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RESULTS
ABSTRACT
MATERIALS AND METHODS
Context More than a million athletes in the
United States and Canada participate annually in
contact ice hockey. Collision is allowed at youth
levels although size and physical maturity differ
considerably among players less than 16 years of
age. A better understanding of how these factors
affect head impacts in youth ice hockey is
needed. Objective To measure the magnitude of
head impacts sustained by youth ice hockey
players and to compare these impacts across event
type (practice, game), player position, and
location. We also sought to evaluate whether an
association between high-magnitude head impacts
and event type, player position, or location of
impacts existed. Design Prospective experimental
design. Setting Field setting. Patients or Other
Participants 15 male adolescent ice hockey
players (age 13 years mass 48.21 9.93 kg
height 159.57 8.58 cm) were recruited from
the same team. Interventions Data from six
single-axis accelerometers embedded in Reebok RBK
helmets were collected using the Head Impact
Telemetry System. Separate one-way analyses of
variance (ANOVA) were performed for event type,
player position, and location of impact.
Chi-square analyses were also utilized to
determine the association between grouping
factors (event type, player position, location of
impact) and impact magnitude ranges. Main Outcome
Measures The impact magnitude, in gravity force
(g), captured by the accelerometers served as the
dependent variable. Location of head impacts were
categorized as back, front, left, right, or top.
Results 4,543 head impacts were recorded during
58 games and 51 practices (mean 18.98 1.64 g
). Game impacts (19.36 1.66 g) were greater
than practice impacts (17.72 1.56 g)
(F1,454125.55 P forwards (centers and wingers) (19.18 1.64 g)
were greater than impacts suffered by defensemen
(18.45 1.65 g) (F1,4541 5.43 P 0.02).
Significant differences between head impact
locations were observed (F4,4538 16.33 P 0.001) impacts to the top of the head (21.85
1.80 g) were significantly greater than impacts
to the back (18.51 1.65 g), front (18.95 1.63
g), left (18.42 1.57 g), and right (18.21
1.58 g) sides. Event type (?2(2)22.70 P 0.001) and impact location (?2(8) 53.75 P 0.001) were associated with magnitude of impacts.
Players were 4.25 times more likely to sustain a
high-magnitude impact in games compared to
practices. High-magnitude impacts to the top of
the head were 4.88, 3.25, and 3 times more likely
than left and right, front, and back sides,
respectively. An association between player
position and magnitude (?2(2) 3.00 P 0.223)
was not observed. Conclusions Youth ice hockey
players sustain helmet impacts nearing 20 g on
average these magnitudes are similar to observed
values in collegiate football players and are
concerning because our sample involves much
younger athletes. The frequencies of top of the
head impacts are greater than those sustained to
other areas of the head, but future biomechanical
studies are needed to better interpret the
implications of this finding. Our ongoing study
may eventually permit a better understanding of
concussions and cervical spine injuries in youth
athletes.
F1,4541 25.55 P 0.02
F4,4538 16.33 P

Game Practice
Forward
Defense
Back Front
Left
Right
Top
Event Type
Player Position
Location of Head Impact
Figure 3. Mean linear head acceleration across
event type, player position, and location of head
impact. Impacts sustained in games were
significantly larger than those sustained in
practices, and forwards tended to sustain larger
head impacts than defensemen. The largest head
impacts were seen by way of blows to or with the
top of the head.
A strong association between more severe head
impacts (80 g) and location of impact was
observed (?2(8) 53.75 P hockey players were 4.88, 3.25, and 3 times more
likely to sustain a severe impact to the top of
the head compared to the sides, front, and back
of the head, respectively.
A strong association was observed between more
severe head impacts (80 g) and event type (?2(2)
22.70 P impacts 4.25 times more likely to occur in games
than in practice. No association with player
position was observed (?2(2) 3.00 P 0.223).
BACKGROUND
Figure 2. Illustrating how impacts were
categorized based on location of head impacts
Sports-related traumatic brain injuries (TBI) are
a major public health concern.1,2
An estimated 1.6 to 3.8 million sports-related
TBI occur each year in the United States.3
There are over 1 million registered youth ice
hockey players in the United States and Canada
millions more participate recreationally.
Players as young as 9 years of age are allowed to
body check in ice hockey. Size and physical matur
ity can differ greatly, especially in adolescents
less than 16 years of age within-age differences
are also evident in players of different skill
level Sports-related concussions are approximatel
y 50 more likely to occur in contact hockey
compared to non-contact play.4
Body checking is the most common mechanism of
injury in ice hockey players injury rates from
this mechanism increases significantly with
age.5 Concussion rate is highest in Bantam-aged p
layers (13/14 years), with as many as 1
concussion per 1000 player-hours.5
CONCLUSIONS
Youth ice hockey players sustain head impacts
similar to Division I collegiate football
players.6 This is of potential concern since the
hockey players in this sample are much smaller
and younger. We observed 4 times more impacts in
games (2700) than in practice (650) whereas,
it is not uncommon for certain positions in
football to sustain as many, if not more, head
impacts in practices compared to games.
Of 41 impacts resulting in a linear head
acceleration of 80 g, only 1 resulted in a
concussion (86.51 g). More injuries will be neede
d in order to better understand the biomechanical
factors associated with sports-related concussion
in youth athletes. Future studies will relate the
biomechanical properties of head impacts with
clinical measures of adolescent concussion
including, but not limited to, neuropsychological
testing, balance performance assessments, and
symptom status. No distinction was made between s
killed and less skilled players in our sample. As
we collect more injuries, well know more about
the effects of exposure (i.e. are less skilled
players more likely to be injured? Or is risk of
injury really a function of on-ice playing time?)
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Mihalik JP, Guskiewicz KM, Bell DR, Marshall SW.
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Figure 1. The protective foam of the ice hockey
helmets were removed from the helmet shell.
Following this, six single-axis accelerometers
were fitted into custom holes cut into the foam.
The figure depicts the location of the helmet
accelerometers in the protective foam (hard shell
removed) in both front (A) and rear (B) views.
The red arrows identify the location of the six
accelerometers as viewed from the inside of a
fully assembled playing ice hockey helmet (C).
ACKNOWLEDGMENTS This project was funded by the On
tario Neurotrauma Foundation (Toronto, Ontario,
Canada) in collaboration with the Injury
Prevention Research Center at The University of
North Carolina (Chapel Hill, NC).