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.

Repetitive bout of controlled soccer heading does not alter heart rate variability metrics: A preliminary investigation

“…However, the two studies vary in several key aspects. The current investigation had individuals successfully perform 40 headers with a 20-min span at a distance of ∼25 m, whereas Harriss et al (19), had players engage in just 5 headers, although these were performed in under a minute at a distance of just ∼8 m. Moreover, they propelled the ball at 21.6 km/h toward the participants, whereas the current protocol used initial velocity of 77.5 ± 3.7 km/h, resulting in average linear and rotational head accelerations near the upper values previously reported (54). Finally, the previous investigation examined spontaneous HRV and cardiac BRS measures in a supine position; whereas in this study they were taken in an upright position, which is known to reduce variation and enhance reproducibility (55).…”

Cognitive function among former professional male soccer players – the HEADING study

“…However, stronger forms of impacts to the head -those associated with higher levels of acceleration compared to the heading 26 Overall, these findings suggest that there is little or no association between heading the ball and reduced cognitive function. This is consistent with the findings of some previous studies 10, 13,14 , recently summarised in a systematic review In our study, we used a questionnaire that was developed, piloted and validated in a group of former professional players.…”

“…We do not find a clear association between exposure to heading and cognitive function later in life. However, stronger forms of impacts to the head – those associated with higher levels of acceleration compared to the heading 26 – were found to be associated with poorer cognitive function, albeit among forwards only. Soccer-related concussions were found to be associated with poorer cognitive function later in life overall, and particularly among defenders and goalkeepers.…”

“…Cumulative exposure to heading and other impacts to the head was estimated from the participants’ playing history obtained from dedicated questionnaire developed with extensive piloting, validation and input from the PFA, the Football Association (FA), and the coaching staff of Sheffield United Football Club 19 . Cumulative exposure was calculated as the number of episodes (exposure to heading impacts, and other impacts to the head) over a playing career, including juvenile, and post retirement 26 . Modelled exposure estimates were used to minimise the presence of potential measurement errors due to recall 27 and to allow the assignment of exposure estimates to participants with missing information (n=12).…”

Cognitive and Behavioral Outcomes in Male and Female NCAA Soccer Athletes across Multiple Years: A CARE Consortium Study

“…Previous work suggested that male soccer players experience a greater number of RHI, but female soccer players experience higher amplitude RHI (21–23). A recent systematic review and meta-analysis suggested that the mean number of RHI from soccer heading per hour was 2.4 in male soccer players and 0.5 in female soccer players, whereas the mean amplitude of RHI was 15.9 g in female soccer players and 13.9 g in male soccer players (24).…”