"Going Backward": Effects of age and fatigue on posterior-directed falls in Parkinson disease

BACKGROUND

Nearly half of persons with Parkinson disease (PD) report fatigue as a factor in their fall history. However, it is unknown whether these self-reported falls are caused by a sensation of fatigue or performance fatigue.

OBJECTIVE

We sought to investigate the influences of performance fatigue and age on postural control in persons with PD.

METHODS

Individuals with PD (n = 14) underwent postural control assessments before (T0) and immediately after (T1) fatiguing exercise. Biomechanical data were gathered on participants completing a treadmill-induced, posterior-directed fall. Performance fatigue was produced using lower extremity resistance exercise on an isokinetic ergometer. Repeated measures ANCOVAs were used with age as a covariate to determine the effects of performance fatigue on biomechanical variables.

RESULTS

After adjustment for age, there was a statistically significant difference in peak center of pressure (COP) latency during the support phase of recovery. Pairwise comparisons demonstrated a decrease in peak ankle displacement from T0 to T1. Age was also found to be significantly related to reaction time and peak knee displacement while participants were fatigued.

CONCLUSIONS

The decreased peak COP latency, along with decreased ankle angular displacement, suggest that persons with PD adopt a stiffening strategy in response to backward directed falls. Postural stiffening is not uncommon in persons with PD and could be a risk factor for falls. Older individuals with PD demonstrate slower mobility scores and decreased reaction times in the setting of fatigue, suggesting a combined effect of the aging and fatigue processes.

Cardiovascular Metrics Associated With Prevention of Aging-Related Parkinsonian Signs Following Exercise Intervention in Sedentary Older Rats

Preservation of motor capabilities is vital to maintaining independent daily living throughout a person's lifespan and may mitigate aging-related parkinsonism, a progressive and prevalent motor impairment. Physically active lifestyles can mitigate aging-related motor impairment. However, the metrics of physical activity necessary for mitigating parkinsonian signs are not established. Consistent moderate intensity (~10 m/min) treadmill exercise can reverse aging-related parkinsonian signs by 20 weeks in a 2-week on, 2-week off, regimen in previously sedentary advanced middle-aged rats. In this study, we initiated treadmill exercise in sedentary 18-month-old male rats to address two questions: (1) if a rest period not longer than 1-week off exercise, with 15 exercise sessions per month, could attenuate parkinsonian signs within 2 months after exercise initiation, and the associated impact on heart rate (HR) and mean arterial pressure (MAP) and (2) if continuation of this regimen, up to 20 weeks, will be associated with continual prevention of parkinsonian signs. The intensity and frequency of treadmill exercise attenuated aging-related parkinsonian signs by 8 weeks and were maintained till 23 months old. The exercise regimen increased HR by 25% above baseline and gradually reduced pre-intervention MAP. Together, these studies indicate that a practicable frequency and intensity of exercise reduces parkinsonian sign severity commensurate with a modest increase in HR after exercise. These cardiovascular changes provide a baseline of metrics, easily measured in humans, for predictive validity that practicable exercise intensity and schedule can be initiated in previously sedentary older adults to delay the onset of aging-related parkinsonian signs.

A pilot study on the design and validation of a hybrid exoskeleton robotic device for hand rehabilitation

STUDY DESIGN

An iterative design process was used to obtain design parameters that satisfy both kinematic and dynamic requirements for the hand exoskeleton. This design was validated through experimental studies.

INTRODUCTION

The success of hand rehabilitation after impairments depends on the timing, intensity, repetition, and frequency, as well as task-specific training. Considering the continuing constraints placed on therapist-led rehabilitation and need for better outcomes, robot-assisted rehabilitation has been explored. Soft robotic approaches have been implemented for a hand rehabilitation exoskeleton as they have more tolerance for alignment with biological joints than those of hard exoskeletons.

PURPOSE OF THE STUDY

The purpose of the study was to design, develop, and validate a soft robotic exoskeleton for hand rehabilitation.

METHODS

A motion capture system validated the kinematics of the soft robotic digit attached on top of a human index finger. A pneumatic control system and algorithms were developed to operate the exoskeleton based on three therapeutic modes: continuous passive, active assistive, and active resistive motion. Pilot studies were carried out on one healthy and one poststroke participant using continuous passive motion and bilateral/bimanual therapy modes.

RESULTS

The soft robotic digits were able to produce required range of motion and accommodate for dorsal lengthening, with trajectories of the center of rotation of the soft robotic joints in close agreement with the center of rotation of the human finger joints.

DISCUSSION

The exoskeleton showed the robust performance of the robot in applying continuous passive motion and bilateral/bimanual therapy.

CONCLUSIONS

This soft robotic exoskeleton is promising for assisting in the rehabilitation of the hand.

Hearing Loss Contributes to Balance Difficulties in both Younger and Older Adults

Objective

The number of steps required to regain balance is an easily obtainable clinical outcome measure. This study assessed whether number of steps during loss of balance could identify older adults with hearing loss who have balance deficits. We aimed to answer two questions: 1) Does hearing loss negatively affect the ability to regain balance, as reflected by an increased number of steps needed to respond to a perturbation while simultaneously attending to speech-in-noise; and 2) Do hearing aids improve balance control, reflected by a decrease in number of steps needed to regain balance?

Methods

20 young adults and 20 older adults with normal hearing, and 19 older adults with hearing loss performed an auditory-balance dual-task. Participants were asked to listen and repeat back sentences from a standardized audiology test, while simultaneously responding to backward surface translations. Outcome measures were performed on the auditory test and number of steps needed to regain balance. Repeated measures ANCOVA models were run in using group, time, hearing levels, and perturbation levels as predictors.

Results

Auditory scores confirmed difficulty hearing speech-in-noise in older adults with hearing loss and no hearing aids, and in young and older adults with normal hearing and simulated hearing loss. Results showed that group, auditory and balance conditions are significantly related to both outcomes measures and time is not significant for steps. Older adults with hearing loss had a significant increase in number of steps needed to regain balance compared to young adults and older adults with normal hearing.

Conclusion

Number of steps may be an appropriate clinical assessment tool for identifying fall risk in older adults with hearing loss. Further research needs to be performed to identify proper assessments and treatment interventions for older adults with hearing loss who have balance deficits.

Aging-related limit of exercise efficacy on motor decline

Identifying lifestyle strategies and allied neurobiological mechanisms that reduce aging-related motor impairment is imperative, given the accelerating number of retirees and increased life expectancy. A physically active lifestyle prior to old age can reduce risk of debilitating motor decline. However, if exercise is initiated after motor decline has begun in the lifespan, it is unknown if aging itself may impose a limit on exercise efficacy to decelerate further aging-related motor decline. In Brown-Norway/Fischer 344 F1 hybrid (BNF) rats, locomotor activity begins to decrease in middle age (12-18 months). One mechanism of aging-related motor decline may be decreased expression of GDNF family receptor, GFRα-1, which is decreased in substantia nigra (SN) between 12 and 30 months old. Moderate exercise, beginning at 18 months old, increases nigral GFRα-1 and tyrosine hydroxylase (TH) expression within 2 months. In aged rats, replenishing aging-related loss of GFRα-1 in SN increases TH in SN alone and locomotor activity. A moderate exercise regimen was initiated in sedentary male BNF rats in a longitudinal study to evaluate if exercise could attenuate aging-related motor decline when initiated at two different ages in the latter half of the lifespan (18 or 24 months old). Motor decline was reversed in the 18-, but not 24-month-old, cohort. However, exercise efficacy in the 18-month-old group was reduced as the rats reached 27 months old. GFRα-1 expression was not increased in either cohort. These studies suggest exercise can decelerate motor decline when begun in the latter half of the lifespan, but its efficacy may be limited by age of initiation. Decreased plasticity of GFRα-1 expression following exercise may limit its efficacy to reverse motor decline.

Service-Learning Enhances Physical Therapy Students' Ability to Examine Fall Risk in Older Adults

Service-learning (SL) is one educational methodology that provides students opportunities to practice and refine affective, cognitive and psychomotor skills in a community-based setting.

PURPOSE

The aims of this study were: 1) to investigate the impact of SL on physical therapy (PT) students' attitudes and perceived clinical competence when working with older adults, and 2) to evaluate the difference between perceptions of students who developed and implemented the SL activity vs those who implemented only.

METHODS

Eighty PT students, (from two consecutive cohorts) enrolled in a first-year geriatrics course, participated in this study. The first cohort designed and implemented the SL activities, while the second cohort only implemented these activities. Student self-perceived anxiety, confidence, knowledge and skills were assessed by pre- and post-SL surveys using a 5- point Likert-like scale.

RESULTS

Both cohorts reported similar anxiety and confidence levels pre-SL. For both cohorts, with the exception of one item, all responses to anxiety items significantly decreased from pre- to post-SL. All students' confidence levels for assessing and mitigating fall risk in older adults increased post-SL (p<0.01). Moreover, students in cohort 1, who designed and delivered SL activities, expressed self-perceived improvement in their ability to interpret results of evaluations, to determine type and severity of balance impairments, and to serve a geriatric population (p<0.05) compared to students in cohort 2 who only implemented the activities.

CONCLUSION

Embedding SL into a geriatrics course decreased self-perceived anxiety and improved student confidence regarding working with older adults. Also, empowering students to be actively involved in the design and implementation of SL increased self-perceived ability in interpreting results from assessments.

Development of a novel visuomotor integration paradigm by integrating a virtual environment with mobile eye-tracking and motion-capture systems

Visuomotor integration (VMI), the use of visual information to guide motor planning, execution, and modification, is necessary for a wide range of functional tasks. To comprehensively, quantitatively assess VMI, we developed a paradigm integrating virtual environments, motion-capture, and mobile eye-tracking. Virtual environments enable tasks to be repeatable, naturalistic, and varied in complexity. Mobile eye-tracking and minimally-restricted movement enable observation of natural strategies for interacting with the environment. This paradigm yields a rich dataset that may inform our understanding of VMI in typical and atypical development.

The Effects of Performance Fatigability on Postural Control and Rehabilitation in the Older Patient

Fatigue is common in older adults and has a significant effect on quality of life. Despite the high prevalence of fatigue in older individuals, several aspects are poorly understood. It is important to differentiate subjective fatigue complaints from fatigability of motor performance because the two are independent constructs with potentially distinct consequences on mobility. Performance fatigability is the magnitude of change in a performance criterion over a given time of task performance. Performance fatigability is a compulsory element of any strength training program, yet strength training is an important component of rehabilitation programs for older adults. The consequences of fatigability for older adults suggest that acute exercise of various types may result in acute impairments in postural control. The effects of performance fatigability on postural control in older adults are evaluated here to aid the rehabilitation clinician in making recommendations for evaluation of fall risks and exercise prescription.

Aging and selective sensorimotor strategies in the regulation of upright balance

Background

The maintenance of upright equilibrium is essentially a sensorimotor integration task. The central nervous system (CNS) has to generate appropriate and complex motor responses based on the selective and rapid integration of sensory information from multiple sources. Since each sensory system has its own coordinate framework, specific time delay and reliability, sensory conflicts may arise and represent situations in which the CNS has to recalibrate the weight attributed to each particular sensory input. The resolution of sensory conflicts may represent a particular challenge for older adults given the age-related decline in the integrity of many postural regulating systems, including musculoskeletal and sensory systems, as well as neural processing and conduction of information. The effects of aging and adaptation (by repeated exposures) on the capability of the CNS to select pertinent sensory information and resolve sensory conflicts were thus investigated with virtual reality (VR) in the present study.

Methods

Healthy young and older adults maintained quiet stance while immersed in a virtual environment (VE) for 1 hour during which transient visual and/or surface perturbations were randomly presented. Visual perturbations were induced by sudden pitch or roll plane tilts of the VE viewed through a helmet-mounted display, and combined with or without surface perturbations presented in a direction that was either identical or opposite to the visual perturbations.

Results

Results showed a profound influence of aging on postural adjustments measured by electromyographic (EMG) responses and displacements of the center of pressure (COP) and body's center of mass (COM) in the recovery of upright stance, especially in the presence of sensory conflicts. Older adults relied more on vision as compared to young adults. Aging affects the interaction of the somatosensory and visual systems on the control of equilibrium during standing and the ability of CNS to resolve sensory conflicts. However, even with a one-hour immersion in VE and exposure to sensory conflicts, it is possible for the CNS to recalibrate and adapt to the changes, while improving balance capability in older adults.

Conclusion

Preventive and rehabilitation programs targeting postural control in older adults should take into account the possible impairment of sensory organization or sensorimotor integration and include VE training under conditions of sensory conflicts.

Age-related changes in postural responses to externally- and self-triggered continuous perturbations

This is a cross sectional study of eight healthy young (age 22+/-2 years) and eight healthy older (age 70+/-5 years) adults who participated in an experiment in which they had to keep their balance while standing on a platform moving in the anterior/posterior direction. The 20 cm peak-to-peak platform movements were sinusoidal at increasing frequencies up to 0.61 Hz. The frequency increases were either sudden and unpredictable (externally-triggered perturbations) or controlled by the subjects themselves (self-triggered perturbations). To maintain balance, all subjects used anticipatory adjustments such as early postural muscle activation, leading to fewer steps being taken, tighter coupling of the center of pressure (COP) and the platform movements, and small COP excursions. These adjustments were found to be lacking for externally-triggered perturbations in older subjects; in these subjects the COP range was larger and more often in less safe regions at the boundaries of the base of support.