The Effect of Repetitive Head Impacts on Postural Control Over the Course of a Single Season

INTRODUCTION: Recently neurocognitive dysfunction has been linked to poor postural control in concussed athletes. While the detrimental effect of repetitive head impacts on cognitive function have been shown to mirror the effects of concussive injury, very little research has investigated the physical consequences of repetitive head impacts. PURPOSE: To observe the effects of RHI on postural control, both static and dynamic, in NCAA Division I athletes over the course of a single season. METHODS: 9 NCAA Division I football athletes (CON) were recruited from a single university as the experimental group, as well as 9 NCAA Division I baseball players (NON) from the same university to serve as non-contact control group. Subjects’ postural control, measured via a force platform, was tested before and after their fall competitive season using a static postural control assessment and dynamic postural control assessment. The static postural control assessment consisted of eyes open (EO) and eyes closed (EC) quiet standing, while the dynamic postural control assessment consisted of the Wii Fit Soccer Heading Game (WiiSoccer), a sport relevant goal-oriented task. Center of pressure data was used to observed peak excursion velocity (PEV) in the medial-lateral (ML) and anterior-posterior (AP) direction, 95% confidence ellipse (CE), and sample entropy (SampEn) in the ML and AP direction. Repetitive head impacts were quantified in the CON group using the Head Impact Telemetry (HIT) System, which is a six-single axis accelerometer helmet unit that was used to record peak linear accelerations. The HIT System was used to quantify the cumulative impact burden (CIB) and average impact magnitude (AIM) among the CON group. RESULTS: Subjects in the CON group experienced a CIB of 1,234.2 g ± 1,0098 g and AIM of 30.7 g ± 6.8 g over the course of 52 practice sessions and 19 game/scrimmage sessions. Repeated measures ANOVA’s revealed a significant difference (p=0.003) in EO SampEn ML between pre (CON: 0.544, NON: 0.548) and post-season testing (CON: 0.433, NON: 0.515). There was also a significant difference (p\u3c 0.001) between pre (CON: 0.657, NON: 0.565) and post-season (CON: 0.548, NON: 0.549). Finally, there was a significant effect (p=0.003) of time by groups in SampEn AP; the CON group had a significantly greater decline between pre (0.657) and post-season (0.548) compared to NON group (0.565 vs. 0.544 respectively). No significant difference was found in the EC or WiiSoccer condition. CONCLUSION: These results suggest that athletic participation does influence static postural control. Nonlinear force plate variables may be the only metrics capable to detecting subtle changes that occur throughout the season. Finally, these results suggest that there was a significant difference between CON and NON during EO condition. This may indicate a deficiency in appropriate integration of visual information, and inability of effective communication between postural control systems during simple tasks in the CON group due to increased exposure to repetitive head impacts