The Influence of Cervical Muscle Characteristics on Head Impact Biomechanics in Football
Schmidt JD, Guskiewicz KM, Blackburn JT, Mihalik JP, Siegmund GP, and Marshall SW. Am J Sport Med. 42 (9). 2014.
Take Home Message: Football players with greater cervical neck muscle strength and size were as likely to sustain larger head impacts as their peers. Football players who had greater cervical stiffness and an ability to decrease the displacement of their head following perturbation were less likely to sustain a moderate and severe head impacts.
While many believe that strengthening cervical muscles may reduce head acceleration after an impact, and thus reduce the risk of concussions, there is very little evidence to verify this concept. If athletes with stronger, larger, or stiffer cervical muscles are less likely to suffer higher magnetic head impacts compared with their peers then this could provide more justification for targeting cervical muscles in a concussion prevention program. Therefore Schmidt and colleagues completed a prospective cohort study to compare the risk of, “sustaining higher magnitude in-season head impacts between athletes with higher and lower preseason performance on cervical muscle characteristics.” Forty-nine football players (34 high school, 15 college) underwent a preseason cervical screening program. The researchers assessed isometric strength in flexion, extension, right and left lateral flexion. The study team also measured the cross-sectional area of the sternocleidomastoid, upper trapezius, and semispinalis capitis muscles with ultrasound. Finally, the researchers assessed cervical stiffness by applying unexpected perturbations in cervical flexion and extension. All athletes were divided into either a high performance (above the median split) or low performance (below the median split) for each cervical characteristics (e.g., strength, stiffness). Following preseason testing, head biomechanics at each game and practice were measured by the Head Impact Telemetry (HIT) system. Researchers observed and recorded 19,775 (19,172 mild, 514 moderate, and 89 severe) head impacts. Only 1 impact (a mild impact) resulted in a diagnosed concussion. Overall, muscle size and strength were not factors in mitigating the severity of head impacts. Athletes with greater cervical stiffness and less displacement following perturbations were at lower risk for sustaining moderate or severe impacts.
While it is commonly believed that stronger cervical muscles will decrease head displacement following impact, this is may not be the whole story. Instead the activation of, and the ability to stiffen cervical muscles may be the key to preventing severe head impacts. This may suggest that clinicians should incorporate neuromuscular training into strength and conditioning programs – to promote cervical muscle activation in anticipation for an impact – because simply strengthening cervical muscles may not be sufficient. Since the research team only followed 49 football players over one season it will be important to find out if these findings are applicable to other sports and specific positions in football. It’ll also be helpful to see whether clinical trials will provide support for using cervical neuromuscular training for reducing head impact severity and concussions. In the meantime, clinicians could try implementing these types of programs with their athletes since the risks of a properly supervised program is low.
Questions for Discussion: Have you implemented a cervical muscle strengthening program for you athletes? If so, do you feel this has led to a decrease in concussions? Do you think we will eventually use concussion prevention programs that include neuromuscular training?
Written by: Kyle Harris
Reviewed by: Jeffrey Driban