Mild traumatic brain injury such as sport-related concussion (SRC) is an acknowledged public health problem (1), with an estimated 2.2 million emergency department visits per year in the United States (2) which likely represents an underestimation of the true incidence of this injury. Symptoms produced by SRC can be either somatic (e.g., headache, neck pain, dizziness, nausea, balance impairment) (3,4), cognitive (e.g., memory loss and slowed reaction time) (5), and/or psychological (e.g., depression and anxiety) (5–7). Sleep–wake disturbance and behavioral changes can also be consequences of an SRC (4,8). After an SRC, these symptoms can be triggered or increased by cognitive or physical exertion which can lead to intolerance to aerobic exercise (9). The neurophysiological factors explaining these symptoms, as well as the effect of physical exertion on them are now better understood and suggest that functional and microstructural injuries to neural tissue are likely involved (10). Among these factors, an altered function of the autonomic nervous system and an impaired cerebral blood flow (11) have been suggested as a neurophysiological explanation for triggered or increased symptoms with physical aerobic exercise. Sport-related concussions have been associated with transient autonomic dysfunction indirectly measured by electrocardiogram and heart rate variability (12–15). These dysfunctions are believed to reflect an altered parasympathetic (at rest) and/or sympathetic (when exercising) modulation (16).
The main advice provided to patients after an SRC has long been to rest until symptoms completely resolve, followed by a stepwise gradual physical and cognitive activation (17–19). More recently, the 2016 Berlin consensus on concussion in sport (8) stated that there is currently insufficient evidence to prescribe rest until complete symptom recovery is achieved after an SRC. Therefore, after a brief period of initial rest (24–48 h after injury), the first stage of the proposed gradual return to cognitive and physical activity strategies recommend the initiation of symptom-limited daily activities, even in the presence of residual symptoms (8). However, the available body of knowledge at the time did not allow to make recommendations about the use of the symptom increase threshold through other stages of the gradual return to cognitive and physical activities.
Numerous studies have demonstrated the beneficial effects of exercise on brain function (20–22). Monitored active rehabilitation programs involving symptom-limited aerobic exercise after SRC have been shown to be safe in cohort studies (23,24), although there is conflicting evidence to support their beneficial effects (25). When a gradual effort is introduced, an initial increase in cerebral blood flow is associated with the rapid rise in cardiac output (26). This appears to be modulated by an increase in brain metabolism and by the autonomic process of cerebral vasodilatation which mainly happens at low to moderate exercise intensities (27). The proposed mechanism of action of symptom-limited aerobic exercise is to stimulate autonomic nervous system function and cerebral blood flow to ultimately improve symptoms. A systematic review on physical exercise after concussion (28) only included one randomized controlled trial (RCT) and found that physical exercise appears to improve perceived symptoms in patients with SRC. The authors concluded that high-quality RCT are needed to clearly determine the effect of exercise in patients with a concussion. Since the publication of this systematic review, several additional RCT have been published.
OBJECTIVES AND HYPOTHESIS
The primary objective of the current systematic review and meta-analysis is to assess the effects of aerobic exercise programs, used alone or in combination with a minimal adjunct interventions (e.g., cognitive activation, coordination exercises or balance exercises) compared with wait-and-see or to control intervention that does not include aerobic exercises, on symptom intensity, time to recovery, balance, cognitive capacity, and adverse events (AE). Our hypothesis is that symptom-limited aerobic exercise programs will lead to better outcomes (i.e., lower level of symptoms and shorter time to recovery).
The Cochrane handbook (29) was used to guide the realization of this systematic review.
Literature search and study selection
A research librarian searched the following databases from their inception to December 13, 2019, without any language restriction: CENTRAL (The Cochrane Library 2019, issue 11), MEDLINE, EMBASE, and EBM reviews. Subject headings (MeSH) and key words included the population (e.g., mild traumatic brain injury, SRC, postconcussion syndrome, brain concussion, contrecoup injury, [brain OR head OR cerebral] trauma), the intervention (e.g., aerobic exercise, cardiovascular exercise, physical activity, physical therapy, active rehabilitation, physical exertion, effort, fitness, conditioning), and the design (e.g., randomized clinical trials, randomized controlled trials, [double-blind OR single-blind] RCT). Each search strategy was adjusted to the specific database. Complete searches, MeSH, and keywords are available in Supplemental Digital Content (see Table, Supplemental Digital Content 1, search strategies, https://links.lww.com/MSS/B995). References from relevant studies and systematic reviews were screened for additional potential trials to be included. After removing duplicates, two independent authors (P.L. and M.B.C.) screened titles and abstracts. All relevant full text articles were then obtained and screened to determine if they met the inclusion criteria. Disagreements were resolved by discussion with a third reviewer (J.S.R.). The inclusion criteria were: 1) RCT; 2) individuals who sustained an SRC without age restriction; 3) aerobic exercise, initiated at any stage after injury, as a main intervention with or without a minimal adjunctive intervention (e.g., cognitive activation, coordination exercises, balance exercises); and 4) written in French or English. The exclusion criteria were: 1) quasi-RCT and cohort studies; and 2) RCT that included moderate and severe traumatic brain injuries.
Aerobic exercises could be compared with wait-and-see or any other intervention (e.g., stretching, education, physiotherapy). Outcomes of interest included symptom intensity (primary outcome), time to recovery, balance, cognitive capacity, and AE. The outcome assessment was performed at the following timepoints: immediately after the exercise program (less than 1 d after the intervention period) and at the end of the study when applicable.
A first reviewer extracted the data (P.L.). A second reviewer (M.O.D.) then corroborated or completed the extraction if data were found to be missing. Data were extracted for participants’ characteristics (number of subjects per arm, gender, duration of symptoms, age), characteristic of intervention in the experimental and control group (duration, frequency, type and intensity of exercises), and outcomes of the intervention for the variables of interest. Authors of the included RCT were contacted for additional unpublished data when needed. The timing of the exercise intervention used in each study was also documented as acute stage (<4 wk) or persistent SRC symptom stage (4 wk or more), as proposed by the Berlin consensus (8). When available, information regarding the allowed intensity of the exercise programs was documented as light, moderate, or vigorous (30).
Methodological quality assessment
The inherent validity of the included studies was assessed through risk of bias (RoB) evaluations by two independent reviewers (P.L. and P.Fa.), using the 13 criteria of the Cochrane risk of bias tool (31). The results reported in Figure 1 represent reviewers’ consensus. Each criterion was rated as “low risk of bias,” “high risk of bias,” or “unclear risk of bias.” A study was considered to be at “high risk of bias” if 6 or less items of the RoB tool were deemed to be at “low risk of bias” OR if a major flaw was detected (32). Major flaws included but were not restricted to major conflict of interest of authors, major methodological shortcoming or inadequate funding bodies.
Descriptive statistics were used to describe intervention groups, outcomes and adverse effects. Standard mean differences with 95% confidence intervals (SMD; 95% CI) were calculated for continuous data, to accommodate the different outcome measures used. Mean differences with 95% CI (MD; 95% CI) were calculated for continuous data outcomes that used the same scales. For dichotomous outcomes, relative risks (RR) were calculated, where RR <1 represents treatment benefit. When data were not extractable and authors could not be contacted, the statistical significance reported in the original study was used. The effect sizes were categorized as small (SMD, less than 0.5), medium (SMD, from 0.5 to 0.8) and large (SMD, 0.8 or higher) (33). Absolute benefits (mean difference between the end and the beginning of study) for every group in individual studies were calculated to indicate the magnitude of treatment effect.
Assessment of heterogeneity and subgroup analysis
Studies were assessed for heterogeneity in preparation for the meta-analysis by considering specific clinical features (population, intervention, comparison, and outcome). Review Manager 5.3 software (Cochrane Collaboration) was used to perform the meta-analysis. Statistical heterogeneity was evaluated by the χ2 test for trend (P > 0.10, I2 < 40%). Results were calculated as pooled SMD or RR using a random model effect.
The overall quality of the summarized evidence was evaluated by two independent reviewers using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach, as recommended by Cochrane (see Table, Supplemental Digital Content 2, GRADE Table, https://links.lww.com/MSS/B996) (29). Domains that may decrease the quality of the evidence include study limitations, consistency of effect, imprecision, indirectness and reporting biases. We defined high-quality evidence as reported by RCT with low RoB that provided consistent, direct and precise results for the outcome. We reduced the quality of the evidence by one level for each domain not met.
- High quality: Further research is very unlikely to change our confidence in the estimate of effect. Consistent findings among 75% of pooled participants in RCT with low RoB are generalizable to the population in question. Sufficient data, with narrow confidence intervals, are available. No reporting biases are known or suspected (all domains are met).
- Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate (one domain is not met).
- Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate (two domains are not met).
- Very low quality: We are very uncertain about the estimate (three domains are not met).
- No evidence: We identified no RCT that measured the outcome.
Description of Studies
Literature search and study selection
The search flow diagram is presented in Figure 2. The literature search revealed a total of 1755 citations. After removing duplicates, 1338 citations were screened, and 53 studies were retained. Forty studies were excluded following full text review. Of the resulting 13 trials, six were research protocols without any results. Therefore, seven RCT (34–40) were included (326 participants).
Characteristics of included studies
The description of included studies is presented in Supplemental Digital Content (see Table, Supplemental Digital Content 3, characteristics of included studies, https://links.lww.com/MSS/B997). Two included studies were from Canada (38,39) and all other trials (34–37,40) were from the United States. The populations in all included trials were adolescents (age range from 13 to 17 years old). Four studies tested aerobic exercise programs in populations with acute SRC and three in populations with persistent symptoms. The interventions included 10 to 30 min of symptom-limited aerobic exercise executed once a day either at home or at a physiotherapy department. Only one trial (34) studied the effect of early gradual physical activation without providing any specific details about exercise intensity. Although the primary objective of that study was to assess the effect of a 5-d strict rest period on acute SRC, the study was included since the comparison group was allowed to initiate early stepwise physical activation after only 1 to 2 d. In the present review, the early physical activation allowed in the study’s control group was considered as the main intervention initiated at the acute stage after injury. The available information on the intensity of exercise for all included RCT is presented in Table 1. Four studies (35,38,39) used a moderate level of aerobic exercise (30), whereas three studies (34,36,37) did not report intensity of exercise. The control interventions varied among studies, and included general stretching programs (36–38), rest (34,35), and clinical management without aerobic exercise (39).
TABLE 1 -
Intensity of exercise and AE.
|RCT (n—Phase SRC)
||Exercise Intensity (30)
|Maerlender et al. (35)
(n = 28—acute SRC)
|Light to moderate intensity (0 to 6 on a 10-point scale)
||AE: participants who reported having performed vigorous exertion were slower to recover (increased recovery time). Small effect size and statistically significant
|Thomas et al. (34)
(n = 99—acute SRC)
|Intensity not reported.*
Varied between light to high intensity but no specific intensity prescription.
|AE not reported
|Kurowski et al. (38)
(n = 30—persistent symptoms after SRC)
|Moderate to vigorous intensity (11 to 16 on Borg scale)
||AE: only one participant had worsening of symptoms (comparison group)
|Chan et al. (39)
(n = 19—persistent symptoms after SRC)
|Moderate intensity (60% of maximal capacity)
||AE: 6 mild AE per group
|Micay et al. (40)
(n = 16—acute SRC)
|Moderate intensity (50% to 70% of age-predicted maximal heart rate)
||AE not reported
|Bailey et al. (37)
(n = 16—persistent symptoms after SRC)
|Intensity not reported* (80% of heart rate of symptoms exacerbation threshold).
*Light to high intensity as long as 80% of heart rate of symptoms exacerbation threshold is respected
|AE not reported
|Leddy et al. (36)
(n = 113—Acute SRC)
|Intensity not reported** (80% of heart rate of symptom exacerbation threshold).
**Light to high intensity as long as 80% of heart rate of symptoms exacerbation threshold is respected
|AE: incidence of participants with delayed symptom recovery (>30 d) was higher in control group n = 7 (median, 58 d; range, 36–62 d) vs n = 2 (median, 50 d; range, 46–54 d).
Difference between groups was not statistically significant P = 0.08
Risk of bias of included studies
The RoB assessment demonstrated an overall significant agreement between the two reviewers (Gwet’s AC1 coefficient = 0.78; P < 0.00001; observed agreement = 89%; agreement by chance = 49%). (41) Three studies had a high RoB (35,37,39) and four studies had low RoB (34,36,38,40) (Fig. 1). Three of four low RoB RCT (34,36,40) included acute SRC populations. Weakness in methodologies includes inappropriate randomization procedure reporting (57%; 4/7) and lack of co-intervention description or avoidance (86%; 6/7). Due to the nature of the interventions, it was not possible to blind the care provider (100%; 7/7). Methodological strengths include an acceptable drop-out rate (87%; 6/7) and intention-to-treat analysis that was performed in the majority of trials (87%; 6/7).
Effect of intervention
Meta-analyses were only possible for symptoms severity, which was assessed by the 22-item Postconcussion Symptom Scale (PCSS) questionnaire in four studies, the 19-item PCSS in one study and the postconcussion symptom inventory in one study. When combining studies that included participants with acute to persistent symptoms, six studies were eligible for meta-analysis. The meta-analysis (Fig. 3A) shows that there is a low level of evidence that symptom-limited aerobic exercise programs are more effective in improving symptom severity immediately after the programs than control interventions (stretching, act-as-usual, strict rest, professional follow-up without aerobic exercises) after an SRC (277 participants; pooled SMD, 0.44; 95% CI, −0.68 to −0.19). When combining only the three RCT that included participants with acute SRC (34,36,40), there is a moderate level of evidence that symptom-limited aerobic exercise programs are more effective to improve symptom severity immediately after the exercise program than control interventions (stretching, strict rest, gradual return to function) (206 participants; pooled SMD, −0.43; 95% CI, −0.71 to −0.15) (Fig. 3B) The effect size of these first two meta-analyses is small (SMD, less than 0.5). Finally, when combining the three RCT that included participants with persistent symptoms (37–39), there is very low-quality evidence that symptom-limited aerobic exercise programs are as effective as the control interventions (stretching, light exercises, professional follow-up without aerobic exercises) (61 participants, pooled SMD, −0.46; 95% CI, −0.98 to 0.05) (Fig. 3C). A summary of the GRADE assessment by population can be found in Supplemental Digital Content (see Table, Supplemental Digital Content 2, GRADE Table, https://links.lww.com/MSS/B996). It was not possible to calculate MD; 95% CI because symptom scales were different across RCT included in the meta-analysis.
Meta-analysis were not possible for the other outcomes, descriptive analysis were performed.
One low RoB study on acute SRC (34) reported the PCSS scores and the number of symptoms that were present among the 22 symptoms of the scale during the recovery period. There was a statistically significant difference between groups in favor of the symptom-limited aerobic exercise group for the total number of symptoms (P < 0.03) and for the total PCSS score (P < 0.03) at the end of a 10-d exercise program. Another low RoB study (38) reported a statistically significant between-group difference for symptomatic recovery with 92% (13/14) of the participants of the control group still perceiving symptoms at the end of study versus 50% (6/12) in the 6-wk symptom-limited aerobic exercise group. In a high RoB study (37) with 15 participants, one participant had a baseline depression score 25% higher than the next highest participant. When they removed that highly depressed participant from their analysis, the difference between groups became statistically significant (P < 0.05) in favor of the symptom-limited aerobic exercise group, with a large effect (n2 = 0.32) when compared with a light exercise program.
Time to recovery
Four trials (34–36,40) assessed the time to recovery. One low RoB trial (36) on acute SRC favored the symptom-limited aerobic exercise group for time to recovery compared with a stretching program. Median time to recovery was 4 d quicker than the stretching group (13 d [interquartile rage, 10–18.5] for the aerobic exercise group and 17 d [interquartile rage, 13–23] for the stretching group [P = 0.009]). On the other hand, three trials (one high RoB (35) and two low RoB RCT [34,40]) reported no significant difference between groups for time to medical clearance when symptom-limited aerobic exercise was compared with rest or to a stepwise gradual return to physical activity after being asymptomatic (8).
The ImPACT test battery was used to assess cognitive capacities in two RCT (one high RoB (39) and one low RoB ), and none of these studies reported any significant difference between groups immediately after the exercise programs.
The balance error scoring system was used in 2 RCT (34,39) to evaluate balance. Both trials (one high RoB (39) and one low RoB (34) RCT) reported no statistically significant difference between the symptom-limited aerobic exercise group and the control groups (professional team management without aerobic exercise (39), and strict rest ) at the end of the programs.
Four trials (35,36,38,39) reported on AE. All AE reported were categorized as mild. One low RoB study (38) reported one AE on 14 participants in the control group and no AE in the exercise group (n = 12). One low RoB study on acute participants (36) reported an incidence of participants with delayed recovery (>30 d) that was higher in stretching group (13.5%; 7/52) than in the symptom-limited aerobic exercise group (3.8%; 2/51). One high RoB study (39) reported six occurrences (no details were provided about these occurrences) of mild AE per group. It is not clear if AE were observed in six different participants. Finally, a high RoB study (35) stated that participants who reported having performed vigorous exertion were slower to recover (small effect size and statistically significant) compared with those who performed light to moderate exertion.
Summary of findings
The objective of this systematic review was to evaluate the effectiveness of aerobic exercise programs on symptom intensity, time to recovery, balance, cognitive capacity, and AE in individuals with SRC. The results show, with a low level of evidence, that aerobic exercise programs are effective, when compared with control interventions, to improve symptom recovery in adolescents that sustained an SRC. Furthermore, moderate evidence shows that initiation of graded symptom-limited aerobic exercise programs in the acute phase of SRC (within 10 d) are effective to improve symptom recovery in adolescents. The effect sizes are small according to Cohen’s effects classification (33), whereas confidence intervals covered the spectrum of small to medium effect sizes. For these two meta-analysis, the level of evidence was downgraded by one level (from moderate to low and from high to moderate respectively), because the pooled studies included mixed types of exercise programs. In fact, one study (34) differed from the others as it used recommendations of a stepwise physical and cognitive symptom-limited activation program without providing specific details. The included RCT provided no evidence of major AE, and no difference between groups was found for AE. These results suggest that it is safe and likely beneficial to initiate graded symptom-limited aerobic exercise in adolescents during the acute phase of SRC.
The results of the meta-analysis for persistent symptoms after SRC showed a trend toward a greater effectiveness for aerobic exercise programs when compared with the control interventions but did not reach statistical significance. This high level of uncertainty resulted from the following factors: the small size of the pooled RCT, large confidence intervals and two of the three pooled studies being characterized by a high RoB associated with a very low level of evidence. Therefore, the hypothesis that aerobic exercise is effective, cannot be confirmed for interventions initiated at the stage of persistent postconcussive symptoms after an SRC. Nevertheless, from a clinical perspective, these results do not indicate any negative effect on symptom recovery or AE associated with symptom-limited aerobic exercise programs. Also, knowing that persistent postconcussive symptoms are multifactorial (42), it is not surprising that an intervention targeting one aspect of the clinical picture provides less improvement.
Considering the general health benefits of maintaining an active lifestyle (30), the practice of symptom-limited aerobic exercise at the stage of persistent postconcussive symptoms should not be avoided, especially in patients that have a motivation to maintain an active lifestyle. The intensity of exercise used in the studies showing a beneficial effect of graded symptom-limited exercise programs in the acute phase (34,36,40) suggests that physical activity up to at least moderate intensity can be used safely with a favorable outcome after an SRC. Conclusions based on the qualitative analysis of the effect of aerobic exercise on time to recovery, cognitive capacities and balance cannot be drawn since data on these outcomes are sparse and are not well reported in most studies. Impairment of cognitive capacities being an important feature after an SRC, future studies should closely monitor cognitive loading and measure this impairment using validated outcome measures.
When compared with other available reviews (25,28,43), this is the first review to include only RCT and use the Cochrane collaboration Handbook as methodological guidance. One of the systematic reviews of the Berlin consensus (25) process included cohort studies and only one RCT (34). This review concluded that there was conflicting evidence that symptom-limited aerobic exercise decreases time to recovery with the majority of literature suggesting a positive effect. The present review included six additional RCT and the level of evidence toward effectiveness of aerobic exercise has increased, specifically for adolescent populations.
Since the Berlin consensus, two other systematic reviews were published (28,44). Sharma et al. (44) reviewed studies on the impact of cognitive and aerobic exercise programs on cognitive and neuroimaging outcomes in populations with mild to severe traumatic brain injuries but did not report outcomes related to symptoms. Results from the six studies included in that review suggest that cognitive and physical exercise improved neuroimaging outcomes but not cognitive capacities. The results on cognition are similar to our findings. Another recent systematic review (28) demonstrated a decrease of symptoms on the PCSS (MD, −13.06; 95% CI, −16.57 to −9.55) associated with aerobic exercise interventions compared with control, based on the pooled analysis of one randomized and 11 nonrandomized trials.
Only seven RCT were included in this review, and three RCT were associated with a high RoB which limits the level of evidence and the level of certainty about the efficacy of the interventions. There were no studies retrieved on adult populations, therefore, the recommendations of this systematic review are limited to adolescents and may not apply to adults. Control groups were diverse, which can affect the reported efficacy of the exercise interventions. Only English and French language studies were included which could lead to a language bias. However, we did not exclude any RCT because of language. Finally, all included RCT were from North America, which can lead to a bias related to culture and sports practiced in this region of the world.
Implication for clinician
Considering current guidelines, clinicians may have concerns with the initiation of aerobic exercise early during the acute phase of a SRC, especially when patients are still symptomatic. Our findings indicate that graded symptom-limited aerobic exercise programs are effective to decrease symptoms and are safe when they are initiated after the recommended 48-h rest period after an SRC in adolescents. Accordingly, even in the presence of residual symptoms after a brief initial rest period, clinicians might consider a recommendation of gradual progression toward moderate-intensity aerobic exercise as long as activity does not result in an increase of symptoms. Although the Berlin consensus defines step 2 of its gradual return to play (RTP) strategy as “light aerobic exercise,” there is no explicit reference to moderate-intensity physical activity for step 3, which is defined as “sport-specific exercise; for example, running or skating drills.” Therefore, progressive symptom-limited aerobic exercise could be recommended up to step 3 of the gradual RTP strategy (8) while not exceeding the perceived sensation of moderate-intensity exercise which has been defined as “Increased breathing and sweating, but still able to maintain a conversation” (30). This recommendation is in line with another narrative review (45). In the future, clinical studies and guidelines about gradual RTP strategies should use a uniform language to describe the recommended intensity of exercise (30) to facilitate the ongoing integration of research findings.
Implication for research
Only seven RCT with a total of 326 subjects evaluated the effect of aerobic exercise on recovery from SRC. There is a need for RCT with large sample size to improve the level of evidence, especially for SRC with persistent symptoms. Upcoming research should also include adult populations since no RCT on adults were identified by this systematic review. The description of the intensity of exercises should use acknowledged vocabulary and measures. Adverse events also need to be compiled in a comprehensive way as it is a sensitive concern among clinicians. There is a need for a standardized description of acute and persistent SRC among RCT.
Since the 2016 Berlin consensus on SRC (8), several RCT on aerobic exercises for SRC emerged from the literature (36–39). Our review adds major findings on the efficacy and safety of aerobic exercise programs in the management of SRC. A moderate level of evidence indicates that graded symptom-limited aerobic exercise is effective to improve symptoms and is safe when used at the acute phase after an SRC in adolescent populations. Moreover, the intensity of the exercise programs used in the published studies suggests that a gradual progression of symptom-limited aerobic activity toward moderate-intensity exercise or step 3 of the graded return-to-sport strategy proposed by the 2016 Berlin consensus can be recommended (8). Further studies are needed 1) to improve the level of certainty of these findings, 2) on adult populations, and 3) with better ways of reporting exercise programs and AE.
Funding: There was no funding body involved in this review.
Competing Interests: P. F., M.-O. D., M. B.-C., and J.-S. R. declare that they have no competing interests. P. L. and P. Fa. are the owners of a private multidisciplinary clinic offering concussion care but this clinic and the authors do not financially support the project. Results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation, and statement that results of the present study do not constitute endorsement by ACSM.
Availability of Data and Material: The data set used and/or analyzed during the current study is available from the corresponding author on request.
Authors’ Contributions: P. L. was the lead author as a PhD candidate. P. L. and J. S. R. are protocol authors. P. L. and M. B. C. participated in the selection phase. P. L. and M. O. D. participated in the data extraction. P. L. and P. Fa. participated in the validity assessment. P. L. and P. Fr. participated in the analysis. All authors contributed to manuscript writing and reviewing.
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