Sang I. Lin

Postural muscle responses following changing balance threats in young, stable older, and unstable older adults

Abstract The authors determined the postural muscle response to support surface perturbations, in relation to aging and level of stability of 16 young adults and 32 older adults who were classified into stable (SOA) and unstable (UOA) groups on the basis of their functional balance abilities. Forward and backward support surface translations of various amplitudes and velocities were used so that postural responses of the standing adults could be elicited. The thigh and leg postural muscle responses were recorded with surface electromyography (EMG). The older groups had significantly longer onset latency in the anterior postural muscles, smaller integrated EMG in the posterior muscles, and greater extent of integrated EMG attenuation over time. The UOA showed longer onset latency in the gastrocnemius following slow backward perturbation and used a greater percentage of the functional capacity of the gastrocnemius muscle than the SOA did. Those findings indicate that the SOA and UOA had limited ability to adapt to changing balance threats; the UOA were more limited than the SOA. When designing balance training programs, therefore, therapists should consider the adults level of functional stability.

Sensitivity of plantar cutaneous sensation and postural stability

BACKGROUND Impaired plantar cutaneous sensation is often seen clinically and can lead to postural instability. It is not clear if the severity of such sensory loss would be associated with postural stability, and if such an association would be affected by sensory redundancy and task difficulty. The purpose of this study was to investigate the association of the degree of somatosensory loss and postural stability by experimentally induced somatosensory loss in healthy young adults. METHODS Twenty-one healthy young adults performed four quiet standing tasks (normal or narrow base, and eyes open or closed) on a force platform under three somatosensory conditions induced by ischemic blocking of afferent conduction below the ankle, normal, partial loss and complete loss. Differences in the standing center of pressure motion between the three sensory loss conditions were compared. FINDINGS There was a significant trend of greater center of pressure motion with increasing severity of sensory loss in all task conditions. The differences in the center of pressure motion between partial and total loss conditions were significant only in conditions where vision was removed and the support surface was narrow. INTERPRETATION Increased severity of experimentally induced loss of plantar cutaneous sensitivity was associated with greater postural sway. Such an association was affected by the availability of visual input and the size of the support surface. Clinically for patients with somatosensory impairments of the foot, postural stability should be given special attention.

Sensorimotor function, balance abilities and pain influence Timed Up and Go performance in older community-living people

Background and aims: The Timed up and Go Test (TUG) is recommended as a screening tool for fall risk in older people. It is assumed that this general mobility test is underpinned by physiological factors such as strength, coordination and balance. However, no studies have examined the range of physiological and psychological factors which influence performance on this test. The aim of this study was to examine the relative contributions of a range of sensorimotor, balance and psychological factors to TUG performance in a large sample of older people. Methods: 280 community-dwelling people aged 65 plus years (mean age 74.9, SD=6.4) underwent the TUG test, as well as quantitative tests of vision, peripheral sensation, strength, reaction time, balance, fear of falling, pain and vitality. Results: The time required to complete the TUG was significantly related to limitations in instrumental activities of daily living and fear of falling. Many physiological and psychological factors were significantly associated with TUG performance in univariate analyses. Stepwise multiple regression analyses identified knee strength, postural sway, reaction time, edge contrast sensitivity, MMSE score, SF12 body pain and general health scores, number of medical conditions and age as significant and independent predictors of TUG performance. Of these measures, the lower limb strength measure explained most variance in TUG times. However, other sensorimotor, balance, psychological and health measures provided important independent information. The combined set of variables explained 43.5% of the variance in TUG times (multiple r=0.65). Conclusions: Findings indicate that, in community-dwelling older people, TUG performance is influenced by lower limb strength, balance, reaction time, vision and pain, in addition to cognitive function and health status.

Effects of a Multifactorial Fall Prevention Program on Fall Incidence and Physical Function in Community-Dwelling Older Adults With Risk of Falls

OBJECTIVE To evaluate effects of a multifactorial fall prevention program on fall incidence and physical function in community-dwelling older adults. DESIGN Multicenter randomized controlled trial. SETTING Three medical centers and adjacent community health centers. PARTICIPANTS Community-dwelling older adults (N=616) who have fallen in the previous year or are at risk of falling. INTERVENTIONS After baseline assessment, eligible subjects were randomly allocated into the intervention group (IG) or the control group (CG), stratified by the Physiological Profile Assessment (PPA) fall risk level. The IG received a 3-month multifactorial intervention program including 8 weeks of exercise training, health education, home hazards evaluation/modification, along with medication review and ophthalmology/other specialty consults. The CG received health education brochures, referrals, and recommendations without direct exercise intervention. MAIN OUTCOME MEASURES Primary outcome was fall incidence within 1 year. Secondary outcomes were PPA battery (overall fall risk index, vision, muscular strength, reaction time, balance, and proprioception), Timed Up & Go (TUG) test, Taiwan version of the International Physical Activity Questionnaire, EuroQol-5D, Geriatric Depression Scale (GDS), and the Falls Efficacy Scale-International at 3 months after randomization. RESULTS Participants were 76±7 years old and included low risk 25.6%, moderate risk 25.6%, and marked risk 48.7%. The cumulative 1-year fall incidence was 25.2% in the IG and 27.6% in the CG (hazard ratio=.90; 95% confidence interval, .66-1.23). The IG improved more favorably than the CG on overall PPA fall risk index, reaction time, postural sway with eyes open, TUG test, and GDS, especially for those with marked fall risk. CONCLUSIONS The multifactorial fall prevention program with exercise intervention improved functional performance at 3 months for community-dwelling older adults with risk of falls, but did not reduce falls at 1-year follow-up. Fall incidence might have been decreased simultaneously in both groups by heightened awareness engendered during assessments, education, referrals, and recommendations.

The cortical control of cycling exercise in stroke patients: An fNIRS study

Stroke survivors suffering from deficits in motor control typically have limited functional abilities, which could result in poor quality of life. Cycling exercise is a common training paradigm for restoring locomotion rhythm in patients. The provision of speed feedback has been used to facilitate the learning of controlled cycling performance and the neuromuscular control of the affected leg. However, the central mechanism for motor relearning of active and passive pedaling motions in stroke patients has not been investigated as extensively. The aim of this study was to measure the cortical activation patterns during active cycling with and without speed feedback and during power‐assisted (passive) cycling in stroke patients. A frequency‐domain near‐infrared spectroscopy (FD‐NIRS) system was used to detect the hemodynamic changes resulting from neuronal activity during the pedaling exercise from the bilateral sensorimotor cortices (SMCs), supplementary motor areas (SMAs), and premotor cortices (PMCs). The variation in cycling speed and the level of symmetry of muscle activation of bilateral rectus femoris were used to evaluate cycling performance. The results showed that passive cycling had a similar cortical activation pattern to that observed during active cycling without feedback but with a smaller intensity of the SMC of the unaffected hemisphere. Enhanced PMC activation of the unaffected side with improved cycling performance was observed during active cycling with feedback, with respect to that observed without feedback. This suggests that the speed feedback enhanced the PMC activation and improved cycling performance in stroke patients. Hum Brain Mapp 34:2381–2390, 2013.

Older adults adopted more cautious gait patterns when walking in socks than barefoot

Walking barefoot or in socks is common for ambulating indoors and has been reported to be associated with increased risk of falls and related injuries in the elderly. This study sought to determine if gait patterns differed between these two conditions for young and older adults. A motion analysis system was used to record and calculate the stride characteristics and motion of the bodys center of mass (COM) of 21 young and 20 older adults. For the walking tasks, the participants walked on a smooth floor surface at their preferred speed either barefoot or in socks in a random order. The socks were commercially available and commonly used. The results demonstrated that while walking in socks, compared with walking barefoot, older adults adopted a more cautious gait pattern including decreased walking speed and shortened stride length as well as reduced COM minimal velocity during the single limb support phase. Young adults, however, did not demonstrate significant changes. These findings suggest that walking with socks might present a greater balance threat for older adults. Clinically, safety precautions about walking in socks should be considered to be given to older adults, especially those with balance deficits.

Depressive symptoms in addition to visual impairment, reduced strength and poor balance predict falls in older Taiwanese people

OBJECTIVE to determine whether depression is an important and independent predictor of falls in community-dwelling older people living in Taiwan. DESIGN longitudinal study. SETTING five randomly selected villages from Tainan city, Taiwan. PARTICIPANTS AND METHODS in total, 280 community-dwelling people not taking anti-depressant medication aged 65-91 years (mean age 74.9). Participants completed the Geriatric Depression Scale and underwent a range of sensorimotor, balance and mobility tasks and were then followed up for 2 years with monthly telephone calls to determine falls incidence. RESULTS of the 260 participants with complete follow-up data, 174 (66.9%) experienced no falls, 51 (19.6%) fell once and 35 (13.5%) fell two or more times. Depressive symptoms were significantly more prevalent in recurrent fallers (40.0%) and once-only fallers (27.5%) compared with non-fallers (16.1%). Negative binomial regression analysis identified depression, poor depth perception, reduced lower limb strength and increased sway as independent and significant predictors of falls. CONCLUSION depressive symptoms were found to be common in older Taiwanese people and associated with an increased fall risk. These findings suggest that in addition to implementing approaches to maximise vision, strength and balance, fall prevention strategies should also include interventions to assess and treat depression.

Age-related changes in the performance of forward reach

Aging is widely considered to be associated with limited balance capacity. It is not clear if forward reach ability is also affected by aging. The purpose of this study was to determine if aging was associated with reduced ability of forward reach or changes in movement patterns. Thirty-three young and 31 older adults were instructed to reach forward as far as possible without losing balance. A motion analysis system was used to record the body kinematics to calculate the joint angle and estimate the motion of center of mass (COM) using a five-segment model. Reach distance (measured from the finger marker), COM displacement, and the distance that the COM exceeded the 2nd toe marker (COM-toe) were used to represent reach performance. The movement patterns were classified as hip, ankle or mixed strategies based upon joint kinematics. It was found that the initial location of the COM was significantly more anterior in the older adults. Older adults were found to have significantly smaller COM displacement and greater hip flexion, but did not differ from young adults in reach distance or COM-toe. Older adults overwhelmingly adopted a hip strategy, but none adopted an ankle strategy. The distribution of the different strategies also differed significantly between groups. These findings suggest that aging appears to be associated with modifications in movement patterns, but not necessarily with a reduction in the ability to approach the boundary of stability. Clinically, balance training for older adults may include the exploration and instruction of atypical movement patterns.

Gender Differences in the Relationship of Social Activity and Quality of Life in Community-Dwelling Taiwanese Elders

This study explores the gender differences in the relationship between social activity and quality of life (QOL). A cross-sectional survey of 220 community-dwelling elderly people was conducted in southern Taiwan. Social activity was classified into six categories. The brief version of the World Health Organization QOL (WHOQOL-BREF) was used to measure QOL. Findings revealed that the associations of six types of social activities with QOL were weaker among women than men. The regression analyses further showed that for women, only religious activity was positively related to total QOL, while for men only involvement in formal group activity was positively related to total QOL.

Effect of plantar desensitization on postural adjustments prior to step initiation

Plantar cutaneous afferent provides information about the contact between the body and the support surface and could affect the anticipatory postural adjustments (APAs). This study investigated the effect of plantar desensitization on the APAs for step initiation. Twenty-five healthy young adults participated in this study and were instructed to begin walking as fast as possible under 4 plantar desensitization conditions, none (NoneD), and desensitization of the stepping, supporting or bilateral (BilD) plantar surfaces, with eyes open or closed. The desensitization was achieved by cold water immersion of the plantar surface for 15 min. Foot switches recorded the timing of the stepping events. Surface electromyography (EMG) recorded the activation of bilateral tibialis anterior. The center of pressure (COP) and ground reaction force (GRF) data were derived from the force platform on which the subject initiated walking. The results showed that during the anticipation phase, the peak COP displacement toward the stepping leg was significantly smaller in BilD than in unilateral desensitization, which in turn was smaller than in NoneD, regardless of vision. The time to reach the peak COP displacement was significantly sooner with plantar desensitization in the eyes open condition. The GRF, EMG and anteroposterior COP displacement or the timing of the stepping events was not affected by plantar desensitization. These findings indicate that plantar cutaneous afferent contributed to the control of the APAs for step initiation by scaling the displacement of the mediolateral COP displacement and loss of its sensitivity could not be compensated by visual inputs.