpose of this study was to evaluate the effects of rapid repetitive passive movement in an average velocity of 90°/s on knee proprioception in the elderly. A repeated-measure design was employed. Two age groups (12 young/12 elderly) were intervened with repetitive passive movements of 60 repetitions to the knee joint via two machines (isokinetic dynamometer/self-designed machine) in separate days. Changes in proprioception were evaluated via joint active repositioning and kinesthesia, both before and after the intervention. The results revealed that all subjects demonstrated good test–retest reliabilities on proprioceptive measurements. For the active repositioning and kinesthesia, significant statistical main effects were found for group and time, but not for machine. No statistical interactions were revealed. Despite of age-related proprioceptive declines, elderly subjects could benefit from rapid repetitive passive movements. This indicates that repetitive passive movement may be an alternative to physical activity for those who are home-bound, in a sedentary lifestyle, or with other health conditions that may limit their abilities to actively maintain or strengthen joint proprioception.

The differential effects of foot sole sensory on plantar pressure distribution between balance and gait

Foot sole tactile sensation provides valuable feedback to the central nervous system. Acutely reduced foot sensation changes plantar pressure distribution in standing and gait; however, the effect of chronic foot sole sensory impairment on plantar pressure distribution is unclear.

PURPOSE

This study aims to examine the effects of peripheral neuropathy (PN) induced chronic sensory loss on plantar pressure distribution in walking and standing.

METHODS

Foot sole sensitivity was tested at the five sites: big toe (BT), 1st metatarsal (M1), 5th metatarsal (M5), mid-foot (MF) and heel (HL). Relative peak pressures (RPP) of the five sites were collected during a 20-s walking on a treadmill at .45 m/s and a 30-s quiet standing with eyes open. Five-way MANOVA was used to examine the influence of sensitivity of each site on overall plantar pressure distribution for standing and walking separately. Tukey's test was used to examine the significant associations.

RESULTS

In standing, the sensitivity of BT affected average RPP at BT significantly (P<.05), where RPP associated with insensitive BT (8.1±5.7%) was greater than with sensitive BT (4.5±4.9%). Furthermore, the RPP at HL was greater for insensitive MF (36.1±17.9%) compared with sensitive MF (23.6±7.4%) (P<.05). No pressure distribution changes were observed in walking.

CONCLUSIONS

Feedback from foot sole tactile sensation in gait is not as significant as in standing, showing standing balance control relies more on feedback control mechanism while gait control relies more on feed forward control mechanism.

Neurosensory mechanotransduction through acid-sensing ion channels

Acid-sensing ion channels (ASICs) are voltage-insensitive cation channels responding to extracellular acidification. ASIC proteins have two transmembrane domains and a large extracellular domain. The molecular topology of ASICs is similar to that of the mechanosensory abnormality 4- or 10-proteins expressed in touch receptor neurons and involved in neurosensory mechanotransduction in nematodes. The ASIC proteins are involved in neurosensory mechanotransduction in mammals. The ASIC isoforms are expressed in Merkel cell-neurite complexes, periodontal Ruffini endings and specialized nerve terminals of skin and muscle spindles, so they might participate in mechanosensation. In knockout mouse models, lacking an ASIC isoform produces defects in neurosensory mechanotransduction of tissue such as skin, stomach, colon, aortic arch, venoatrial junction and cochlea. The ASICs are thus implicated in touch, pain, digestive function, baroreception, blood volume control and hearing. However, the role of ASICs in mechanotransduction is still controversial, because we lack evidence that the channels are mechanically sensitive when expressed in heterologous cells. Thus, ASIC channels alone are not sufficient to reconstruct the path of transducing molecules of mechanically activated channels. The mechanotransducers associated with ASICs need further elucidation. In this review, we discuss the expression of ASICs in sensory afferents of mechanoreceptors, findings of knockout studies, technical issues concerning studies of neurosensory mechanotransduction and possible missing links. Also we propose a molecular model and a new approach to disclose the molecular mechanism underlying the neurosensory mechanotransduction.