Diagnoses and time to recovery among injured recreational runners in the RUN CLEVER trial
Diagnoses and time to recovery among injured recreational runners in the RUN CLEVER trial
Benjamin Mulvad 1 2
Rasmus Oestergaard NielsenID 2
Martin Lind 1 2
Daniel Ramskov 0 2
0 Department of Physiotherapy, University College of Northern Denmark , Aalborg , Denmark
1 Division of Sports Traumatology, Department of Orthopedics, Aarhus University Hospital , Aarhus , Denmark , 2 Section for Sports Science, Department of Public Health, Aarhus University , Aarhus , Denmark
2 Editor: Manoj Srinivasan, The Ohio State University , UNITED STATES
Funding: The Danish Rheumatism Association
(https://www.gigtforeningen.dk/) provided a DKK
75.000 grant for this study. The funder had no role
in study design, data collection and analysis,
decision to publish, or preparation of the
The purpose of the present study was to describe the incidence proportion of different types
of running-related injuries (RRI) among recreational runners and to determine their time to
A sub-analysis of the injured runners included in the 839-person, 24-week randomized trial
named Run Clever. During follow-up, the participants reported levels of pain in different
anatomical areas on a weekly basis. In case injured, runners attended a clinical examination at
a physiotherapist, who provided a diagnosis, e.g., medial tibial stress syndrome (MTSS),
Achilles tendinopathy (AT), patellofemoral pain (PFP), iliotibial band syndrome (ITBS) and
plantar fasciopathy (PF). The diagnose-specific injury proportions (IP) and 95% confidence
intervals (CI) were calculated using descriptive statistics. The time to recovery was defined
as the time from the first registration of pain until total pain relief in the same anatomical
area. It was reported as medians and interquartile range (IQR) if possible.
A total of 140 runners were injured at least once leading to a 24-week cumulative injury
proportion of 32% [95% CI: 26%; 37%]. The diagnoses with the highest incidence proportion
were MTSS (IP = 16% [95% CI: 9.3%; 22.9%], AT (IP = 8.9% [95% CI: 3.6%; 14.2%], PFP
(IP = 8% [95% CI: 3.0%; 13.1%]. The median time to recovery for all types of injuries was 56
days (IQR = 70 days). Diagnose-specific time-to-recoveries included 70 days (IQR = 89
days) for MTSS, 56 days (IQR = 165 days) for AT, 49 days (IQR = 63 days) for PFP.
The most common running injuries among recreational runners were MTSS followed by AT,
PFP, ITBS and PF. In total, 77 injured participants recovered their RRI and the median time
Competing interests: The authors have declared
that no competing interests exist.
to recovery for all types of injuries was 56 days and MTSS was the diagnosis with the
longest median time to recovery, 70 days.
Running is a very popular type of exercise and the number of runners worldwide has grown
over the past decades [
]. Among recreational runners, the most supported motives are to
keep healthy, to maintain stamina and to reduce weight or avoid increasing their weight [
Running contributes to a range of health-related benefits such as lowering overall body fat,
optimizing the composition of fat molecules in the blood, lowering the resting heart rate and
improving the overall cardiovascular fitness [
]. In general, runners have a 25–40% reduced
risk of premature mortality and live approximately 3 years longer than non-runners [
Owing to the health benefits and because of the considerable interest in running illuminating
barriers to continued running deserves to be a key public health priority.
In Denmark, it has been estimated that 5% of the adult population, equivalent to 260,000
individuals, suffer from a running-related injury (RRI) on a yearly basis [
]. Running is hence
the sports activity that contributes with most annual sports injuries in Denmark. When
evaluated in a population of runners, 1-year injury incidence proportions have been reported in the
range from 43.2% to 84.9% in different types of runners [
]. Running injuries were the most
common reason for permanently dropping out of a running regime among males, and the
third-most common reason among females according to a 10-year prospective cohort study
]. Direct economic costs of running-related injuries range from 0.3% to 4.6% of national
healthcare expenditure [
]; and some injured runners come to suffer from permanent physical
disability making them unable to exercise due to pain or discomfort [
]. Indeed, the
combination of mental and physical consequences increases the likelihood of lapsing into a sedentary
lifestyle during and after injury recovery.
Running-related injuries usually occur in the lower extremity [
]. Some of the most
frequent diagnoses amongst runners are patellofemoral pain (PFP), iliotibial band syndrome
(ITBS) and plantar fasciosis (PF), with proportions in relation to all injuries ranging between
10–17%, 4–8%, and 5–8%, respectively [
]. Commonly, runners receive a referral to a
physiotherapist for treatment purposes . Here, many runners are concerned with the time
to recovery. To provide answers, insights into diagnose-specific time-to-recoveries are needed.
Unfortunately, there is a literature gap concerning the time to recovery for classical
runningrelated injuries such as PFP, ITBS and PF. Among novice runners, the median time to recovery
of all types of RRIs has been estimated to approximately 10 weeks with diagnose-specific
recoveries ranging between 26 days to 174 days [
]. Still, no study has investigated the time to
recovery among injured recreational runners. Consequently, the purposes of the present study
were to describe the incidence proportion of different types of running-related injuries among
recreational runners, engaged in the Run Clever trial [
], and to determine their time to
recovery measured in days.
Materials and methods
The present paper presents a sub-analysis of the injured participants from the Run Clever trial.
The Run Clever trial was a randomized 24-week follow-up intervention study including
recreational runners. The intervention was two different running schedules, the main outcome was
RRIs and the participants were followed by weekly questionnaires. The two running schedules
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were founded on the same framework, 3 running sessions per week, and an identical 8 weeks
preconditioning period followed by 16 weeks of intervention. The intervention training period
was organized in cycles of 4 weeks with progression. One group, the intensity training group,
had a fixed running volume but the amount of hard pace was increased during the cycles of
progression. The other group, the volume training group, focused on increasing the total
running volume per week but only performed at an easy or moderate pace. The original purpose
was to compare overall risk of injury between progression in running intensity and running
]. The Run Clever trial was approved by The Ethics Committee Northern Denmark
and the Danish Data Protection Agency (N-20140069). Prior to recruitment, on January 23rd
2015, the trial was registered at Clinicaltrials.gov under registration number: NCT02349373.
Healthy persons between 18 and 65 years of age were eligible for inclusion in the Run
Clever trial. They had to be recreational runners free of injury in their lower extremities in the
past 6 months. A recreational runner was defined as a person who had been running 1 to 3
weekly sessions for at least 6 months. The approach of recruiting participants and further
criterions for inclusion or exclusion of the Run Clever trial are described in detail elsewhere [
The sub-sample included in the present study, were participants included in the Run Clever
trial who sustained at least one RRI during the follow-up period.
At baseline, each participant was provided access to an internet-based training diary. After
being registered in the diary, the participants received weekly automated e-mails including a
link to an online questionnaire on injury-related pain. The questionnaire contained questions
regarding symptoms of overuse or injuries based on the Oslo Sports Trauma Research Center
Questionnaire (OSTRC) [
]. The OSTRC was modified with two additional questions and an
additional option of answers to adapt it for the Run Clever Trial. When discomfort or an injury
was registered in the OSTRC questionnaire, the participant informed on their pain in different
anatomical areas, and the options were the “foot”, “ankle”, “front of lower leg”, “calf”, “knee”,
“thigh”, “hamstrings”, “groin”, “glutes”, “hip” and “lower back”. The questionnaires were
distributed as e-mails every Sunday to the participants’ e-mail address. The participants had to
complete it whether or not suffering an injury, hereby getting information of any experienced
pain the previous week. In case no response was received during the Sunday, a reminder
email was sent to the participant the following Monday (the day after).
In line with most recent scientific work, a RRI was defined as any physical pain or
complaints from muscles, joints, bones or tendons of the lower extremities or back as a result of
]. It had to reduce the training performance such as distance, frequency, intensity
or pace for at least 7 days [
]. When a participant reported a RRI via the weekly
injury-questionnaire, an appointment with a certified physiotherapist, who was part of a study-specific
diagnostic team, was made. The physiotherapist performed the clinical examinations in their
respective clinics, generally within a week, and used a standardized examination procedure
]. The physiotherapist made the standardized examination of the foot, ankle, lower leg,
knee, thigh, hip or back and compared their findings with standardized, non-validated
diagnostic criterions for different diagnoses [
]. The diagnosis was based on the medical history
and objective findings. When the physiotherapist had completed an examination, the
diagnosis (e.g., medial tibias stress syndrome (MTSS), Achilles tendinopathy (AT)) and date of
examination was registered and reported to the database. No treatment or plans of rehabilitation
was delivered, only a few pieces of advice at the most. However, the participant was allowed to
search for treatment and receive treatment elsewhere.
The definition of time to recovery was based on the responses in the weekly OSTRC-scores
on pain as well as the diagnostic examination by the physiotherapist. The date of examination
and diagnosis provided by the physiotherapist were compared to the responses from the
weekly OSTRC-scores to identify if pain reported via the OSTRC in the affected anatomical
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site corresponded with the anatomical location of the diagnosis provided by the
physiotherapists. Based on this, the time to recovery was defined as the time from the first registered pain
in a specific anatomical area until total pain relief in the same anatomical area. Date of
recovery was defined as the date total pain relief occurred, which, then, was followed by at least
three weeks without pain in the relevant anatomical site. If a participant was pain-free for a
week but reported pain the following two weeks in the same anatomical location, the
participant was still classified as being injured. However, if new pain arose in the same anatomical
site after three weeks without pain, it was considered as a new injury. If a participant sustained
two different RRIs or more during the follow-up period, only the first injury was included in
The injured runners were excluded from the analyses on time to recovery if they did not
meet the following eligibility criteria: (i) the injury had to recover before at end of 24-week
follow-up, (ii) they had to answer at least ten of the weekly administered questionnaires, (iii)
their pain had to be registered in the same anatomical location as the one registered by the
physiotherapist, (iv) they needed to register pain (e.g., in some cases, no pain was registered at
all), (v) they had to register a date of injury occurrence or (vi) the time to recovery had to be
plausible compared to the diagnosis (e.g., we found pain for one week following a broken leg
The Kaplan-Meier estimator was used to calculate the proportion of injury-free Run Clever
participants as a function of weeks. As these methods takes into account censoring, the
proportion of injured participants after 24-week follow-up is not number of injured runners divided
by the total sample size as the latter approach assumes complete follow-up for all runners.
Data on time to recovery was evaluated using histograms and 95% prediction intervals to
decide if it was normally distributed. As this was not the case, non-parametric statistics were
used to present time to recovery as medians and IQRs. At least five recovered injuries were
required to include these calculations. The data-management and analyses presented are
performed using STATA/SE version 14 and Microsoft Excel 2010.
A total of 839 runners participated the Run Clever Trial of whom 521 (62%) were female and
318 (38%) were male. The mean age was 39.2 (±10.0) years. 140 sustained at least one RRI
during the follow-up period. A Kaplan-Meier graph visualizing the proportion of injury-free
runners as a function of follow-up time is presented in Fig 1 showing that 32% [95% CI: 26; 37] of
the population sustain injury over the 24 weeks. Of these, 28 injured runners were excluded
since they did not meet the requirements for inclusion to the analyses (Fig 2). Among the
remaining 112 injured runners, 82 (73%) were female and 30 (27%) were male, and their mean
age was 41.4 years (minimum: 21 years, maximum: 63 years). A total of 1225 injury
questionnaires were distributed to injured participants of which 1064 (87%) were returned successfully.
The most common RRI was MTSS reported among 18 incident cases (16% [95% CI: 9.3;
22.9]). This was followed by AT (n = 10; 8.9% [95% CI: 3.6; 14.2]), PFP (n = 9; 8% [95% CI:
3.0; 13.1]), ITBS (n = 8; 7.1% [95% CI: 2.4; 11.9] and PF (n = 8; 7.1% [95% CI: 2.4; 11.9]. In
total, these five diagnoses account for 47% of the injuries. The remaining incident cases were
classified within 20 other diagnosis-groups (Table 1).
At the end of follow-up 35 participants remained injured. Therefore, a total of 77 incident
cases recovered from their RRIs before the end of follow-up and were included in the analyses
on time to recovery (Table 2). The overall median time to recovery was 56 days (IQR = 70)
regardless the injury diagnoses. In the diagnose-specific recoveries, the shortest median time
to recovery was observed among participants sustaining PF with 35 days (IQR = 70). As
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Fig 1. Kaplan-Meier graph. Kaplan-Meier graph visualizing the proportion of injury-free runners as a function of follow-up time. The results revealed 32% [95% CI: 26;
37] of the runners sustained injury over the 24 weeks.
opposed to this, MTSS had the longest median time to recovery with 70 days (IQR = 89). Eight
participants suffered two running-related injuries, and none suffered from three or more
injuries during follow-up.
During the 24-week follow-up in the Run Clever trial, 32% of the recreational runners
sustained at least one RRI. Compared with previous research this seems similar to the incidence
proportion 25.9% of the novice runners in a study by Buist et al. suffering from a RRI during
the 8-week observation period [
]. Moreover, Taunton et al. found an incidence proportion
of RRI to be 29.5% during the 13-week training protocol before the Vancouver Sun Run [
Finally, in a systematic review on injuries among different types of runners, incidence
proportions of RRIs were reported in the range between 20% to 80% [
]. However, these differences
should be interpreted with caution because of different injury definitions and different
durations of follow-up across studies. The overall median time to recovery across RRI diagnoses
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Fig 2. Flowchart. Flowchart visualizing the flow of runners sustaining injuries during the Run Clever trial.
was 56 days among the recreational runners analyzed. Previously, the median time to recovery
among novice runners has been found to exceed 70 days [
MTSS was the RRI diagnosis with the highest incidence proportion followed by AT, PFP,
ITBS, and PF. Interestingly, these diagnoses are also among the five most common diagnoses
found in previous research [
12, 13, 21
]. Collectively, the five diagnoses accounted for almost
half the injuries sustained (47%) in the present study. This is also similar to previous studies
revealing these injuries to target 42.6%, 51.8% and 41% of the injured runners, respectively
]. Consequently, across various studies it is not uncommon that almost half the RRIs
are distributed between these five diagnoses. The RRI diagnosis with the longest recovery time
was medial meniscus injury followed by hamstring injury. However, the most incident RRI
diagnoses, MTSS, AT, PFP, ITBS and PF in the present study were also among the top 10 RRI
with the longest recovery time.
A strength of the present study is the weekly status updates, which reduced the risk of recall
bias and information problems. Furthermore, the diagnostic approach, encompassing a
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standardized physical examination performed by a study-specific diagnostic team of
physiotherapists, ensured a greater certainty of accurate injury diagnosis as well as exact date of injury
Very few comparable studies exist, but an interesting finding is the time to recovery among
the recreational runners sustaining MTSS of median 70 days. Since, comparable recovery
times of 72 days in a study on novice runners [
], 82 days among infantry recruits in the
British army [
], and 58 days among 15 military recruits from the Royal Dutch army [
However, differences in the populations investigated and definitions of recovery should be
considered. The main reason for the discrepancy in definition of injury recovery between the
present study and the previous DANORUN study also including runners by Nielsen et. al,
stems from the different ways the data was collected [
]. The electronical database facilitated
more frequent and standardized follow-up in the Run Clever trial allowing for a better
evaluation of the levels of pain and symptoms. Furthermore, the altered definition of injury recovery
enabled to avoid runners being labeled injury-free though they participated in running with
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Still, some limitations exist. Firstly, in total, 35 participants did not recover their RRIs
before the end of follow-up. For instance, only 3 of the 7 runners with medial meniscal
injured recovered. For these three runners, the median time-to-recovery was 89 days.
However, if the remaining four runners had been followed until recovery it is likely the case that
the median time-to-recovery would have been longer. This underestimation targets many
diagnose-specific recovery-times as the proportion of individuals with medial meniscus
injury, MTSS, ITB and AT who became injury-free ranged from 42.3%–70%, respectively.
Further, comparing time to recovery in the current study, to recovery times from the study
by Nielsen et al. [
] a considerable difference in the diagnoses specific maximum values
reported becomes evident. A reason for this may be the definition of recovery in the current
study including a margin of three consecutive pain-free weeks was different that the one
used in other studies. Consequently, an extended follow-up time would have been preferred
to reduce the loss of data.
Secondly, the diagnostic approach was standardized to reduce the risk of subjective
information bias regarding the diagnosing for which reason every injury was diagnosed on the
basis of a physical examination and the injured runner’s anamnesis. Making a diagnosis
adhering to the guidelines was not always possible, which makes the objectivity less solid. Thirdly,
the definition of recovery is complex. The RRI was deemed to be recovered after three
successive weeks without any pain during running in the related anatomical site, but no physical
examination or test was performed to make sure full recovery was attained. Moreover, the
experience of pain might be diverse in different injuries so that the three-week distinction
might be undiscriminating.
Despite various limitations in the present study, the results may be of interest for both
researchers and clinicians dealing with RRIs. The present study is a prospective analysis of
data obtained from the Run Clever trial in which information on new injury onset and exact
diagnosing were very important and as proper as possible. However, a major drawback was
the lack of continually follow-up on the accuracy on the information submitted by the injured
The cumulative incidence proportion of injured participants in the Run Clever trial was 32%.
The injuries were classified across 25 different diagnoses with MTSS, AT, PFP, ITBS and PF as
the most frequent ones. Altogether, these five diagnoses accounted for 47% of all injuries. The
median time to recovery for all types of injuries was 56 days. MTSS was the diagnosis with the
longest median time to recovery of 70 days.
S1 Dataset. A STATA.dta file.
The authors wish to acknowledge the physiotherapists who made a priceless contribution by
willingly and free of charge, diagnosing injured participants. The Danish Rheumatism
Association (https://www.gigtforeningen.dk/) provided a DKK 75.000 grant for this study. The
funder had no role in study design, data collection and analysis, decision to publish, or
preparation of the manuscript.
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Conceptualization: Rasmus Oestergaard Nielsen, Daniel Ramskov.
Data curation: Benjamin Mulvad, Rasmus Oestergaard Nielsen, Martin Lind, Daniel
Formal analysis: Benjamin Mulvad, Rasmus Oestergaard Nielsen.
Funding acquisition: Daniel Ramskov.
Investigation: Martin Lind.
Methodology: Rasmus Oestergaard Nielsen.
Project administration: Daniel Ramskov.
Software: Rasmus Oestergaard Nielsen.
Supervision: Martin Lind.
Writing – original draft: Benjamin Mulvad.
Writing – review & editing: Rasmus Oestergaard Nielsen, Martin Lind, Daniel Ramskov.
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