Journal of Aging and Physical Activity, 2015, 23, 187-193 http://dx.doi.org/10.1123/japa.2013-0244 © 2015 Human Kinetics, Inc.

Official Journal of ICAPA www.JAPA-Journal.com ORIGINAL RESEARCH

Relationship of Falls and Fear of Falling to Activity Limitations and Physical Inactivity in Parkinson’s Disease Mon S. Bryant, Diana H. Rintala, Jyh-Gong Hou, and Elizabeth J. Protas Aim: To investigate the relationships between falls, fear of falling, and activity limitations in individuals with Parkinson’s disease (PD). Design/methods: Cross-sectional study of individuals with mild to moderate PD (N = 83). Associations among demographic data, fall frequency, disease severity, motor impairment, ability to perform activities of daily living (ADL), Activities Balance Confidence Scale, Iowa Fatigue Scale, Comorbidity Index, and Physical Activity Scale for Elders were studied. Results: Frequent fallers had more ADL limitations than nonfallers (p < .001) and rare fallers (p = .004). Frequent fallers reported a lower percentage of ability to perform ADL than nonfallers (p = .003). Frequent fallers and rare fallers were less physically active than nonfallers (p = .015 and p = .040, respectively). Frequent fallers and rare fallers reported a higher level of fear of falling than nonfallers (p = .031 and p = .009, respectively). Conclusions: Falls and fear of falling were associated with more ADL limitations and less physical activity after adjusting for physical impairments. Keywords: Parkinson’s disease, falls, fear of falling, physical inactivity, activities of daily living

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by cardinal features including tremor, rigidity, bradykinesia, and postural instability. These motor impairments gradually compromise general mobility and functional activities. In addition, PD is one of the most common neurological disorders leading to falls (Syrjälä, Luukinen, Pyhtinen, & Tolonen, 2003) due to gait disturbances and postural instability (Stolze et al., 2004). Falls can lead to physical injuries, restriction in activities of daily living (ADL), and functional decline (Grimbergen, Munneke, & Bloem, 2004). In one study, fear of falling was reported by 45.8% of the patients with PD, and 44.1% of the patients reported reduced daily activities as a result of falling (Bloem et al., 2001). The negative impact of gait disorders and the risk of falling on quality of life, including loss of independence, are widely recognized (Michałowska, Fiszer, Krygowska-Wajs, & Owczarek, 2005). Fear of future falls is an underestimated consequence of falling (Grimbergen et al., 2004). Nilsson and colleagues reported that experiencing falls and the fear of falling led to activity avoidance in individuals with PD (Nilsson, Drake, & Hagell, 2010). These factors may therefore cause self-imposed restriction of daily activity, decrease other physical activities (Bloem & Bhatia, 2004), and incline individuals with PD toward a sedentary lifestyle (Speelman et al., 2011). Patients with PD have been found to be 29% less physically active than controls (van Nimwegen et al., 2011). Disease severity, gait impairment, and disability in activities of daily living are associated with decreased daily physical activity (van Nimwegen et al., 2011). There have been a few studies on Bryant is with Research Service, Michael E. DeBakey Veterans Affairs Medical Center, Houston, TX; the Department of Physical Medicine & Rehabilitation, Baylor College of Medicine, Houston, TX; and the School of Health Professions, University of Texas Medical Branch, Galveston, TX. Rintala is with the Department of Physical Medicine & Rehabilitation, Baylor College of Medicine, Houston, TX. Hou is with Lehigh Neurology, Lehigh Valley Health Network, Allentown, PA. Protas is with the School of Health Professions, University of Texas Medical Branch, Galveston, TX. Address author correspondence to Mon S. Bryant at [email protected].

physical activity limitations in relation to gait impairment, disease severity, and freezing of gait (Tan, McGinley, Danoudis, Iansek, & Morris, 2011; Ellis et al., 2011; Hiorth, Lode, & Larsen, 2013), but not to frequency of falls. Fatigue is common in PD and has been reported by 37–58% of patients (Beiske, Loge, Hjermstad & Svensson, 2010). Fatigue might cause reduction in the level of physical activity. In this study, we also investigated its contribution to the level of physical activity. Understanding the relationship of falls and fear of falling to activity limitations and physical activity might encourage clinicians to assess these problems and design and evaluate interventions to overcome them. The purposes of this study were to: (1) assess the extent of activity limitations in individuals with PD who experienced falls and (2) identify factors associated with activity limitation and physical inactivity. We hypothesized that (1) frequent fallers would have more ADL limitation and less physical activity compared with those who fell less often, (2) a greater fear of falling and higher levels of fatigue would have a similar negative impact on these outcomes, and (3) fall frequency and fear of falling would account for significant proportions of variation in the outcome measures after accounting for physical limitations.

Methods Participants Eighty-three individuals with idiopathic PD were recruited from outpatient movement disorder clinics and PD support groups in the areas of Houston and Galveston, Texas from 2008 to 2011. All participants were diagnosed with idiopathic PD and received pharmacological therapy. All were able to ambulate independently and were community-dwelling individuals with PD. Persons who lived in skilled nursing facilities were not included in the study. All participants were able to follow instructions and independently respond to questionnaires. Individuals with severe cognitive deficits were excluded by using the Neurobehavioral Cognitive Status Examination (Cognistat; Oehlert et al., 1997). 187

188  Bryant et al.

Procedures All participants read and signed an approved consent form before participation. The study was approved by the Institutional Review Boards for Human Subject Research for Baylor College of Medicine and Affiliated Hospitals and the University of Texas Medical Branch. The Unified Parkinson Disease Rating Scale (UPDRS; Fahn et al., 1987) was administered by a neurologist with expertise in PD and movement disorders. The Cognistat was administered by a neuropsychologist. A research assistant asked the participants about their medical history and administered questionnaires, which assessed demographic status, years since diagnosis of PD, comorbidity, fatigue, fear of falling, and physical activity.

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Outcome Measures—Activity Limitation and Physical Activity Activity limitation was assessed by the UPDRS-ADL Scale (UPDRS Section II; items 5–17) and the Schwab and England Activities of Daily Living Scale (SE-ADL; UPDRS Section VI; Schwab & England, 1969). The UPDRS-ADL scale assesses the ability to perform a range of common ADL tasks that usually are problematic in individuals with PD, including salivation and sensory complaints. A higher score indicates greater difficulty in performing ADL. The score for item 13 (falling) was omitted in this study to prevent violation of the assumptions of independence for correlation and regression analysis. The SE-ADL is rated from 0% (bedridden with vegetative functioning) to 100% (completely independent without awareness of difficulty) and provides the overall percentage of the ability to perform ADL based primarily on independency and awareness of difficulty. The UPDRS-ADL and the SE-ADL scales are interview-based assessments. Physical activity was assessed using the Physical Activity Scale for the Elderly (PASE). It was administered by a research assistant as an interview. It measures the level of physical activity in elderly persons within the previous week. The PASE consists of 12 questions regarding the frequency and duration of various activities. The two main components of the PASE are household-related activities (e.g., housework, lawn care, home repair, gardening, and volunteer activity) and structured exercises (e.g., sports, jogging, swimming, strengthening and endurance exercises). The total score was calculated according to the instruction manual by multiplying activity frequency or duration per week, or participation in an activity (yes/ no) by empirically-derived weights. Total scores can range from 0 to 400, with higher scores reflecting higher levels of physical activity. The PASE reasonably represents the types of activities in which elderly persons usually participate (Washburn, Smith, Jette, & Janney, 1993).

Potential Correlates of Activity Limitation and Physical Activity Frequency of falling was categorized by using the score for item 13 of the UPDRS-ADL Scale, in which frequency of falling is rated using a five-point ordinal scale (0 = none; 1 = rare falling; 2 = occasionally falls, less than once per day; 3 = falls an average of once daily; and 4 = falls more than once daily). The rating was based on an interview with the participants by the neurologist. Three fall frequency groups were formed (0 = nonfallers, 1 = rare fallers, ≥ 2 = frequent fallers). The frequent fallers group combined scores of 2 or higher to avoid very small groups.

The Activities-specific Balance Confidence (ABC) Scale (Powell & Myers, 1995) was used to estimate fear of falling. The ABC scale was developed to assess subjective balance confidence, a construct similar to fear of falling (Lohnes & Earhart, 2010; Powell & Myers, 1995). Participants were asked to rate their self-perceived balance confidence level from 0 (no confidence) to 100 (complete confidence) in performing 16 activities of daily living. The mean score across all 16 activities was calculated and used to estimate the level of fear of falling (Mak & Pang, 2009). A lower mean ABC score indicates a higher level of fear of falling. The Hoehn and Yahr Staging Scale (HY; Hoehn & Yahr, 1967) was used to rate severity of PD. The scale stages the progression or severity of the disease on a 1–5 scale based on whether the symptoms are unilateral or bilateral, whether there is impairment of balance, and if there is functional capability in relation to normal activities. A particular HY stage provides a description of where an individual is in the possible progression of the disease. Motor impairment was assessed with the UPDRS-Motor score (Section III; items 18–31). The UPDRS motor section is rated by direct examination or observation. The score enables clinicians to quantify the type, number, and severity of motor impairments from PD. The Charlson Comorbidity Index (CCI; Charlson et al., 1986) is administered as an interview to obtain information and medical history to assess risk based on all diseases or illnesses the subject has. The scale is a weighted index that takes into account the number and seriousness of each comorbid disease and the age of the person to predict the risk of death. The comorbid diseases are clustered based on their clinical similarities and weights are assigned using observed mortality rates. Some of the illnesses in the scale are myocardial infarction, peripheral vascular disease, cerebral vascular disease, dementia, pulmonary disease, cancer, renal disease, diabetes, metastatic tumor, and AIDS. Higher index scores indicate more severe comorbidity. The Iowa Fatigue Scale (IFS) was used to assess level of fatigue. The IFS is an 11-item self-report questionnaire to assess level of fatigue during the past month in four domains: cognitive (e.g., I have trouble concentrating), fatigue (e.g., I feel worn out), energy (e.g., I feel energetic), and productivity (e.g., I do quite a lot within a day). Each item in the IFS is rated on an ordinal scale ranging from 1 (not at all) to 5 (extremely). Positively worded items are reverse scored. The sum of the 11 items reflects total general fatigue, with a possible range of 11–55 and higher scores reflecting more fatigue (Hartz, Bentler, & Watson, 2003).

Statistical Analysis All analyses were performed using IBM SPSS version 21.0 (IBM, Chicago, IL). Descriptive statistics for demographic and clinical variables were calculated. One-way analyses of variance (ANOVAs) with Bonferroni post hoc tests were performed to determine significant differences in the clinical variables among the three fall frequency groups (nonfallers, rare fallers, frequent fallers). A chi square analysis was performed to assess the relationship of fall frequency with sex. Relationships of the other variables with fall frequency were indicated by Spearman’s rho correlation (rs). Variables that were found to be significantly related to fall frequency were entered into a series of hierarchical multiple regression analyses to determine the contribution of frequency of falls and fear of falling to ADL limitations and level of physical activity after accounting for physical impairment (HY,

Falls, Fear of Falling, and Activity Limitations in PD   189

UPDRS-Motor, and IFS). Fall frequency was dummy coded for the regression analyses (rare fallers vs. nonfallers and frequent fallers vs. nonfallers). A two-block model using the enter method (i.e., all preselected variables entered at the same time within each block) was used in all regression analyses. The significance level for all tests was set at p < .05.

Results

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Eighty-three persons with a mild or moderate stage of PD participated in the study. Their mean UPDRS-Motor score was 18.77 ± 8.96 and their mean HY score was 2.50 ± 0.52. Fifty-nine (71.08%) were men, and 24 (28.92%) were women. Thirty-one (37.3%) were classified as nonfallers, 35 (42.2%) as rare fallers, and 17 (20.5%) as frequent fallers. Two of the frequent fallers had a score of 3 (falls an average of once a day) and the rest had a score of 2 (occasional falls).

Comparison of Demographic and Clinical Characteristics, ADL Limitations, Physical Activity, and Fear of Falling in Nonfallers, Rare Fallers, and Frequent Fallers Clinical characteristics of the three fall frequency groups are displayed in Table 1. The results of the one-way ANOVA indicated that the three groups were not significantly different in age, sex, years since diagnosis of PD, and comorbidity. There were significant differences among the groups for HY (F = 6.58, p = .002), UPDRS-Motor (F = 3.18, p = .047), IFS (F = 3.27, p = .043), UPDRS-ADL (F = 11.86, p < .001), SE-ADL (F = 6.25, p = .003), PASE (F = 5.19, p = .008), and ABC (F = 5.74,

p = .005). Pairwise comparisons among the three groups were performed for all variables that had a significant overall group difference (Table 1).

Correlations of Fall Frequency With Physical Impairment, ADL Limitations, Physical Activity, and Fear of Falling Spearman’s rho (rs) correlation analysis demonstrated that fall frequency significantly correlated with disease severity, motor impairment, fatigue, ability to perform ADL tasks, percentage of overall ability to perform ADL, level of physical activity, and level of fear of falling (Table 2).

Contribution of Falls to ADL Limitations and Physical Inactivity Variables of interest that demonstrated significant correlations with fall frequency were used in a hierarchical multiple regression analysis using the UPDRS-ADL as the dependent variable (Table 3). Physical impairments, including disease severity (HY), motor impairment (UPDRS-Motor), and fatigue (IFS) were entered in step 1 and explained 35.2% of the variation in the UPDRS-ADL scores. After fall frequency and fear of falling (ABC) were entered at step 2, the total variance explained by the model as a whole was 50.6%. Fall frequency and fear of falling explained a significant 15.3% of additional variance in ADL limitation after adjusting for physical impairment. In a similar analysis using the SE-ADL as the dependent variable, disease severity (HY), motor impairment (UPDRS-Motor), and fatigue (IFS) were entered in step 1 and explained 33.7% of the variation in SE-ADL (Table 4). After fall frequency and fear of

Table 1  Clinical Characteristics of Individuals With PD According to Fall Frequency (N = 83) Clinical Characteristics

Nonfallers (N = 31)

Rare Fallers (N = 35)

Frequent Fallers (N = 17)

69.03 ± 9.27

69.77 ± 9.08

70.71 ± 7.86

Male

20 (64.5%)

25 (71.4%)

14 (82.4%)

Female

11 (35.5%)

10 (28.6%)

3 (17.6%)

Age (years) Sexa (N and %)

Year since diagnosis of PD

7.84 ± 5.07

8.60 ± 5.38

7.15 ± 6.13

Disease severity (HY)

2.26 ± 0.48

2.60 ± 0.50+

2.74 ± 0.47*

Motor impairment (UPDRS-Motor)

16.00 ± 7.76

19.43 ± 10.19

22.47 ± 6.92*

Comorbidity (CCI)

4.61 ± 1.91

4.94 ± 2.00

5.35 ± 1.46

26.87 ± 11.98

28.49 ± 11.15

34.88 ± 5.29 *

9.68 ± 3.74

11.91 ± 5.02

16.35 ± 4.85*,++

Fatigue (IFS) Daily activity limitations (UPDRS-ADL)b Percentage of daily activity limitations (SE-ADL)

89.52 ± 6.75

83.57 ± 11.73

79.12 ± 11.76*

Physical activity (PASE)

123.68 ± 59.51

88.53 ± 57.80+

74.44 ± 46.39*

Fear of falling (ABC)

74.94 ± 16.45

58.95 ± 24.54+

58.15 ± 21.24*

Note. Figures are mean and standard deviation unless indicated otherwise. ABC = Activities-specific Balance Confidence Scale; ADL = activities of daily living; CCI = Charlson Comorbidity Index; HY = Hoehn and Yahr Scale; IFS = Iowa Fatigue Scale; PASE = Physical Activity Scale for the Elderly; PD = Parkinson’s disease; SE-ADL = Schwab and England Activities of Daily Living Scale; UPDRS = Unified Parkinson’s Disease Rating Scale. a Chi-square test. b UPDRS-ADL excluding item 13 (falling). Significant pairwise differences (p < .05): + Nonfallers vs. rare fallers; ++ Rare fallers vs. frequent fallers; * Nonfallers vs. frequent fallers.

190  Bryant et al.

falling (ABC) were entered at step 2, the total variance explained by the final model as a whole was 42.8%. Fall frequency and fear of falling explained a significant 9.1% of additional variance in the SE-ADL score after adjusting for physical impairment. In a third hierarchical multiple regression analysis using physical activity (PASE) as the dependent variable, physical impairments entered in step 1 explained 15% of the variance in the PASE scores (Table 5). After fall frequency and fear of falling were entered at step 2, the total variance explained by the model as a whole was

28.9%. Fall frequency and fear of falling explained a significant 13.9% additional variance in physical activity after adjusting for physical impairment.

Discussion Our results demonstrated that frequent falls and fear of falling were significantly associated with ADL limitations and physical inactivity, after adjusting for physical impairments. Clinical variables that significantly correlated with fall frequency were entered as independent variables in a series of hierarchical regression analyses. Our aim was to determine if fall frequency and fear of falling were significant contributors to the dependent variables assessing ADL limitations (UPDRS-ADL and SE-ADL) and physical activity (PASE). Disease severity (HY), motor impairment (UPDRS-Motor), and fatigue (IFS) were entered in the first step to control for physical impairments. Fall frequency and fear of falling (ABC) were entered in the second step. In all three regressions models, the second step significantly explained additional variability in the outcome measures. In the final models, fear of falling had a significant standardized coefficient (β) with all three dependent variables. Fall frequency (frequent fallers vs. nonfallers) and motor impairment had a significant β only with UPDRS-ADL, and disease severity (HY) had a significant β only with SE-ADL. Falls are common in individuals with PD. Sixty-two percent of the participants in this study experienced either rare falls or frequent falls (i.e., occasional falls, less than once per day or daily falls). This is similar to the incidence of falls reported by other investigators (Pickering et al., 2007; Bohnen et al., 2009; Kerr et al., 2010; Wood, Bilclough, Bowron, & Walker, 2002). Our finding on the relationship of falls with ADL limitation was in agreement with previous publications (Bloem et al., 2001; (Michałowska et al., 2005; Brozova, Stochl, Roth, & Ruzicka, 2009; Hiorth et al., 2013). Hiorth and colleagues (2013) reported that falling was associated with higher scores on the UPDRS-ADL and was an important constraint for daily activities. In a prospective study on epidemiology, clinical impact and prediction of falls, a fear of future falls, and restriction of daily activities

Table 2  Correlation Between Clinical Characteristics and Fall Frequency Spearman’s rho

(P-value)

Age

.025

.821

Sexa

1.703b

.427

Years since diagnosis of PD

–.048

.668

Disease severity (HY)

.373

.001

Motor impairment (UPDRS-Motor)

.276

.011

Comorbidity scale

.142

.199

Fatigue (IFS)

.254

.021

Daily activity limitations (UPDRS-ADL)c

.460

< .001

Percentage of daily activity limitations (SE-ADL, %)

–.396

< .001

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Clinical Characteristics

Physical activity (PASE)

–.328

.002

Fear of falling (ABC)

–.322

.003

Note. ABC = Activities-specific Balance Confidence Scale; ADL = activities of daily living; HY = Hoehn and Yahr Scale; IFS = Iowa Fatigue Scale; PASE = Physical Activity Scale for the Elderly; PD = Parkinson’s disease; SE-ADL = Schwab and England Activities of Daily Living Scale; UPDRS = Unified Parkinson’s Disease Rating Scale. a Chi-square test. b Chi-square statistic. c UPDRS-ADL excluding item 13 (falling).

Table 3  Hierarchical Multiple Regression Analysis Assessing the Variance in UPDRS-ADL Scores Explained by Fall Frequency and Fear of Falling After Accounting for Physical Impairments

Model

Independent Variables

Step 1

HY

Step 2

B

SE

β (P-value)

R2

∆R2 F of ∆R2 (df) (P-value)

0.583

0.929

.059 (.532)

.352

.352

UPDRS-Motor

0.309

0.054

.542 (< .001)

14.32 (3,79)

IFS

0.064

0.043

.136 (.142)

(< .001)

HY

–0.846

0.894

–.086 (.347)

UPDRS-Motor

0.198

0.056

.347 (.001)

7.86 (3, 76) (< .001)

IFS

0.015

0.040

.032 (.710)

Rare faller

0.726

0.999

.071 (.470)

Frequent faller

4.527

1.268

.360 (.001)

ABC

–0.069

0.024

–.300 (.005)

.506

.153

Note. ABC = Activities-specific Balance Confidence Scale; ADL = activities of daily living; HY = Hoehn and Yahr Scale; IFS = Iowa Fatigue Scale; UPDRS = Unified Parkinson’s Disease Rating Scale.

Falls, Fear of Falling, and Activity Limitations in PD   191

Table 4  Hierarchical Multiple Regression Analysis Assessing the Variance in SE-ADL Scores Explained by Fall Frequency and Fear of Falling After Accounting for Physical Impairments

Model

Independent Variables

Step 1

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Step 2

B

SE

β (P-value)

R2

HY

–10.827

1.984

–.520 (< .000)

.337

UPDRS-Motor

–0.186

0.116

–.154 (.112)

IFS

0.007

0.092

.007 (.941)

HY

–8.572

2.032

–.411 (< .000)

∆R2 F of ∆R2 (df) (P-value) .337 13.41 (3, 79) (< .001)

.428

.091

UPDRS-Motor

0.035

0.128

.029 (.786)

4.01 (3, 76)

IFS

0.067

0.090

.068 (.459)

(.011)

Rare faller

–0.698

2.27

–.032 (.759)

Frequent faller

–4.399

2.88

–.166 (.131)

ABC

0.159

0.054

.329 (.004)

Note. ABC = Activities-specific Balance Confidence Scale; HY = Hoehn and Yahr Scale; IFS = Iowa Fatigue Scale; SE-ADL = Schwab and England Activities of Daily Living Scale; UPDRS = Unified Parkinson’s Disease Rating Scale.

Table 5  Hierarchical Multiple Regression Analysis Assessing the Variance in PASE Scores Explained by Fall Frequency and Fear of Falling After Accounting for Physical Impairments

B

SE

β (P-value)

R2

∆R2 F of ∆R2 (df) (P-value)

HY

–41.385

12.325

–.362 (.001)

.150

.15

Model

Independent Variables

Step 1

Step 2

UPDRS-Motor

–0.376

0.718

–.057 (.602)

4.65 (3, 79)

IFS

0.472

0.569

.087 (.409)

(.005)

HY

–24.466

12.423

–.214 (.053)

1.053

0.781

.160 (.181)

4.95 (3, 76) (.003)

UPDRS-Motor

0.881

0.551

.162 (.114)

Rare faller

IFS

–16.034

13.877

–.135 (.252)

Frequent faller

–34.856

17.610

–.239 (.051)

0.987

0.328

.373 (.004)

ABC

.289

.139

Note. ABC = Activities-specific Balance Confidence Scale; HY = Hoehn and Yahr Scale; IFS = Iowa Fatigue Scale; PASE = Physical Activity Scale for the Elderly; UPDRS = Unified Parkinson’s Disease Rating Scale.

were reported as sequelae of falls in 59 patients with PD (Bloem et al., 2001). Fear of falling was found to have the greatest impact on mobility and ADL dimensions of the Parkinson’s Disease Quality of Life Questionnaire (Brozova et al., 2009). The ABC Scale evaluates 16 functional mobility tasks that might put an individual at risk for falls (Mak & Pang, 2009) and is used to estimate fear of falling. Fear of falling is a nonepisodic, inherent mental characteristic that likely influences an individual’s behavior permanently and leads to activity restrictions (Brozova et al., 2009). Despite numerous reports on fear of falling and prediction of falls, fear of falling has not been directly investigated as having an association with ADL limitations and physical inactivity in individuals with PD. Our results clearly demonstrated that fear of falling was associated with both ADL limitations and physical inactivity.

Motor impairment and fall frequency were significantly associated with UPDRS-ADL, but not with the SE-ADL. Physical impairments including HY, UPDRS-Motor, and fatigue (IFS) accounted for 33.7% of the variation in overall activity limitation as measured by the SE-ADL. Disease severity and fear of falling significantly contributed to decreased SE-ADL, accounting for an additional 9.1% of the variance, after adjusting for physical impairments. Persons with PD had higher levels of fear of falling than healthy individuals of similar age (Adkin, Frank, & Jog, 2003), and fear of falling has been found to be associated with postural instability and decreased physical performance (Adkin et al., 2003; Jacobs, Horak, Tran, & Nutt, 2006). Fear of falling is prevalent in individuals with PD and it may lead to self-inflicted activity limitations and a sedentary lifestyle (Nilsson, Drake, & Hagell, 2010). Avoidance of

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192  Bryant et al.

activity was found to be a negative consequence of fear of falling in a prospective study in community-living elderly persons (Yardley & Smith, 2002). We reported in this study that fear of falling was associated with ADL limitations as measured by the SE-ADL more strongly than fall frequency. Fall frequency demonstrated a significant association with the UPDRS-ADL scale (excluding item 13) but failed to be a significant contributor to the variance in the SE-ADL. This discrepancy was possibly due to the specificity and constructs of the two measures. The UPDRS-ADL is a self-rated scale consisting of 13 items of a mixture of PD-related physical impairments (e.g., handwriting, speech, salivation, swallowing) and ADL items reflecting basic function and mobility (e.g., dressing, walking, eating, freezing while walking) (Hariz, Lindberg, Hariz, & Bergenheim, 2003). From a construct validity perspective, the UPDRS-ADL items appear to logically relate to balance, gait impairments, and falling (Landers et al., 2008). The SE-ADL reflects the participant’s general estimation of his or her ability to perform ADL with respect to (1) level of dependency, (2) degree of slowness, and (3) awareness of difficulty. The estimation is expressed as a percentage in 10% increments. Scores can range from 0% to 100%, with 100% representing complete independence without awareness of difficulty. This estimation does not assess specific elements that likely relate to falls as the UPDRS-ADL does. Our results demonstrated that fear of falling was associated with physical inactivity as measured by the PASE. An association between fear of falling and activity avoidance was reported previously in patients with PD, but physical activity was not measured with a standardized instrument (Rahman, Griffin, Quinn, & Jahanshahi, 2011). We demonstrated that physical impairments explained 15% of the variance in the level of physical activity. An additional 13.9% of the variance was explained by fall frequency and fear of falling. The final model explained only 28.9% of the total variance, leaving a large amount (71.1%) of unexplained variance in physical activity requiring further investigation. This suggests that other contributing factors account for variability in physical activity. Other possible factors might include socioeconomic status, accessibility, transportation, family support, and education. These variables were not investigated in this study. In brief, we did not find strong associations between our studied variables and level of physical activity. Physical activity is influenced by many factors (i.e., physical factors, psychosocial factors, and environmental factors) and therefore, strong associations with any one variable cannot be expected. Nonlinear relationships of falls and physical activity could exist in persons with PD as has been previously reported in the elderly (Graafmans, Lips, Wijlhuizen, Pluijm, & Bouter, 2003). People with PD who have higher levels of physical activity and ADL may fall more than those with lower levels of activity and ADL due to a greater exposure to environmental threats. Surprisingly, fatigue was not associated with the ADL limitations and physical inactivity. The IFS comprises four domains: cognitive, fatigue, energy, and productivity. The IFS total score might not be a good measure of the physical fatigue that is likely to contribute to decreased ADL limitations or physical inactivity. Our findings were similar to a previous report that the amount of explained variance of physical activity by fatigue was small, suggesting that fatigue is only a minor factor in the complex of behavioral aspects that affect physical activity in individuals with PD (Elbers et al., 2009). We acknowledge some limitations concerning our study. First, the sample was a cross-sectional cohort; therefore we

could not assess the possible causal direction of the relationships between frequency of falls, fear of falling, ADL limitations, and physical inactivity. Physical inactivity could have occurred before the diagnosis of PD, soon after the diagnosis of PD, or later as the PD progressed. Second, self-report might be influenced by either over- or underestimation by the individual, and is subject to recall bias and self-perceived burden. We minimized the risk of recall bias by the exclusion of severely cognitivelyimpaired persons. Third, we did not explore the living arrangements (i.e., alone versus with spouse, significant others, or other family members) because there were only six participants in the sample that lived alone. Fourth, the participants were community-dwelling persons with PD. Our results cannot be generalized to institutionalized persons with PD. Finally, environment or neighborhood characteristics were not studied. Neighborhood characteristics (e.g., green space, enjoyable scenery, safety, traffic, uneven surfaces) might have influenced the amount of outdoor physical activity.

Conclusion Despite extensive work done in the area of falls and its related factors in individuals with PD, the relationship of falls and fear of falling to activity limitations and physical inactivity have been less well explored. We examined the extent of activity limitations and physical inactivity in individuals with PD who had different fall frequencies. Frequent fallers had more advanced disease severity, more severe motor impairment, more ADL limitations, lower levels of physical activity, and higher levels of fear of falling than rare fallers and nonfallers. Activity limitations and physical inactivity were significantly correlated with fear of falling, fall frequency, and physical impairments from PD. The clinical implication is that fall history and assessment of fear of falling should be routinely evaluated due to their significant association with activity limitation and physical inactivity. Acknowledgments This work was supported partially by grant R01 HD051844 from the Eunice Kennedy Shriver National Institute of Child Health & Human Development. Dr. Bryant received research support from the Department of Veterans Affairs, Veterans Health Administration, Rehabilitation Research and Development Service, CDA-2 Grant No. B7878W (Bryant, MS), the Michael E. DeBakey VA Medical Center, Houston, TX. We thank all the participants for their time and effort. We thank Ann Charness, Steve Rivas, and Angel Fernandez for their assistance in the study.

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