Written By Alexander J. Morgan
Introduction
A concussion or mild traumatic brain injury (mTBI) occurs when an external force to the head or body results in a combination of rapid linear, rotational, and/or translational forces on the brain. Such forces either directly or indirectly promote a cascade of pathophysiological processes that alter tissue and axonal integrity, as well as cerebrovascular function (2,8,13,22). Unique to the tactical population are blast-related mTBIs that add another subset of physiological and psychological mechanisms and effects (2). For most mTBI cases, after a brief rest period of 24-to-72 hours it is recommended that individuals begin a progressive exercise protocol to limit chronic symptomology and improve time to recovery (9,10,14,24). Ideally the protocol is inclusive of activities of daily living, environmental stimuli, sport/occupational demands, and does not exacerbate symptoms (2,8,13,16,22).
The role a Strength and Conditioning Coach has in a mTBI reconditioning case can be confusing. Understanding the application of subsymptom aerobic exercise and review of an overarching progressive exercise protocol can provide clarification. Because these challenges fall on a wide-scale, subsymptom aerobic exercise is proposed to advantageously position practitioners to provide adequate exercise prescription. An attempt to positively influence symptom resolution and time to recovery. As a disclaimer, it needs to be noted that mTBIs are a complex injury that affect those who suffer them on an individual basis. The overall process starts and ends with the overseeing physician and/or physician medical designee(s).
The Utility of Subsymptom Aerobic Exercise Reviewed
Subsymptom aerobic exercise is the use of steady state low-to-moderate intensity exercise that is below an individual’s threshold for experiencing symptoms related to their mTBI. Only one part of a multifaceted return-to-duty pathway, subsymptom aerobic exercise is to be employed following medical clearance, and in a clinical and/or reconditioning training environment. In the pursuit of determining an optimal protocol, a critical appraisal of the literature was conducted.
A common methodology used was the Buffalo Concussion Treadmill Test (BCTT) to calculate 80% of participant heart rate (HR) at symptom exacerbation, which becomes their HRThreshold. This was then the prescribed intensity for an aerobic exercise duration of 20 minutes with an additional warm-up (5 minutes) and cool-down (5-10 minutes) that was completed daily (10,14,24). BCTT re-tests then can be completed weekly to progress or regress intensity. Another methodology was to use a stepwise protocol over the course of eight sessions. This progressed sessions from 10 minutes at 50% of participant age-predicted maximal HR, to 20 minutes at the same intensity, while the remaining six sessions remained at 20 minutes with an increase of 5% of participant age-predicted maximal HR until 70% was reached. These sessions took place on two consecutive days followed by a day of rest, totalling a duration of 11 days (9).
In collaboration with these articles and related methodologies, it was concluded in a recent systematic review and meta-analysis that subsymptom aerobic exercise had moderate evidence supporting its role in improving recovery time and decreasing symptom severity (4,18). Subsymptom aerobic exercise evidently supports improved recovery time, symptom resolution, and decrease in total symptom scores (9,10,14,24). Considering these findings, it was determined that within the realm of reconditioning, subsymptom aerobic exercise is safe and the best option for a progressive exercise protocol aiding in symptom resolution while avoiding delayed recovery (4). Stemming from the most recent consensus statement, it’s apparent that subsymptom activity exists, but there are limited tools to guide practitioners through the intervention (8,16). With these findings being seen in both adolescents and the adult population, they could relate to both force recruits up to those with many years served. Allowing for a synthesized protocol to be created and become a reference for medical staff who oversee members rehabilitation.
Application: Programming Considerations
With intervention specifics slightly differing, when synthesized, three options were outlined (Figure 1) that are dependent on what the practitioner has available to them resource-wise; 1) exercise prescription with BCTTs and a HR monitor; 2) exercise prescription with BCTTs and speed zones; and 3) exercise prescription with no symptom exacerbation measures, but with progressive HR stages starting at 50% of age-predicted HR and increasing by 5%. Circumstantial considerations then include individual medical and exercise status/history, physical literacy, self-efficacy, and future research findings (1).
Figure 1. Three Options for the implementation of subsymptom aerobic exercise.
Once the overseeing physician or physician medical designee has determined the patient to be safe to proceed with physical reconditioning, the progressive exercise protocol can begin. The process ideally involving both Physiotherapists and Strength and Conditioning (S&C) Coaches working in tandem. With Physiotherapists passing the responsibility of developing one’s physical characteristics to pre-injury levels to the S&C Coach in the mid-to-late stages of the rehabilitation process. This allows the Physiotherapist to focus on other symptoms experienced that could be career-limiting (e.g. vestibular symptomology). All while the physician or physician medical designee(s) may be referring to other practitioners of the integrated support team that should be considered as early as possible to focus on other aspects including mental health outcomes (7). However, understanding that not all environments offer the privilege to operate as a trans- or inter-disciplinary team, a S&C Coach should understand their role. Figure 2 demonstrates a framework specific to the S&C Coach and the reconditioning process.
Figure 2. Subsymptom aerobic exercise framework
A successful result would be passing a relevant job specific test (as a bona fide occupational requirement). An unsuccessful result would be a relay back to medical due to a persistent lack of progress and the potential need for additional interventions that is not in the S&C Coach’s scope of practice. An example of this would be the difference between an individual progressing through stages one-to-five or a lack of progression >7 days after a third attempt of stage 3 using the DoD clinical recommendations from 2022 (19). This would demonstrate on a larger scale how a holistic model considers operational readiness and medical employment limitations in garrison and while deployed.
Conclusion and Limitations
It has been demonstrated in the literature that avoiding relative rest and participating in symptom-limited activity can improve concussion/mTBI recovery time (2,8,13,16,22). As a primary guideline, this includes subsymptom aerobic exercise that evidently improves time to recovery (9,10,14,24). Although investigated to a lesser extent, resistance training can then safely and sensibly be included. This global approach addresses all the needs of the individual to limit risk of injury when returning-to-duty while simultaneously aiming to improve injury specific symptomology (18).
In conjunction with the three-options provided in Figure 1, the BCTT does not impact recovery outcomes or acutely increase symptom severity (11). It is suggested to use the BCTT to determine individual symptom exacerbation HR (i.e. HRThreshold) pre-intervention and weekly thereafter. Due to the presence of autonomic nervous system (ANS) dysfunction, establishing an exercise tolerance threshold seems essential to avoiding symptom exacerbation (8,12). As used in the framework, clarification is provided on the S&C Coach’s role and when it starts and ends.
Limitations of this development expand from the novelty of this area of research. The military demographic comes with a unique host of considerations unparalleled in sport. Pending applied sport science projects, specificity such as training exercises versus operational exposures, direct blast mTBI mechanisms, and population-specific comorbidities need to be considered (2,20,23). Furthermore, applied sport science can begin looking at preventative measures with specialists (e.g. breachers and snipers) with higher rates of exposure such as blast biosensor and biomarker monitoring (2,15). The severity of mTBIs cannot be overlooked, and it us crucial to understand that subsymptom aerobic exercise is one part of a puzzle that ultimately needs to be overseen by a physician and/or physician medical designee(s).
Author Bio
Alexander J. Morgan, MSc., CSCS, RSCC, CEP is a Strength & Conditioning Specialist with Canadian Special Operations Forces Command where he focuses on training and educating unit members alongside project development. While continuing to work privately through Area 13 Training Systems, prior to working in the tactical setting, Alex worked in collegiate sport as well as in research and development.
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