J Head Trauma Rehabil Vol. 30, No. 2, pp. E55–E61 c 2015 Wolters Kluwer Health, Inc. All rights reserved. Copyright
The Reliability, Validity, and Feasibility of Physical Activity Measurement in Adults With Traumatic Brain Injury: An Observational Study Leanne Hassett, PhD; Anne Moseley, PhD; Alison Harmer, PhD; Hidde P. van der Ploeg, PhD Objective: To determine the reliability and validity of the Physical Activity Scale for Individuals with a Physical Disability (PASIPD) in adults with severe traumatic brain injury (TBI) and estimate the proportion of the sample participants who fail to meet the World Health Organization guidelines for physical activity. Design and Participants: A single-center observational study recruited a convenience sample of 30 community-based ambulant adults with severe TBI. Protocol: Participants completed the PASIPD on 2 occasions, 1 week apart, and wore an accelerometer (ActiGraph GT3X; ActiGraph LLC, Pensacola, Florida) for the 7 days between these 2 assessments. Results: The PASIPD test-retest reliability was substantial (intraclass correlation coefficient = 0.85; 95% confidence interval, 0.70-0.92), and the correlation with the accelerometer ranged from too low to be meaningful (R = 0.09) to moderate (R = 0.57). From device-based measurement of physical activity, 56% of participants failed to meet the World Health Organization physical activity guidelines. Conclusion: The PASIPD is a reliable measure of the type of physical activity people with severe TBI participate in, but it is not a valid measure of the amount of moderate to vigorous physical activity in which they engage. Accelerometers should be used to quantify moderate to vigorous physical activity in people with TBI. Key words: brain injuries, motor activity, physiotherapy specialty, questionnaires, reproducibility of results
P
HYSICAL INACTIVITY is one of the most important global public health problems of the 21st century because inactivity has been identified as a leading risk factor globally for mortality.1,2 Worldwide, it is estimated that physical inactivity causes 6% to 10% of the major noncommunicable diseases of coronary heart disease, type 2 diabetes, and breast and colon cancer and causes 9% of premature mortality, or 5.3 million deaths
Author Affiliations: Faculty of Health Sciences, Clinical and Rehabilitation Sciences Research Group (Drs Hassett and Harmer), The George Institute for Global Health, Sydney Medical School (Drs Hassett and Moseley), and Sydney School of Public Health (Dr van der Ploeg), The University of Sydney, Sydney, New South Wales, Australia; and Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU Medical Center, Amsterdam, the Netherlands (Dr van der Ploeg). This study was funding by the Menzies Foundation. The authors thank clients and physiotherapy staff of the Liverpool Brain Injury Rehabilitation Unit, and Christy Bruce and Anna Wong, from the Liverpool Hospital Physiotherapy Department. The authors declare no conflicts of interest. Corresponding Author: Leanne Hassett, PhD, Discipline of Physiotherapy, Faculty of Health Sciences, The University of Sydney, 75 East St, Lidcombe, Sydney, New South Wales 2141, Australia ([email protected]). DOI: 10.1097/HTR.0000000000000047
in 2008.3 The World Health Organization’s (WHO’s) global recommendations for physical activity state that adults aged 18 to 64 years should undertake at least 150 minutes of moderate-intensity, or at least 75 minutes of vigorous-intensity, physical activity throughout the week (or an equivalent combination of the two).2 The WHO also recommends that this activity is accumulated in bouts of at least 10 minutes. At present, it is estimated globally that about 31% of adults fail to meet this level of physical activity,4 and among people with disabilities, exact figures are not available, but some studies report figures that are twice as high.5 People with disability from severe traumatic brain injury (TBI) are likely to be restricted in their participation in daily physical activities due to the sequelae of their injury, as well as environmental and societal barriers.6,7 For example, it may be difficult to walk to the local shops due to both the physical impairment of poor balance and an environmental barrier such as uneven footpaths. The cognitive impairment of diminished drive and the behavioral disturbance of depression may also decrease the likelihood of those with severe TBI leaving their home to be physically active. Over time, this physical inactivity is likely to lead to decreased aerobic capacity8,9 and increased body mass index,10 which, in turn, E55
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may lead to further physical inactivity. The probable consequences of physical inactivity in this population are decreases in general health status leading to increased risk of death,11 decreased quality of life, and increased lifetime cost of the injury, which is already estimated in Australia to cost $4.8 million.12 Studies measuring physical activity levels in people with severe TBI confirm that larger proportions are classified as inactive compared with able-bodied groups.13–16 However, these estimates are based on subjective recall data (self-report measurement). It is unclear how valid these estimates are among people with severe TBI, given the cognitive impairments that may impact on their ability to recall their physical activity over 7 days. Despite 23% of research on physical activity in TBI being focused on measurement, the accuracy (reliability and validity) of self-report-based measures has not been established.13 Therefore, the primary aim of this study was to test the reliability and validity of a subjective selfreport–based measure of physical activity (the Physical Activity Scale for Individuals with a Physical Disability [PASIPD]) against an objective measure (accelerometer) in adults with severe TBI. The secondary aims were to determine the feasibility of collecting objective, devicebased physical activity measures (using accelerometry) in adults with severe TBI and to measure the level of physical activity within this sample. METHODS Design and participants A single-center observational study was conducted. Current or past clients of the Liverpool Brain Injury Rehabilitation Unit, Sydney, Australia, were invited to participate if they fulfilled the following eligibility criteria: (1) sustained at least a very severe TBI (ie, posttraumatic amnesia period >1 week assessed using the Modified Oxford Post-Traumatic Amnesia Scale17 ) more than 1 year ago; (2) living in the community and cohabitating with at least 1 person (to enable assistance with application of the device-based measure of physical activity); (3) aged between 15 and 65 years; (4) able to complete a 6-minute walk test with or without walking aids; (5) written medical clearance; (6) classified as a low or moderate risk with exercise testing18 ; and (7) were not participants in an earlier study.8 Thirty participants were considered the minimum number required for this validation study. Those clients who agreed to participate provided written informed consent. Ethical approval was obtained from the South Western Sydney Local Health District Human Research Ethics Committee. Protocol Each participant attended the Liverpool Brain Injury Rehabilitation Unit twice, approximately 1 week
apart. The first session comprised collection of demographic and anthropometric data; cardiovascular risk screening18 ; a 6-minute walk test; and an interview to complete the self-report–based measure of physical activity: the PASIPD.19,20 Participants were also fitted with a device-based measure of physical activity: an accelerometer (ActiGraph GT3X; ActiGraph LLC, Pensacola, Florida). They were familiarized with the operation of the accelerometer and were provided with written instructions on its usage. Participants were asked to wear the accelerometer during waking hours (except when showering, bathing, or swimming) for the 7 days following the first session while maintaining their typical weekly schedule. At a predetermined time each morning, participants were sent daily SMS (short message service) reminders to apply the accelerometer. Participants were also asked to keep a daily activity log to verify the data collected by the accelerometer. The second session involved return of the accelerometer and activity log, and an interview to complete a second PASIPD. Outcome measures Physical Activity Scale for Individuals with a Physical Disability The PASIPD is a 13-item 7-day recall physical activity questionnaire that subjectively measures physical activity completed in the domains of transport, leisure, household, and occupation.19 The first item concerns sedentary behavior and is used to familiarize the respondent with the format of the questionnaire and is not scored. As with the Dutch version,20 we combined question 10 (lawn work or yard care) and question 11 (outdoor gardening) into a single question, as this also better represents the Australian context, thus making it a 12-item questionnaire. Each question is assigned an intensity rating in metabolic equivalents (METs) to reflect the oxygen requirements of the task relative to resting metabolism (1 MET = 3.5 mL/kg/min). For example, question 4 about moderate sport and leisure activities is assigned a MET value of 4, indicating that those types of activities require 4 times the oxygen consumption compared with at rest. The MET value is multiplied by the average hours daily (determined from the frequency and duration that the activities were performed over the 7 days), and the scores for each question are summed to provide a total physical activity score, expressed in MET hours per day. Given this questionnaire assesses total physical activity in all domains, results cannot be compared with the public health recommendation of 150 minutes of moderate-intensity leisure time physical activity per week (equating to 7.5 MET hours per week). In the study conducted by the authors of the PASIPD, who measured physical activity among 372 people with
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Accuracy of Physical Activity Measurement in Adults With TBI mixed disability, the mean PASIPD total score was 20.2 (SD = 14.5; range, 0.0-67.9) MET hours per day.19
ActiGraph accelerometer model GT3X ActiGraph GT3X is a noninvasive triaxial accelero meter that weighs 27 g with dimensions of 3.8 × 3.7 × 1.8 cm (about the size of a matchbox) that detects vertical accelerations ranging from 0.05 to 2.5 g, which are converted into activity counts per second at a frequency of 30 Hz. It also records the number of steps taken during the wear time. Participants were instructed to wear the accelerometer on the right hip, attached via an adjustable elastic belt, for 7 consecutive days during waking hours (except during water activities or bathing). Data were collected in 1-second epochs. Wearing compliance was verified by the acquired data. ActiGraph GT3X is the most researched accelerometer in the physical activity and public health field over the last 15 years and has been shown to be a valid instrument.21 Applying the Freedson cutoff points22 for determining the intensity of ambulatory physical activity, it has also been validated among people with TBI who were independent community walkers with gait inefficiencies.23
Statistical analysis Accelerometer data management Accelerometer data were analyzed using ActiLife 5 software. One-second epochs were reintegrated to 1-minute epochs for data analysis. Wear-time authentication was performed on each participant’s data set to determine whether data were to be included in the analysis. Acceptable wear time was set a priori and defined as 4 days or more of 9 hours or more per day. Data were considered as non–wear time and excluded if there were 60 consecutive minutes of zeros (indicating nonuse) or if counts exceeded 20 000 per minute (indicating malfunction). Acceptable data were analyzed to determine daily activity counts, step counts, cutoff points, and bouts of moderate to vigorous physical activity (MVPA). The cutoff points were defined using the Freedson equation22 to determine the daily time and percentage of wear time in vigorous (>5738 counts per minute), moderate (19525737 counts per minute), light (101-1951 counts per minute), and sedentary (≤100 counts per minute) physical activity. Bouts of MVPA were defined as lasting at least 10 minutes, with allowance for 2 minutes of below moderate-intensity activity. Finally, the daily accelerometer data and the recorded data in the activity log were compared for obvious inconsistencies (eg, equipment failure) and data considered erroneous were not included in the analysis.
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Data analysis Statistical Package for the Social Sciences 18 software (SPSS, Inc, Chicago, Illinois) was used for data analysis. The Shapiro-Wilk test was used to determine if the continuous data were normally distributed. Descriptive statistics (mean and SD for normally distributed continuous data and median and interquartile ranges for other data) were calculated for demographic, injury-related, 6-minute walk test, anthropometric and accelerometry data, and each domain and total score for the PASIPD. Intraclass correlation coefficient (ICC) (type 2, 1) and its 95% confidence interval (CI) were used to assess the test-retest reliability of the domains and total score for the PASIPD. The benchmarks suggested by Shrout24 for interpreting reliability were used, that is, 0.8 to 1.0 is substantial, 0.61 to 0.80 is moderate, 0.41 to 0.60 is fair, 0.11 to 0.40 is slight, and 0.00 to 0.10 is virtually none. A Bland-Altman plot was used to visualize the extent of agreement between the 2 measurements of the PASIPD.25 Spearman correlation coefficients were determined between the second PASIPD and accelerometry data to assess the validity of self-report measurement of physical activity. The benchmarks suggested by Dusick26 for interpreting Spearman coefficients were used, that is, 0.9 to 1, very strong correlation; 0.7 to 0.89, strong correlation; 0.5 to 0.69, moderate correlation; 0.3 to 0.49, moderate to low correlation; 0.16 to 0.29, weak to low correlation; and below 0.16, correlation too low to be meaningful. A scatterplot was used to visualize the relationship between the second PASIPD and the accelerometer measured time in MVPA. The accelerometer data were used to determine the proportion (95% CI) of participants who met the WHO guidelines for physical activity. Both the broad (undertake at least 150 minutes of moderate-intensity physical activity or at least 75 minutes of vigorous-intensity physical activity throughout the week) and stricter (activity is accumulated in bouts of at least 10 minutes) criteria were used.2 Confidence intervals for the proportions were computed using the Wilson score method.27 RESULTS Thirty participants were recruited and their characteristics are described in Table 1. The sample was similar to the typical TBI population,11,28 that is, mostly male participants, with injuries caused by road traffic accidents. Nineteen people (63%) had sustained an extremely severe TBI (>28 days posttraumatic amnesia) and the other 11 (37%) had sustained very severe TBI (posttraumatic amnesia 7-28 days), a median of 36 months before testing. The mean body mass index was at the upper end of normal, and their median walk speed for the 6-minute walk test was higher than reported in other studies on TBI.29–31 No participants used a walking aid to complete www.headtraumarehab.com
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Clinical characteristic of participantsa
20
TABLE 1
Value
Gender (male:female) Age, mean (SD), y Time since injury, median (IQR), mo Injury severity, length of posttraumatic amnesia, median (IQR), d Cause of injury (RTA:falls:violence) Body mass index, mean (SD), kg/m2 6-minute walk test distance,b median (IQR), m 6-minute walk test speed,b median (IQR), m/s
20:10 33 (11) 36 (20-54) 35 (17-61)
+1.96 SD 10.6
10 5
Mean 0
0.9
–5 –1.96 SD –8.9
–10
17:6:7 –15
24.7 (4.8)
0
10
20
30
40
Mean of PASIPD1 and PASIPD2
573 (514-630) 1.6 (1.4-1.8)
Abbreviations: IQR, interquartile range; RTA, road traffic accidents. a n = 30 unless otherwise specified. b n = 29.
the 6-minute walk test; however, 9 participants were observed to walk with significant gait inefficiencies. Primary aim: Reliability and validity of the PASIPD The first and second PASIPD scores were collected for all participants. The PASIPD total score test-retest reliability was substantial, with an ICC of 0.85 (95% CI, 0.70-0.92). The PASIPD domains of physical activity test-retest reliability were fair for active transport (ICC = 0.55; 95% CI, 0.24-0.76), moderate for occupation (ICC = 0.73; 95% CI, 0.51-0.86) and leisure (ICC = 0.79; 95% CI, 0.60-0.89), and substantial for household TABLE 2
PASIPD1–PASIPD2
Variable
15
Figure 1. Bland-Altman plot comparing PASIPD in MET hours per day collected on 2 occasions 1 week apart. MET indicates metabolic equivalents; MVPA, moderate to vigorous physical activity; PASIPD, Physical Activity Scale for Individuals with a Physical Disability; PASIPD2, second assessment PASIPD.
(ICC = 0.89; 95% CI, 0.78-0.95). Bland-Altman analysis (see Figure 1) of the first and second PASIPD total score data showed good levels of agreement, with the mean difference between measurements being 0.9 MET hours per day and 24 of the 30 (80%) data points being within ±5 MET hours per day. The 95% limits of agreement were 10.6 and −8.9 MET hours per day, with only 2 data points falling outside of these limits. The correlation between the second PASIPD and the accelerometry data was too low to be meaningful for time in MVPA, weak to low for activity counts per day and step count per day, and moderate for the percentage of time in sedentary and light physical activity (see Table 2; Figure 2).
Values and correlations of the PASIPD and accelerometry data
Outcome PASIPD First assessment Second assessment (PASIPD2) Accelerometer Activity counts per day Step count per day Time in MVPA per day, min Percentage of wear time spent in sedentary activity Percentage of wear time spent in light activity
n
Mean (SD)
30 30
13.6 (9.0) 12.5 (8.8)
25 25 25 25
237 272 (103 698) 6 830 (2 803) 29 (21) 64.8 (8.7)
25
31.5 (8.2)
Spearman correlation with PASIPD2
0.23 0.26 0.09 − 0.57a 0.57a
Abbreviations: MVPA, moderate to vigorous physical activity; PASIPD, Physical Activity Scale for Individuals with a Physical Disability; PASIPD2, second assessment PASIPD. a P < .01.
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Accuracy of Physical Activity Measurement in Adults With TBI
Figure 2. Scatterplot of second PASIPD against average time in MVPA per day measured with the accelerometer. The 3 unshaded points represent PASIPD2 scores less than 10 but average time in MVPA 60 minutes or more per day. MVPA indicates moderate to vigorous physical activity; PASIPD, Physical Activity Scale for Individuals with a Physical Disability; PASIPD2, second assessment PASIPD.
Secondary aim: Feasibility of device-based measurement Acceptable accelerometry data (≥4 days of ≥9 hours per day) were collected from 26 participants (87%). However, data were lost for 1 participant consequent to an error that occurred when reintegrating from a 1-second to 1-minute epoch length. Accelerometer data (activity counts and step counts) were subjectively compared with activity logs, and days of reported high and low activity matched well. The 4 participants who failed to meet our a priori definition of acceptable data had acceptable data only for 1 day (2 participants), 2 days (1 participant), and 3 days (1 participant). Among the 25 participants with acceptable data, the mean number of wear days was 6.1 (SD = 0.8) and the mean number of hours the accelerometer was worn per day was 13.2 (SD = 1.2). Secondary aim: Level of physical activity On the basis of the self-report measurement of physical activity, physical activity occurred in all 4 domains (transport, leisure, household, and occupational); however, total levels were low (mean second PASIPD score = 12.5 (SD = 8.8) MET hours per day). The most frequently reported domains of physical activity were active transport (97%), light housework (87%), and moderate leisure sport/recreation (83%) and the least reported domain was household home repairs (10%) (see Figure 3). On the basis of the device-based measurement, 56% of participants (95% CI, 37-73) failed to meet the global guidelines for physical activity in adults aged 18 to 64 years (ie, at least 150 minutes of moderate-intensity physical activity per week). If the stricter criterion for these guidelines is used (ie, accumulated in bouts of at least 10 minutes), 92% of participants (95% CI, 75-98) failed to meet the guidelines.
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Figure 3. Frequencies of answers (often, sometimes, seldom, never) given per question of the second the Physical Activity Scale for Individuals with a Physical Disability; ranked in order from most frequently participated to least participated.
DISCUSSION The main finding of this study is that the PASIPD is a reliable measure of the type (or domains) of physical activity people with severe TBI participate in but is not a valid measure of the amount of MVPA in which they engage. Importantly, this study also showed that it is feasible to collect device-based measurement of physical activity in people with severe TBI (acceptable wear-time accelerometry data collected for 26/30 participants) with the support of daily SMS reminders. This adherence rate is greater than that achieved in studies among the general population: for example, only 68% of participants in a large American population-based study wore the accelerometer for the acceptable 4 days of 10 hours per day wear time.32 These findings indicate that objective measures, that is, accelerometers, should be used to quantify MVPA in studies of people with TBI. This will allow accurate determination of the percentage of people with TBI who meet physical activity guidelines. In addition, questionnaires such as the PASIPD can be used to provide complementary and important information regarding the types of physical activity that comprise a person’s regular physical activity but cannot be used to assess whether physical activity guidelines have been achieved. Weak correlations between device-based and reportbased measures of physical activity have similarly been reported in previous studies of people with disabilities20,33 and in able-bodied people.34,35 This relationship may be weak because device-based and report-based methods quantify different aspects of physical activity,36 with device-based methods measuring movement of the body part to which the device is attached and self-report methods measuring the individuals’ perception of their physical activity.36 In addition, self-report measures may be less accurate than device-based measures because of social desirability bias and because they rely on accurate recall of frequency, duration, and intensity of many physical activities over a number of days.36,37 This recall is likely to be even www.headtraumarehab.com
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more challenging for people with cognitive impairments associated with severe TBI; however, as we did not measure the extent of cognitive impairment among participants in the present study, we cannot assert this with certainty. In our study, the correlation between the PASIPD and time in MVPA (R = 0.09) was classified as too low to be meaningful but correlations were somewhat higher between the PASIPD and accelerometer counts or steps. This may be the consequence of using the Freedson equation to determine the cutoff points between sedentary, light, and moderate to vigorous physical activity. The Freedson equation was derived from walking tasks among able-bodied people; hence, it may be less accurate than newer cutoff points that categorize the intensity of nonambulatory free-living tasks38 such as cycling and gardening—tasks that participants reported in their activity logs. Even so, we chose to use the Freedson equation as it has been validated using indirect calorimetry among TBI community walkers with gait inefficiencies, albeit only in walking tasks.23 Future research using newer analytical techniques such as pattern recognition may provide more accurate estimates of ambulatory and nonambulatory physical activity among people with gait inefficiencies.39,40 Another explanation for the low correlation between the PASIPD and time in MVPA is that report-based methods measure participants’ relative intensity of a task (ie, their perception of how hard they were working in comparison with their maximal capacity) whereas device-based methods measure the absolute intensity of a task (ie, the actual acceleration of the limb converted into activity counts and classified as an absolute intensity-reflecting energy expenditure to perform the task). Among people who are deconditioned and have inefficient gait patterns, such as many of the participants in our study, the disparity between the relative and absolute intensity is likely to be greater.40 This is because for a given physical activity they will be working at a higher percentage of their peak capacity than a fitter person or a person with a normal walking pattern. Combining accelerometer data with heart rate data (such as the ActiHeart device) could be used in future research to further explore the relationship between relative and absolute intensity of physical activity in this population.
Data from the PASIPD indicated that 97% of participants reported active transport physical activity (see Figure 2). This finding is not surprising, as at least 50% of people with severe TBI do not return to driving.41 The 3 participants who spent on average 60 minutes or more in MVPA per day and scored less than 10 on the PASIPD (see Figure 2) did not drive and hence relied on active transport (ie, walking, cycling). Active transport is assigned a light-intensity weighting in the PASIPD; however, walking or cycling for transport may actually entail a moderate intensity. This study is a small, single-center study using a convenience sample of community-dwelling adults with severe TBI and thus selection bias may have influenced our results. To accurately determine the prevalence of physical inactivity and to better target interventions to address this problem, a population representative study is required. Subjective measurement of physical activity in this study demonstrated that people with TBI report low levels of physical activity, similar to the activity levels reported in other populations with neurological disorders.33,42 Objective device-based measurement revealed that the majority of people with TBI do not meet current physical activity guidelines. These findings suggest that interventions to increase physical activity in the TBI population need to be investigated, and this sentiment is echoed in a recent review on this topic that calls for future research to focus on expansion of intervention and implementation studies.13 CONCLUSION The PASIPD is a reliable measure of the type of physical activity adults with severe TBI participate in, but because of the poor validity of this instrument to determine the intensity of physical activity, accelerometers should be used to quantify MVPA in this population. However, further research is needed to increase the accuracy of device-based measurement among people with gait inefficiencies. The majority of adults with severe TBI in the current study did not meet the WHO physical activity guidelines and because of the serious implications of this risk factor for morbidity and mortality, interventions aimed at increasing physical activity need to be investigated.
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Accuracy of Physical Activity Measurement in Adults With TBI 6. Hassett LM, Moseley AM, Tate R, Harmer A. Fitness training for cardiorespiratory conditioning after traumatic brain injury. Cochrane Database Syst Rev. 2008;(2):CD006123. 7. Driver S, Ede A, Dodd Z, Stevens L, Warren AM. What barriers to physical activity do individuals with a recent brain injury face? Disabil Health J. 2012;5(2):117–125. 8. Hassett LM, Harmer AR, Moseley AM, Mackey MG. Validity of the modified 20-metre shuttle test: assessment of cardiorespiratory fitness in people who have sustained a traumatic brain injury. Brain Inj. 2007;21(10):1069–1077. 9. Mossberg KA, Ayala D, Baker T, Heard J, Masel B. Aerobic capacity after traumatic brain injury: comparison with a nondisabled cohort. Arch Phys Med Rehabil. 2007;88(3):315–320. 10. Bhambhani Y, Rowland G, Farag M. Effects of circuit training on body composition and peak cardiorespiratory responses in patients with moderate to severe traumatic brain injury. Arch Phys Med Rehabil. 2005;86(2):268–276. 11. Baguley IJ, Nott MT, Howle AA, et al. Late mortality after severe traumatic brain injury in New South Wales: a multicentre study. Med J Aust. 2012;196(1):40–45. 12. Access Economics. The Economic Cost of Spinal Cord Injury and Traumatic Brain Injury in Australia. Parkville, Victoria, Australia: The Victorian Neurotrauma Initiative, The University of Melbourne; 2009. 13. Pawlowski J, Dixon-Ibarra A, Driver S. Review of the status of physical activity research for individuals with traumatic brain injury [published online ahead of print January 15, 2013]. Arch Phys Med Rehabil. doi:10.1016/j.apmr.2013.01.005. 14. Katz-Leurer M, Rotem H, Keren O, Meyer S. Recreational physical activities among children with a history of severe traumatic brain injury. Brain Inj. 2010;24(13/14):1561–1567. 15. Reavenall S, Blake H. Determinants of physical activity participation following traumatic brain injury. Int J Ther Rehabil. 2010;17(7):360–367. 16. Gordon WA, Sliwinski M, Echo J, McLoughlin M, Sheerer MS, Meili TE. The benefits of exercise in individuals with traumatic brain injury: a retrospective study. J Head Trauma Rehabil. 1998;13(4):58–67. 17. Pfaff A, Tate RL. Manual for the Modified Oxford Post-Traumatic Amnesia Scale (MOPTAS). Sydney, New South Wales, Australia: Brain Injury Rehabilitation Unit, Liverpool Hospital; 2004. 18. American College of Sports Medicine. Guidelines for Exercise Testing and Prescription. 6th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2000. 19. Washburn RA, Zhu W, McAuley E, Frogley M, Figoni SF. The Physical Activity Scale for Individuals with Physical Disabilities: development and evaluation. Arch Phys Med Rehabil. 2002;83(2):193–200. 20. van der Ploeg HP, Streppel KR, van der Beek AJ, van der Woude LH, Vollenbroek-Hutten M, van Mechelen W. The Physical Activity Scale for Individuals with Physical Disabilities: test-retest reliability and comparison with an accelerometer. J Phys Act Health. 2007;4(1):96–100. 21. Plasqui G, Westerterp KR. Physical activity assessment with accelerometers: an evaluation against doubly labeled water. Obesity (Silver Spring). 2007;15(10):2371–2379. 22. Freedson PS, Melanson E, Sirard J. Calibration of the Computer Science and Applications, Inc., accelerometer. Med Sci Sports Exerc. 1998;30(5):777–781.
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23. Tweedy SM, Trost SG. Validity of accelerometry for measurement of activity in people with brain injury. Med Sci Sports Exerc. 2005;37(9):1474–1480. 24. Shrout PE. Measurement reliability and agreement in psychiatry. Stat Methods Med Res. 1998;7(3):301–317. 25. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1(8476):307–310. 26. Dusick DM. Introduction to Inferential Statistics. BOLD Educational Software; 2012. http://bold-ed.com/statsbook.htm. Accessed March 4, 2013. 27. Newcombe RG. Two-sided confidence intervals for the single proportion: comparison of seven methods. Stat Med. 1998;17(8):857– 872. 28. Abelson-Mitchell N. Epidemiology and prevention of head injuries: literature review. J Clin Nurs. 2008;17(1):46–57. 29. Mossberg KA. Reliability of a timed walk test in persons with acquired brain injury. Am J Phys Med Rehabil. 2003;82(5):385–390; quiz 391–392. 30. van Loo MA, Moseley AM, Bosman JM, de Bie RA, Hassett L. Test-retest reliability of walking speed, step length and step width measurement after traumatic brain injury: a pilot study. Brain Inj. 2004;18(10):1041–1048. 31. Williams G, Weragoda N, Paterson K, Clark R. Cardiovascular fitness is unrelated to mobility limitations in ambulant people with traumatic brain injury. J Head Trauma Rehabil. 2013;28(6):E1–E7. 32. Troiano RP, Berrigan D, Dodd KW, Masse LC, Tilert T, McDowell M. Physical activity in the United States measured by accelerometer. Med Sci Sports Exerc. 2008;40(1):181–188. 33. van den Berg-Emons RJ, L’Ortye AA, Buffart LM, et al. Validation of the Physical Activity Scale for Individuals with Physical Disabilities. Arch Phys Med Rehabil. 2011;92(6):923–928. 34. Ekelund U, Sepp H, Brage S, et al. Criterion-related validity of the last 7-day, short form of the International Physical Activity Questionnaire in Swedish adults. Public Health Nutr. 2006;9(2):258–265. 35. Friedenreich CM, Courneya KS, Neilson HK, et al. Reliability and validity of the Past Year Total Physical Activity Questionnaire. Am J Epidemiol. 2006;163(10):959–970. 36. Troiano RP, Pettee Gabriel KK, Welk GJ, Owen N, Sternfeld B. Reported physical activity and sedentary behavior: why do you ask? J Phys Act Health. 2012;9:S68–S75. 37. Ainsworth BE, Caspersen CJ, Matthews CE, Masse LC, Baranowski T, Zhu W. Recommendations to improve the accuracy of estimates of physical activity derived from self-report. J Phys Act Health. 2012;9:S76–S84. 38. Matthews CE. Calibration of accelerometer output for adults. Med Sci Sports Exerc. 2005;37(11)(suppl):S512–S522. 39. Freedson P, Bowles HR, Troiano R, Haskell W. Assessment of physical activity using wearable monitors: recommendations for monitor calibration and use in the field. Med Sci Sports Exerc. 2012;44(1)(suppl 1):S1–S4. 40. Strath SJ, Pfeiffer KA, Whitt-Glover MC. Accelerometer use with children, older adults, and adults with functional limitations. Med Sci Sports Exerc. 2012;44(1)(suppl 1):S77–S85. 41. Novack TA, Labbe D, Grote M, et al. Return to driving within 5 years of moderate-severe traumatic brain injury. Brain Inj. 2010;24(3):464–471. 42. Raymond J, Harmer AR, Temesi J, van Kemenade C. Glucose tolerance and physical activity level in people with spinal cord injury. Spinal Cord. 2010;48(8):591–596.
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The Reliability, Validity, and Feasibility of Physical Activity Measurement in Adults With Traumatic Brain Injury: An Observational Study Leanne Hassett, PhD; Anne Moseley, PhD; Alison Harmer, PhD; Hidde P. van der Ploeg, PhD Objective: To determine the reliability and validity of the Physical Activity Scale for Individuals with a Physical Disability (PASIPD) in adults with severe traumatic brain injury (TBI) and estimate the proportion of the sample participants who fail to meet the World Health Organization guidelines for physical activity. Design and Participants: A single-center observational study recruited a convenience sample of 30 community-based ambulant adults with severe TBI. Protocol: Participants completed the PASIPD on 2 occasions, 1 week apart, and wore an accelerometer (ActiGraph GT3X; ActiGraph LLC, Pensacola, Florida) for the 7 days between these 2 assessments. Results: The PASIPD test-retest reliability was substantial (intraclass correlation coefficient = 0.85; 95% confidence interval, 0.70-0.92), and the correlation with the accelerometer ranged from too low to be meaningful (R = 0.09) to moderate (R = 0.57). From device-based measurement of physical activity, 56% of participants failed to meet the World Health Organization physical activity guidelines. Conclusion: The PASIPD is a reliable measure of the type of physical activity people with severe TBI participate in, but it is not a valid measure of the amount of moderate to vigorous physical activity in which they engage. Accelerometers should be used to quantify moderate to vigorous physical activity in people with TBI. Key words: brain injuries, motor activity, physiotherapy specialty, questionnaires, reproducibility of results
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HYSICAL INACTIVITY is one of the most important global public health problems of the 21st century because inactivity has been identified as a leading risk factor globally for mortality.1,2 Worldwide, it is estimated that physical inactivity causes 6% to 10% of the major noncommunicable diseases of coronary heart disease, type 2 diabetes, and breast and colon cancer and causes 9% of premature mortality, or 5.3 million deaths
Author Affiliations: Faculty of Health Sciences, Clinical and Rehabilitation Sciences Research Group (Drs Hassett and Harmer), The George Institute for Global Health, Sydney Medical School (Drs Hassett and Moseley), and Sydney School of Public Health (Dr van der Ploeg), The University of Sydney, Sydney, New South Wales, Australia; and Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU Medical Center, Amsterdam, the Netherlands (Dr van der Ploeg). This study was funding by the Menzies Foundation. The authors thank clients and physiotherapy staff of the Liverpool Brain Injury Rehabilitation Unit, and Christy Bruce and Anna Wong, from the Liverpool Hospital Physiotherapy Department. The authors declare no conflicts of interest. Corresponding Author: Leanne Hassett, PhD, Discipline of Physiotherapy, Faculty of Health Sciences, The University of Sydney, 75 East St, Lidcombe, Sydney, New South Wales 2141, Australia ([email protected]). DOI: 10.1097/HTR.0000000000000047
in 2008.3 The World Health Organization’s (WHO’s) global recommendations for physical activity state that adults aged 18 to 64 years should undertake at least 150 minutes of moderate-intensity, or at least 75 minutes of vigorous-intensity, physical activity throughout the week (or an equivalent combination of the two).2 The WHO also recommends that this activity is accumulated in bouts of at least 10 minutes. At present, it is estimated globally that about 31% of adults fail to meet this level of physical activity,4 and among people with disabilities, exact figures are not available, but some studies report figures that are twice as high.5 People with disability from severe traumatic brain injury (TBI) are likely to be restricted in their participation in daily physical activities due to the sequelae of their injury, as well as environmental and societal barriers.6,7 For example, it may be difficult to walk to the local shops due to both the physical impairment of poor balance and an environmental barrier such as uneven footpaths. The cognitive impairment of diminished drive and the behavioral disturbance of depression may also decrease the likelihood of those with severe TBI leaving their home to be physically active. Over time, this physical inactivity is likely to lead to decreased aerobic capacity8,9 and increased body mass index,10 which, in turn, E55
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may lead to further physical inactivity. The probable consequences of physical inactivity in this population are decreases in general health status leading to increased risk of death,11 decreased quality of life, and increased lifetime cost of the injury, which is already estimated in Australia to cost $4.8 million.12 Studies measuring physical activity levels in people with severe TBI confirm that larger proportions are classified as inactive compared with able-bodied groups.13–16 However, these estimates are based on subjective recall data (self-report measurement). It is unclear how valid these estimates are among people with severe TBI, given the cognitive impairments that may impact on their ability to recall their physical activity over 7 days. Despite 23% of research on physical activity in TBI being focused on measurement, the accuracy (reliability and validity) of self-report-based measures has not been established.13 Therefore, the primary aim of this study was to test the reliability and validity of a subjective selfreport–based measure of physical activity (the Physical Activity Scale for Individuals with a Physical Disability [PASIPD]) against an objective measure (accelerometer) in adults with severe TBI. The secondary aims were to determine the feasibility of collecting objective, devicebased physical activity measures (using accelerometry) in adults with severe TBI and to measure the level of physical activity within this sample. METHODS Design and participants A single-center observational study was conducted. Current or past clients of the Liverpool Brain Injury Rehabilitation Unit, Sydney, Australia, were invited to participate if they fulfilled the following eligibility criteria: (1) sustained at least a very severe TBI (ie, posttraumatic amnesia period >1 week assessed using the Modified Oxford Post-Traumatic Amnesia Scale17 ) more than 1 year ago; (2) living in the community and cohabitating with at least 1 person (to enable assistance with application of the device-based measure of physical activity); (3) aged between 15 and 65 years; (4) able to complete a 6-minute walk test with or without walking aids; (5) written medical clearance; (6) classified as a low or moderate risk with exercise testing18 ; and (7) were not participants in an earlier study.8 Thirty participants were considered the minimum number required for this validation study. Those clients who agreed to participate provided written informed consent. Ethical approval was obtained from the South Western Sydney Local Health District Human Research Ethics Committee. Protocol Each participant attended the Liverpool Brain Injury Rehabilitation Unit twice, approximately 1 week
apart. The first session comprised collection of demographic and anthropometric data; cardiovascular risk screening18 ; a 6-minute walk test; and an interview to complete the self-report–based measure of physical activity: the PASIPD.19,20 Participants were also fitted with a device-based measure of physical activity: an accelerometer (ActiGraph GT3X; ActiGraph LLC, Pensacola, Florida). They were familiarized with the operation of the accelerometer and were provided with written instructions on its usage. Participants were asked to wear the accelerometer during waking hours (except when showering, bathing, or swimming) for the 7 days following the first session while maintaining their typical weekly schedule. At a predetermined time each morning, participants were sent daily SMS (short message service) reminders to apply the accelerometer. Participants were also asked to keep a daily activity log to verify the data collected by the accelerometer. The second session involved return of the accelerometer and activity log, and an interview to complete a second PASIPD. Outcome measures Physical Activity Scale for Individuals with a Physical Disability The PASIPD is a 13-item 7-day recall physical activity questionnaire that subjectively measures physical activity completed in the domains of transport, leisure, household, and occupation.19 The first item concerns sedentary behavior and is used to familiarize the respondent with the format of the questionnaire and is not scored. As with the Dutch version,20 we combined question 10 (lawn work or yard care) and question 11 (outdoor gardening) into a single question, as this also better represents the Australian context, thus making it a 12-item questionnaire. Each question is assigned an intensity rating in metabolic equivalents (METs) to reflect the oxygen requirements of the task relative to resting metabolism (1 MET = 3.5 mL/kg/min). For example, question 4 about moderate sport and leisure activities is assigned a MET value of 4, indicating that those types of activities require 4 times the oxygen consumption compared with at rest. The MET value is multiplied by the average hours daily (determined from the frequency and duration that the activities were performed over the 7 days), and the scores for each question are summed to provide a total physical activity score, expressed in MET hours per day. Given this questionnaire assesses total physical activity in all domains, results cannot be compared with the public health recommendation of 150 minutes of moderate-intensity leisure time physical activity per week (equating to 7.5 MET hours per week). In the study conducted by the authors of the PASIPD, who measured physical activity among 372 people with
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Accuracy of Physical Activity Measurement in Adults With TBI mixed disability, the mean PASIPD total score was 20.2 (SD = 14.5; range, 0.0-67.9) MET hours per day.19
ActiGraph accelerometer model GT3X ActiGraph GT3X is a noninvasive triaxial accelero meter that weighs 27 g with dimensions of 3.8 × 3.7 × 1.8 cm (about the size of a matchbox) that detects vertical accelerations ranging from 0.05 to 2.5 g, which are converted into activity counts per second at a frequency of 30 Hz. It also records the number of steps taken during the wear time. Participants were instructed to wear the accelerometer on the right hip, attached via an adjustable elastic belt, for 7 consecutive days during waking hours (except during water activities or bathing). Data were collected in 1-second epochs. Wearing compliance was verified by the acquired data. ActiGraph GT3X is the most researched accelerometer in the physical activity and public health field over the last 15 years and has been shown to be a valid instrument.21 Applying the Freedson cutoff points22 for determining the intensity of ambulatory physical activity, it has also been validated among people with TBI who were independent community walkers with gait inefficiencies.23
Statistical analysis Accelerometer data management Accelerometer data were analyzed using ActiLife 5 software. One-second epochs were reintegrated to 1-minute epochs for data analysis. Wear-time authentication was performed on each participant’s data set to determine whether data were to be included in the analysis. Acceptable wear time was set a priori and defined as 4 days or more of 9 hours or more per day. Data were considered as non–wear time and excluded if there were 60 consecutive minutes of zeros (indicating nonuse) or if counts exceeded 20 000 per minute (indicating malfunction). Acceptable data were analyzed to determine daily activity counts, step counts, cutoff points, and bouts of moderate to vigorous physical activity (MVPA). The cutoff points were defined using the Freedson equation22 to determine the daily time and percentage of wear time in vigorous (>5738 counts per minute), moderate (19525737 counts per minute), light (101-1951 counts per minute), and sedentary (≤100 counts per minute) physical activity. Bouts of MVPA were defined as lasting at least 10 minutes, with allowance for 2 minutes of below moderate-intensity activity. Finally, the daily accelerometer data and the recorded data in the activity log were compared for obvious inconsistencies (eg, equipment failure) and data considered erroneous were not included in the analysis.
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Data analysis Statistical Package for the Social Sciences 18 software (SPSS, Inc, Chicago, Illinois) was used for data analysis. The Shapiro-Wilk test was used to determine if the continuous data were normally distributed. Descriptive statistics (mean and SD for normally distributed continuous data and median and interquartile ranges for other data) were calculated for demographic, injury-related, 6-minute walk test, anthropometric and accelerometry data, and each domain and total score for the PASIPD. Intraclass correlation coefficient (ICC) (type 2, 1) and its 95% confidence interval (CI) were used to assess the test-retest reliability of the domains and total score for the PASIPD. The benchmarks suggested by Shrout24 for interpreting reliability were used, that is, 0.8 to 1.0 is substantial, 0.61 to 0.80 is moderate, 0.41 to 0.60 is fair, 0.11 to 0.40 is slight, and 0.00 to 0.10 is virtually none. A Bland-Altman plot was used to visualize the extent of agreement between the 2 measurements of the PASIPD.25 Spearman correlation coefficients were determined between the second PASIPD and accelerometry data to assess the validity of self-report measurement of physical activity. The benchmarks suggested by Dusick26 for interpreting Spearman coefficients were used, that is, 0.9 to 1, very strong correlation; 0.7 to 0.89, strong correlation; 0.5 to 0.69, moderate correlation; 0.3 to 0.49, moderate to low correlation; 0.16 to 0.29, weak to low correlation; and below 0.16, correlation too low to be meaningful. A scatterplot was used to visualize the relationship between the second PASIPD and the accelerometer measured time in MVPA. The accelerometer data were used to determine the proportion (95% CI) of participants who met the WHO guidelines for physical activity. Both the broad (undertake at least 150 minutes of moderate-intensity physical activity or at least 75 minutes of vigorous-intensity physical activity throughout the week) and stricter (activity is accumulated in bouts of at least 10 minutes) criteria were used.2 Confidence intervals for the proportions were computed using the Wilson score method.27 RESULTS Thirty participants were recruited and their characteristics are described in Table 1. The sample was similar to the typical TBI population,11,28 that is, mostly male participants, with injuries caused by road traffic accidents. Nineteen people (63%) had sustained an extremely severe TBI (>28 days posttraumatic amnesia) and the other 11 (37%) had sustained very severe TBI (posttraumatic amnesia 7-28 days), a median of 36 months before testing. The mean body mass index was at the upper end of normal, and their median walk speed for the 6-minute walk test was higher than reported in other studies on TBI.29–31 No participants used a walking aid to complete www.headtraumarehab.com
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Clinical characteristic of participantsa
20
TABLE 1
Value
Gender (male:female) Age, mean (SD), y Time since injury, median (IQR), mo Injury severity, length of posttraumatic amnesia, median (IQR), d Cause of injury (RTA:falls:violence) Body mass index, mean (SD), kg/m2 6-minute walk test distance,b median (IQR), m 6-minute walk test speed,b median (IQR), m/s
20:10 33 (11) 36 (20-54) 35 (17-61)
+1.96 SD 10.6
10 5
Mean 0
0.9
–5 –1.96 SD –8.9
–10
17:6:7 –15
24.7 (4.8)
0
10
20
30
40
Mean of PASIPD1 and PASIPD2
573 (514-630) 1.6 (1.4-1.8)
Abbreviations: IQR, interquartile range; RTA, road traffic accidents. a n = 30 unless otherwise specified. b n = 29.
the 6-minute walk test; however, 9 participants were observed to walk with significant gait inefficiencies. Primary aim: Reliability and validity of the PASIPD The first and second PASIPD scores were collected for all participants. The PASIPD total score test-retest reliability was substantial, with an ICC of 0.85 (95% CI, 0.70-0.92). The PASIPD domains of physical activity test-retest reliability were fair for active transport (ICC = 0.55; 95% CI, 0.24-0.76), moderate for occupation (ICC = 0.73; 95% CI, 0.51-0.86) and leisure (ICC = 0.79; 95% CI, 0.60-0.89), and substantial for household TABLE 2
PASIPD1–PASIPD2
Variable
15
Figure 1. Bland-Altman plot comparing PASIPD in MET hours per day collected on 2 occasions 1 week apart. MET indicates metabolic equivalents; MVPA, moderate to vigorous physical activity; PASIPD, Physical Activity Scale for Individuals with a Physical Disability; PASIPD2, second assessment PASIPD.
(ICC = 0.89; 95% CI, 0.78-0.95). Bland-Altman analysis (see Figure 1) of the first and second PASIPD total score data showed good levels of agreement, with the mean difference between measurements being 0.9 MET hours per day and 24 of the 30 (80%) data points being within ±5 MET hours per day. The 95% limits of agreement were 10.6 and −8.9 MET hours per day, with only 2 data points falling outside of these limits. The correlation between the second PASIPD and the accelerometry data was too low to be meaningful for time in MVPA, weak to low for activity counts per day and step count per day, and moderate for the percentage of time in sedentary and light physical activity (see Table 2; Figure 2).
Values and correlations of the PASIPD and accelerometry data
Outcome PASIPD First assessment Second assessment (PASIPD2) Accelerometer Activity counts per day Step count per day Time in MVPA per day, min Percentage of wear time spent in sedentary activity Percentage of wear time spent in light activity
n
Mean (SD)
30 30
13.6 (9.0) 12.5 (8.8)
25 25 25 25
237 272 (103 698) 6 830 (2 803) 29 (21) 64.8 (8.7)
25
31.5 (8.2)
Spearman correlation with PASIPD2
0.23 0.26 0.09 − 0.57a 0.57a
Abbreviations: MVPA, moderate to vigorous physical activity; PASIPD, Physical Activity Scale for Individuals with a Physical Disability; PASIPD2, second assessment PASIPD. a P < .01.
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Accuracy of Physical Activity Measurement in Adults With TBI
Figure 2. Scatterplot of second PASIPD against average time in MVPA per day measured with the accelerometer. The 3 unshaded points represent PASIPD2 scores less than 10 but average time in MVPA 60 minutes or more per day. MVPA indicates moderate to vigorous physical activity; PASIPD, Physical Activity Scale for Individuals with a Physical Disability; PASIPD2, second assessment PASIPD.
Secondary aim: Feasibility of device-based measurement Acceptable accelerometry data (≥4 days of ≥9 hours per day) were collected from 26 participants (87%). However, data were lost for 1 participant consequent to an error that occurred when reintegrating from a 1-second to 1-minute epoch length. Accelerometer data (activity counts and step counts) were subjectively compared with activity logs, and days of reported high and low activity matched well. The 4 participants who failed to meet our a priori definition of acceptable data had acceptable data only for 1 day (2 participants), 2 days (1 participant), and 3 days (1 participant). Among the 25 participants with acceptable data, the mean number of wear days was 6.1 (SD = 0.8) and the mean number of hours the accelerometer was worn per day was 13.2 (SD = 1.2). Secondary aim: Level of physical activity On the basis of the self-report measurement of physical activity, physical activity occurred in all 4 domains (transport, leisure, household, and occupational); however, total levels were low (mean second PASIPD score = 12.5 (SD = 8.8) MET hours per day). The most frequently reported domains of physical activity were active transport (97%), light housework (87%), and moderate leisure sport/recreation (83%) and the least reported domain was household home repairs (10%) (see Figure 3). On the basis of the device-based measurement, 56% of participants (95% CI, 37-73) failed to meet the global guidelines for physical activity in adults aged 18 to 64 years (ie, at least 150 minutes of moderate-intensity physical activity per week). If the stricter criterion for these guidelines is used (ie, accumulated in bouts of at least 10 minutes), 92% of participants (95% CI, 75-98) failed to meet the guidelines.
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Figure 3. Frequencies of answers (often, sometimes, seldom, never) given per question of the second the Physical Activity Scale for Individuals with a Physical Disability; ranked in order from most frequently participated to least participated.
DISCUSSION The main finding of this study is that the PASIPD is a reliable measure of the type (or domains) of physical activity people with severe TBI participate in but is not a valid measure of the amount of MVPA in which they engage. Importantly, this study also showed that it is feasible to collect device-based measurement of physical activity in people with severe TBI (acceptable wear-time accelerometry data collected for 26/30 participants) with the support of daily SMS reminders. This adherence rate is greater than that achieved in studies among the general population: for example, only 68% of participants in a large American population-based study wore the accelerometer for the acceptable 4 days of 10 hours per day wear time.32 These findings indicate that objective measures, that is, accelerometers, should be used to quantify MVPA in studies of people with TBI. This will allow accurate determination of the percentage of people with TBI who meet physical activity guidelines. In addition, questionnaires such as the PASIPD can be used to provide complementary and important information regarding the types of physical activity that comprise a person’s regular physical activity but cannot be used to assess whether physical activity guidelines have been achieved. Weak correlations between device-based and reportbased measures of physical activity have similarly been reported in previous studies of people with disabilities20,33 and in able-bodied people.34,35 This relationship may be weak because device-based and report-based methods quantify different aspects of physical activity,36 with device-based methods measuring movement of the body part to which the device is attached and self-report methods measuring the individuals’ perception of their physical activity.36 In addition, self-report measures may be less accurate than device-based measures because of social desirability bias and because they rely on accurate recall of frequency, duration, and intensity of many physical activities over a number of days.36,37 This recall is likely to be even www.headtraumarehab.com
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more challenging for people with cognitive impairments associated with severe TBI; however, as we did not measure the extent of cognitive impairment among participants in the present study, we cannot assert this with certainty. In our study, the correlation between the PASIPD and time in MVPA (R = 0.09) was classified as too low to be meaningful but correlations were somewhat higher between the PASIPD and accelerometer counts or steps. This may be the consequence of using the Freedson equation to determine the cutoff points between sedentary, light, and moderate to vigorous physical activity. The Freedson equation was derived from walking tasks among able-bodied people; hence, it may be less accurate than newer cutoff points that categorize the intensity of nonambulatory free-living tasks38 such as cycling and gardening—tasks that participants reported in their activity logs. Even so, we chose to use the Freedson equation as it has been validated using indirect calorimetry among TBI community walkers with gait inefficiencies, albeit only in walking tasks.23 Future research using newer analytical techniques such as pattern recognition may provide more accurate estimates of ambulatory and nonambulatory physical activity among people with gait inefficiencies.39,40 Another explanation for the low correlation between the PASIPD and time in MVPA is that report-based methods measure participants’ relative intensity of a task (ie, their perception of how hard they were working in comparison with their maximal capacity) whereas device-based methods measure the absolute intensity of a task (ie, the actual acceleration of the limb converted into activity counts and classified as an absolute intensity-reflecting energy expenditure to perform the task). Among people who are deconditioned and have inefficient gait patterns, such as many of the participants in our study, the disparity between the relative and absolute intensity is likely to be greater.40 This is because for a given physical activity they will be working at a higher percentage of their peak capacity than a fitter person or a person with a normal walking pattern. Combining accelerometer data with heart rate data (such as the ActiHeart device) could be used in future research to further explore the relationship between relative and absolute intensity of physical activity in this population.
Data from the PASIPD indicated that 97% of participants reported active transport physical activity (see Figure 2). This finding is not surprising, as at least 50% of people with severe TBI do not return to driving.41 The 3 participants who spent on average 60 minutes or more in MVPA per day and scored less than 10 on the PASIPD (see Figure 2) did not drive and hence relied on active transport (ie, walking, cycling). Active transport is assigned a light-intensity weighting in the PASIPD; however, walking or cycling for transport may actually entail a moderate intensity. This study is a small, single-center study using a convenience sample of community-dwelling adults with severe TBI and thus selection bias may have influenced our results. To accurately determine the prevalence of physical inactivity and to better target interventions to address this problem, a population representative study is required. Subjective measurement of physical activity in this study demonstrated that people with TBI report low levels of physical activity, similar to the activity levels reported in other populations with neurological disorders.33,42 Objective device-based measurement revealed that the majority of people with TBI do not meet current physical activity guidelines. These findings suggest that interventions to increase physical activity in the TBI population need to be investigated, and this sentiment is echoed in a recent review on this topic that calls for future research to focus on expansion of intervention and implementation studies.13 CONCLUSION The PASIPD is a reliable measure of the type of physical activity adults with severe TBI participate in, but because of the poor validity of this instrument to determine the intensity of physical activity, accelerometers should be used to quantify MVPA in this population. However, further research is needed to increase the accuracy of device-based measurement among people with gait inefficiencies. The majority of adults with severe TBI in the current study did not meet the WHO physical activity guidelines and because of the serious implications of this risk factor for morbidity and mortality, interventions aimed at increasing physical activity need to be investigated.
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