# The Effects of Concussions on Static Postural Stability
## 2 Materials and Methods  
A total of thirty healthy collegiate volunteers (age 21.63 \(\pm\) 2.50 years; height 1.70 \(\pm\) 0.14 m; weight 75.00 \(\pm\) 15.58 kg; 9 males; 2 left leg dominants; 17 with a history of concussions) without current or recent history of neurological, visual, vestibular, or musculoskeletal abnormalities were recruited for the study. Participants with a history of lower extremity fractures, surgery, back pain, or joint sprains within the last three months were excluded from the study. The study was approved by the institutional review board (IRB-AY22-23-301). The sample size was calculated using G*Power statistical software (3.1.9.6) with an effect size of 0.25, a desired power of 0.8, and an alpha level of 0.05. The study consisted of a single session for each participant, conducted over the course of one day. Participants were instructed to refrain from vigorous leg workouts the day before testing. Upon arrival at the laboratory, informed consent was obtained, followed by completing a Physical Activity Readiness Questionnaire (PARQ+) to inquire about any existing pathology. To get the concussion history, the participants answered an online-based survey, which asked whether they had any concussions, how many concussions they had, how many concussions were diagnosed by a medical professional (e.g., medical doctor, nurse, athletic trainer, etc. ), when their last concussion was, and the activity(ies) led to their concussion(s). Then, the participants' demographics and anthropometric data were recorded, and the dominant leg was determined using the ball-kick test (i.e., asking the participants, \"If I gave you a ball to kick, which leg you would use\") [16]. After recording these, they were familiarized with the study protocols, including standing on the force plate in a standardized body position. During each trial, the participants were advised to stand in the middle of the force plate, feet shoulder-width apart, keeping the arms along the body, looking forward with gaze fixed, without talking. The participants were allowed to practice standing on the force plate during familiarization. Following familiarization, the testing started. The protocol included three tests: baseline stability test, Clinical Test of Sensory Interaction and Balance (CTSIB) test, and unilateral stability test administered in the same order for every participant. Static postural stability was assessed using an AMTI force platform (Advanced Mechanical Technology, Inc., Watertown, MA, USA) at a rate of 100 Hz and analyzed using bioanalysis software version 2.2 (Watertown, MA, USA) [17]. During the baseline stability test, the participants' static postural stability was assessed while standing on the force plate, on both feet, and with their eyes opened. Three 20-s trials were recorded for this test. The CTSIB test included four conditions: standing on the force plate on both feet and eyes opened (firm BL EO condition), standing on the force plate on both feet and eyes closed (firm BL EC condition), standing on a foam pad placed on the force plate on both feet and eyes opened (foam BL EO condition), and standing on a foam pad placed on the force plate on both feet and eyes closed (foam BL EC condition) (Figure 1). During this test, three trials were recorded for each condition, each 10 s long. As the postural sway variables of interest, the maximum COP excursion in the anterior-posterior direction (COP-X max), minimum COP excursion in the anterior-posterior di  
Figure 1: **(Left)**: A participant standing on the force platform on both feet during the clinical test of sensory interaction and balance (CTSIB) test; (**Middle**): A participant standing on a foam pad placed on the force platform on both feet during CTSIB test; (**Right**): A participant standing on the force platform on one foot during unilateral stability test.