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CHAPTER 1
Epidemiology of Sports Injuries
and Illnesses
Debbie Palmer-Green
Senior Research Fellow, Arthritis Research UK, Centre for Sport, Exercise & Osteoarthritis, University of Nottingham,
Nottingham, UK
OVERVIEW
• Sports injury and illness epidemiology research is continuing to
grow
• Study design and methods can influence the conclusions made
• The definition of injury/illness, and rate and severity indices
should be appropriate to the cohort of interest
• Identifying injury and illness causes will help to provide
additional risk information
• Prevention initiatives should target the injury/illness issues posing
the greatest risk
Introduction
Recognition of the importance of sports injury and illness epi-
demiologyresearchhasgrowninthelast10yearswithnational
and international governing bodies of sport regularly conduct-
ing surveillance at major sporting events. Most sports involve
some element of risk with regard to athlete injury or illness, some
signicantly more so than other (Table 1.1).
Although much of the literature is focused on rehabilitation of
athlete injuries (and illnesses), it is just as important to try and pre-
vent them from occurring, or if it is not possible to prevent them
completely at least lessen the severity and impact when injuries and
illnesses do occur. In order to correctly prioritise and accurately tar-
get prevention initiatives to reduce injuries and illnesses in sport, it
is important to understand the magnitude of the problem, that is,
the rate and severity, and the causes. Conducting systematic moni-
toringofathleteinjuriesandillnessesinsportisessentialtoprovide
theevidencebasetoinformthesepreventionstrategies.Inorderto
get accurate and reliable data epidemiological study designs must
be robust, and issues related to the design and implementation of
injury and illness surveillance studies are discussed later, with illus-
trative examples provided.
ABC of Sports and Exercise Medicine, Fourth Edition.
Edited by Gregory P. Whyte, Mike Loosemore and Clyde Williams.
© 2015 John Wiley & Sons, Ltd. Published 2015 by John Wiley & Sons, Ltd.
Table 1.1 Rates of overall injuries and illnesses in the Olympic sports
Sport No. of
athletes
No. of
injuries (%)
No. of
illnesses (%)
Archery 128 2 (1.6) 10 (7.8)
Athletics 2079 368 (17.7) 219 (10.5)
Diving 136 11 (8.1) 7 (5.1)
Swimming 931 50 (5.4) 68 (7.3)
Synchronised swimming 104 14 (13.5) 13 (12.5)
Water polo 260 34 (13.1) 21 (8.1)
Badminton 164 26 (15.9) 5 (3.0)
Basketball 287 32 (11.1) 9 (3.1)
Beach volleyball 96 12 (12.5) 18 (18.8)
Boxing 283 26 (9.2) 18 (6.4)
Canoe slalom 83 2 (2.4) 4 (4.8)
Canoe sprint 249 7 (2.8) 14 (5.6)
BMX 48 15 (31.3) 2 (4.2)
MTB 76 16 (21.1) 5 (6.6)
Road cycling 210 19 (9.0) 7 (3.3)
Track cycling 167 5 (3.0) 16 (9.6)
Equestrian 199 9 (4.5) 11 (5.5)
Fencing 246 23 (9.3) 13 (5.3)
Football 509 179 (35.2) 62 (12.2)
Artistic gymnastics 195 15 (7.7) 5 (2.6)
Rhythmic gymnastics 96 7 (7.3) 1 (1.0)
Trampoline 32 2 (6.3) 1 (3.1)
Handball 349 76 (21.8) 17 (4.9)
Hockey 388 66 (17.0) 29 (7.5)
Judo 383 47 (12.3) 16 (4.2)
Modern pentathlon 72 6 (8.3) 1 (1.4)
Rowing 549 18 (3.3) 40 (7.3)
Sailing 380 56 (14.7) 38 (10.0)
Shooting 390 15 (3.8) 17 (4.4)
Table tennis 174 11 (6.3) 12 (6.9)
Taekwondo 128 50 (39.1) 14 (10.9)
Tennis 184 21 (11.4) 4 (2.2)
Triathlon 110 16 (14.5) 7 (6.4)
Volleyball 288 20 (6.9) 8 (2.8)
Weightlifting 252 44 (17.5) 10 (4.0)
Wrestling 343 41 (12.0) 16 (4.7)
Source: Adapted from Engebretsen et al. 2013. Reproduced with permission
from BMJ Publishing Group Ltd.
Study design and population
e ability to describe the incidence, nature and causes of injuries
and illnesses reliably has been recognised through the development
of injury/illness surveillance consensus statements. Standardising
1
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2 ABC of Sports and Exercise Medicine
Table 1.2 Examples of injury and illness definitions used in epidemiological
studies
a. Any physical complaint sustained by a player … irrespective of the need
for medical-attention or time-loss from activities
b. Any musculoskeletal complaint … that received medical-attention regard-
less of the consequence with respect to absence from competition and/or
training
c. Any physical complaint (not related to injury) that received medical-
attention regardless of the consequence with respect to absence from
competition and/or training
d. Any physical complaint sustained by a player during a match or training …
that prevented the player from taking a full part in all … activities … for
more than 1 day following the day of injury
study design and data collection makes it possible to compare
results between studies. Firstly, the target population (or cohort) to
be studied must be identied. Sometimes what denes a population
is obvious, for example, in a study recording the number of injuries
during the 2011 Rugby World Cup, the players competing during
theWorldCuparethepopulationcohort.Itisimportanttonotethe
period of observation (i.e. again this may be naturally dictated by
the cohort): who is going to record the data (i.e. team physician for
medical data; coaches for training and competition exposure data),
the methods of data collection (paper or electronic) and the type of
study. Retrospective studies collect historical data over a set period
of time, while prospective studies follow the cohort over a set future
period of time. Prospective studies are generally more reliable than
retrospective studies due to issues with the latter of memory recall
bias, where even over short periods of time, more severe or more
recent injuries and illness are likely to be remembered, but the less
severe and more historical episodes are more likely to be forgotten.
Injury/illness definition
A universal denition of injury and illness, applicable to all sports,
would be convenient and simple. Although this has not yet been
achieved, the development of consensus statements has unied
much of the research currently being undertaken (Table 1.2).
Classification of injuries and illnesses
e majority of epidemiological studies have focused on the
aetiology of ‘medical-attention’ and/or ‘time-loss’ denitions of
injury and illness incidents, but few have related these events to an
athlete’s consequential physical limitations. For example, time-loss
classications are somewhat categorical in their use of the term
(i.e. complete absence), when in reality many athletes continue to
compete and train at high levels when experiencing pain and/or
loss of function through injury or illness. Hence, there is a need to
consider an additional level of classication focused on levels of
impairment or performance restriction (Figure 1.1).
e classication and, therefore, the level of data collection
required will need to be determined based on the study population,
that is, recording all injuries including ‘medical-attention’ may not
be appropriate for studies with large populations, or for contact
sports (i.e. rugby) where the number of recorded injuries may be
high, as this will create an overwhelming burden for recording
on medical sta. Conversely, using a ‘time-loss’ only classication
wherethereareasmallnumberofacutetraumaticinjuriesbutan
abundance of overuse chronic performance restriction injuries, for
example, within swimming, may also not be appropriate. Once you
have your injury and illness denition, it is this sub-classication
that determines what becomes a recordable event. It is important
to understand when comparing studies which injuries and illnesses
are included, and which are excluded.
Rate of injury and illness
Reporting only absolute number of injuries or illnesses provides
limited information about the risks to the sample population,
without consideration for the volume or period of exposure
to that risk, i.e., relative hours training/competing, number of
athletes, number of weeks/months or seasons. e two most
common methods of presenting the rate of injury or illness are
incidence and prevalence. Traditionally, incidence is calculated
taking the number of injuries (new and/or recurrent) divided
by the total participant exposure time, and is presented as stan-
dard per 1000 h, to allow for inter-sport comparison. Incidence
values for training and competition should always be reported
separately (Table 1.3).
In the absence of hours of training and competition exposure,
injuries can be expressed per 1000 athletes, or per 1000 athlete expo-
sures (where one training session or competition run = 1 exposure).
Unlike injuries, illnesses are not dened as occurring during train-
ing or competition hence are not usually expressed as a function of
TL
TL
Medical attention
(without time-loss)
(a)(b)
Medical attention
(without time-loss or performance-
restriction)
Performance
restriction
(without time-loss)
Figure 1.1 (a) Traditional hierarchy of injury/illness
definition and classification, TL = time-loss.
(b) Alternative hierarchy of injury/illness definition and
classification
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Epidemiology of Sports Injuries and Illnesses 3
Table 1. 3 Example calculation for incidence of injury
A rugby club plays 48 matches in a season,
during this time the players suffer 41 injuries
Exposure time = 48 (matches) × 1.33 (length of match in hours)
× 15 (number of players in the study team on pitch)
= 960 player match hours
Incidence = (41/960) × 1000
= 43 injuries/1000 match hours
Table 1. 4 Example calculation for prevalence of illness
A swimming squad of 45 athletes has 3 athletes
suffer 4 illnesses during 1 week
Prevalence = (3/45) × 100
= 6.7%
Table 1. 5 Example severity category grouping
Minimal 2–3 days
Mild 4–7 days
Moderate 8–28 days
Severe >28 days
time (i.e. per 1000 athlete training or competition hours/exposures),
but rather per 1000 athletes, or as prevalence.
Prevalence is used to calculate the proportion of the population
that is injured or ill at a given time point (point prevalence) or
over a set period of time (period prevalence). When calculating
prevalence, it is important to remember that the number of individ-
uals is key in expressing injury/illness as a percentage of the cohort
(or team), rather than the absolute number of injuries or illnesses.
For example, over the course of a season, a squad of 30 athletes
may report 40 injuries, that is, multiple injuries per athlete. It is not
possible to have more than 100% of the squad injured; hence, it is
thenumberofathletesinjured/illoutofthefullsquadof30thatis
calculated (Table 1.4).
Severity of injury and illness
e severity of injury and illness may be implicit in the level
recorded, that is, an illness resulting in performance restriction
versus complete time-loss, implies the latter illness is of greater
severity. Traditionally, the number of days aected is the univer-
sally accepted way of reporting severity, and this is calculated as
the number of days from the date of injury/illness to the date of
return to full tness. Days of severity may also be grouped within
recommended severity categories (Table 1.5). In addition to the
number of days, recording the level of pain on a visual analogue
scale can provide an additional layer of information about the
athletes’ perception of the injury/illness severity.
Risk factors for injury and illness
Outcomes from epidemiological studies should include the rate and
severity of injury and illness as a function of each risk factor, that is,
location of injury and cause of illness (Table 1.6).
Table 1. 6 Example risk factors for injury/illness
Risk factors Examples
Time of season Pre-season; month; week
Environment Competition/match or training; playing position
Training Sport specific; running; weight training;
cardiovascular
Cause of injury Contact; non-contact; acute traumatic; chronic
overuse; recurrence
Location of injury Head; shoulder; lumbar spine; thigh; knee;
ankle
Type of injury Sprain; fracture; concussion; contusion;
tendinopathy
Affected illness system Respiratory; gastrointestinal; cardiovascular;
allergic; dental
Cause of illness Infection; exercise induced; environmental;
pre-existing
Table 1. 7 Comparison of injury rate, severity and burden
Injury location No. of
injuries
Injury
rate (%)
Average
severity
(days)
Total days
lost
Burden
(%)
Shoulder 3 6 17.6 52.8 7.5
Lumbar spine 5 12 24.5 122.5 17.5
Thigh 19 38 6.7 127.3 18.1
Knee 8 16 41.2 329.6 46.9
Ankle 14 28 5.0 70 10.0
Total 49 100 14.3 702.2 100
Itisimportanttoconsiderbothwhatismostcommonand
what is most severe when prioritising prevention strategies. For
example, should eorts be focused on those injuries or illnesses
that are most common (but maybe not very severe) or those that
are most severe (but maybe not very common). An alternative way
toanswerthisquestionwouldbetolookatthetotaldayslostor
overall injury/illness burden (also known as risk), when determin-
ing overall importance for the direction of targeting prevention
initiatives (Table 1.7).
Summary
Using sport injury/illness epidemiology consensus statements and
common methodology will help produce valid and accurate study
results, as well as allow inter-study comparisons to be made. e
denition, rate and severity of injury and illness as well as more
detailed information on the causes of injury/illness, relevant to the
population of study, are key in correctly identifying areas of risk and
allowing eective targeting of prevention initiatives.
Further reading
Brooks, J.H.M. & Fuller, C.W. (2006) e inuence of methodological issues
on the results and conclusions from epidemiological studies of sports
injuries: illustrative examples. Sports Medicine, 36 (6), 459–472.
Engebretsen, L., Soligard, T., Steen, K. et al. (2013) Sports injuries and ill-
nesses during the London Summer Olympic Games 2012. British Journal of
Sports Medicine, 47 (7), 407–414.
Fuller, C.W., Ekstrand, J., Junge, A. et al. (2006) Consensus statement on injury
denitions and data collection procedures in studies of football (soccer)
injuries. British Journal of Sports Medicine, 40 (3), 193–201.
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4 ABC of Sports and Exercise Medicine
Fuller, C.W., Sheerin, K. & Targett, S. (2013) Rugby World Cup 2011: Inter-
national Rugby Board injury surveillance study. British Journal of Sports
Medicine, 47, 1184–1191.
van Mechelen, W., Hlobil, H. & Kemper, H. (1992) Incidence, severity, aetiol-
ogy and prevention of sports injuries: a review of concepts. Sports Medicine.,
14, 82–99.
Palmer-Green, D., Fuller, C., Jaques, R. et al. (2013) e Injury/Illness Per-
formance Project (IIPP): a novel epidemiological approach for recording
the consequences of sports injuries and illnesses. Journal of Sports Medicine.
http://dx.doi.org/10.1155/2013/523974 [Article ID 523974, 9 pages]
