Abstract
Background Physical inactivity is a risk factor for noncommunicable diseases. Incurring an injury has been identified as a barrier to physical activity. However, it is not known which factors, if any, are associated with reduced activity among general injury populations.
Objective The 2 study objectives were: (1) to investigate changes in physical activity frequency from before an injury to 3 months after the injury and (2) to examine the association of preinjury, injury-related, and postinjury factors with reduced physical activity frequency in participants with a range of injury types.
Design This was a cohort study.
Methods Participants (N=2,856) who were 18 to 64 years of age were asked about preinjury demographic and health factors, injury-related factors, and postinjury factors. Data were collected through telephone interviewing (88%), a postal questionnaire (11%), and face-to-face interviewing (0.5%) 3 months after the injury.
Results Of the 2,793 participants for whom complete physical activity data were available, 55% (n=1,536) had reduced physical activity 3 months after the injury event. Preinjury and injury-related factors associated with a greater risk of reduced physical activity included living with non-family members; a lower extremity dislocation, sprain, or strain; and an injury with greater anatomical severity. Postinjury factors associated with reduced physical activity included greater disability, pain or discomfort, poor general health, not having returned to work, and having a worse-than-expected recovery 3 months after the injury. A large proportion (61%) of this cohort with injuries was seen by physical therapists.
Limitations Data collection was retrospective and based on participant recall.
Conclusions A large proportion of participants had reduced physical activity 3 months after the injury. Knowledge about preinjury, injury-related, and postinjury characteristics associated with reduced physical activity may help health care professionals identify people at risk of not returning to their preinjury physical activity frequency.
Physical inactivity is a risk factor for noncommunicable diseases, such as type 2 diabetes, cardiovascular diseases, and some types of cancer.1,2 The World Health Organization recommends: “Adults aged 18–64 years should do at least 150 minutes of moderate-intensity physical activity throughout the week, or do at least 75 minutes of vigorous-intensity physical activity throughout the week, or an equivalent combination of moderate- and vigorous-intensity physical activity.”3 However, worldwide, one-quarter of adults do not undertake sufficient physical activity.3 In New Zealand, the Ministry of Health recommends that adults undertake “at least 30 minutes of moderate intensity physical activity on most, if not all, days of the week.”4 Despite this recommendation, according to the New Zealand Health Survey, only 51% of people 15 years of age or older were physically active on at least 5 days of the preceding week.5
Physical inactivity is more common in high-income countries, women, and people of older ages.6 Other factors, such as health status, self-efficacy, occupation, and history of physical activity, have also been associated with levels of physical activity.7,8 Incurring an injury has been identified as a barrier to physical activity,9 and health care professionals, such as physical therapists, may consider people's physical activity levels in their treatment and rehabilitation of people after injury. It has been recommended that “all injuries should be evaluated specific to their impact on PA [physical activity].”10(p113) However, to our knowledge, it is not empirically known how physical activity levels change after injury in populations with a range of injury types or which factors are associated with a reduction in physical activity. Previous research examining physical activity after injury has largely been restricted to specific injury types (such as knee injuries related to sports or fitness activity),10 limited to hospitalized patients,11 or focused specifically on a return to sports activity12 rather than physical activity in general. A study examining a broad range of musculoskeletal injuries reported that 30.5% of men and 24.4% of women had permanently stopped their exercise program after injury.13 Factors associated with a reduction in physical activity in these studies included demographic aspects (such as occupational group11 and education level11) and injury-related aspects (such as the perceived severity of an injury13 and [within their examination of knee injuries] particular types of injuries10).
In the present study, we examined a range of injury types, including injuries requiring or not requiring hospitalization and work-related or non–work-related injuries. The aims of this study were: (1) to investigate changes in physical activity frequency from before an injury event to 3 months after the injury event and (2) to examine the association of preinjury, injury-related, and postinjury factors with reduced physical activity frequency. We hypothesized that not all participants would return to their preinjury physical activity frequency. We also hypothesized that preinjury demographic and health factors (such as older age, occupation, greater disability, and chronic conditions) would be associated with reduced physical activity after injury, that factors related to the injury itself would be associated with reduced physical activity, and that postinjury factors (such as ongoing pain or discomfort) would be associated with reduced physical activity.
Method
Participants
Participants (N=2,856) were from the Prospective Outcomes of Injury Study (POIS), a cohort study undertaken in New Zealand to examine various outcomes after injury; the POIS has been described previously.14,15 In brief, people who were 18 to 64 years of age and had incurred an injury that was likely to be serious enough to involve more than 1 week off work or some sort of rehabilitative assistance were recruited through the Accident Compensation Corporation (ACC) entitlement claims register. The ACC is New Zealand's universal no-fault accident insurer, which provides injury coverage regardless of whether the injury occurred at work, at home, recreationally, or on the road and regardless of whether the person with the injury was employed.16 Participants were recruited from 5 regions in New Zealand between 2007 and 2009. The POIS inclusion criteria required that participants had incurred, within the preceding 4 months, an injury (of any type and at any anatomical site) for which they were placed on the ACC entitlement claims register. People who had injuries that were related to self-harm or that were on the ACC sensitive-claims register (which is for mental injury caused by criminal acts)17 were excluded, as were people who spoke insufficient English or Māori.15 Initial contact with potential participants was made by the ACC, and those not opting out of the study were then contacted by POIS interviewers.15 Of the 4,881 potential participants who could be contacted by POIS interviewers, 2,856 (participation proportion: 59%) were entered into the POIS.18
Data Collection
Data regarding the injury site and type were collected from the ACC (which receives information from health care professionals). Data about hospitalization were obtained from the New Zealand Ministry of Health National Minimum Dataset. All other data were collected from participants with a questionnaire that was administered via computer-assisted telephone interviewing (88%; n=2,514), a postal questionnaire (11%; n=328), or, for a small proportion of participants (0.5%; n=14), face-to-face interviewing.15 Participants were interviewed approximately 3 months after the injury event (median=3.2 months; 25th percentile=2.5 months; 75th percentile=4.2 months). This time frame was determined by the wider POIS project, in which various outcomes were examined. Participants were asked about a range of preinjury, injury-related, and postinjury factors, including the frequency of physical activity. A team of (on average) 12 trained interviewers carried out POIS interviews, which took (on average) 60 minutes.19 Data were anonymized for analyses.
Outcome variable.
Physical activity was assessed with a question from the New Zealand Physical Activity Questionnaire (short form).20 Participants were asked about the number of days that they engaged in “at least 30 minutes of moderate activity (including brisk walking) that made you breathe a little harder than normal, or at least 15 minutes of vigorous activity that made you breathe a lot harder than normal (‘huff and puff’)” during the 7 days immediately before the injury occurred. The same question was asked for the 7 days before their 3-month interviews. In the present study, a day of being “physically active” was defined as undertaking at least 30 minutes of moderate activity or 15 minutes of vigorous activity.
Exposure variables.
Exposure variables were broadly categorized as preinjury demographic and health factors, injury-related factors, and postinjury factors; many were described in detail previously21,22 but are summarized here.
Preinjury demographic and health factors.
Sociodemographic factors included age (at the time of the interview), sex, and highest level of education. The level of education was assessed with 2 questions from the 2006 New Zealand census,23 and responses were categorized as “postsecondary school,” “secondary school,” or “none.” Participants were asked about the adequacy of their household income for their daily needs24; household income was categorized as “adequate” (if participants responded “just enough,” “enough,” or “more than enough”) or “inadequate” (if they responded “not enough”). For participants who were employed, occupation was classified as “professional,” “technical,” “trade or manual,” or “unclassified” with the New Zealand Standard Classification of Occupations.25 Participants were asked about their preinjury living arrangements,23 which were categorized as living “alone,” “with non-family members,” or “with family members” (ie, partner or relatives). Preinjury satisfaction with social relationships was assessed with a single question: “Overall, how would you rate your social relationships?” Responses were categorized as “satisfied” (if participants responded “completely satisfied” or “mostly satisfied”) or “dissatisfied” (if participants responded “neither satisfied nor dissatisfied,” “mostly dissatisfied,” or “completely dissatisfied”).
Participants were asked about a range of preinjury health factors. Preinjury general health was assessed with a single question: “In general, would you say your health before your injury was excellent, very good, good, fair, poor, or do not know?”26 Responses were categorized as “good or better” (for the response “excellent,” “very good,” or “good”) or “fair or poor” (for the response “fair” or “poor”). Self-efficacy was assessed with a modified version of the General Self-Efficacy Scale27; good self-efficacy was defined as a score of greater than 25 (possible scores: 0–40). Participants were asked 2 Diagnostic and Statistical Manual of Mental Disorders, 3rd ed (DSM-III) depression screening questions (loss of interest in daily activities and feeling sad/blue/depressed)28 and were classified as having depressive-type episodes if they answered “yes” to either question. Questions modified from the 2006/2007 New Zealand Health Survey29 were used to ask participants about the presence or absence of 21 specific health conditions (diagnosed by a physician and lasting, or expected to last, for at least 6 months); responses were categorized as “0,” “1,” or “2 or more” chronic conditions. Preinjury disability was assessed with the brief World Health Organization Disability Assessment Schedule II (score range: 0–48),30 which included 12 questions relating to the 30 days before the injury. Responses were dichotomized according to whether the summed score was <10 (no or less disability) or ≥10 (greater disability).31 Participants were asked about preinjury pain or discomfort on the day before the injury event with the relevant dimension of the EQ-5D.32 This has 3 response options (“no problems,” “some problems,” and “extreme problems”); participants who responded as having “some” or “extreme” problems were classified as having pain or discomfort.
Participants' self-reported height and weight were used to calculate the body mass index, which was categorized as <30 kg/m2 or ≥30 kg/m2.21,33 Participants who did not report either their height or their weight were categorized as having an “unknown” body mass index. Participants were asked whether they had a prior injury that was affecting them at the time of the injury for which they were recruited into the present study; possible responses were “yes,” “no,” and “do not know.”
Injury-related factors.
The anatomical site and type of injury were classified into 11 variables on the basis of the most frequent injury type and site combinations.34 Participants could have more than one injury type; the classification “yes” or “no” was applied to each type. The anatomical severity of the injury was assessed with the New Injury Severity Score (NISS)35 and categorized as 1 to 3 (least severe), 4 to 6, and greater than 6 (most severe). Hospitalization was defined as being admitted to a hospital or being treated at an emergency department for more than 3 hours within 7 days of the injury event. Participants were asked whether the injury was caused by an accident or whether it was due, or possibly due, to an assault. In addition, participants were asked whether they perceived the injury to be a threat to their life when the injury occurred and whether they perceived the injury to be a threat for long-term disability. Possible responses to each question were “yes,” “no,” “maybe/possibly,” and “do not know”; the responses “yes” or “maybe/possibly” were grouped together for analysis.
Postinjury factors.
Postinjury factors, when applicable, were assessed 3 months after the injury event with the same measures as those used for preinjury factors. These factors included disability, pain or discomfort, general health status, and satisfaction with social relationships. Participants who were in paid employment before their injury were asked whether they were back at work (“yes” or “no”). In addition, participants were asked whether they were seen by a physical therapist or an occupational therapist for their injury. Recovery expectations were assessed by asking the following question: “Overall, is your injury better or worse than you expected at this point?” Response options were categorized as “worse than expected” (for “much worse” or “somewhat worse”) or “as expected or better than expected” (for “as expected,” “somewhat better,” or “much better”).
Data Analysis
The frequency of physical activity was analyzed descriptively. Changes in physical activity frequency were assessed from the 7 days before the injury event to the 7 days before the interview 3 months after the injury event. The data were dichotomized into “physical activity not reduced” (ie, unchanged or increased) and “physical activity reduced.” Univariable analyses were undertaken with chi-square tests. Modified Poisson regression modeling was used to analyze factors associated with a reduction in physical activity.36 This type of analysis allows direct estimation of the relative risk instead of approximation through an odds ratio when the outcome variable is binary.
On the basis of previous findings6–8 and prior knowledge about likely risk factors, the variables age, sex, household income, time between the injury event and the interview, occupation, and chronic conditions were forced into each multivariable model. Initially, each exposure variable was examined separately with just the forced variables. Exposure variables with P values of less than .30 were then included in further multivariable models. This large P value threshold was used to safeguard against the possibility of eliminating variables because of the masking of confounding effects. Multivariable models were developed separately for preinjury and injury-related variables and for postinjury variables because, in practice, preinjury and injury-related information would be available at the time of the injury, whereas postinjury variables could be assessed 3 months following injury.
Including the 6 forced-in variables, the preinjury and injury-related model initially comprised 26 variables and the postinjury model comprised 14 variables. Backward stepwise elimination with a P value threshold of .10 was used to identify a subset of variables for the final multivariable models; stages of elimination were checked for contextual appropriateness. The final multivariable models included all participants for whom complete data were available for all variables in the models. Analyses were undertaken with Stata statistical software (13.1).37
Role of the Funding Source
The Prospective Outcomes of Injury Study was funded by the Health Research Council of New Zealand (2007–2013) and co-funded by the Accident Compensation Corporation of New Zealand (2007–2010).
Results
Complete data for physical activity were available for 2,793 participants (98%), and analyses were restricted to these participants. The participants' mean age was 41 years (SD=13), and 61% were men. Injuries were of a range of anatomical sites and injury types. The mean NISS value for the injuries was 3.7 (SD=3.2), and 25% of participants were hospitalized because of their injuries.
Before their injury, 55% of participants (n=1,539) reported being physically active on at least 5 of the preceding 7 days. Three months after the injury event, this proportion declined to 28% (n=778). Before their injury, 12% of participants (n=339) reported that they were not physically active on any of the preceding 7 days; 3 months after the injury event, this proportion increased to 38% (n=1,067). When the number of days of physical activity 3 months after the injury was compared with those before the injury, 55% of participants (n=1,536) decreased their frequency of physical activity, 37% (n=1,032) did not change their frequency of physical activity, and 8% (n=225) increased their frequency of physical activity (Tab. 1). Of the participants who were physically active on 5 to 7 days before their injury, 30% (n=455/1,539) were not physically active on any of the 7 days before the interview 3 months after their injury.
Numbers of Participants Undertaking at Least 30 Minutes of Moderate or 15 Minutes of Vigorous Physical Activity for 7 Days (n=2,793)
In univariable analyses, the preinjury variables associated with a change in the frequency of physical activity were age, household income, education level, social relationships, living arrangements, occupation, general health, pain or discomfort, and disability (Tab. 2). Several injury types were associated with a change in physical activity frequency; participants were less likely to have a reduced frequency of physical activity if they had an upper extremity dislocation, sprain, or strain or an upper extremity open wound. Conversely, they were more likely to have a reduced frequency of physical activity if they had a lower extremity dislocation, sprain, or strain or a lower extremity open wound. Participants who had an injury with greater anatomical severity, those who were hospitalized because of their injury, and those who perceived their injury to be a threat to their life or for disability were also more likely to have a reduced frequency of physical activity 3 months after the injury (Tab. 3).
Univariable Associations of Preinjury Factors With Physical Activity 3 Months After Injury (n=2,793)
Univariable Associations of Injury-Related Factors With Physical Activity 3 Months After Injury (n=2,793)
The postinjury variables (3 months after the injury event) associated with a greater likelihood of reduced physical activity were poor general health, greater disability, problems with pain or discomfort, and not having returned to work. Participants who were seen by a physical therapist or an occupational therapist after their injury were also more likely to have a reduced frequency of physical activity, as were participants who were dissatisfied with their social relationships and those whose recovery was worse than they expected (Tab. 4).
Univariable Associations of Postinjury Factors With Physical Activity 3 Months After Injury (n=2,793)
In the final multivariable model for preinjury and injury-related factors, participants who were 50 to 64 years of age were 10% (95% confidence interval [CI]=1%, 18%) less likely to have a reduced frequency of physical activity 3 months after the injury than those who were 18 to 29 years of age. Women were 8% (95% CI=1%, 16%) more likely to have a reduced frequency of physical activity than men. Participants living with non-family members were 15% (95% CI=4%, 27%) more likely to have a reduced frequency of physical activity than those living with family members. Participants who had an upper extremity fracture were 10% (95% CI=1%, 18%) less likely to have a reduced frequency of physical activity than those who did not have an upper extremity fracture. Participants who had a lower extremity dislocation, sprain, or strain were 11% (95% CI=3%, 20%) more likely to have a reduced frequency of physical activity than those who did not have that type of injury. A more severe injury and a perception that the injury was either a threat to life or a threat for disability also were associated with a reduced frequency of physical activity (Tab. 5).
Final Multivariable Analysis for Preinjury or Injury-Related Factors Predicting a Reduction in Physical Activity 3 Months After Injury (n=2,230)a
In the final multivariable model for postinjury factors, participants with greater disability were 40% (95% CI=29%, 51%) more likely to have a reduced frequency of physical activity than those with less or no disability. Participants with pain or discomfort were 28% (95% CI=16%, 42%) more likely to have a reduced frequency of physical activity than those without pain or discomfort. Participants with poor general health 3 months after the injury event were 12% (95% CI=4%, 20%) more likely to have a reduced frequency of physical activity than those with good general health. Participants who did not return to work and those whose recovery was worse than they expected also were more likely to have a reduced frequency of physical activity (Tab. 6).
Final Multivariable Analysis for Postinjury Factors Predicting a Reduction in Physical Activity 3 Months After Injury (n=2,488)a
Because several of these aspects may have been explained by injury severity or injury type, we undertook post hoc analyses with injury severity (NISS) and 4 injury types (upper extremity fracture; upper extremity dislocation, sprain, or strain; lower extremity fracture; and lower extremity dislocation, sprain, or strain) included in the multivariable model for postinjury factors. When these factors were included in the final model, the overall findings remained essentially unchanged. Injury severity was not statistically significant (P=.319). A lower extremity dislocation, sprain, or strain was the only 1 of the 4 injury types that was statistically significant; participants who had this type of injury had a 13% greater likelihood of reduced physical activity (95% CI=4%, 23%; P=.004) than those who did not have this type of injury.
Discussion
The main findings of the present study were that a substantial proportion of participants (55%) reported a reduction in the frequency of their physical activity 3 months after the injury. The proportion of participants who were not physically active on any of the preceding 7 days increased from 12% before the injury to 38% 3 months after the injury. Among those who were undertaking physical activity on at least 5 of the 7 days before the injury, 30% were not physically active on any of the 7 days before the interview 3 months after the injury.
Preinjury and injury-related factors associated with a higher risk of reduced physical activity included living with non-family members; a lower extremity dislocation, sprain, or strain; an injury with greater anatomical severity; and a perception that the injury was a threat to life or a threat for disability. Postinjury factors associated with a higher risk of reduced physical activity included greater disability, pain or discomfort, poor general health, not having returned to work, and having a worse-than-expected recovery 3 months after the injury.
The strengths of the present study were the inclusion of a wide range of injury types and the inclusion of a large proportion of participants (75%) with injuries that did not involve hospitalization (often studies of injury outcomes are restricted to participants recruited at a hospital).14,38 Participants were asked about a wide range of preinjury and postinjury factors. Several validated outcome measures (such as the EQ-5D32 and the World Health Organization Disability Assessment Schedule II30) were included, and physical activity data were obtained for a large proportion of participants (98%).
A limitation of the present study was that participants were asked to recall their preinjury physical activity levels (and other measures) 3 months after the injury event. Participants with poorer outcomes 3 months after the injury may have remembered their preinjury physical activity differently than those with better outcomes, leading to recall bias. However, the POIS was not specifically focused on physical activity; this variable was only one of many collected. Recalled general health status was previously examined in this cohort,39 and although there may have been an upward bias, it was found to be of a small magnitude.
Although we considered a range of potential risk factors in the present study, there may have been additional relevant factors. We did not collect data about the types of physical activity in which the participants engaged either before or after the injury event or about the specific reasons behind changes in physical activity. Although the present study included a broad range of injuries serious enough to warrant an ACC entitlement claim, we cannot necessarily generalize the study findings to people with injuries that would not be likely to involve this type of claim or to people not in the age range of the study participants (18–64 years).
The findings of the present study have clinical implications for health care providers, such as physical therapists, who treat people after an injury. Health care providers have the opportunity to help address general physical activity levels. Although some of the factors identified in the present study were not modifiable, were present before the injury event, or both, perhaps health care professionals could use them to identify people with characteristics that might increase their risk of not returning to their preinjury physical activity frequency. Targeted attention to general physical activity levels could then be provided. For example, the finding that having a more severe injury and a perception of a threat to life or a threat for disability were associated with reduced physical activity is not surprising and provides a logical explanation for reduced physical activity. However, given that a perceived threat to life and a perceived threat for disability were independently associated with reduced physical activity, even when injury severity and type were included in the model, perhaps health care professionals could consider such perceptions as prompts to focus attention on restoring preinjury physical activity levels.
The magnitude of the strength of the associations with the factors identified in the present study was relatively small and might not greatly elevate a person's risk of reduced physical activity. However, the findings should be considered in the contexts of physical inactivity being a known risk factor for noncommunicable diseases,1,2 the high prevalence and burden of noncommunicable diseases,2 the substantial proportion of participants who did not return to their preinjury physical activity frequency, and the potential opportunity for intervention. In addition, the relative risks were estimates for independent effects, and there might be high-risk combinations for people with more than one risk factor.
Many of the study participants were seen by physical therapists after their injury (61%); of those participants, a larger proportion had reduced physical activity 3 months after the injury than had unchanged or increased physical activity. This finding may reflect the injury severity or the injury type and was observed only in univariable analyses. Health care professionals, such as physical therapists, should consider ways of restoring or maintaining general physical activity levels in people with injuries, particularly those who have characteristics associated with a higher risk of reduced physical activity. For example, in the present study, we found that people with a lower limb dislocation, sprain, or strain were more likely to have a reduced frequency of physical activity 3 months after the injury; health care professionals may wish to consider how people with this type of injury can remain physically active. It may also be useful for health care policy makers to consider how to facilitate physical activity in people who have been injured (eg, by considering environments and access to facilities). Return to work is an indicator used during rehabilitation after injury. However, other indicators, such as return to preinjury physical activity levels, also are important.40 Most of the participants in the present study had injuries that did not involve hospitalization, yet the reduction in the frequency of physical activity was marked. The importance of injuries not requiring hospitalization in adverse outcomes was noted previously21,22,41 and was highlighted again in the present study.
In the present study, a large proportion of participants had a reduced frequency of physical activity 3 months after the injury, despite the fact that most of the injuries did not involve hospitalization. Preinjury, injury-related, and postinjury characteristics associated with reduced physical activity were identified. These characteristics may help health care professionals identify people at greater risk of not resuming their preinjury physical activity levels after injury and may enable them to provide additional support or intervention to these people. In future research, investigators should consider: (1) a longer follow-up after injury to determine further changes in physical activity over time and (2) strategies for improving the restoration of physical activity in people at risk of reduced physical activity after an injury. Identifying high-risk combinations of factors also should be considered.
Footnotes
Dr Harcombe and Associate Professor Derrett provided concept/idea/research design. All authors provided writing and data analysis. Associate Professor Derrett provided data collection, project management, fund procurement, and institutional liaisons. Dr Samaranayaka and Associate Professor Derrett provided consultation (including review of manuscript before submission).
This study was granted ethics approval by the New Zealand Health and Disability Multi-Region Ethics Committee (MEC/07/07/093).
The Prospective Outcomes of Injury Study was funded by the Health Research Council of New Zealand (2007–2013) and co-funded by the Accident Compensation Corporation of New Zealand (2007–2010). The views and conclusions in the article are those of the authors and may not represent those of the funding sources.
- Received February 4, 2016.
- Accepted July 7, 2016.
- © 2016 American Physical Therapy Association
References
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