ORIGINAL RESEARCH ARTICLE
Health and Economic Burden of Running-Related Injuries
in Dutch Trailrunners: A Prospective Cohort Study
Luiz Carlos Hespanhol Junior1 • Willem van Mechelen1,2,3,4 • Evert Verhagen1,3,5
Published online: 25 May 2016
 The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract
Background Trailrunning
is
becoming
very
popular.
However, the risk and burden of running-related injuries
(RRI) in trailrunning is not well established.
Objective To
investigate
the
prevalence,
injury
rate,
severity, nature, and economic burden of RRIs in Dutch
trailrunners.
Methods This prospective cohort study included 228
trailrunners aged 18 years or over (range 23–67), and was
conducted between October 2013 and December 2014.
After completing the baseline questionnaire, the Oslo
Sports Trauma Research Center Questionnaire on Health
Problems was administered every 2 weeks to collect data
on RRIs. Participants who reported RRIs were asked about
healthcare utilization (direct costs) and absenteeism from
paid work (indirect costs). RRI was deﬁned as disorders of
the musculoskeletal system or concussions experienced or
sustained during participation in running.
Results The mean prevalence of RRIs measured over time
was 22.4 % [95 % conﬁdence interval (CI) 20.9–24.0], and
the injury rate was 10.7 RRIs per 1000 h of running (95 %
CI 9.4–12.1). The prevalence was higher for overuse
(17.7 %; 95 % CI 15.9–19.5) than for acute (4.1 %; 95 %
CI 3.3–5.0) RRIs. Also, the injury rate was higher for
overuse (8.1; 95 % CI 6.9–9.3) than for acute (2.7; 95 % CI
2.0–3.4) RRIs. The median of the severity score was 35.0
[25–75 %, interquartile range (IQR) 22.0–55.7], and the
median of the duration of RRIs was 2.0 weeks (IQR
2.0–6.0) during the study. The total economic burden of
RRIs was estimated at €172.22 (95 % CI 117.10–271.74)
per RRI, and €1849.49 (95 % CI 1180.62–3058.91) per
1000 h of running. An RRI was estimated to have a direct
cost of €60.92 (95 % CI 45.11–94.90) and an indirect cost
of €111.30 (95 % CI 61.02–192.75).
Conclusions The health and economic burden of RRIs
presented in this study are signiﬁcant for trailrunners and
for society. Therefore, efforts should be made in order to
prevent RRIs in trailrunners.
Electronic supplementary material The online version of this
article (doi:10.1007/s40279-016-0551-8) contains supplementary
material, which is available to authorized users.
& Luiz Carlos Hespanhol Junior
l.hespanhol@outlook.com
1
Amsterdam Collaboration on Health and Safety in Sports,
Department of Public and Occupational Health and the
EMGO? Institute for Health and Care Research,
VU University Medical Center Amsterdam, Van der
Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
2
School of Human Movement and Nutrition Sciences, Faculty
of Health and Behavioural Sciences, University of
Queensland, Brisbane, QLD, Australia
3
UCT/MRC Research Unit for Exercise Science and Sports
Medicine (ESSM), Department of Human Biology, Faculty
of Health Sciences, University of Cape Town, Cape Town,
South Africa
4
School of Public Health, Physiotherapy and Population
Sciences, University College Dublin, Dublin, Ireland
5
Australian Centre for Research into Injury in Sport and its
Prevention, Federation University Australia, Ballarat, VIC,
Australia
123
Sports Med (2017) 47:367–377
DOI 10.1007/s40279-016-0551-8
Key Messages
At any given time, one in ﬁve trailrunners report
having a running-related injury (RRI).
Of the RRIs in trailrunners, 75.2 % were overuse
injuries, and the prevalence of overuse RRIs was
fourfold higher than acute RRIs.
The indirect cost of RRIs (related to absenteeism
from paid work) was twofold higher than the direct
cost (related to healthcare utilization).
1 Introduction
Physical activity is a cost-effective and cost-saving inter-
vention to improve overall health and gain healthy life-
years [1–4]. There is evidence claiming that physical
activity participation in outdoor environments has a larger
beneﬁcial effect on physical and mental wellbeing than
participation in indoor physical activities [5]. Coinciden-
tally, trailrunning, a mode of running consisting of running
in the outdoors on unpaved and hilly/mountain terrains, is
quickly gaining in popularity worldwide. The trailrunning
community is composed of well trained trailrunners who
participate in ultra-marathon events ([42.2 km), but also
increasingly by trailrunning enthusiasts who partake in
trailrunning events with shorter distances.
Running is a very popular mode of exercise among
people seeking an active lifestyle [6, 7]. Next to being
beneﬁcial for health [8–10], running also carries a risk of
running-related injuries (RRI) with incidence rates ranging
from 7.7 [95 % conﬁdence interval (CI) 6.9–8.7] to 17.8
(95 % CI 16.7–19.1) RRIs per 1000 h of running in
recreational and novice runners, respectively [11]. How-
ever, prospective data on the risk and burden (including
costs) of RRIs in trailrunning are sparse, especially in
cohorts including trailrunning enthusiasts that compose the
general trailrunning population.
Most RRIs have an overuse nature [12] of which the
symptoms can last for several weeks [13]. Also, these
injuries can negatively inﬂuence physical activity partici-
pation [14, 15]. Consequently, measuring overuse injuries
next to acute injuries is important to understand the overall
burden of RRIs [15]. However, measuring overuse injuries
is challenging, because of their non-identiﬁable and gradual
onset, and also due to ﬂuctuation of symptoms over time
[16]. Most studies about running have measured RRIs
leading to consequences, such as time loss (i.e. running
sessions not fully accomplished or completely missed due
to RRIs) and/or medical attention [17]. Deﬁning RRI based
only on these consequences could underestimate the overall
burden of RRIs, since minor injuries not resulting in such
consequences would be neglected [18, 19]. Also, to register
overuse injuries accurately, one needs a long follow-up time
including regular measurement intervals in order to
chart the gradual onset and ﬂuctuations of symptoms related
to overuse RRIs [16, 18]. Such data are sparse in the RRI
literature, and completely missing in trailrunning.
The purpose of this study was therefore to prospectively
investigate the prevalence, injury rate, severity, nature, and
economic burden of acute and overuse RRIs in Dutch
trailrunners. Such data may assist in the development of
RRI prevention programs in this mode of running, and also
may assist in decisions related to allocation of public health
ﬁnancial resources.
2 Methods
2.1 Participants
This study was composed of a convenience sample of the
general Dutch trailrunning population. Individuals engaged
in trailrunning were invited to partake in the study via ﬂyer
cards
distributed
during
trailrunning
events
in
The
Netherlands, and also by social media channels, newslet-
ters, and the MudSweatTrails (MST) website [20]. The
ﬂyer cards and additional recruitment sources guided the
individuals to the project’s website containing further
information and the option to enroll in the study. Individ-
uals who agreed to participate through online informed
consent, aged 18 years or over, reported running on
unpaved surfaces on a regular basis, and who completed
the baseline questionnaire were included in the study. A
sample size calculation a priori was not possible because of
a lack of information on the prevalence of RRIs repeatedly
measured over time at the commencement of this study.
The study was approved by the medical ethics committee
of the VU University Medical Center Amsterdam, The
Netherlands.
2.2 Study Design
This was a prospective open cohort study conducted
between October 2013 and December 2014. This cohort
was composed of a dynamic sample, i.e., the participants
entered into the study at different time-points and, there-
fore, they had different follow-up periods. However, all
participants were followed for at least 6 months. After
giving informed consent, a link to a secure online baseline
questionnaire was sent by e-mail to the participants. This
368
L. C. H. Junior et al.
123
questionnaire asked about demographics, running experi-
ence, participation in other sports, current medical condi-
tions, previous (last 12 months) RRIs, and current RRIs.
Online follow-up questionnaires were completed every
2 weeks via a secure link sent by email. The aim of these
follow-up questionnaires was to collect data about the
participants’ running exposure (overall exposure and on
unpaved surfaces speciﬁcally) and to record any health
problems experienced in the preceding 2 weeks. In case of
a sustained RRI, information about healthcare utilization
and absenteeism from paid work related to the RRI were
also registered through the same follow-up questionnaires
(conditional branching questions). If no response was
received within 1 week, a reminder was sent by e-mail
encouraging the participant to complete the follow-up
questionnaire.
2.3 Health Problems Registration
In order to prospectively register health problems during
the follow-up, the translated and adapted Dutch version of
the Oslo Sports Trauma Research Center (OSTRC) Ques-
tionnaire on Health Problems was included in the follow-
up questionnaires [21, 22]. The OSTRC questionnaire was
proposed and validated to register and monitor sports-re-
lated health problems over time, i.e., acute injuries, overuse
injuries, and illnesses [23]. The internal consistency
(Cronbach’s a) of the OSTRC questionnaire was estimated
at 0.96 and 0.91 for overall problems (including illnesses)
and overuse injuries, respectively [21, 23].
The OSTRC questionnaire consisted of four key ques-
tions on: (1) the extent to which injury, illness, or other
health problems have affected running participation; (2)
running volume; (3) running performance; and (4) the
extent to which the individual has experienced symptoms
during the previous 2 weeks. If no problems were reported
on these four key questions, the questionnaire was ﬁnished.
If a problem was reported on any of the four key questions,
the participant was asked to specify whether the problem
was an illness or an injury. In the case of an illness, the
questionnaire was ﬁnished. In case of an injury, partici-
pants were asked to report the anatomical location (one
possible answer per RRI), injury type (one possible answer
per RRI), a description of the symptoms (open question),
injury onset, the number of days of time loss (deﬁned as the
number of training sessions not fully accomplished or
completely missed due to injury), and whether the injury
was related to running. In the case of multiple injuries
within the fortnight, the participants were asked to register
the injury that caused most complaints. Other injuries could
be reported
in an open question. Participants were
instructed to report all problems, regardless of whether or
not they had already reported the same problem in previous
follow-up questionnaires.
2.4 Classiﬁcation of Health Problems
Health problems were classiﬁed as injuries if they were
‘‘disorders of the musculoskeletal system or concussions,’’
and were classiﬁed as illnesses if they ‘‘involved other
body systems’’ [21]. One investigator who is also a phys-
iotherapist (LCHJ) evaluated each reported injury case by
case. Injuries were classiﬁed as RRI when they were
reported as such by the participants, and when the phys-
iotherapist conﬁrmed that they were experienced or sus-
tained during participation in running. Subsequently, RRIs
were subcategorized into acute (the onset could be linked
to a speciﬁc injury event) or overuse injuries (could not be
linked to a clearly identiﬁable event) [21]. The Orchard
Sports Injury Classiﬁcation System version 10 (OSICS-10)
[24] was used to provide a diagnostic classiﬁcation for each
RRI.
Substantial health problems were deﬁned as those
leading to moderate or major reductions in training vol-
ume, moderate or major reductions in running perfor-
mance, or complete inability to run, as identiﬁed in the
response options of the key questions 2 or 3 of the OSTRC
questionnaire [21].
A recurrent RRI was deﬁned as an RRI at the same
location and of the same type of the index RRI, even if it
concerned re-injuries (after full recovery) or exacerbations
(not full recovery) [25].
2.5 Economic Consequences of Running-Related
Injuries (RRIs)
Participants who had reported an RRI were asked about
their healthcare utilization (direct costs) and days of pro-
ductivity loss related to paid work (indirect costs) due to
RRIs for the duration of their reporting of symptoms. This
information was collected through conditional branching
questions in the follow-up questionnaires. The cost evalu-
ation was performed from a societal perspective, consid-
ering all RRI-related costs regardless of who pays or
beneﬁts [26]. Table 1 provides the cost categories that were
registered and related monetary costs used in this evalua-
tion. All prices were standardized to the year 2009
according to the Dutch Health Insurance Board [27] and
corrected for inﬂation until the year 2014 [28]. Costs of
absenteeism from paid work were estimated based on the
mean income [27] and working hours of the Dutch popu-
lation according to age and gender [29].
Health and Economic Burden of Running Injuries in Trailrunners
369
123
2.6 Data Analysis
Microsoft Excel 2011 version 14.5.8 (Microsoft Cor-
poration, Redmond, WA, USA) and R version 3.2.3 (R
Foundation for Statistical Computing, Vienna, Austria)
were used to analyze the data. Descriptive analysis was
performed to present baseline and follow-up data. Per-
centages were calculated for categorical variables. The
mean and its 95 % CI were calculated for continuous data
with Gaussian distribution, otherwise the median and the
25–75 % interquartile range (IQR) were calculated.
2.6.1 Prevalence and Injury Rate Calculations
Prevalence repeatedly measured over time is considered
the preferable measure to describe the overall burden of
injuries in sports involving overuse injuries [16]. The
mean prevalence of RRIs repeatedly measured over time
was calculated according to previous recommendations
[16, 21, 23]. For each 2-week period, the prevalence was
calculated by dividing the number of participants report-
ing RRIs during that period by the number of total
questionnaire
respondents
during
the
same
period.
Thereafter, the mean prevalence and its 95 % CI were
calculated by summing all prevalences measured every
2 weeks, divided by the number of 2-week time-periods.
The injury rate was calculated by dividing the number of
RRIs by the sum of total running exposure in hours [18,
30]. The number of RRIs was calculated based on the
number of unique RRIs identiﬁed during the follow-up.
Results were expressed as the number of RRIs per 1000 h
of running and its 95 % CI.
2.6.2 Severity
In order to monitor the progress of the RRIs over time, a
severity score ranging from 0 to 100 was calculated for each
RRI based on the response options of the four key questions
of the OSTRC questionnaire [21]. Average severity scores
were calculated by taking the mean of the severity scores
measured every 2 weeks for each RRI. The cumulative
severity score (sum of the severity scores measured every
2 weeks) was calculated as an estimation of the total impact
that each RRI had had over the course of the study. The
average and cumulative time loss were also calculated for
each RRI as the same manner as the severity score.
2.6.3 Costs
Mean direct, indirect, and total costs were estimated per
RRI, per 1000 h of running, and per most commonly
reported RRIs. The participants could present more than
one RRI during the study, resulting in dependent obser-
vations. Therefore, the difference in costs between overuse
and acute RRIs were estimated using linear mixed models
with random intercept at the participant level, adjusted for
the following possible confounders measured at baseline:
age, gender, body mass index (BMI), running experience,
practice of other sports, chronic condition, medication use,
current RRIs, and previous RRIs. As the cost per 1000 h of
running is a rate between cumulative measures at the
population level (i.e., sum of costs divided by the sum of
total running exposure in hours multiplied by 1000),
adjustment for possible confounders was not possible. Cost
data are nonparametric, therefore, 95 % CIs were obtained
by bootstrapping the data with 2000 replications [31–33],
as recommended for economic evaluations [26].
3 Results
3.1 Participants, Response Rate, and Running
Exposure
A total of 228 trailrunners, 171 males (75.0 %) and 57
females (25.0 %), were included in the study. The baseline
results are summarized in Table 2. Five male participants
entered no data in the follow-up questionnaires, corre-
sponding to an attrition rate of 2.2 %. As the participants
entered in the study in different time-points, they had dif-
ferent follow-up periods. However, all participants were
followed for at least 6 months. The median of the follow-
up period was 34.0 weeks (IQR 28.0–36.0), and the
response rate measured every 2 weeks was 77.3 % (IQR
57.6–88.1). The median and IQR for the weekly running
exposure can be found in Table 3. On average, 22.8 %
Table 1 Monetary costs applied in the cost analysis
Description
Cost, €
Healthcare costs (direct costs)
General practitioner (per visit, 10 min)
30.79
General practitioner (per telephone
consultation)
15.40
Medical specialist (per visit)
79.17
Physiotherapist (per visit)
39.59
Costs of productivity loss (indirect costs)
Absenteeism from paid work (per hour)*
31.22 (9.78–43.95)
Prices standardized to the year 2009 according to the Dutch Health
Insurance Board [27] and adjusted for inﬂation until the year 2014
[28]
* Indirect costs for paid work were estimated based on the mean
income [27] and working hours [29] of the Dutch population
according to age and gender. The value for paid work is the mean
price followed by the minimum and maximal values according to
standardized prices by age and gender, adjusted for inﬂation [28]
370
L. C. H. Junior et al.
123
(95 % CI 20.1–25.6) of the trailrunners participated in
trailrunning events every 2 weeks. The median of the
distance of the trailrunning events was 28.0 km (IQR
17.5–39.1),
ranging
from
3
(minimum)
to
230 km
(maximum).
3.2 Prevalence, Injury Rate, Severity, and Nature
of RRIs
The absolute number, prevalence, injury rate, and severity
measures of RRIs can be found in Table 4. A total of 148
participants (66.4 %) reported 242 RRIs during the follow-
up. Of the injured participants, 68 (45.9 %) reported mul-
tiple RRIs (i.e., different OSICS-10 diagnostic classiﬁca-
tions). The percentage of injured participants who reported
other RRIs within the 2-week time-period was 4.7 % (IQR
4.0–7.2).
The mean prevalence of RRIs measured every 2 weeks
was 22.4 % (95 % CI 20.9–24.0). For males, the mean
prevalence of RRIs was 23.0 % (95 % CI 21.3–24.7), and
for females this was 20.7 % (95 % CI 18.2–23.2), with a
mean difference of 2.3 percentage points (95 % CI -1.0 to
5.6). The mean prevalence of RRIs was higher for overuse
than for acute RRIs, with a mean difference of 13.6 per-
centage points (95 % CI 10.3 to 16.9).
The injury rate was 10.7 RRIs per 1000 h of running
(95 % CI 9.4–12.1). For males, the injury rate was 11.3
(95 % CI 9.7–12.9), and for females this was 9.1 (95 % CI
6.6–11.6), with an injury rate difference of 2.2 RRIs per
1000 h of running (95 % CI -0.7 to 5.1). The injury rate
Table 2 Baseline data of the participants
All participants
n = 228
Male
n = 171
Female
n = 57
Age, years
43.4 (42.2–44.6)
43.8 (42.4–45.2)
42.4 (39.9–44.8)
Height, cm
178.9 (177.8–180.1)
182.4 (181.4–183.4)
168.4 (166.8–170.0)
Weight, kg
72.5 (71.1–74.0)
76.5 (75.2–77.9)
60.6 (58.9–62.2)
BMI, kg/m2
22.6 (22.3–22.8)
23.0 (22.7–23.3)
21.3 (20.9–21.8)
Total running experience, n (%)
Up to 1 year
7 (3.1 %)
7 (4.1 %)
–
1–2 years
18 (7.9 %)
13 (7.6 %)
5 (8.8 %)
2–5 years
43 (18.9 %)
35 (20.5 %)
8 (14.0 %)
More than 5 years
160 (70.2 %)
116 (67.8 %)
44 (77.2 %)
Trailrunning experience, n (%)
Up to 6 months
22 (9.6 %)
16 (9.4 %)
6 (10.5 %)
6–12 months
38 (16.7 %)
31 (18.1 %)
7 (12.3 %)
1–2 years
59 (25.9 %)
38 (22.2 %)
21 (36.8 %)
2–5 years
71 (31.1 %)
56 (32.7 %)
15 (26.3 %)
More than 5 years
38 (16.7 %)
30 (17.5 %)
8 (14.0 %)
Practice of other sports, n (%)
Yes
152 (66.7 %)
111 (64.9 %)
41 (71.9 %)
No
76 (33.3 %)
60 (35.1 %)
16 (28.1 %)
Chronic condition, n (%)
Yes
40 (17.5 %)
27 (15.8 %)
13 (22.8 %)
No
188 (82.5 %)
144 (84.2 %)
44 (77.2 %)
Current medication use, n (%)
Yes
26 (11.4 %)
16 (9.4 %)
10 (17.5 %)
No
202 (88.6 %)
155 (90.6 %)
47 (82.5 %)
Current RRI, n (%)
Yes
41 (18.0 %)
33 (19.3 %)
8 (14.0 %)
No
187 (82.0 %)
138 (80.7 %)
49 (86.0 %)
Previous RRI (last 12 months), n (%)
Yes
96 (42.1 %)
71 (41.5 %)
25 (43.9 %)
No
132 (57.9 %)
100 (58.5 %)
32 (56.1 %)
Continuous data are given as mean and 95 % conﬁdence interval
BMI body mass index, RRI running-related injury
Health and Economic Burden of Running Injuries in Trailrunners
371
123
was higher for overuse than for acute RRIs, with an injury
rate difference of 5.4 RRIs per 1000 h of running (95 % CI
4.1 to 6.8).
A total of 54.1 % (n = 131) of the RRIs were classiﬁed
as substantial (i.e., leading to moderate or major reductions
in training volume, moderate or major reductions in run-
ning performance, or complete inability to run). Fifty-nine
RRIs (24.4 %) neither resulted in time loss nor in medical
attention. Overuse RRIs lasted longer and presented a
higher
cumulative
severity
score
than
acute
RRIs
(Table 4). The most commonly reported RRIs were
Achilles tendon injury (12.8 %, n = 31), calf muscle
injury (10.7 %, n = 26), knee pain undiagnosed (8.7 %,
n = 21), and ankle sprain (7.0 %, n = 17). A breakdown
list with all RRIs reported during this study can be found in
the Electronic Supplementary Material.
Table 3 Running exposure during the follow-up
All participants
n = 223
Male
n = 166
Female
n = 57
Total running exposure
Duration (h/week)
3.5 (2.0–5.0)
3.5 (2.0–5.0)
3.5 (2.0–5.3)
Frequency (times/week)
2.5 (1.5–3.5)
2.5 (1.5–3.5)
2.5 (2.0–3.5)
Distance (km/week)
33.6 (19.5–50.0)
35.0 (20.0–50.0)
32.5 (17.5–50.0)
Running exposure on unpaved surfaces
Duration (h/week)
1.5 (0.5–3.0)
1.5 (0.5–2.8)
1.8 (0.8–3.0)
Frequency (times/week)
1.0 (0.5–2.0)
1.0 (0.5–2.0)
1.5 (0.5–2.0)
Distance (km/week)
15.0 (6.0–28.0)
15.0 (6.0–27.5)
16.0 (7.5–30.0)
Results are given as median and 25–75 % interquartile range (IQR)
Table 4 Absolute number, mean prevalence measured over time (every 2 weeks), injury rate, and severity measures of running-related injuries
(RRIs)
RRIs
Total
Overuse
Acute
Time loss
Medical attention
Overall
Number of RRIs registered
n = 242
n = 182
n = 60
n = 174
n = 72
Prevalence, mean (95 % CI)
22.4 % (20.9–24.0)
17.7 % (15.9–19.5)
4.1 % (3.3–5.0)
15.1 % (14.0–16.2)
5.9 % (5.1–6.7)
Injury rate, number of RRIs per
1000 h of running (95 % CI)
10.7 (9.4–12.1)
8.1 (6.9–9.3)
2.7 (2.0–3.4)
7.7 (6.6–8.9)
3.2 (2.4–3.9)
Severity measures, median (IQR)
Average severity score
35.0 (22.0–55.7)
31.1 (20.0–55.0)
37.0 (28.0–57.2)
43.0 (28.6–63.0)
55.0 (34.5–70.2)
Cumulative severity score
55.5 (28.0–122.0)
63.0 (25.2–122.0)
50.0 (33.8–116.0)
78.0 (37.0–165.0)
132.0 (66.0–278.0)
Average time loss, days
2.0 (0.0–4.7)
2.0 (0.0–4.5)
2.8 (1.0–5.1)
3.3 (1.8–6.0)
4.0 (1.5–7.3)
Cumulative time loss, days
3.0 (0.0–10.0)
3.0 (0.0–10.0)
3.5 (1.0–8.0)
5.0 (3.0–15.5)
12.0 (3.0–28.2)
Duration, weeks
2.0 (2.0–6.0)
4.0 (2.0–6.0)
2.0 (2.0–4.0)
4.0 (2.0–6.0)
6.0 (3.5–10.0)
Substantial
Number of RRIs registered
n = 131
n = 94
n = 37
n = 120
n = 58
Prevalence, mean (95 % CI)
9.9 % (9.1–10.8)
7.3 % (6.5–8.0)
2.3 % (1.4–3.1)
9.4 % (8.6–10.2)
3.7 % (3.1–4.3)
Injury rate, number of RRIs per
1000 h of running (95 % CI)
5.8 (4.8–6.8)
4.2 (3.3–5.0)
1.6 (1.1–2.2)
5.3 (4.4–6.3)
2.6 (1.9–3.3)
Severity measures, median (IQR)
Average severity score
54.5 (39.9–68.3)
54.5 (39.7–68.8)
51.0 (41.2–67.3)
54.8 (41.1–69.2)
59.6 (44.1–76.6)
Cumulative severity score
109.0 (66.0–198)
113.0 (71.2–230.5)
80.0 (50.0–159.0)
117.5 (66.0–226.0)
168.0 (80.0–287.2)
Average time loss, days
4.0 (2.0–6.8)
4.0 (2.0–6.9)
4.0 (2.0–6.0)
4.2 (2.8–7.0)
5.0 (3.0–8.3)
Cumulative time loss, days
7.0 (4.0–20.0)
8.5 (4.0–23.8)
5.0 (3.0–16.0)
9.5 (4.0–21.5)
14.0 (4.0–31.5)
Duration, weeks
4.0 (2.0–8.0)
5.0 (2.0–9.5)
4.0 (2.0–6.0)
4.0 (2.0–8.0)
6.0 (4.0–10.0)
Substantial RRIs were deﬁned as those leading to moderate or major reductions in training volume, moderate or major reductions in running
performance, or complete inability to run
95 % CI 95 % conﬁdence interval, IQR 25–75 % interquartile range
372
L. C. H. Junior et al.
123
3.3 Economic Burden of RRIs
In total, 332 healthcare consultations (21 general practi-
tioner, 47 medical specialist, and 264 physiotherapy con-
sultations) and 102 days of productivity loss related to paid
work were registered. A total (direct plus indirect) cost of
€41,677.13 was calculated for the 242 RRIs. The direct
cost was €14,742.39 (€569.64 related to general practi-
tioner,
€3720.99
related
to
medical
specialist
and
€10,451.76 related to physiotherapy consultations) and the
indirect cost was €26,934.74 (related to absenteeism from
paid work).
The costs per RRI, per 1000 h of running and per most
commonly reported RRIs can be found in Table 5. Overuse
RRIs presented higher physiotherapy costs than acute
RRIs, and acute RRIs presented higher costs related to
general practitioner than overuse RRIs. There were no
statistically signiﬁcant differences in costs per 1000 h of
running between males and females. Of the four most
commonly reported RRIs, calf muscle injuries presented
the highest direct and indirect costs.
4 Discussion
4.1 Trailrunners and Running Exposure
The sample of the current study was composed by Dutch
trailrunners who were recruited during trailrunning events,
or through trailrunning channels, like the MST website
[20], regardless of age, gender, running experience, com-
petition level, or training exposure (e.g., volume and
intensity). As presented in Table 3, Dutch trailrunners
usually train on paved and unpaved tracks. This could be
explained by the fact that most Dutch trailrunners live in
city areas, and, therefore, they do not have easy and fast
access to trail tracks that usually are composed by rugged,
muddy, and/or mountain terrains. However, trailrunners
need to train on a regular basis to be prepared for the
trailrunning events that usually have longer distances
(median of 28 km in the current study). Therefore, the
sample of trailrunners in the current study can be consid-
ered representative of the general Dutch trailrunning pop-
ulation. Furthermore, the characteristics of the Dutch
trailrunners who participated in this study may also be
similar to recreational trailrunners in other countries.
4.2 Prevalence and Injury Rate of RRIs
The results of this study have shown that the mean
prevalence of RRIs measured every 2 weeks is between
20.9 and 24.0 % (95 % CI) in trailrunners. In other words,
one out of ﬁve trailrunners may be expected to sustain
RRIs during a 2-week time-period. The prevalence esti-
mates of this study are not comparable with other studies in
the literature, since this is the ﬁrst study to report the
prevalence of RRIs repeatedly measured over time in
trailrunners. In addition, previous studies on trailrunning
have used different methods and RRI deﬁnitions [34, 35].
This hampers comparisons. For example, the incidence
proportion of lower limb musculoskeletal injuries (22.2 %)
found during the Al Andalus Ultimate Trail 2010 held in
southern Spain [35] was similar to the prevalence repeat-
edly measured over time reported in the current study,
although these are two different measures.
Hespanhol Junior et al. [15] have used similar methods
as the one used in the current study to investigate RRIs in
inexperienced runners training for an event. The study
design, surveillance system, RRI deﬁnition and RRI clas-
siﬁcations were the same in both studies, although the
population and the follow-up period were different. The
mean prevalence of all RRIs and the mean prevalence of
overuse RRIs found in the current study were lower than
the mean prevalences reported by Hespanhol Junior et al.
[15]. This may be explained by differences in running
experience [11] and training volume [36] between these
two populations.
As explained in the methods, a priori sample size cal-
culation was not possible because of missing information
on the prevalence of RRIs repeatedly measured over time
in a general trailrunning population at the commencement
of this study. However, the study of Hespanhol Junior et al.
[15] was recently available. Therefore, a post hoc sample
size calculation based on the results reported in Hespanhol
Junior et al. [15] and the results of the current study was
possible. The sample size was estimated based on calcu-
lations for longitudinal studies with repeated measurements
[37]. The prevalence of RRIs repeatedly measured over
time in the study of Hespanhol Junior et al. [15] was
30.8 % (95 % CI 25.6–36.0), and in the current study was
22.4 %
(95 %
CI
20.9–24.0).
Considering
a = 0.05,
b = 0.8, 17 repeated measurements (i.e., median of
34 weeks of follow-up with repeated measurements every
2 weeks), a correlation coefﬁcient of the repeated mea-
surements of 0.24 (calculated in the current study for the
purpose of this sample size calculation), and a response
rate of 77.3 % (reported in the current study), the sample
size calculation suggested a cohort of 152 participants.
Based on this calculation, the sample size of the current
study was appropriate. This calculation may be useful as a
reference for sample size calculations for future longitu-
dinal studies with repeated measurements on RRIs.
Comparisons of injury rates of RRIs across studies are
difﬁcult because of differences in RRI deﬁnitions [11, 17,
19]. However, the time loss injury rate in trailrunners found
in the current study [7.7 RRIs per 1000 h (95 % CI
Health and Economic Burden of Running Injuries in Trailrunners
373
123
Table 5 Economic burden of running-related injuries (RRIs) in trailrunners
Overall
Direct cost
Indirect cost
Total
General
practitioner
Medical specialist
Physiotherapy
Absenteeism from
paid work
Cost per RRI, €
All injuries, n = 242
172.22 (117.10 to 271.74)
60.92 (45.11 to 94.90)
2.35 (1.08 to
4.14)
15.38 (8.51 to
27.41)
43.19 (30.96 to 60.20)
111.30 (61.02 to
192.75)
Overuse, n = 182
174.40 (108.52 to 302.65)
69.96 (48.18 to 102.90)
1.44 (0.51 to
3.54)
17.84 (9.57 to
31.88)
50.68 (35.02 to 72.00)
104.44 (50.88 to
205.16)
Acute, n = 60
165.61 (78.19 to 363.54)
33.50 (18.55 to 55.33)
5.13 (2.05 to
10.52)
7.92 (1.32 to
22.43)
20.45 (9.90 to 41.57)
132.11 (44.36 to
301.15)
Difference (overuse
minus acute)
16.60 (-161.98 to 179.61)
31.05 (16.31 to 76.70)*
-3.85 (-10.42 to
-3.66)*
3.79 (-14.19 to
23.45)
27.43 (23.68 to 50.98)*
-14.88 (-210.93 to
99.40)
Cost per 1000 h of running, €
All participants,
n = 223
1849.49 (1180.62 to 3058.91)
654.22 (465.82 to 942.68)
25.28 (11.61 to
44.41)
165.13 (91.35 to
291.60)
463.81 (323.26 to 686.48)
1195.27 (635.76 to
2346.03)
Male, n = 166
1783.44 (1013.66 to 3321.43)
548.35 (353.32 to 966.17)
19.46 (7.41 to
37.99)
142.93 (57.17 to
290.63)
385.96 (238.25 to 631.36)
1235.09 (582.51 to
2622.02)
Female, n = 57
2034.97 (1032.15 to 4630.62)
951.52 (621.73 to 1630.91)
41.63 (10.41 to
104.08)
227.45 (80.28 to
454.90)
682.44 (398.56 to 1137.39)
1083.45 (279.82 to
3134.15)
Difference (males
minus females)
-251.52 (-2671.36 to 1380.54)
-403.17 (-1107.63 to 118.15)
-22.17 (-92.86
to 10.32)
-84.52 (-339.59
to 109.56)
-296.47 (-801.50 to 50.16)
151.64 (-1751.25
to 1485.12)
Cost per most commonly reported RRIs, €
Achilles tendon
injury, n = 31
67.60 (30.08 to 148.10)
46.68 (19.16 to 111.10)
1.99 (0.00 to
12.32)
10.22 (0.00 to
53.23)
34.48 (13.68 to 69.77)
20.91 (0.00 to
128.43)
Calf muscle injury,
n = 26
135.85 (49.22 to 391.91)
56.00 (23.19 to 123.85)
1.18 (0.00 to
6.58)
21.32 (5.66 to
63.18)
33.50 (11.50 to 80.89)
79.86 (0.00 to
384.14)
Knee pain
undiagnosed, n = 21
13.20 (2.83 to 33.33)
13.20 (3.05 to 31.67)
–
–
13.20 (2.92 to 33.73)
–
Ankle sprain, n = 17
82.20 (8.48 to 346.78)
20.96 (5.16 to 50.47)
–
–
20.96 (5.28 to 53.78)
61.24 (0.00 to
319.48)
All costs are presented in euros (€). Mean values are followed by the bias-corrected and accelerated 95 % conﬁdence interval estimated by bootstrapping (2000 replications)
* Signiﬁcant difference between overuse and acute RRIs

The difference in costs between overuse and acute RRIs were estimated using linear mixed models with random intercept at the participant level, adjusted for the following possible
confounders measured at baseline: age, gender, body mass index (BMI), running experience, practice of other sports, chronic condition, medication use, current RRIs, and previous RRIs
374
L. C. H. Junior et al.
123
6.6–8.9)] was similar to the injury rate in recreational
runners reported by Videbaek et al. [7.7 RRIs per 1000 h
(95 % CI 6.9–8.7)] [11], that was summarized based on
studies with time loss RRI deﬁnitions.
According to the literature, overuse RRIs occur more
frequently than acute RRIs [12, 15]. The results of the
current study support this observation for trailrunning,
since the prevalence of overuse RRIs was fourfold higher
than acute RRIs, and the injury rate of overuse RRIs was
threefold higher than acute RRIs. Most of the time, running
can be described as an aerobic physical activity that
requires long duration exertion with few changes in
movement patterns. Therefore, overuse injuries with a
gradual onset mechanism resulting from repetitive micro-
trauma would be more expected in trailrunning than inju-
ries with a sudden onset.
4.3 Severity of RRIs
Severity measures are important to understand the extent to
which sports injuries affect health [38]. A strength of this
study was the continuous and valid method used to monitor
the severity of sports injuries, irrespective of time loss or
medical attention [21]. In fact, 24.4 % of the RRIs reported
in this study neither resulted in time loss nor medical
attention. Therefore, the results of this study support the
hypothesis that measuring RRIs based only on time loss or
medical attention deﬁnitions will lead to an underestima-
tion of the burden of RRIs.
The longer duration of overuse RRIs can explain why
the cumulative severity score was higher for overuse than
for acute RRIs. More than half of the RRIs were classiﬁed
as substantial, meaning that they caused a moderate or
major reduction in running volume or running perfor-
mance, or had caused a complete inability to participate in
running. This result supports the hypothesis that RRIs may
reach such severity levels that they can lead to dropping out
of running participation [14, 15]. The implication is that
RRIs may lower the motivation to participate in running, a
great ally against the burden of physical inactivity, which is
a leading risk factor for the global disease burden [39] and
mortality [40]. In fact, running is effective in reducing
mortality and disability [8, 9]; however, the adherence to
running participation is essential to reach such health
beneﬁts [9, 10].
4.4 Economic Burden of RRIs
To the best of our knowledge, this is the ﬁrst study
reporting the total, direct, and indirect costs of RRIs in
trailrunners. The cost per RRI in trailrunners found in the
current study was €172.22 (95 % CI 117.10–271.74),
which was comparable to the cost per RRI found in
runners
training
for
an
event
(€173.72;
95 %
CI
57.17–318.76) [15] and higher than the costs per RRI
found in novice runners (€83.22; 95 % CI 50.42–116.02)
[41]. These cost estimates are lower than the economic
burden generally reported for sports injuries in other
athletic populations [42, 43]. However, comparisons
with other sports and populations should be made with
caution where the study methods and follow-up periods
were different.
Healthcare consultations related to RRIs were threefold
higher than the number of days of productivity loss related
to paid work. However, the indirect cost of RRIs was
twofold higher than the direct cost. Interestingly, the
indirect-direct cost ratio was higher for acute RRIs (indi-
rect cost fourfold higher than direct cost) than for overuse
RRIs (indirect cost 1.5-fold higher than direct cost), indi-
cating that the productivity loss impact may be higher for
acute RRIs. Other studies have also shown higher indirect
than direct costs related to sports injuries [43–47]. These
results indicate that productivity loss is the main contrib-
utor to the economic burden of sports injuries, with a sig-
niﬁcant impact on societal ﬁnancial resources. As such,
policymakers should always take into account the direct
and especially the indirect costs of sports injuries to drive
their policies.
To put our results into perspective: according to MST,
7500 people participate in trailrunning events organized by
them each year. Based on the results of the current study,
one trailrunner runs approximately 3.5 h per week (i.e.,
182 h per year). Therefore, one could expect to have a total
cost related to RRIs of more than €2.5 million yearly, only
accounting for trailrunners participating in the MST events.
This ﬁgure represents around 0.4 % of all annual sports
injury costs in The Netherlands [47]. Although not a large
proportion, if RRIs in trailrunning are prevented, maybe
hundreds of thousands of euros could be saved and redi-
rected to other public health areas. This assumption shows
the ﬁnancial impact that RRIs in trailrunning could have
for society.
There is sound evidence showing that physical activity
is a cost-effective method to improve overall health, and
gain healthy life-years [1–4]. Evidence also suggests that
the health beneﬁts of running outweigh the related risks
and costs [4, 8–10]. Therefore, running may be advised for
people who seek to improve their health by means of
engaging in strenuous physical activity. Nonetheless, RRIs
are a preventable side effect of such active engagement and
prevention is warranted. Effective prevention of injuries
will not only reduce the individual burden in terms of
injury and costs, but will also improve joyful and contin-
uing participation in running.
Health and Economic Burden of Running Injuries in Trailrunners
375
123
4.5 Limitations
This study was composed of a convenience sample. As
presented in Table 4, most RRIs reported in the current
study were overuse injuries, i.e., those that have a non-
identiﬁable and gradual onset, and also present ﬂuctuation
of symptoms over time. Consequently, the RRIs reported in
the current study represent all RRIs that could be a result of
running exposure on paved, unpaved, or both surfaces (the
most likely assumption). The RRIs were self-reported and
then classiﬁed by a healthcare professional (LCHJ) based
on the RRI description given by the participants. A con-
ﬁrmation of the RRI diagnoses during face-to-face con-
sultations was not possible due to logistic reasons. Data
about medicines taken and diagnostic tests due to RRIs
were not collected. This could have lead to an underesti-
mation of the direct costs of RRIs. The cost analysis was an
estimation based on Dutch standardized prices for health-
care utilization [27], and the mean income [27] and
working hours of the Dutch population for absenteeism
from paid work [29], all adjusted for inﬂation [28]. Despite
the fact that this methodology has been accepted and rec-
ommended [26], it is important to realize that the cost
results were estimated and do not represent actual costs.
5 Conclusions
On average, one out of ﬁve trailrunners reported RRIs every
2 weeks. Overuse RRIs represented 75.2 % of all RRIs
registered during the follow-up. A total of 54.1 % of all
RRIs were classiﬁed as substantial. The economic burden
(direct plus indirect costs) of RRIs was estimated at €172.22
(95 % CI 117.10–271.74) per RRI, and €1849.49 (95 % CI
1180.62–3058.91) per 1000 h of running. Healthcare uti-
lization (direct costs) contributed to 35.4 % of these costs
and absenteeism from paid work (indirect costs) to 64.6 %.
Acknowledgments Luiz Carlos Hespanhol Junior is a PhD candidate
supported by CAPES (Coordenac¸a˜o de Aperfeic¸oamento de Pessoal
de Nı´vel Superior), process number 0763/12-8, Ministry of Education
of Brazil. The authors wish to thank MudSweatTrails and Marc
Weening for their assistance during the recruitment, and all trail-
runners who participated in this study.
Compliance with Ethical Standards
Funding This study had no funding sources.
Conﬂict of interest Luiz Carlos Hespanhol Junior and Evert Ver-
hagen declare that they have no conﬂicts of interest. Willem van
Mechelen declares that he is director-shareholder of VU University
Medical Center spin-off company Evalua Nederland B.V. (http://
www.evalua.nl), and non-executive board member of Arbo Unie B.V.
(http://www.arbounie.nl). Both companies operate on the Dutch
Occupational Health Care market.
Ethical approval All procedures performed in studies involving
human participants were in accordance with the ethical standards of
the institutional and/or national research committee and with the 1964
Helsinki Declaration and its later amendments or comparable ethical
standards.
Informed consent Informed consent was obtained from all individ-
ual participants included in the study.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a link
to the Creative Commons license, and indicate if changes were made.
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Health and Economic Burden of Running-Related Injuries in Dutch Trailrunners: A Prospective Cohort Study.
Hespanhol Junior, Luiz Carlos,van Mechelen, Willem,Verhagen, Evert