# The Effects of Concussions on Static Postural Stability
## 1 Introduction  
Concussions are defined as a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces [1]. Concussions could be identified as a significant intrinsic factor that could affect an athlete's postural stability. Postural control must happen in order to maintain a myriad of activities and postures [2], and thus, the deficits can result from a sensory, motor, or cognitive impairment [2]. [PERSON] [3] found that \(-\)67-77% of the people who had a concussion experienced dizziness, which resulted in a risk factor for a longer recovery. Other symptoms of concussions include facial and neck pain, blurred vision, sleep disturbance, headache, memory and concentration [1, 2]. However, the non-modifiable and modifiable risk factors of concussions are not well understood [4]. Concussions can affect everyday life, whether that be in sports, recreation, or work [5], and can affect someone's performance and injury risk. Having a concussion diagnosed immediately after a blow or hit to the head allows for an active management approach, which can result in faster recovery and prevent a secondary injury [5]. In [PERSON]'s [3] literature review, the authors found that 3-10 days post-injury, the concussed individuals had balance impairments. Research shows that most people who have suffered a concussion recover completely, but about 10-15% of individuals who have had a concussion do not recover completely and suffer from post-concussion syndrome (PCS) [6]. More specifically, some research specifies that it can takeup to 3 to 6 months to recover [7]. Roughly 40% of concussed people have impairments that affect their daily life [8; 9; 10], while 25% still cannot return to work one-year post-injury [8]. Furthermore, some people have persistent symptoms that require active rehabilitation [5]. The outcome of concussions depends on the severity of the concussion. Clinically, the individuals with concussions are categorized as grade 1, grade 2, and grade 3, depending on their symptoms. In this categorization, amnesia, confusion, and loss of consciousness are the main symptoms to consider. There are different guidelines that exist for this categorization, such as the Colorado Sports Concussion Grading Scale, the American Academy of Neurology Concussion Grading Scale, and the Cantu Sports Concussion Grading Scale. In all grading scales, transient confusion is considered grade 1, and loss of consciousness is considered a grade 3 [3]. Lifetime concussion symptoms lead to an increased risk of falls and motor disturbances [11]. Decreased postural control and neurocognitive function are both side effects of someone who has had a concussion [12]. As well as over 23% of concussed people complain about being dizzy [4]. Dizziness can be a result of either inner ear disorders and central nervous system disorders [4]. Some of these disorders include benign paroxysmal positional vertigo and post traumatic migraine [4]. The central nervous system (CNS) plays a key role in postural equilibrium [13]. For the CNS to maintain equilibrium and execute coordinated and appropriate musculoskeletal responses, it must process and integrate information from the somatosensory (proprioceptive), vestibular, and visual systems [13]. The feedback received from the peripheries must be processed in the CNS to send messages to the muscles in the extremities to contract appropriately for the body to maintain postural stability [13]. Thus far, the results from studies that investigated the effects of concussions on balance are controversial. [PERSON] [14] found that postural stability was not affected by a concussion. [PERSON] [13] found that when the task became more complex by altering the somatosensory, vestibular, or visual feedback during the trial, the balance impairment increased in the individuals who had a mild traumatic brain injury (mTBI).