Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Mechanical and Materials Engineering

Supervisor

Mao, Haojie

Abstract

With the rising concern of concussions in contact sports, it is believed that cervical muscles could play a vital role in attenuating force to the head. However, the biomechanical effect of cervical muscles on head and brain response is not clearly understood. This study adopted a finite element head and neck model to replicate football impacts under various loading conditions to study the effect of neck muscles on head kinematics. Our results indicate that neck muscles have the highest amount of internal energy absorption in early impact, particularly at the time when peak head kinematics develop. Both deep and superficial muscles are equally important in stabilizing the head. Early muscle activation was found to have no effect on rotational based injury metrics (BrIC), but relative movement of the head before impact could increase brain strain. Furthermore, our results demonstrate that reduced neck stiffness due to fatigue may increase head responses, increasing the likelihood of sustaining repetitive concussions.

Summary for Lay Audience

Mild traumatic brain injury (mTBI), commonly known as concussion, is a major concern in contact sports particularly in American football. Although a lot of changes have been made to the game of football by introducing new protective gears such as helmets to reduce the risk of head injury, the number of concussions is still on the rise each year for both young and professional athletes. It is believed that developing neck strength and stiffness through proper muscle training and awareness of impact could help mitigate concussive force to the head. Due to methodological constraints and ethical concerns, it is very difficult to conduct studies at the tissue level to understand the proper influence of neck and head response on human volunteers.

We adopted a novel computational approach using a detailed and validated finite element head and neck model (50th percentile male - GHBMC) to investigate the effect of cervical muscles in concussive impacts on head with various loading conditions. The impact locations and velocities were based on NOCSAE (National Operating Committee on Standards for Athletic Equipment) linear impactor testing standards. Our findings show that, of all the major anatomical regions, cervical muscles absorb the most internal energy early in impacts, implying a role in stabilizing the head at the time when peak head responses are developed. Moreover, our results have helped us find the importance of both deep and superficial neck muscles, as we ranked each muscle based on their internal energy absorption. Further results from our studies suggest that in low velocity impacts, activating muscles could help to reduce head injuries, but not decrease the likelihood of mTBI in an average male. Muscle fatigue caused by prolonged games has been associated to a decrease in neck force output, and we discovered that it can raise peak head kinematics as well as other injury metric parameters. This could increase the likelihood of concussions or have more serious repercussions, such as a second concussion.

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