Concussions are brain injuries that are caused by biomechanical impact and result in functional neurological disturbance (24). Although concussion symptom profiles are diverse and vary between individuals, there are 4 generally accepted symptom sets: cognitive (eg, difficulty thinking or remembering), somatic (eg, headache, nausea, light or sound sensitivity), mood (eg, depression or anxiety), and sleep related (eg, trouble falling or staying asleep) (24). These injuries are particularly common in pediatric populations where the incidence of concussion is rising (11,43). While the majority of pediatric concussion cases resolve within an expected 4-week window (24), nearly 30% may result in long-term symptoms (4,5,20). Delayed recovery can lead to poor academic outcomes (28), health-related quality of life (10,27,31), and mental health (12).
Accordingly, research into an effective treatment for concussion has become a priority. Submaximal aerobic exercise has recently emerged as a leading candidate for the treatment of concussion symptoms (14,18,19). The rapidly accumulating evidence on the benefits of exercise in concussion has been summarized by multiple meta-analyses (7,17,33), the most recent of which examined 23 studies (N = 2547), finding that submaximal aerobic exercise has a large, positive effect (Hedges g = 1.71) on concussion recovery (7). A paradigm shift in concussion management is occurring, wherein submaximal aerobic exercise is supplanting prolonged rest as a management strategy in both pediatric and adult concussion (18,35,40).
However, levels of habitual physical activity and sedentary time in children with concussion have not been studied using accelerometry, and we do not yet know whether these levels differ from their typically developing peers or whether they vary by sex (as do many other clinical features of concussion [16,26]). In a field where the deleterious impacts of prolonged rest on recovery are being increasingly recognized (13,33,38), a lack of knowledge of habitual physical activity and sedentary time during early recovery after pediatric concussion represents a critical knowledge gap. Not only are we unaware of whether there is a potentially symptom prolonging physical activity deficit that needs to be overcome in pediatric concussion, but we also do not know of the impact of concussion on a critical aspect of daily functioning, namely participation in routine activity. In a cohort of adults with concussion (n = 180), per a self-recall questionnaire, 85% identified as meeting physical activity guidelines preinjury, compared with 28% postconcussion (25). Similar data are not available on children. Such data, however, create the opportunity to examine whether current exercise interventions aimed at providing a once-a-day aerobic stimulus are adequate (14,18,19), or if interventions that increase levels of habitual physical activity and reduce overall sedentariness throughout the day are warranted.
Habitual physical activity can be objectively quantified using accelerometers (37,39), which permit high temporal resolution quantification of movement by measuring multiaxis accelerations. Accelerometers have been used in many pediatric neurological and chronic disease populations to compare the activity of these children with their typically developing peers (8,21,22), providing insights about the intensity, time, and frequency of physical activity that recall surveys cannot capture. In concussion, accelerometry has been used to begin to understand the relationship between concussion symptoms and activity (22,41,42), although no controlled studies have quantified levels of sedentary time and habitual physical activity.
This study was performed to characterize accelerometer-measured physical activity patterns of children with concussion (as they recovered within the first month of injury) in comparison to their healthy peers. Learning more about how natural habitual physical activity and sedentary time are accumulated within the first month after concussion can aid in clinical management and informing the next wave of exercise intervention research.
Methods
This study was approved by the Hamilton Integrated Research Ethics Board (www.hireb.ca), and informed consent/assent along with parental consent was obtained for each participant.
Design
This study is a secondary analysis of accelerometer data collected as part of a prospective cohort study (led by the senior authors) aimed at developing protocols for safe resumption of activity following pediatric concussion. At the time of injury, children with concussion were advised to follow return-to-activity guidelines in accordance with recent consensus statements (24), with no further clinical follow-up. In brief, these guidelines (24) facilitated a graduated and stepwise return-to-sport, wherein concussion patients were advised by members of our clinical team to begin with symptom-limited activities, then light aerobic exercise, then noncontact sport-specific exercises (with the ultimate goal of returning to sport). While these guidelines were developed for sport-related concussion (hence their focus on return-to-sport), they are clinically applicable to the broader concussion population, given the demonstrated benefits of exercise on symptom recovery following concussion. Therefore, we were able to observe and study habitual physical activity in children with concussion in a generalizable context, namely one wherein return-to-activity guidelines are provided acutely (in the emergency department or by a family physician) without strict enforcement or follow-up. As such, this study provides insight into habitual physical activity in children with concussion as they progress through their first month of injury.
Participants
Children (aged 6–17) presenting acutely to the emergency department at McMaster Children’s Hospital (2014–2016), or to affiliated community physicians and sports medicine clinics, who received a diagnosis of concussion were referred to the research team. Written informed consent from parents and assent/consent (as appropriate) was obtained. Exclusion criteria were more severe brain injury or complex injuries involving multiple organ systems, and clinically diagnosed neurological or developmental disorder.
Participants with a concussion were matched 1:1 with healthy controls. The healthy controls were children who participated in prior studies in our lab, either as participants in longitudinal physical activity studies of healthy children or as controls of children from clinical populations. Patients with concussion were matched to healthy controls on 3 criteria, namely chronological age, sex, and season/month the accelerometer was worn. Matching for season/month (within 60 d) was important given known accelerometer-measured seasonal variation in both sedentary and active time in children (1).
Procedures
At initial intake, participants were provided with a waist-worn accelerometer to measure habitual physical activity. More specifically, the accelerometer used was the ActiGraph GT3x, a triaxial axes accelerometer that is small, light weight, and unobtrusive during daily wear. This unit has also been shown to measure physical activity in acquired brain injury with high reproducibility (2). The accelerometer was set to record movement at 30 Hz. Participants were instructed to wear the accelerometer on their right hip while awake, except when engaged in water-based activities. Participants with concussion were asked to wear the device throughout their recovery, up to a maximum of 6 months (with devices being swapped or recharged during scheduled clinical visits to permit long-term data collection, as necessary). The current study, however, focuses on the first 4 weeks, or the expected timeframe for recovery. Healthy controls (cases from 2010 to 2020) were asked to wear the device for 7 to 9 consecutive days. Furthermore, participants were given a logbook and instructed to note every time the device was taken off and reworn. Younger children were assisted by parents, as needed, in completing the logbook.
All accelerometer data were downloaded in 3-second epochs, which were selected to reflect the median bout duration of high-intensity activities observed in children (3). Data were processed in ActiLife Software (ActiGraph). A semiautomated data cleaning procedure was used to detect any periods ≥5 minutes of zeros. Each of these bouts was inspected and only nonwear periods identified using the participant logbooks were excluded from subsequent data processing. Days with missing logbook entries were also excluded from the analysis. The manually cleaned data were then scored to determine activity by intensity, using the validated Evenson cut points (9). These cut points were scaled to 3-second epoch data, and included time spent in sedentary time (0–25 counts/15 s), light physical activity (LPA; 26–573 counts/15 s), moderate physical activity (MPA; 574–1002 counts/15 s), and vigorous physical activity (VPA; 1003+ counts/15 s).
A sedentary bout analysis was also performed to quantify the length of individual sedentary bouts and the time between them. Sedentary bouts were defined as at least 1 epoch (3 s) in length with an activity count ≤100 counts per minute, with a drop time of no more than 2 epochs. This meant that within any given sedentary bout, up to 6 seconds of nonsedentary time was ignored (ie, dropped), which would be akin to a positioning adjustment or reaching for a remote control or phone.
Data Analysis
Data were imported into SPSS Statistics for Windows (version 27, IBM Corp Released 2020). Minimum wear time criteria were ≥600 minutes of for ≥4 days (30). For hour-by-hour analyses, we included only hours with ≥50 minutes of wear time to ensure that the data were representative of the activities performed in the hour. Once the final sample of participants with valid wear data was acquired, daily average and hour-by-hour average activity and sedentary time were computed at the single-subject and group levels. Normality was assessed using Shapiro–Wilk tests, and independent sample t tests were then used to compare accelerometer data by group, at both the daily and hourly levels. More specifically, sedentary time, LPA, MPA, and VPA were compared between groups, with Bonferroni corrections to adjust for family-wise multiple comparisons. Furthermore, we examined the association between sedentary time and activity levels with days postinjury. General linear models were developed (to understand activity as a function of time postinjury) with sedentariness and activity levels as outcomes, and days postinjury and age as predictors; distribution of residuals was subsequently tested.
Results
Overview
Sixty children with concussion that met our inclusion/exclusion criteria and 60 healthy controls (from our historical database) were included in this analysis. Children with concussion wore their accelerometers for significantly longer overall; however, wear time per day was not significantly different between groups. These data along with demographics and the number of days and hours dropped from the analysis for not meeting wear time requirements, per group, are reported in Table 1. This table also provides information on the number of weekday and weekend wear days, which provides a proxy for the number of days the accelerometer was worn while in school.
Demographic and Wear Time Data
| Concussion (n = 60) | Control (n = 60) | P | |
|---|---|---|---|
| Age, y | 12.74 (2.85) | 12.43 (2.71) | .542 |
| Sex, M:F | 29:31 | 29:31 | — |
| Wear time, overall, d | 15.84 (5.79) | 7.28 (1.39) | <.001 |
| Wear time/day, min/d | 794.93 (59.37) | 797.90 (53.67) | .775 |
| Weekday:weekend, ratio | 2.95:1.00 | 2.82:1.00 | .759 |
| Days dropped, n (%) | 121 (12.5%) | 54 (12.3%) | .962 |
| Hours dropped, n (%) | 1190 (14.5%) | 909 (15.2%) | .317 |
Note: Statistical comparisons between cohorts were made using independent samples t tests as data were normally distributed.
Groupwise Activity and Inactivity Differences
Sedentary time was higher in children with concussion in comparison with healthy controls (mean difference [MD], 38.3 min/d; P = .006). Accordingly, LPA (MD, −19.5 min/d; P = .008), MPA (MD, −9.8 min/d; P < .001), and VPA (MD, −12.0 min/d; P < .001) were significantly lower in children with concussion relative to controls (Table 2). Girls with concussion were significantly more sedentary than boys with concussion (MD, 50.8 min/d; P = .010) and less active with respect to LPA (MD, −25.0 min/d; P = .010) and MPA (MD, −8.7 min/d; P = .004). There were no differences between healthy boys and girls. However, girls with concussion were significantly more sedentary and less active, across all intensities, than healthy girls (Table 3).
Group-Wise Sedentariness and Activity Levels
| Concussion, mean (SD) (n = 60) | Control, mean (SD) (n = 60) | Mean difference 95% CI | t stat (118 df) | P | |
|---|---|---|---|---|---|
| Minutes/day | |||||
| Sedentary | 618.8 (77.2) | 580.5 (72.7) | 38.3 (11.2 to 65.4) | 2.800 | .006* |
| LPA | 130.2 (42.9) | 149.7 (35.2) | −19.5 (−5.3 to −33.7) | −2.717 | .008* |
| MPA | 27.2 (10.6) | 37.0 (11.7) | −9.8 (−5.7 to −13.8) | −4.799 | <.001* |
| VPA | 18.7 (12.6) | 30.7 (15.7) | −12.0 (−6.9 to −17.2) | −4.362 | <.001* |
Abbreviations: CI, confidence interval; df, degrees of freedom; LPA, light physical activity; MPA, moderate physical activity; VPA, vigorous physical activity.
*Significant findings at Bonferroni-corrected P value of α/4 (.0125).
Sex-Based Differences in Sedentariness and Activity Between Groups
| Children with concussion | Healthy controls | |||||
|---|---|---|---|---|---|---|
| Boys (n = 29) | Girls (n = 31) | t stat, P | Boys (n = 29) | Girls (n = 31) | t stat, P | |
| Minutes/day | ||||||
| Sedentarya | 592.5 (60.2) | 643.3 (83.9) | −2.677, .010* | 567.0 (68.2) | 592.2 (75.5) | −1.347, .183 |
| LPAa | 143.1 (36.7) | 118.1 (45.3) | 2.335, .012* | 150.8 (25.8) | 148.7 (42.2) | .226, .822 |
| MPAa | 32.2 (9.7) | 23.5 (10.1) | 3.024, .004* | 38.5 (12.0) | 35.7 (11.5) | .920, .361 |
| VPAa | 22.3 (10.6) | 15.3 (13.5) | 2.367, .011* | 34.3 (16.3) | 27.6 (14.7) | 1.672, .100 |
Abbreviations: LPA, light physical activity; MPA, moderate physical activity; VPA, vigorous physical activity.
aSignificantly different from healthy girls (P < .0125).
*Significant findings at Bonferroni-corrected P value of α/4 (.0125).
Hourly analyses showed that from 8:00 AM to 9:00 PM, children with concussion were consistently more sedentary and less active than their healthy peers (Figure 1). Data from the earlier hours (ie, before 8:00 AM) were not included in the analysis owing to limited availability of valid accelerometer data during this time. The effect sizes for the differences in hour-by-hour accelerometer-measured sedentary time and activity between children with concussion and healthy controls are presented in Figure 2.
—Hour-by-hour sedentariness and activity (from 8:00 AM to 12:00 AM) in children with concussion in comparison with healthy controls. The numbers within the cells represent the average number of minutes of sedentariness or activity per hour (all differences significant except the hours of 10 PM and 11 PM). The bars represent minutes per hour. LPA indicates light physical activity; MPA, moderate physical activity; ns, nonsignificant; VPA, vigorous physical activity
Citation: Pediatric Exercise Science 36, 2; 10.1123/pes.2023-0016
—The effect sizes (Cohen d) associated with the comparisons presented in Figure 1. Lighter cell colors represent larger effect sizes. LPA indicates light physical activity; MPA, moderate physical activity; ns, nonsignificant; Sed, sedentary; VPA, vigorous physical activity.
Citation: Pediatric Exercise Science 36, 2; 10.1123/pes.2023-0016
Sedentary Bout Analysis
Our sedentary bout analysis revealed that healthy children had significantly more short sedentary bouts/hour (<1 min) than children with concussion. However, children with concussion engaged in a significantly greater number of 5- to 10-minute sedentary bouts/hour than healthy controls (see supplemental digital content, namely Supplementary Tables S1 & S2 [available online]).
Activity, Inactivity, and Sedentary Bouts as a Function of Days Postinjury
General linear models predicting activity levels as a function of days postinjury and age were only significant for models (unstandardized betas reported) with MPA (βDays Post = 0.177, t2,842 = 2.432, P = .015) and VPA (βDays Post = 0.265, t2,842 = 3.227, P = .001) as the outcomes. Therefore, as time postinjury increased, there were modest increases in minutes of daily MPA and VPA, but not sedentary time or LPA. Furthermore, as days post injury increased, the number of short (namely, 1–5 min) sedentary bouts that children completed per day decreased (βDays Post = −0.377, t2,842 = −2.109, P = .035).
Discussion
This is the first study to characterize habitual physical activity and sedentary time using accelerometry in children with concussion in comparison to healthy controls. Given the nature of this observational study, wherein children with concussion were given return-to-activity guidelines which were not subsequently strictly enforced, it is generalizable to the broader state of pediatric concussion. We report that children with concussion are significantly more sedentary and less active (with respect to LPA, MPA, and VPA) than matched healthy controls; this is observed throughout the day, from 8:00 AM to 9:00 PM. Sex-specific analyses showed that girls with concussion are less active (across all intensities studied) and more sedentary than boys with concussion as well as healthy girls. Increased days postinjury significantly predicted higher levels of MPA and VPA—but not sedentary time or LPA—in children with concussion (as well as fewer 1–5 min sedentary bouts), which may be expected as a natural part of concussion recovery.
Prolonged Inactivity in Concussion
We identified a MD of 38.3 minutes per day (95% confidence interval, 11.2 to 65.4) of increased sedentary time in children with concussion compared with their healthy peers, which amounts to nearly 4.5 hours a week. This difference is even greater when comparing girls with concussion with healthy girls, where the MD in sedentary time is 51.1 minutes per day, or approximately 6 hours over a week. Concussion guidelines now suggest that prolonged rest should be avoided after the first 24 to 48 hours of injury (24), and a recent randomized trial (38), large-scale cohort study (13), and systematic review (33) support this notion. However, what constitutes prolonged rest (or sedentariness) is not yet well-defined, as indicated in the most recent sport concussion guidelines (24). Our data do not establish a definition of prolonged rest postconcussion, but they do aid in the quantification of the magnitude of the physical activity observed within the first month of injury. Instead of (or in addition to) prescribing a designed 20-minute period of aerobic activity as is current best practice (14,18,19), advising patients to interrupt their sitting may be advantageous, especially given the known benefits of such actions on multiple health outcomes in healthy and other clinical populations (1,23,32). The optimal amount of sedentary time and physical activity following concussion, and whether a single bout of activity has greater benefits than interrupted sitting, requires further study.
Engaging Key Stakeholders in the Exercise Discussion
With the accumulation of data on the benefits of exercise in concussion, the traditional “rest-is-best” approach is being overturned, with an “exercise is medicine” mindset becoming more commonplace. However, a knowledge translation gap still exists, wherein primary care providers have not yet adopted this new approach to concussion management; more than 80% of concussion patients are still advised to rest for more than 2 days, despite contrary evidence from recent guidelines and reviews (7,24,35). A recent study aimed at providing primary care providers with guidelines for deimplementing prolonged rest found that the intervention improved knowledge about avoiding prolonged rest postconcussion, and increased clinician adherence to guideline recommendations from 25% to nearly 90% (36). Furthermore, per research on military service members with concussion, primary care providers relaying information to patients about the consequences of prolonged rest led to patients more promptly resuming physical activity and self-reporting lower levels of symptoms sooner (29). Future research should not only continue to build on the evidence, but also ensure that key findings are translated to relevant knowledge users.
Toward F.I.T.T. Informed Exercise Interventions in Concussion
The bulk of exercise research in concussion has been on submaximal aerobic exercise (34). Studying the impact of low- to moderate-intensity aerobic activity was motivated by the desire to engage patients in a safe, symptom-limited amount of activity that had a high likelihood of being well-tolerated. The optimal exercise frequency, intensity, time, and type (F.I.T.T.) of exercise in concussion has not been directly studied, though such study is necessary to maximize clinical benefit and increase exercise adherence in clinical populations (6). Recently, however, research has started to provide insight into F.I.T.T principles for exercise prescription in concussion. Accelerometer studies show that engaging in moderate to vigorous physical activity following concussion can lead to longer recovery times (22), which supports the continued use of low- to moderate-intensity graded submaximal aerobic exercise programs at this time (18). Furthermore, in adolescents, participating in low-intensity aerobic exercise for less than 100 minutes per week was associated with greater symptom burden at 1-month postinjury, while exercising more than 160 minutes per week resulted in symptom resolution when assessed at the same timepoint (15). These data, in addition to the current findings that quantify the physical activity debt observed in pediatric concussion, are helpful for building toward an understanding of the optimal frequency and time of exercise interventions in concussion. Our data (Figures 1 and 2) also show that the effect sizes for the difference in sedentary time between children with concussion and healthy controls are greatest from 8:00 AM to 1:00 PM, and then again from 8:00 PM to 9:00 PM. Given that sedentariness is observed throughout the day, but particularly so during school-going hours, there may be opportunity to incorporate physical activity programs as part of return-to-learn programs.
Accelerometery in Concussion-Exercise Research
Despite the recognized importance of physical activity on concussion symptoms, accelerometer research in pediatric concussion has been limited. To date, studies have used accelerometry to assess the relationship between physical activity with subsequent outcome in noncontrolled cohort studies. More specifically, one study showed that the number of accelerometer-measured steps from days 1 to 3, 4 to 5, and 6 to 7 postinjury were significantly correlated with symptom scores at each of these intervals, and the increased activity (ie, number of steps) from days 1 to 3 postinjury predicted lower activity on days 4 to 5 postinjury (41). A second study by this group reported that there was no association between physical and cognitive activity and time to concussion recovery (42). Another group studied male youth hockey players wearing accelerometers in the early stages of injury and found that those in the “high” activity group (based on a median split, performing more than 148.5 min of MVPA/day) took significantly longer to recover than those in the “low” activity group (22). Our study, in comparing accelerometer-measured sedentariness and activity between cohorts of concussed and healthy children, shows that there are considerable differences in sedentary time and physical activity within the first month of injury.
Limitations and Future Directions
Our study is limited by the absence of symptom data that preclude exploration of the association between accelerometer-measured physical activity and clinical outcome. Furthermore, given the lack of data on compliance with physical activity guidelines which were provided to all participants by members of our clinical team at intake, we are not able to address whether the physical activity patterns we observed were due to said guidelines. Furthermore, the cause of concussion was heterogenous (with the leading causes, in order, being sport, motor vehicle collisions, and nonsport-related falls). We were unable to control for differences in physical activity that may be a function of cause of injury.
Participants in our study also wore the accelerometer over their right hip; whether there are differences in measured activity based on location of wear remains unknown. Furthermore, for our sedentary bout analysis, we used a 6-second droptime as this length of time was estimated to not be physiologically relevant yet akin to slight movement such as repositioning or reaching for a device. Drop time criterion can be better established by future research.
Additional research is required to understand the threshold of total volume or number of bouts of sedentary time beyond which concussion recovery is compromised. Alternate accelerometer-based physical activity metrics, including indices of movement variability, can also provide more insight into how activity patterns differ in children with concussion in comparison with their healthy peers. Cohort studies and longitudinal research examining how acute clinical features of the injury associate with subsequent physical activity are needed for identifying children at high risk of sedentariness postconcussion.
Conclusions
This is the first study to profile accelerometer-measured physical activity and sedentariness following pediatric concussion, finding that in the first month of injury children with concussion are more sedentary (MD, 38.3 min/d) and less active (across all intensities studied) than their healthy peers. We also report as time postinjury increases, levels of MPA and VPA increase in children with concussion, which may be consistent with natural recovery. Future exercise-concussion research should examine the impact of interventions that reduce sedentary time, and in general engage key stakeholders (including primary care providers) to improve knowledge translation and the adoption of exercise in clinical practice.
Acknowledgments
This research was supported by the Canadian Institutes of Health Research (#31257), as well as Doctoral support to Sharma from the Canadian Institutes of Health Research (CIHR-CGS-D, #157864). Timmons is the Canada Research Chair in Child Health & Exercise Medicine.
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