The background for this study was a concern that heading and sub-concussive head impacts could cause cognitive impairments among football (soccer) players. Controlled heading is however, no longer considered as a major risk factor for developing cognitive deficits, but the neuropsychological consequences of football-related sub-concussive and concussive impacts await further confirmatory investigation. In addition, no prospective study has previously investigated the acute effects of sub-concussive head impacts on neuropsychological performance.
Thus, the overall main objective of this study was to examine the effect of minor head impacts in professional football with respect to signs of neuronal tissue damage or reduced neuropsychological function.
The main effect variables in the study were the changes in serum concentration for protein S100B, a biochemical marker of brain injury, and neuropsychological performance as assessed by a commercially available computerised test battery (CogSport).
The participants were players in the Norwegian professional top league (Tippeligaen). Baseline blood sampling and neuropsychological testing were performed for all players in Tippeligaen prior to the 2004 and 2005 seasons (>70% estimated participation rate). A player who experienced a head impact during a league match was followed up with blood sampling within one hour after the match and the following morning along with a neuropsychological follow-up test. Videotapes of the incidents were collected from the Norwegian Broadcasting Corporation (NRK) and reviewed. A group of players without head impact was also tested after a league match to serve as controls.
Paper I: The reproducibility for the CogSport test was investigated based on 232 Norwegian professional football league players completing two consecutive neuropsychological tests at the baseline testing prior to the 2004 season. The computerised test battery showed excellent reproducibility for the reaction time measures and these measures were therefore recommended as the test’s primary outcome variables. However, a small but significant practise effect was found and a dual baseline testing with rejection of the first test is advised to minimise this effect.
Paper II: In this paper we found no effect of previous concussions and self-reported heading exposure on the neuropsychological performance in Norwegian professional football players. The results were based on the neuropsychological test results for the 271 players who were tested at baseline 2004. The vast majority (96.1%) of these football players revealed in addition no evidence of cognitive impairments when compared to normative data.
Paper III: This paper discussed the results from the analysis of the S100B samples. In addition to the head impacts and the controls that were recruited from the regular league matches, three teams (N=48) performed one high-intensity exercise session without heading and one low-intensity exercise with heading exercises. The serum levels of S100B were measured before the first training and within one and twelve hours after each of the two training sessions.
Of the total of 228 head impacts registered during the two football seasons, 65 (28.5%) impacts were followed up with blood samples one hour after the impact and 40 (17.5%) the following morning. Both football training and football matches led to a transient increase in serum S100B up to the cut-off level for what is considered as borderline pathological values. Minor head impacts did not cause an additional increase in the S100B level beyond what was measured after a regular match. All serum S100B values were below what is measured for hospital-admitted minor head trauma patients. Thus, there is no evidence suggesting that there is significant brain tissue injury associated with minor head impacts in football. However, the S100B sample might not be an ideal marker for brain injury in athletes due to the increases seen after physical activity only.
Paper IV: A total of 44 (19.3%) of the 228 identified head impacts in the two seasons were followed up with neuropsychological testing the following day. The video analyses indicated that there seemed to be a shift towards a concentration of the more severe incidents in the followed up group. Nevertheless, in more than 60% of these incidents the player went back to play immediately after the impact and only six of the impacts were reported in as concussions that resulted in time-loss from football activities.
Still, an acute reduction in neuropsychological performance was found after these minor head impacts in football, even in allegedly asymptomatic players. However, the followed-up impacts represented the more severe spectrum of the mild head traumas in football. Still, only six of these impacts were reported as concussions. The test performance was reduced from one year to the next in footballers who had experienced head impacts during the season, but all tests were within the normal range. Consequently, the clinical significance of this finding is uncertain.
Investigators: This study is a collaborative effort between the Oslo Sports Trauma Research Center and the FIFA-Medical Assessment and Research Center.
Principal investigator: Roald Bahr MD PhD, Oslo Sports Trauma Research Center
PhD-fellow and test coordinator: Truls M. Straume-Næsheim MD, Oslo Sports Trauma Research Center