Influence of lower limb isokinetic muscle strength and power on the occurrence of falls in community-dwelling older adults: A longitudinal study.

INTRODUCTION: Previous studies have highlighted the association between lower limb muscle strength and falls in older adults. However, a comprehensive understanding of the specific influence of each lower limb muscle group on fall occurrences remains lacking. OBJECTIVE: This study aimed to investigate the impact of knee, ankle, and hip muscle strength and power on falls in older adults, with the goal of identifying which muscle groups are more predictive of fall risk in this population. METHODS: This longitudinal observational study enrolled 94 community-dwelling older adults. Muscle strength and power of the ankle's plantiflexors and dorsiflexors, knee flexors and extensors, and hip flexors, extensors, adductors, and abductors were assessed using a Biodex System 4 Pro® isokinetic dynamometer. Fall occurrences were monitored through monthly telephone contact over a year. RESULTS: Participants, with a median age of 69 years (range 64-74), included 67% women, and 63.8% reported a sedentary lifestyle. Among them, 45,7% of older adults were classified as fallers. Comparative analyses revealed that non-fallers displayed significantly superior isokinetic muscle strength in the hip abductors and adductors, along with higher muscle power in the hip abductors, hip flexors, and knee flexors compared to fallers. Multivariate logistic regression analysis indicated that a 1 Nm/Kg increase in hip abductor strength reduced the chance of a fall by 86.3%, and a 1 Watt increase in hip flexor power reduced the chance of a fall by 3.6%. CONCLUSION: The findings indicate that hip abductor strength and hip flexor power can be considered protective factors against falls in independent older adults in the community. These findings may contribute to developing effective fall-prevention strategies for this population.

Immediate Effects of Lower Limb Sensory Simulation Using Smart Socks to Stabilize Gait in People with Parkinson's Disease.

People with Parkinson's disease (PD) experience gait impairment that can lead to falls and poor quality of life. Here we investigate the feasibility of using smart socks to stimulate the lower limbs of people with PD to reduce excessive step time variability during walking. We hypothesised that rythmic excitation of lower limb afferents, matched to a participant's comfortable pace, would entrain deficient neuro-muscular signals resulting in improved gait. Five people with mild to moderate PD symptoms (70 ± 9 years) were tested on medication before and after a 30-minute familierization session. Paired t-tests and Cohen's d were used to assess gait changes and report effect sizes. Participant experiences were recorded through structured interviews. Lower limb stimulation resulted in an acute 15% increase in gait speed (p=0.006, d=0.62), an 11% increase in step length (p=0.04, d=0.35), a 44% reduction in step time variability (p=0.03, d=0.91), a 22% increase in perceived gait quality (p=0.04, d=1.17), a 24% reduction in mental effort to walk (p=0.02, d=0.79) and no statistical difference for cadence (p=0.16). Participants commented positively on the benefit of stimulation during training but found that stimulation could be distracting when not walking and the socks hard to put on. While the large effects for step time variability and percieved gait quality (Cohen's d > 0.8) are promising, limitations regarding sample size, potential placebo effects and translation to the home environment should be addressed by future studies.Clinical Relevance- This study demonstrates the feasibility of using smart stimulating socks to reduce excessive step time variability in people with PD. As step time variability is a risk factor for falls, the use of smart textiles to augment future rehabilitation programs warrants further investigation.

Prefrontal and Motor Planning Cortical Activity during Stepping Tasks Is Related to Task Complexity but Not Concern about Falling in Older People: A fNIRS Study.

This study investigated the effect of concern about falling on neural efficiency during stepping in older people. Community-dwellers aged >65 years were categorised as having low (n = 71) and high (n = 28) concerns about falling based on the Iconographical Falls Efficacy Scale (IconFES 10-item, scores <19 and ≥19, respectively). Participants performed a choice stepping reaction time test (CSRT), an inhibitory CSRT (iCSRT), and a Stroop stepping test (SST)) on a computerised step mat. Cortical activity was recorded using functional near-infrared spectroscopy. There were no significant differences in stepping response times or cortical activity in the dorsolateral prefrontal cortex (DLPFC), supplementary motor area (SMA), and premotor cortex (PMC) between those with and without concern about falling. However, stepping response times and cortical activity in the PFC, SMA, and PMC were significantly higher in the SST compared with the CSRT in the whole sample. PMC activity was also higher in the SST compared to the iCSRT. These findings demonstrate that cortical activity is higher in cognitively demanding stepping tasks that require selective attention and inhibition in healthy older people. The lack of association between concern about falling and neural efficiency during stepping in this older sample may reflect their only moderate scores on the IconFES.

Combined Reactive and Volitional Step Training Improves Balance Recovery and Stepping Reaction Time in People With Parkinson's Disease: A Randomised Controlled Trial.

BACKGROUND: Falls are frequent and devastating events for people with Parkinson's disease (PD). Here, we investigated whether laboratory-based reactive step training combined with home-based volitional step training was effective in improving balance recovery and stepping ability in people with PD. METHODS: Forty-four people with idiopathic PD were randomized into intervention or control groups. Intervention participants performed unsupervised volitional step training using home-based exergames (80+ minutes/week) for 12 weeks and attended reactive step training sessions in which they were exposed to slip and trip perturbations at 4 and 8 weeks. Control participants continued their usual activities. Primary outcomes were balance recovery following an induced-trip/slip and choice stepping reaction time (CSRT) at the 12-week reassessment. Secondary outcomes comprised sensorimotor, balance, cognitive, psychological, complex stepping (inhibitory CSRT and Stroop Stepping Test [SST]), gait measures, and falls experienced in everyday life. RESULTS: At reassessment, the intervention group had significantly fewer total laboratory-induced falls and faster CSRT compared to the control group (P < .05). The intervention group also had significantly faster inhibitory CSRT and SST movement times and made fewer mistakes in the SST (P < .05). There were no significant differences in the rate of every day falls or other secondary outcome measures between the groups. CONCLUSION: Combined volitional and reactive step training improved balance recovery from an induced-perturbation, voluntary stepping time, and stepping accuracy in cognitively challenging tests in people with PD. Further research is required to determine whether such combined step training can prevent daily-life falls in this population.

Impact of mobile phone use on accidental falls risk in young adult pedestrians.

Background: Mobile phone use is known to be a distraction to pedestrians, increasing their likelihood of crossing into oncoming traffic or colliding with other people. However, the effect of using a mobile phone to text while walking on gait stability and accidental falls in young adults remains inconclusive. This study uses a 70 cm low friction slip hazard and the threat of hazard to investigate the effects of texting while walking on gait stability, the ability to recover balance after a slip hazard and accidental falls. Methods: Fifty healthy young adults performed six walking tasks, and one seated texting task in random order. The walks were conducted over a 10-m walkway. Four progressive hazard levels were used: 1) Seated; 2) Normal Walk (walking across the walkway with no threat of a slip); 3) Threat (walking with the threat of a slip); and 4) Slip (walking with an actual 70 cm slip hazard). The three walking conditions were repeated twice with and without the mobile phone texting dual-task. Gait kinematics and trunk posture were recorded using wearable sensors attached to the head, trunk, pelvis and feet. Study outcomes were analyzed using repeated measures analysis of variance with significance set to P≤.05. Results: Mobile phone use significantly impaired postural balance recovery when slipping, as demonstrated by increased trunk sway. Mobile phone use negatively impacted gait stability as demonstrated by increased step time variability and decreased harmonic ratios. Increased hazard levels also led to reduced texting accuracy. Conclusions: Using a mobile phone to text while walking may compete with locomotor tasks, threat assessment and postural balance control mechanisms, which leads to an increased risk of accidental falls in young adults. Pedestrians should therefore be discouraged through new educational and technology-based initiatives (for example a "texting lock" on detection of walking) from texting while walking on roadside footpaths and other environments where substantial hazards to safety exist.

Facilitating Access to Current, Evidence-Based Health Information for Non-English Speakers.

Scientific communication is crucial for the development of societies and the advancement of knowledge. However, many countries, and, consequently, their researchers, clinicians and community members, lack access to this information due to the information being disseminated in English rather than their native language. In this viewpoint, we aim to discuss the impacts of this problem and also outline recommendations for facilitating non-English speakers' access to current, evidence-based health information, thus extending the impact of science beyond academia. First, the authors discuss the barriers to accessing scientific health information for non-English speakers and highlight the negative impact of imposing English as a predominant language in academia. Next, the authors discuss the impacts of reduced access to clinical information for non-English speakers and how this reduced access impacts clinicians, clients, and health systems. Finally, the authors provide recommendations for enhancing access to scientific communication worldwide.

Effects of telehealth on functional capacity, mental health and quality of life among older people with dementia: LAPESI telehealth protocol for a randomized controlled trial.

BACKGROUND: Telehealth can be an alternative action at a distance that can help as a form of motor intervention, alleviating the deleterious effects arising from social distancing on functional capacity, mental health and quality of life among older people with dementia during the COVID-19 pandemic. PURPOSE: We aim to analyze the effects of a telehealth program on functional capacity, mental health and quality of life among older people with dementia and their caregivers. METHODS: seventy-eight individuals with mild and moderate dementia and their caregivers will answer an anamnesis and be evaluated through Clinical Dementia Assessment Score. They will also be evaluated by blinded examiners in terms of functional capacity (Activities of Daily Living Questionnaire and World Health Organization Disability Assessment Schedule 2.0), mental health (Mini-Mental State Examination, Clock Drawing Test, Verbal Fluency test and the Neuropsychiatric Inventor) and quality of life (Quality of Life in Alzheimer's Disease scale). Afterward, the volunteers will be randomized into the telehealth training group and the control group. The TR will perform systematic physical and cognitive exercises in 50-min sessions three times a week with professional monitoring, while the CG will receive non-systematized guidance, both for 12 weeks. Participants will be evaluated at baseline, immediately after the three-month interventions and with a 12-week follow- up. DISCUSSION: Technological approaches such as telehealth can be a viable alternative in home care service during times of pandemic. We expect that older people with dementia and their caregivers have high adherence to the telehealth program and improve their functional capacity, mental health and quality of life of older people with dementia. Telehealth is an alternative that can contribute to public policies and the development of effective intervention strategies that neutralize adverse outcomes. It can also be presented as an alternative to home care services, which could reduce demands for health resources.

A pilot investigation of reliability and validity of balance and gait assessments using telehealth with healthy older adults.

BACKGROUND: The use of telehealth has increased since the COVID-19 pandemic; however, the lack of reliable and valid tools to measure balance and gait remotely makes assessing these outcomes difficult. Thus, we investigated whether balance and gait measures used in clinical practice are reliable and valid when assessed remotely through telehealth. METHOD: In this pilot study, we investigated 15 healthy older adults who performed validated tests: Timed Up and Go simple, dual cognitive and motor tasks; Berg Balance Scale; Functional Gait Assessment and Dynamic Gait Index. The tests were assessed on two dates: (i) face-to-face, (ii) and remotely, via videoconference between 7 and 14 days after the initial assessment. Participants also undertook the Physiological Profile Assessment (PPA) to assess their risk of falling. Reliability was measured using intraclass correlation (ICC) two-way mixed with absolute agreement to contrast the score of the assessments undertaken face-to-face and remotely in real-time and recorded. We also assessed inter-rater reliability. Criterion validity was measured using Pearson correlation between the tests that were undertaken remotely and PPA. RESULTS: All tests showed good reliability between face-to-face and real-time telehealth (ICC = 0.79-0.87) and face-to-face and recorded telehealth (ICC = 0.78-0.88) assessments and good to excellent inter-rater reliability (ICC = 0.80-1.00). Correlation between the tests and PPA were significantly (p < 0.05) moderate for real-time (r = -0.68-0.64) and recorded (r = -0.69-0.71) telehealth assessments. CONCLUSIONS: The good reliability between face-to-face and remote measurements together with moderate validity of these measures to assess fall risk suggest that health professionals could use these measures to evaluate the balance and gait of healthy older adults remotely.

Assessment of Force Production in Parkinson's Disease Subtypes.

Muscle weakness is a secondary motor symptom of Parkinson's disease (PD), especially in the subtype characterized by postural instability and gait difficulty (PIGD). Since the PIGD subtype also presents worse bradykinesia, we hypothesized that it also shows a decreased rate of force development, which is linked to an increased risk of falling in PD. Therefore, we investigated the effects of PD and PD subtypes on a force production profile and correlated the force production outcomes with clinical symptoms for each PD subtype. We assessed three groups of participants: 14 healthy older adults (OA), 10 people with PD composing the PIGD group, and 14 people with PD composing the tremor-dominant group. Three knee extension maximum voluntary isometric contractions were performed in a leg extension machine equipped with a load cell to assess the force production. The outcome measures were: peak force and rate of force development (RFD) at 50 ms (RFD50), 100 ms (RFD100), and 200 ms (RFD200). We observed lower peak force, RFD50, RFD100, and RFD200 in people with PD, regardless of subtypes, compared with the OA group (p < 0.05 for all comparisons). Together, our results indicated that PD affects the capacity to produce maximal and rapid force. Therefore, future interventions should consider rehabilitation programs for people with PD based on muscle power and fast-force production, and consequently reduce the likelihood of people with PD falling from balance-related events, such as from an unsuccessful attempt to avoid a tripping hazard or a poor and slower stepping response.

Cognitive and Motor Cortical Activity During Cognitively Demanding Stepping Tasks in Older People at Low and High Risk of Falling.

Background: Choice stepping reaction time tasks are underpinned by neuropsychological, sensorimotor, and balance systems and therefore offer good indices of fall risk and physical and cognitive frailty. However, little is known of the neural mechanisms for impaired stepping and associated fall risk in older people. We investigated cognitive and motor cortical activity during cognitively demanding stepping reaction time tasks using functional near-infrared spectroscopy (fNIRS) in older people at low and high fall risk. Methods: Ninety-five older adults [mean (SD) 71.4 (4.9) years, 23 men] were categorized as low or high fall risk [based on 12-month fall history (≥2 falls) and/or Physiological Profile Assessment fall risk score ≥1]. Participants performed a choice stepping reaction time test and a more cognitively demanding Stroop stepping task on a computerized step mat. Cortical activity in cognitive [dorsolateral prefrontal cortex (DLPFC)] and motor (supplementary motor area and premotor cortex) regions was recorded using fNIRS. Stepping performance and cortical activity were contrasted between the groups and between the choice and Stroop stepping conditions. Results: Compared with the low fall risk group (n = 71), the high fall risk group (n = 24) exhibited significantly greater DLPFC activity and increased intra-individual variability in stepping response time during the Stroop stepping task. The high fall risk group DLPFC activity was greater during the performance of Stroop stepping task in comparison with choice stepping reaction time. Regardless of group, the Stroop stepping task elicited increased cortical activity in the supplementary motor area and premotor cortex together with increased mean and intra-individual variability of stepping response times. Conclusions: Older people at high fall risk exhibited increased DLPFC activity and stepping response time variability when completing a cognitively demanding stepping test compared with those at low fall risk and to a simpler choice-stepping reaction time test. This increased hemodynamic response might comprise a compensatory process for postural control deficits and/or reflect a degree of DLPFC neural inefficiency in people with increased fall risk.

Impact of COVID-19 Pandemic on Life-Space Mobility of Older Adults Living in Brazil: REMOBILIZE Study.

Background: The COVID-19 pandemic hit Brazil in a scenario of substantial socioeconomic and health inequalities. It is unknown the immediate impact of social restriction recommendations (i.e., lockdown, stay-at-home) on the life-space mobility of older people. Objective: To investigate the immediate impact of COVID-19 pandemic on life-space mobility of community-dwelling Brazilian older adults and examine the social determinants of health associated with change in life-space mobility. Design: Baseline data from a prospective cohort study (REMOBILIZE Study). Setting: Community. Subject: A convenience snowball sample of participants aged 60 and older (n = 1,482) living in 22 states in Brazil. Methods: We conducted an online and phone survey using an adapted version of the Life-Space Assessment (LSA). Linear regression models were used to investigate social determinants of health on the change in LSA score. Results: Regardless of their gender and social determinants of health, participants showed a significant reduction in life-space mobility since COVID-19 pandemic outbreak. Life-space mobility reduction was higher among black individuals, those living alone and aged between 70 and 79. Other variables associated with change in life-space mobility, to a lesser extent, were sex, education and income. Conclusion: Social restriction measures due to pandemic caused substantial reduction in older adults' life-space mobility in Brazil. Social inequalities strongly affected vulnerable groups. Concerted actions should be put in place to overcome the deterioration in life-pace mobility amongst these groups. Failure in minimizing health inequalities amplified by the pandemic may jeopardize the desired achievements of the Decade of Healthy Aging.

Mild and marked executive dysfunction and falls in people with Parkinson's disease.

BACKGROUND: Executive dysfunction and risk of falling are hallmarks of Parkinson's disease (PD). However, it is unclear how executive dysfunction predisposes people with PD to falling. OBJECTIVES: To: (i) identify sensorimotor, balance, and cardiovascular risk factors for falls that discriminate between those with normal executive function and those with mild and marked executive dysfunction in people with PD and (ii) determine whether mild and marked executive dysfunction are significant risk factors for falls when adjusting for PD duration and severity and freezing of gait (FOG). METHODS: Using the Frontal Assessment Battery, 243 participants were classified into normal executive function (n = 87), mild executive dysfunction (n = 100), and marked executive dysfunction (n = 56) groups. Participants were asked if they had episodes of FOG in the last month and were assessed with the Movement Disorders Society - Unified Parkinson's Disease Rating Scale (MDS-UPDRS), the Hoehn and Yahr Scale, the physiological profile assessment, and tests of orthostatic hypotension, coordinated stability, and gait and were then followed-up prospectively for falls for 32-52 weeks. RESULTS: Several PD-specific (elevated Hoehn and Yahr stage, higher MDS-UPDRS scale scores, a history of FOG, Postural Instability and Gait Difficulty subtype, and longer PD duration), sensorimotor (poor vision, knee extension weakness, slow simple reaction time), and balance (greater postural sway and poor controlled leaning balance) factors discriminated among the normal executive function and mild and marked executive dysfunction groups. Fall rates (mean ±â€¯SD) differed significantly among the groups (normal executive function: 1.0 ±â€¯1.7; mild executive dysfunction: 2.8 ±â€¯5.2; marked executive dysfunction: 4.7 ±â€¯7.3) with the presence of both mild and marked executive dysfunction identified as significant risk factors for falls when adjusting for three measures of PD severity (Hoehn and Yahr scale scores, disease duration, and FOG). CONCLUSIONS: Several PD-specific, sensorimotor, and balance factors differed significantly among the normal, mild, and marked executive dysfunction groups and both mild and marked executive dysfunction were identified as independent risk factors for falls in people with PD.

Effect of different types of exercises on psychological and cognitive features in people with Parkinson's disease: A randomized controlled trial.

BACKGROUND: Parkinson's disease (PD) is a neurodegenerative and progressive disease marked by the presence of motor and non-motor symptoms, as psychological and cognitive impairment. Physical exercises have been prescribed as complementary therapy for PD, and the type of intervention and duration of the intervention should be taken into account. OBJECTIVE: We aimed to compare the effect of different exercise modalities (functional mobility, multimodal and cognitive) and length (4 and 8 months) on psychological and cognition in people with PD. This study followed the CONSORT extension for non-pharmacological trials. METHODS: In this randomized controlled trial, we assessed 107 participants between 2011 and 2013. At the end of 3 years, participants with PD (mild to moderate stages) who achieved the criteria were assessed considering 3 different groups of exercise: Multimodal (n=38), Functional Mobility (n=33) and Mental/Leisure (n=36). All 3 interventions were performed for 32 weeks, twice a week, with 60min for each session (64 sessions in total). Psychological and cognitive function were assessed at baseline and after 4 and 8 months. RESULTS: The Functional Mobility and Mental/Leisure training had a potential effect on maintaining cognitive function (executive function, attention and work memory). The Multimodal training did not show a benefit for cognitive features and was not even able to delay the progressive decline in cognitive functions; however, this modality had a positive effect on physical stress after 8 months of exercise. CONCLUSIONS: An intervention that requires high complexity and specific activities, such as locomotor and cognitive exercise, provides a maintenance effect against the degeneration in cognition associated with the progression of PD and thus can delay the progressive decline in cognitive function in PD.

Lockdown During COVID-19 and the Increase of Frailty in People With Neurological Conditions.

Governments around the globe have introduced quarantine, lockdown, and mandatory isolation to slow the transmission of COVID-19. These public health and policy measures aim to protect the public and vulnerable people. This perspective paper argues that the impacts of lockdown (such as social disconnection, reduced exercise, and fewer physiotherapy treatments) may be amplified for people with neurological conditions with subsequent increases in frailty. The paper outlines why this may occur, and explores how adverse impacts for these vulnerable populations may be minimized through strategies such as telehealth, exercise programs, and health policies.

People With Parkinson's Disease Exhibit Reduced Cognitive and Motor Cortical Activity When Undertaking Complex Stepping Tasks Requiring Inhibitory Control.

BACKGROUND: People with Parkinson's disease (PD) have difficulties generating quick and accurate steps in anticipation of and/or in response to environmental hazards. However, neural mechanisms underlying performance in cognitively demanding stepping tasks are unclear. OBJECTIVE: This study compared activation patterns in cognitive and motor cortical regions using functional near-infrared spectroscopy (fNIRS) between people with PD and age-matched healthy older adults (HOA) during stepping tasks. METHODS: Fifty-two people with PD and 95 HOA performed a simple choice stepping reaction time test (CSRT) and 2 cognitively demanding stepping tests (inhibitory CSRT [iCSRT] and Stroop stepping test [SST]) on a computerized step mat. Cortical activation in the dorsolateral prefrontal cortex (DLPFC), Broca's area, supplementary motor area (SMA), and premotor cortex (PMC) were recorded using fNIRS. Stepping performance and cortical activity were contrasted between groups and between the CSRT and the iCSRT and SST. RESULTS: The PD group performed worse than the HOA in all 3 stepping tests. A consistent pattern of interactions indicated differential hemodynamic responses between the groups. Compared with the CSRT, the PD group exhibited reduced DLPFC activity in the iCSRT and reduced SMA and PMC activity in the SST. The HOA exhibited increased DLPFC, SMA, and PMC activity when performing the SST in comparison with the CSRT task. CONCLUSIONS: In contrast to the HOA, the PD group demonstrated reduced cortical activity in the DLPFC, SMA, and PMC during the more complex stepping tasks requiring inhibitory control. This may reflect subcortical and/or multiple pathway damage with subsequent deficient use of cognitive and motor resources.

A consensus guide to using functional near-infrared spectroscopy in posture and gait research.

BACKGROUND: Functional near-infrared spectroscopy (fNIRS) is increasingly used in the field of posture and gait to investigate patterns of cortical brain activation while people move freely. fNIRS methods, analysis and reporting of data vary greatly across studies which in turn can limit the replication of research, interpretation of findings and comparison across works. RESEARCH QUESTION AND METHODS: Considering these issues, we propose a set of practical recommendations for the conduct and reporting of fNIRS studies in posture and gait, acknowledging specific challenges related to clinical groups with posture and gait disorders. RESULTS: Our paper is organized around three main sections: 1) hardware set up and study protocols, 2) artefact removal and data processing and, 3) outcome measures, validity and reliability; it is supplemented with a detailed checklist. SIGNIFICANCE: This paper was written by a core group of members of the International Society for Posture and Gait Research and posture and gait researchers, all experienced in fNIRS research, with the intent of assisting the research community to lead innovative and impactful fNIRS studies in the field of posture and gait, whilst ensuring standardization of research.

Biomechanical analysis of sit-to-walk in different Parkinson's disease subtypes.

BACKGROUND: The Parkinson's disease Postural Instability and Gait Difficulty subtype is well-known to exhibit higher levels of gait and postural instability and higher frequency of falls. However, no studies have investigated the impact of Parkinson's disease subtypes when performing a highly-challenging postural task, such as sit-to-walk. This task is often used daily and can highlight balance impairments. Thus, the aim of this study was to compare Tremor Dominant and Postural Instability and Gait Difficulty subtypes during sit-to-walk measured by performance, kinematic and kinetic analyses. METHODS: Twenty-four people with Parkinson's disease participated in this study, and were divided into two groups: Tremor Dominant (n = 14) and Postural Instability and Gait Difficulty subtype (n = 10). They performed the sit-to-walk under a time constraint (to pick up a phone placed 4 meters away in order to answer an urgent call). Sit-to-walk overall performance, kinetic and kinematic data were assessed as outcome measures. FINDINGS: The Postural Instability and Gait Difficulty group demonstrated a slower anteroposterior center-of-mass velocity at seat-off, a longer duration of transitional phase and poorer movement fluidity. Furthermore, the Postural Instability and Gait Difficulty group showed a longer sit-to-walk total time. These results indicate that the Postural Instability and Gait Difficulty group performed the task slowly and split the task into two subtasks (sit-to-stand and walking), rather than performing a single, continuous task. INTERPRETATION: The Postural Instability and Gait Difficulty group is unable to perform the sit-to-walk continuously, which might reflect the clinical impairments observed in this Parkinson's disease subtype.