Evidence for Acute Electrophysiological and Cognitive Changes Following Routine Soccer Heading

Abstract

Introduction: There is growing concern around the effects of concussion and sub-concussive impacts in sport. Routine game-play in soccer involves intentional and repeated head impacts through ball heading. Although heading is frequently cited as a risk to brain health, little data exist regarding the consequences of this activity. This study aims to assess the immediate outcomes of routine football heading using direct and sensitive measures of brain function.

Methods: Nineteen amateur football players (5 females; age 22±3y) headed machine-projected soccer balls at standardized speeds, modelling routine soccer practice. The primary outcome measure of corticomotor inhibition measured using transcranial magnetic stimulation, was assessed prior to heading and repeated immediately, 24h, 48h and 2weeks post-heading. Secondary outcome measures were cortical excitability, postural control, and cognitive function.

Results: Immediately following heading an increase in corticomotor inhibition was detected; further to these electrophysiological alterations, measurable reduction memory function were also found. These acute changes appear transient, with values normalizing 24h post-heading.

Discussion: Sub-concussive head impacts routine in soccer heading are associated with immediate, measurable electrophysiological and cognitive impairments. Although these changes in brain function were transient, these effects may signal direct consequences of routine soccer heading on (long-term) brain health which requires further study.

Keywords: Sports concussion; Sub-concussion; Transcranial magnetic stimulation; Traumatic brain injury.

Fig. 1

Snapshots of the cortical silent period (cSP) of two participants measured by TMS before (a) and immediately after heading (b) illustrating a typical lengthening in cSP immediately following heading. The cSP was quantified as the period of time between the delivered TMS pulse (dashed line) and the resumption of uninterrupted EMG activity (arrows).

Fig. 2

Change in cortical silent period (cSP) duration for each participant from baseline to immediately following the heading protocol.

Fig. 3

Difference in cSP in ms after heading relative to baseline. Immediately after heading cSP duration increased on average by 5.3(± 5.7)ms (*p < 0.05) which within participants is an 5.4(± 4.8)% average increase from baseline values. This increase detectable immediately after heading normalized over the four follow-up timepoints (p < 0.05) with values apparently returning to baseline level. Error bars indicate the 95% confidence intervals.

Fig. 4

Difference in memory performance (log transformed error score difference) after heading relative to baseline. Immediately after heading, errors were higher compared to baseline on both the (a) Spatial Working Memory SWM (*p < 0.05) and (b) Paired Associated Learning PAL (*p < 0.01) tasks. This increase evident immediately after heading normalized over the four follow-up timepoints (p < 0.01) with error scores apparently returning to baseline level. Error bars indicate the 95% confidence intervals.