A Systematic Review of Head Impacts and Acceleration Associated with Soccer

Abstract

Epidemiological studies of the neurological health of former professional soccer players are being undertaken to identify whether heading the ball is a risk factor for disease or premature death. A quantitative estimate of exposure to repeated sub-concussive head impacts would provide an opportunity to investigate possible exposure-response relationships. However, it is unclear how to formulate an appropriate exposure metric within the context of epidemiological studies. We have carried out a systematic review of the scientific literature to identify the factors that determine the magnitude of head impact acceleration during experiments and from observations during playing or training for soccer, up to the end of November 2021. Data were extracted from 33 experimental and 27 observational studies from male and female amateur players including both adults and children. There was a high correlation between peak linear and angular accelerations in the observational studies (p < 0.001) although the correlation was lower for the experimental data. We chose to rely on an analysis of maximum or peak linear acceleration for this review. Differences in measurement methodology were identified as important determinants of measured acceleration, and we concluded that only data from accelerometers fixed to the head provided reliable information about the magnitude of head acceleration from soccer-related impacts. Exposures differed between men and women and between children and adults, with women on average experiencing higher acceleration but less frequent impacts. Playing position appears to have some influence on the number of heading impacts but less so on the magnitude of the head acceleration. Head-to-head collisions result in high levels of exposure and thus probably risk causing a concussion. We concluded, in the absence of evidence to the contrary, that estimates of the cumulative number of heading impacts over a playing career should be used as the main exposure metric in epidemiological studies of professional players.

Keywords: age; association football; epidemiology; heading; mild traumatic brain injuries (mTBIs); peak linear acceleration (PLA); playing position; repetitive sub-concussive head impacts (RSHIs); sex; soccer.

Figure 1

The literature search and review process.

Figure 2

Scatter plot of mean peak linear and angular acceleration, by experimental (squares and diamonds) and observational (cross and plus) studies. Symbol area reflects the number of measurements associated with the mean.

Figure 3

Geometric mean PLA by method of data collection for observational studies.

Figure 4

Number of head impacts per hour for male and female players, categorised by heading and mixed head impacts.

Figure 5

Geometric mean PLA for various types of head impact during play, for male and female players.

Figure 6

Geometric mean PLA from observational studies subdivided by age.

Figure 7

Forest plot of PLA for each observational study by activity or playing position, subdivided by early youth and youth.