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Traumatic brain injury, concussion, and subconcussion are different clinical conditions associated with head injury. These conditions share a common origin, mechanical forces directly or indirectly transmitted to the head. In sports, modalities with high exposure to head traumas require further investigation, especially those in which strikes directly to the head are allowed and a determinant of success, such as combat sports. The causes and effects of brain injuries in combat sports such as Mixed Martial Arts, boxing, Muay Thai, and kickboxing are complex and require a comprehensive investigation of many factors. The objective of this dissertation was to explore the main causes that justify combat sports as the main sport sample when it comes to head injury and the effects of chronic exposure to head trauma in this population. Original studies were developed to assess the head injury risk in competition and in training, the level of knowledge of athletes and coaches, and the consequences of chronic exposure to head traumas in the balance function, brain activity, and spinal cord excitability. The risk of a fight ending due to head strikes in competition is directly related to the weight category, and the risk seems to be exacerbated in female athletes. Combat sports athletes are exposed to numerous strikes to the head in simulated fights on a weekly basis in training, when healthcare professionals are absent. During this time that makes up the bulk of exposures, therefore, athletes and coaches are the ones managing potential cases of concussion. However, coaches are not familiar with assessment tools and don’t often seek out concussion knowledge. Alarmingly, coaches, often prior athletes themselves, are the main source of concussion knowledge for their athletes. High exposure to head trauma both in competition and training in addition to iv poor knowledge and behavior are liable to cause consequences in the nervous system. Athletes chronically exposed to head trauma presented subtle deficits in static balance in the most basic human stance, which is the double-leg over a firm surface. Moreover, while the literature consistently shows impairments in brain function, our study expanded the association between head trauma and nervous system deficits to the least studied component of the nervous system, the spinal cord. While athletic training promotes neuroplastic benefits in spinal cord excitability, these were hindered in a sample of athletes chronically exposed to head traumas. The studies in this dissertation demonstrated that athletes in combat sports are chronically exposed to intentional and repetitive head traumas, and that this exposure is likely associated with long-term functional detriments in balance and spinal cord excitability. / Graduate

Unintentional injuries present a major threat to the health and welfare of humans. Over 120,000 deaths and over 30,000,000 non-fatal injuries are estimated annually in the United States. The leading causes of nonfatal injuries vary with age, but falls, motor vehicle collisions (occupants), and being struck by or against are among the top 4 leading causes of unintentional injury for all ages. The loading mechanism that cause forces to be transmitted to the body during these events can cause a wide assortment of injury types with a range of severities. Understanding the biomechanical response to loading in these environments can facilitate efforts in injury mitigation. Biomechanical responses can be quantified by performing controlled laboratory experiments with human volunteers and surrogates, such as anthropomorphic test devices (ATDs) and post mortem human surrogates (PMHSs). The overall objective of this dissertation is to quantify the biomechanical response to loading regimes present in motor vehicle collisions, falls, and when being struck by or against an object using human volunteers and surrogates. Specifically, the research will achieve the following: quantify the dynamic responses of human volunteers, Hybrid III ATD, and PMHSs in low-speed frontal sled tests; quantify the neck response of human volunteers and PMHSs in low-speed frontal sled tests; quantify the kinetic and kinematic responses of PMHSs and the Hybrid III ATD in high-speed frontal sled tests; characterize thoracic loading as a result of same level falls using a Hybrid III ATD; and quantify the ability of children to swing sword-like toys and the human kinematic response that could be anticipated as a result of forceful impact using a Hybrid III 6-year old head and neck. / Ph. D.

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