Head impact exposure
sustained by football players on days of diagnosed concussion

J.G., Greenwald R.M., Chu J.J., Crisco J.J., Rowson S., Duma S.M., Broglio
S.M., McCallister T.W., Guskiewicz K.M., Mihalik J.P., Anderson S., Schnebel
B., Brolinson P.G., Collins M.W. Medicine and Science in Sport and Exercise.
2013; 45: 737-746

Take Home Message:
Players sustained more head impacts and higher severity of impacts on days of
diagnosed concussion compared to days with no diagnosed concussion. Also, peak
linear acceleration was the best predictor of immediately diagnosed

prevention methods are difficult to develop because we lack an understanding of
the relationship between head impact mechanics and subsequent concussions. We
can improve our understanding by measuring impact forces during sporting
events; however; most studies have only included a small number of athletes,
which limited the ability to determine which biomechanical characteristics
result in injury among football athletes. Therefore, the purpose of this study
was to compare frequency and kinematic response of head impacts on days with
and without a diagnosis of concussion and identify sensitivity and specificity
of single-impact severity measures to diagnose concussive injuries. Football players from 8 colleges and 6 high schools wore
instrumented [Head Impact Telemetry (HIT) system] helmets, which recorded measures of head impact exposure
(i.e., frequency, location, and kinematic response of head impacts) during a 6-year
period. A total of 161,732 head impacts were recorded over 10,972 player days among
95 football athletes diagnosed with a concussion. This yielded 105 cases of
diagnosed concussions (8 players sustained 2 concussions and 1 player sustained
3 concussions).
Seventy percent of the concussions occurred during a game or scrimmage. In 45
concussion cases the players were removed immediately after injury and
diagnosed with a concussion. In the remaining 60 cases the athletes continued
to play, which resulted in a delayed diagnosis. Measurements from the HIT
system were compared between days with and without diagnosed concussion. The
authors found that the frequency and severity of head impacts were greater on
days with diagnosed concussion compared to days with no concussion diagnosis. For
cases that were immediately diagnosed with concussion after head impact the
magnitude of peak head acceleration was the most sensitive factor in detecting concussions.
Peak rotational acceleration was the least sensitive measure to detect a
concussion compared to all other kinematic measures.

was the largest collection of real-time biomechanical data from head impacts
within an athletic population associated with the diagnosis of concussion. The
key findings presented in this study indicate that players sustain both a
greater number and severity of head impacts on days with diagnosed concussion
compared to days with no diagnosed concussion. However, it is important to
remember that these findings are primarily applicable to football players that
are immediately diagnosed with a concussion since the authors excluded the 60
cases with a delayed diagnosis of concussion. Athletes with a delayed diagnosis
are important because the authors previously found that this is the majority of concussions and the mechanism of their concussion is not as easy to identify. It was also
interesting to note that rotational acceleration was found to be the least
sensitive of all the severity measures to detect an immediately diagnosed
concussion since previous research suggested that poorer outcomes come from a
rotational injury rather than from linear impacts. Finally, kinematic
measurements on days without a concussion were almost identical to previously
reported measurements among football players that had no diagnosed concussion,
which demonstrates the repeatability of this method to assess concussion.. Overall,
this data may help us develop better prevention methods (e.g., equipment, rule
changes) or eventually help clinicians detect athletes exposed to dangerous
head impacts. Do you think a rule change would help decrease the number of
concussions? Do you think having a concussion threshold will help diagnose some

by: Jane McDevitt MS, ATC, CSCS
by: Jeffrey


Beckwith JG, Greenwald RM, Chu JJ, Crisco JJ, Rowson S, Duma SM, Broglio SP, McAllister TW, Guskiewicz KM, Mihalik JP, Anderson S, Schnebel B, Brolinson PG, & Collins MW (2013). Head Impact Exposure Sustained by Football Players on Days of Diagnosed Concussion. Medicine and Science in Sports and Exercise, 45 (4), 737-746 PMID: 23135363