Little bit of background
Over the past week I found myself reading some of the literature regarding existing physical training (i.e. primarily neuromuscular training) practices to prevent sport-related concussion risk. This, I must say, was for the purpose of collaborating in a research project, however I believe it also makes a useful blog post.
If you can't be bothered to read the entirety of the article I've summarized the key points I found in my (limited) search for existing evidence in the infographic below. I must say, I do think there is both scope and a need for prospective investigations on physical training concussion prevention interventions, particularly one that encompasses elements of technical skill, impact anticipation and musculoskeletal structure. It is pretty clear that investigating one physical training strategy in isolation will not yield as strong of an argument in preventing such a highly unpredictable and multifactorial injury as is a traumatic brain injury.
Every year, 1.6-3.8 million sport and recreation-related mild traumatic brain injuries occur in the USA alone (Schneider et al., 2016). Upon brief scanning of the available literature, it appears to be generally accepted that the primary mechanism of sport-related concussions is a rotational acceleration of the head upon contact (Tierney et al., 2008; Collins et al., 2014; Schneider et al., 2017). Of the risk factors discussed in the sport-related concussion literature some include: sex, age, anthropometric characteristics (e.g. neck length to head ratio, neck circumference), level of play, neck strength, reaction time, vision and anticipation ability, prior concussions and sport-specific risk factors (e.g. body checking in ice hockey, heading in soccer, tackling technique in football and rugby) (Waltzman & Sarmiento, 2018; Honda et al., 2018). To this end, concussion prevention efforts, as it pertains to physical training, have been focused on increasing neck strength and cervical musculature (i.e. neck circumference), improving reaction time and peripheral vision ability.
Findings on the protective effect of neck strength are inconclusive across the literature. Studies conducted by Collins et al. (2014), Eckner et al. (2014), Gutierrez et al. (2014), and Hrysomallis (2016) suggested that greater neck strength and girth served to decrease the severity of blows to the head, thereby decreasing the number of concussions sustained. Similarly, a review of preventative strategies against brain injuries in soccer by Caccese & Kaminski (2016), found that a balanced neck flexor and extensor strength and stiffness decrease head acceleration during purposeful soccer heading. The proposed mechanism of prevention seems to be that a greater isometric neck strength allows the athlete to brace the cervical musculature upon a blow to the head, which absorbs and dissipates the force transmitted from the blow away from the head. However, studies conducted by Mihalik et al. (2011) and Schmidt et al. (2014) found no association between neck strength and girth and the severity of head impacts. It is quite remarkable that although the protective mechanism of neck strength is understood to be the rapid bracing action of the cervical musculature upon contact, that training interventions involving reactive isometric contractions (e.g. following an external perturbation) have not been documented (It may well be that I did not come across any in my search for existing evidence).
It appears that neck strength training programmes are effective for untrained and trained populations across athletic disciplines. However, the diversity in measurements of neck strength and regimens of training (i.e. isometric, isotonic) across the literature, as well as differences in the neck strength of different athletes (which are partly due to variations in neck muscle mass), may be responsible for the equivocal findings regarding its efficacy for concussion prevention (Hrysomallis, 2016). The unpredictability of inciting events may also be responsible for the inconclusive findings as it pertains to sport-related concussion incidence in injury prevention studies. It has been suggested that the enhanced awareness and education on sport-related concussion in recent years may play a role in the reporting and diagnosis of head injuries in sport, which may explain the increases in concussion rates in recent years regardless of prevention efforts (Yang et al., 2017).
Throughout the literature it is suggested that anticipating hits may lead to preventing sport-related concussions. This is because hit anticipation decreases head impact severity (Mihalik et al., 2010). With anticipation of the hit, athletes are able to brace and activate their neck musculature to help keep their head stable (i.e. limit head acceleration). To anticipate a hit however, the athletes must have good vision and fast reaction times. As such, studies have also investigated the role of vision and reaction time training for concussion prevention (Clark et al., 2015a, 2015b; Harpham et al., 2014). It must be noted that (unsurprisingly) effective reaction time training is the only wholly agreed upon intervention in helping prevent concussions (Honda et al., 2018). A limitation of the available evidence is that the three training prevention practices have only been investigated in isolation, when clearly their optimal protective effect is interdependent (i.e. with poor reaction time, vision ability becomes redundant and the protective effect of neck strength is limited). Future research on the combined effect of the three strategies may provide clarity in regard to best-practice concussion prevention in sports. In addition, studies examining evidence-based prevention training programs among athletes younger than 14 years old or beyond the high-school level are very much lacking (Waltzman & Sarmiento, 2018; Schneider et al., 2017; Collins et al., 2014; Hyrsomallis., 2016). Finally, given that postural stability and control have been recommended as means for identifying concussion-related neurophysiological abnormality and to determine readiness to resume competitive activity post-concussion (Guskiewicz et al., 2001; Cavanauh et al., 2005), there exists, in my humble opinion, a large opportunity to investigate the protective potential of trunk stability and proprioceptive training against sport-related concussion.
Questions that remain unanswered
1. Which neck-strength training regimen (i.e. isometric, concentric, eccentric, plyometric) offers the greatest preventative effect against sport-related concussions?
2. Is the preventative effect of neck-strength on sports-related concussion dependent or independent of anthropological factors (i.e. neck circumference, neck to head circumference ratio)?
3. Does combined neck and trunk neuromuscular training reduce concussion risk to a greater extent compared to neck strengthening alone?
4. Is there a threshold of neck strength to prevent concussions? Is this relative to the athlete (e.g. Football players have stronger necks than soccer players)?
5. What is the minimum frequency, volume or density of physical training practices (i.e. neck-strength, reaction time or vision training) that yields protective effects against sport-related concussion? (Fisher et al. (2016) do however suggest a 2d/wk for 8 wks of 1 set to muscular failure for previously untrained population)
6. What effect does neck strength and girth have on helmeted vs. non-helmeted athletes?
7. To what degree have studies investigating the effect of neck-strength on reducing sport-related concussion risk been limited by reporting bias?
Some key papers for your interest
· Schneider, D. K., Grandhi, R. K., Bansal, P., Kuntz, G. E., Webster, K. E., Logan, K., ... & Myer, G. D. (2017). Current state of concussion prevention strategies: a systematic review and meta-analysis of prospective, controlled studies. British journal of sports medicine, 51(20), 1473-1482.
· Honda, J., Chang, S. H., & Kim, K. (2018). The effects of vision training, neck musculature strength, and reaction time on concussions in an athletic population. Journal of exercise rehabilitation, 14(5), 706.
· Hrysomallis, C. (2016). Neck muscular strength, training, performance and sport injury risk: a review. Sports Medicine, 46(8), 1111-1124.
· Collins, C. L., Fletcher, E. N., Fields, S. K., Kluchurosky, L., Rohrkemper, M. K., Comstock, R. D., & Cantu, R. C. (2014). Neck strength: a protective factor reducing risk for concussion in high school sports. The journal of primary prevention, 35(5), 309-319.
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Thanks for your time and interest.
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