Repetitive Head Impacts in Football Do Not Impair Dynamic Postural Control

Abstract

Purpose: The purpose of this study was to assess the effect of repetitive head impacts experienced by football players compared to noncontact athletes on dynamic postural control during both single-task (ST) and dual-task (DT) conditions.

Methods: Thirty-four football players wearing accelerometer instrumented helmets and 13 cheerleaders performed a dynamic postural control battery, consisting of ST and DT gait initiation, gait, and gait termination, both prior to and following the football season. A 2 (group) × 2 (time) repeated measures ANOVA compared performance across 32 dynamic postural outcomes. A linear regression was performed on postural control change scores with common head impact kinematics serving as the independent variables.

Results: The football players experienced a mean of 538.1 ± 409.1 head impacts in the season with a mean linear acceleration of 27.8g ± 3.2g. There were no significant interactions for any of the ST or DT dynamic postural control tasks. There was a significant relationship between head impact kinematics and the lateral center of pressure displacement during the anticipatory postural adjustment phase (r = 0.26, P = 0.010) and transitional phase (r = 0.511, P = 0.042) during ST gait initiation. For both measures, the number of impacts exceeding 98g was the only significant predictor of decreased center of pressure displacement.

Conclusions: A single competitive football season did not adversely affect dynamic postural control when comparing football players to cheerleaders who do not experience repetitive head impacts. Furthermore, there were limited relationships with head impact kinematics suggesting that a single season of football does not adversely affect most outcome measures of instrumented dynamic postural control. These findings are consistent with most studies which fail to identify clinical differences related to repetitive head impacts.

Figure 1.. Laboratory Set-up.

The participants begin each GI trial with one foot on force plate #1 and one foot on force plate #2. The participant initiated gait and their first heel strike impacted either force plate #3 or #4 and the participant continued down the GAITRite mat and stopped approximately 2.5 meters thereafter. The GT trials occurred in reverse direction with the individuals traversing the GAITRite mat before terminating gait with the penultimate step on either force plate #3 or #4 and the terminating step occurring with one foot on force plate #1 and one foot on force plate #2.

Figure 2A.

Exemplar of Gait Initiation (GI) Center of Pressure (COP) displacement for Right Foot initial step. Movement initiation is operationally defined as the first change (± 2 SD from the mean of the first 500 ms of quiet stance) in posterior displacement of the COP. The APA component ends at the most posterior and medial position towards the initial swing limb. The transitional component ends at the maximum translation towards the initial stance limb. The locomotor component ends at toe-off of the initial stance limb.

Figure 2B.

Exemplar of Gait Termination (GT) Center of Pressure displacement. The Braking Phase represents the transition from penultimate step (left foot) to the termination step (right foot) with the left foot then ending forward locomotion during the Transitional and Stabilization phases.

Figure 3A.

There was significant relationship between the number of impacts exceeding 98g’s and the change in COP displacement during the APA lateral displacement phase of GI (P=0.002). The APA ML displacement is calculated as Post minus Pre, thus a negative number reflects decreased displacement and a positive number reflects increased displacement.

Figure 3B.

There was significant relationship between the number of impacts exceeding 98g’s and the change in COP displacement during the Transitional component of GI (P=0.026). The transitional phase displacement is calculated as Post minus Pre, thus a negative number reflects decreased displacement and a positive number reflects increased displacement.