Excessive Progression in Weekly Running Distance and Risk of

Transcription

[
research report
]
Journal of Orthopaedic & Sports Physical Therapy®
Downloaded from www.jospt.org at A T Still Univ Hlth Sci on July 18, 2015. For personal use only. No other uses without permission.
Copyright © 2014 Journal of Orthopaedic & Sports Physical Therapy®. All rights reserved.
RASMUS ØSTERGAARD NIELSEN, PT, MHSc1,2 • ERIK THORLUND PARNER, PhD3 • ELLEN AAGAARD NOHR, PhD4,5
HENRIK SØRENSEN, PhD1 • MARTIN LIND, PhD6 • STEN RASMUSSEN, MD2,7
Excessive Progression in Weekly Running
Distance and Risk of Running-Related
Injuries: An Association Which Varies
According to Type of Injury
R
unning-related injuries are common, especially in novice
runners.4,6,24 From a preventive perspective, study of
the underlying mechanisms leading to such injuries is
needed,33 as there is currently very limited knowledge
TTSTUDY DESIGN: An explorative, 1-year prospective cohort study.
TTOBJECTIVE: To examine whether an associa-
tion between a sudden change in weekly running
distance and running-related injury varies according to injury type.
TTBACKGROUND: It is widely accepted that a
sudden increase in running distance is strongly
related to injury in runners. But the scientific
knowledge supporting this assumption is limited.
TTMETHODS: A volunteer sample of 874 healthy
novice runners who started a self-structured
running regimen were provided a global-positioningsystem watch. After each running session during the
study period, participants were categorized into 1
of the following exposure groups, based on the progression of their weekly running distance: less than
10% or regression, 10% to 30%, or more than 30%.
The primary outcome was running-related injury.
TTRESULTS: A total of 202 runners sustained a
running-related injury. Using Cox regression analysis, no statistically significant differences in injury
rates were found across the 3 exposure groups. An
increased rate of distance-related injuries (patel-
lofemoral pain, iliotibial band syndrome, medial
tibial stress syndrome, gluteus medius injury,
greater trochanteric bursitis, injury to the tensor
fascia latae, and patellar tendinopathy) existed
in those who progressed their weekly running
distance by more than 30% compared with those
who progressed less than 10% (hazard ratio =
1.59; 95% confidence interval: 0.96, 2.66; P = .07).
TTCONCLUSION: Novice runners who progressed
their running distance by more than 30% over
a 2-week period seem to be more vulnerable
to distance-related injuries than runners who
increase their running distance by less than 10%.
Owing to the exploratory nature of the present
study, randomized controlled trials are needed to
verify these results, and more experimental studies
are needed to validate the assumptions. Still,
novice runners may be well advised to progress
their weekly distances by less than 30% per week
over a 2-week period.
TTLEVEL OF EVIDENCE: Prognosis, level 1b–.
J Orthop Sports Phys Ther 2014;44(10):739-747.
Epub 25 August 2014. doi:10.2519/jospt.2014.5164
TTKEY WORDS: etiology, novice, prospective
about injury prevention.34 Interestingly, Hreljac15 pragmatically
stated that all overuse injuries in
runners are linked to training errors. This statement is supported
by others who work with causality
and injury in sport.19,30
Training error is, unfortunately, a
vague term because it covers a broad range
of flaws in the running regimen. To name
a few, these flaws may include excessive
mileage, a rapid change in intensity, and
a sudden increase in running distance.
While difficult to define, it is a general
belief that a sudden excessive increase
in running distance may overwhelm the
ability for adaptive changes and tissue
repair, which ultimately leads to injury.15
To date, the scientific knowledge to support a link between sudden increases in
weekly mileage and injury development
is extremely limited.24 Yet, Jacobs and
Berson16 reported that one third of runners with injuries described that they had
changed their running routines just prior
to their injury development.
The so-called “10% rule” is commonly
used as a guideline for a maximum training progression by runners, coaches,
Section of Sport Science, Department of Public Health, Aarhus University, Aarhus, Denmark. 2Orthopaedic Research Unit. Science and Innovation Center, Aalborg University
Hospital, Aalborg, Denmark. 3Section of Biostatistics, Department of Public Health, Aarhus University, Aarhus, Denmark. 4Section of Epidemiology, Department of Public Health,
Aarhus University, Aarhus, Denmark. 5Institute of Clinical Research, University of Southern Denmark, Odense, Denmark. 6Department of Orthopaedic Surgery, Aarhus University
Hospital, Aarhus, Denmark. 7Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. The Ethics Committee of Central Denmark Region (M-20110114) approved
the protocol for this study. This study received direct funding from the Orthopaedic Surgery Research Unit, Science and Innovation Center, Aalborg Hospital; Aarhus University;
and the Danish Rheumatism Association. Furthermore, Garmin Ltd and adidas Group made it possible to buy global-positioning-system watches and running shoes at a reduced
price. Address correspondence to Rasmus Østergaard Nielsen, Section of Sport Science, Department of Public Health, Faculty of Health Science, Aarhus University, Dalgas
Avenue 4, Room 438, DK-8000 Aarhus C, Denmark. E-mail: [email protected] t Copyright ©2014 Journal of Orthopaedic & Sports Physical Therapy®
1
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[
and clinicians.17 Although the 10% rule
is widely accepted, a well-designed randomized controlled trial failed to identify an increased risk of injury in novice
runners progressing their weekly running distance by 24% over an 8-week
period compared to those progressing
their weekly running distance by the recommended 10% over a 12-week period.6
Based on the results of this study, the
10% rule and its relationship to injury
development should be reconsidered.
Perhaps cumulative progressions over
8 and 12 weeks are not sudden enough.
Possibly, changes in running routines
over, for instance, a 2-week period may
more likely lead to injuries. In addition,
a higher progression rate may be needed
to identify a difference in injury risk. In
a recent case-control analysis, injured
runners had an average progression in
weekly distance prior to injury of 31%,
whereas the noninjured controls had a
progression of 22%.25 Unfortunately, the
sample size in the study was small (n =
60), and only 13 runners sustained an
injury. It was therefore concluded that
the results from that study should be interpreted with extreme caution, and the
need for more large-scale prospective
studies was emphasized.
The inclusion of all types of runningrelated injuries into a statistical analysis
may be problematic, as different runningrelated injuries may develop based on the
types of errors in the running regime. It
seems plausible that some injuries may
more likely develop owing to sudden increases in running distance, while others may more likely develop owing to a
sudden increase in running pace.26 A
biomechanical rationale for the possible
underlying mechanism for the development of some pace-related injuries has
been suggested,3 and a number of studies
have directly linked a fast pace or sprinting to the following injuries: Achilles tendinopathy,14 hamstring strains,8,13 tibial
stress fractures,10,11 and iliopsoas strains.1
Conversely, sudden increases in running distance may be linked to other
types of running-related injuries, such as
research report
iliotibial band syndrome,20 patellofemoral pain,32 patellar tendinopathy,12 and
medial tibial stress syndrome.18 A recent
biomechanical study by Schache et al29
provides a rationale for the mechanisms
that lead to injuries in the anterior part
of the knee. During slow-speed running,
the cumulative load at the knee joint is
higher than the cumulative load during
faster running. It is hypothesized that
when running slower for longer distances (especially when fatigued), a sudden
increase in mileage may be associated
with an increased risk of running-related
injuries in the anterior part of the knee.
Similar assumptions could be made for
other anatomical locations, such as the
lateral part of the hip and the medial part
of the lower leg. Accordingly, distancerelated injuries could be hypothesized
to be patellofemoral pain, iliotibial band
syndrome, medial tibial stress syndrome,
gluteus medius injury, greater trochanteric bursitis, injury to the tensor fascia
latae, and patellar tendinopathy.
To determine if a sudden increase in
running distance may be associated with
the development of running-related injuries, it would be possible, for instance,
to follow a large cohort of runners prospectively and register their running routines using a valid method,25 calculate the
change in weekly running distance over
a 2-week period, diagnose each injury
by clinical examination, and divide the
injuries into categories prior to analysis.
Using this approach, it may be possible
to determine whether the hazard of sustaining specific distance-related injuries
increases in novice runners who pro
gress their weekly running distance by
more than 30% just prior to injury. The
purpose of the present study was, therefore, to examine whether an association
between a sudden change in weekly running distance and running-related injury
varies according to the type of injury. We
hypothesized that the injury rate would
be significantly higher in novice runners
who had a progression of weekly running distance of more than 30% than in
novice runners with a progression of less
]
than 10%, and that the increased injury
rate would only be present for distancerelated injuries, such as patellofemoral
pain, iliotibial band syndrome, medial
tibial stress syndrome, gluteus medius
injury, greater trochanteric bursitis, injury to the tensor fascia latae, and patellar tendinopathy.
METHODS
T
he Danish Novice Running project (DANO-RUN) was a prospective, observational cohort study with
a 1-year follow-up.21 The study protocol
was presented to the Ethics Committee of
Central Denmark Region, which waived
the request for approval because observational studies do not need ethics approval
according to Danish law. Recruitment
procedures and inclusion and exclusion
criteria have been presented in previously
published work.22,23 Of the 1530 individuals who volunteered for the study, 579
were excluded prior to baseline evaluation. At baseline investigation, an additional 18 individuals were excluded due to
a variety of reasons. A detailed description
of the reasons for excluding these 597 individuals is presented elsewhere.22 Finally,
933 participants (464 female, 469 male)
were enrolled in the study after signing an
informed-consent form.
Baseline Investigation
At baseline, the body mass index (BMI)
of all participants was calculated. Subsequently, the participants were provided
with a pair of neutral running shoes (Supernova Glide 3; adidas Group, Herzogenaurach, Germany) and were asked
to use this shoe in all running sessions
during the following year. In addition,
each participant was provided with a
global-positioning-system (GPS) watch
(Forerunner 110 M; Garmin Ltd, Schaffhausen, Switzerland), which has previously been shown to accurately measure
the distance covered by runners.25 Participants were instructed to upload every training session (running only) they
completed during the year to an internet-
740 | october 2014 | volume 44 | number 10 | journal of orthopaedic & sports physical therapy
9/16/2014 4:42:23 PM
based training diary (http://www.vilober.
dk/). In case of missing GPS data, they
were told to upload the time and distance
manually. After the baseline evaluation,
the participants initiated their running
program, which was self-structured.
Each participant decided when and
where to run, with no restrictions with
regard to time, duration, and intensity of
each training session. Similarly, each participant decided on the change in weekly
running distance. Participants were told
that they would receive the shoes and
GPS watch for free if they completed a
minimum of 52 running sessions during
the 1-year follow-up.
Novice runners included in the
DANO-RUN study,21 n = 933
Excluded, n = 3
• Sustained injuries prior to
baseline
n = 930
Excluded, n = 34
• Sustained injuries in the first 2
weeks
n = 896
Excluded, n = 23
• Uninjured, left the study in the
first 2 weeks
Running-Related Injuries
The primary outcome was the first running-related injury to occur during the
1-year period. A running-related injury
was defined as “any musculoskeletal
complaint of the lower extremity or back
caused by running that restricted the
amount of running (distance, duration,
pace, or frequency) for at least 1 week.”
This definition was a modified version of
the definition used by Buist et al.5 If the
participants sustained a running-related
injury during the study period, they were
instructed to contact the medical team
via their personal training diary. Then,
the participant was contacted by telephone, and an appointment for a clinical
examination was made during which he
or she was examined by a physiotherapist, preferably no later than 1 week after
the telephone conversation. A standardized examination procedure and nonvalidated guidelines for the diagnostic
criteria were used to classify each injury.
If the physiotherapist was unable to diagnose the injury at the clinical examination, an additional examination including
diagnostic imaging was performed at a
nearby hospital, which was needed for
approximately 25% of all injury cases.
At each clinical examination, the running-related injury was classified as being
based on overuse or on trauma. Injuries
occurring during the first 2 weeks of the
running program (n = 34) were excluded
Included, n = 873
Remained uninjured, n = 671
Sustained
distance-related
injuries, n = 76
Sustained
pace-related
injuries, n = 58
Sustained a running-related injury,
n = 202
Sustained other
overuse
injuries, n = 52
Sustained
traumatic injury
types, n = 16
FIGURE 1. Flow chart of the exclusions prior to analyses. When investigating the cause-specific injury probability
(TABLE 2; all subanalyses), the uninjured, the 76 sustaining distance-related injuries, the 58 sustaining pacerelated injuries, the 52 sustaining other overuse injuries, and the 16 sustaining traumatic injuries are included.
Abbreviation: DANO-RUN, Danish Novice Running project.
because (1) these injuries were hypothesized to have occurred because the initial
running distance during the first week
was too long, and (2) it was not possible
to calculate the progression in running
distance during the first 2 weeks. A total
of 873 of the 933 individuals originally
included in the DANO-RUN study were
included in the present analyses, after
exclusion of those who sustained injuries
in the first 2 weeks and the 23 uninjured
individuals who left the study for reasons
other than injury in the first 2 weeks. A
flow chart of the exclusions prior to the
analyses is provided in FIGURE 1.
Injured participants were asked to
report the specific day or training session at which the symptoms started. This
day was identified as the day the injury
occurred. Patellofemoral pain, iliotibial
band syndrome, and patellar tendinopathy have previously been linked to excessive running distance.26 Additionally, we
hypothesized that the development of
medial tibial stress syndrome, gluteus
medius injury, greater trochanteric bursitis, and injury to the tensor fascia latae
would be linked to excessive progression
in running distance. The assumption that
these injuries are likely to be distance re-
9/16/2014 4:42:23 PM
[
lated and not pace related remains to be
further validated, and, as a consequence,
the analyses presented in this article
should be considered as explorative.
TABLE 1
Variable
Change in Weekly Running Distance
The primary exposure of interest was
the ratio between 2 weekly distances expressed as a percentage of change. The
ratio was calculated in the following manner. After each running session during
the study period, the sum of kilometers
from that session was added to the sum
of kilometers covered in a 6-day period
prior to that session. Accordingly, the
cumulative number of kilometers over a
1-week period (week 1) was determined.
Then, the cumulative running distance
from days 7 to 13 prior to the training session of interest (week 0) was calculated.
Based on these 2 absolute distances from
week 1 and week 0, the progression or
regression (%) between these 2 periods
was calculated by dividing the 2 absolute
distances and then multiplying the result
by 100 [ratio between weekly distances
= (total running distance week 1)/(total
running distance week 0) × 100].
The ratio between weekly distances
was a covariate that was time dependent,
in the sense that progression (a positive
ratio) or regression (a negative ratio)
could change many times during the
study period (effectively, after each running session). This enabled data analysis
of a time-dependent exposure variable
that allowed the participants to move
into other exposure groups (or stay in the
same exposure group) each time they ran.
Importantly, this approach is much different from the average change in running
distance, which is not time dependent and
has been used as the exposure of interest
in many previously published studies.24
After calculating the ratio after each
running session, the change in weekly
distance (progression or regression) was
categorized into 1 of the following 3 exposure groups (in statistical terms, exposure states): progression less than 10%
or regression, progression between 10%
and 30%, and progression greater than
]
research report
Characteristics of the 873 Participants,
Stratified by Injury Status*
All (n = 873)
Injury Free (n = 671)
Injured (n = 202)
Sex, n
P Value†
.59
‡
Male
441
335
106
Female
432
336
96
Age, y§
37.2  10.3
36.7  10.2
39.0  10.3
BMI, kg/m2§
26.1  4.2
25.9  4.3
26.6  4.2
Fat percentage§║
28.1  9.3
27.6  9.4
29.5  9.3
Previous RRI, n‡
<.01
.05
.01
<.01
Yes
156
105
51
No
717
566
151
Yes
327
242
85
No
546
429
117
Previous non-RRI, n‡
.13
Abbreviations: BMI, body mass index; RRI, running-related injury.
*Values are mean  SD unless otherwise indicated. All variables were measured or reported prior to or
at the baseline investigation.
†
The P values correspond to the tests for difference between injured and injury free.
‡
Chi-square test used to compare injured and injury free.
§
Unpaired t test used to compare injured and injury free.
║
Measured by bioelectrical impedance.
30%. The 10% cutoff was chosen based
on the general belief that a graded training program could become injurious at a
progression in weekly distance of more
than 10%.24 The 30% cutoff was chosen
based on the findings from a pilot study.25
Because most participants varied in their
running routine, each runner was able to
move between the 3 exposure groups (less
than 10% or regression, 10% to 30%, or
greater than 30%) every time that runner
completed a new running session during
the study period. Statistically, such movement between exposure groups is known
as multistate transition.28 Importantly,
when a hazard ratio (HR) was calculated
in the present study, it was based solely
on the 3 exposure groups, with the goal
of answering the following question: “Is it
hazardous to progress by more than 30%
over a 2-week period?”
If a runner did not run in week 0, it
was not possible to calculate a ratio between the weekly distances in week 1 and
week 0, because the denominator was
zero. In such cases, participants were
categorized into a “not available” group.
To summarize, after each running ses-
sion, participants were continuously categorized into 1 of the 4 groups (less than
10% progression or regression [reference
group], 10% to 30% progression, greater
than 30% progression, or not available).
Statistical Analysis
The HRs between exposure groups and
running-related injury were estimated
using Cox regression, with the number of
kilometers during the training sessions as
the time scale. In statistics, an exposure
that can change over time is known as a
time-dependent covariate. This concept
enables each participant to move between
exposure states continuously (after each
running session) using delayed entry in
the Cox regression model.28 In the analyses, cause-specific hazards of the instantaneous risk of injury from a specific injury
category (distance-related injuries, pacerelated injuries, other overuse injuries, and
traumatic injuries) were calculated using
competing risks. The HRs were compared
across injury categories, with the less than
10% group as the reference group. The
unit of analysis was each runner. Participants were censored in case of pregnancy,
9/16/2014 4:42:24 PM
TABLE 2
Results From the Cox Regressions Linking
Injury Rate With Distance Progression
Exposure State
Hazard Ratio*
P Value
All injuries (n = 202)†
<10%
1 (reference)
10%-30%
0.99 (0.55, 1.82)
.99
>30%
1.17 (0.84, 1.63)
.36
Distance-related injuries (n = 76)‡
<10%
1 (reference)
10%-30%
1.03 (0.37, 2.90)
.96
>30%
1.59 (0.96, 2.66)
.07
Pace-related injuries (n = 58)§
<10%
1 (reference)
10%-30%
0.91 (0.32, 2.63)
.86
>30%
0.83 (0.44, 1.57)
.56
Other overuse injuries (n = 52)║
<10%
1 (reference)
10%-30%
0.63 (0.15, 2.70)
.53
>30%
0.84 (0.40, 1.77)
.65
Traumatic injuries (n = 16)¶
<10%
1 (reference)
10%-30%
3.16 (0.62, 16.25)
.17
>30%
2.09 (0.61, 7.20)
.24
*Values in parentheses are 95% confidence interval. Due to the low number of injuries in the 10% to
30% progression exposure group (n = 2-4, TABLE 3), the hazard ratios between this group and the
reference group should be interpreted with caution.
†
All 202 injured novice runners (all injuries) were included in the analyses.
‡
Included the 76 runners sustaining distance-related injuries (patellofemoral pain, iliotibial band
syndrome, medial tibial stress syndrome, patellar tendinopathy, gluteus medius injury, greater
trochanteric bursitis, and injury to the tensor fascia latae).
§
Included the 58 runners who sustained pace-related injuries (plantar fasciitis, Achilles tendinopathy,
tibial stress fracture, hamstring injuries, iliopsoas injuries, and injuries to the triceps surae muscles).
║
Included the 52 runners who sustained injuries of the medial meniscus, other stress fractures, and
other overuse injuries not included in the distance-related or pace-related injury categories.
¶
Included the 16 runners sustaining traumatic injuries, such as ankle inversion injuries.
disease, lack of motivation, unwillingness
to attend clinical examination for runningrelated injury, or end of follow-up at 1 year,
whichever came first. The assumption of
proportional hazards was evaluated by
log-minus-log plots. In addition, at least
10 injuries per predictor variable included in the Cox regression analysis had to
be present to perform a valid statistical
analysis.27 Because a considerable number of the events were used to perform the
crude analysis, an adjusted analysis that
included more confounders than previous
running-related injury, BMI, fat percentage, and age could not be performed. Because the hazards were not proportional
in the not available group, the data from
this exposure group were not presented in
the main results. Hazard ratios were considered statistically significant at P≤.05. In
addition, for proper interpretation of study
results, estimated effect size and estimated
precision (95% confidence limits) were
calculated.31 All analyses were performed
using Stata Version 12 (StataCorp LP, College Station, TX).
RESULTS
A
total of 202 of the 873 novice
runners included in the study sustained a running-related injury. De-
mographic characteristics of the runners,
divided by injury status, are presented
in TABLE 1. During the study period, the
participants ran a total of 148 491 km in
35 410 training sessions. After participants completed each running session,
it was possible to calculate the exposure
group to which the participant belonged
at that given time point: for 16 253 sessions (46%) the progression (or regression) was less than 10%, for 1939 sessions
(5.5%) the progression was between 10%
and 30%, and for 7507 sessions (21%)
the progression was greater than 30%.
Finally, it was not possible to calculate
a progression for 9711 running sessions
(27.5%).
The primary result revealed that the
injury rate was modified by injury diagnoses in the greater than 30% progression group, based on the results from the
analysis of pace-related injuries (TABLE
2, third analysis) and distance-related
injuries (TABLE 2, second analysis) being significantly different (P<.05). In
the analysis that included all injuries,
no significant differences in injury rates
were found across exposure groups (TABLE 2, first analysis). However, if injuries
were restricted to patellofemoral pain,
iliotibial band syndrome, medial tibial
stress syndrome, patellar tendinopathy,
gluteus medius injury, greater trochanteric bursitis, and injury to the tensor
fascia latae (TABLE 2, second analysis),
an increased rate of sustaining an injury
was observed in those runners who progressed their weekly running distance by
greater than 30% compared with those
who progressed less than 10% (HR =
1.59; 95% confidence interval: 0.96,
2.66; P = .07). The estimate changed
minimally after adjusting for age, BMI,
fat percentage, and previous history of
running-related injury (HR = 1.59; 95%
confidence interval: 0.96, 2.68; P = .07).
Although nonsignificant, the estimates
from the analysis that included plantar
fasciitis, Achilles tendinopathy, tibial
stress fracture, hamstring injuries, iliopsoas injuries, and gastrocnemius and
soleus injuries revealed that the injury
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[
research report
A
0.20
Injury Risk
0.15
0.10
0.00
0
50
100
150
200
150
200
Cumulated Running Distance, km
B
0.20
0.15
Injury Risk
0.05
0.10
0.05
0.00
0
50
100
Cumulated Running Distance, km
FIGURE 2. Graphs visualizing the cause-specific injury probabilities for the (A) less than 10% and the (B) greater
than 30% strata during the first 200 km of running. The blue line is the cause-specific injury probability of
distance-related injuries (patellofemoral pain, iliotibial band syndrome, medial tibial stress syndrome, patellar
tendinopathy, gluteus medius injury, greater trochanteric bursitis, and injury to the tensor fascia latae). The orange
line is the cause-specific injury probability of pace-related injuries (plantar fasciitis, Achilles tendinopathy, tibial
stress fracture, hamstring injuries, iliopsoas injuries, and injuries to the triceps surae muscles). The green line
is the cause-specific injury probability of other types of overuse injuries. The red line is the cause-specific injury
probability of traumatic injuries, such as ankle inversion injuries.
rate decreased in relation to increasing
progression in running distance (TABLE 2,
third analysis). A plot of the cause-specific injury probability is presented in FIGURE
2. The observed and expected numbers of
injuries in each exposure group are presented in TABLE 3.
DISCUSSION
T
he present study revealed that
novice runners who progressed
their weekly running distance by
greater than 30% were more vulnerable
to distance-related injuries, such as patellofemoral pain, iliotibial band syndrome,
medial tibial stress syndrome, patellar
tendinopathy, gluteus medius injury,
greater trochanteric bursitis, and injury
to the tensor fascia latae, than runners
who progressed their running distance
less than 10% (TABLE 2, second analysis).
Such a relationship was not present for
other injury types like traumatic injuries
(TABLE 2, fifth analysis) or pace-related injuries like Achilles tendinopathy, plantar
fasciitis, tibial stress fracture, hamstring
injuries, iliopsoas injuries, and calf injuries (TABLE 2, third analysis). Interestingly, no dose-response relationship was
revealed, because it was equally hazardous to increase the weekly running distance by 10% to 30% compared to less
than 10%. Accordingly, a greater difference in progression rates less than 10%
versus 10% to 30% may therefore be
]
needed to adequately evaluate the hazard
involved in a sudden increase in weekly
running distance over a 2-week period.
In addition, only specific injuries must
be included in the analysis to reveal any
differences in hazards between exposure
groups.
Clinically, this knowledge must be
used with caution when designing a running program, because multiple changes
between groups (multistate transitions28)
over time may affect injury risk considerably. In the present study, we examined
1 change in group over a 2-week period
(from week 0 to week 1) in relation to injury risk. We did not take into account
the cumulative distance in the week prior to week 0 (week –1) and the change
in progression/regression from week –1
to week 0, or the change in progression
from week –2 to week –1. In the present study, the 30% cutoff was found to
be associated with an increased injury
rate. If, for example, a runner increased
his or her weekly distance by 36%, there
was an increased injury rate for distancerelated injuries. If the increase remained
less than 30%, the injury rate was lower,
which could have led the runner to assume that just keeping the increase to
less than 30% would keep the injury rate
low, no matter how the runner scheduled
his or her running. Such an assumption
must, however, be made with extreme
caution. The injury rate may be low
when increasing the weekly distance by,
for instance, 5%, then by 7%, and finally
by 3%. But the injury rate may be high
when progressing from 25% to 25% and
finally to 25% over a 4-week period, even
though the progression did not exceed
30%. Clinicians should, therefore, be
cautious about advising runners to increase their running distance at a high
progression level, even though our results
suggest that runners may be at low risk if
the progression does not exceed 30%. For
now, it seems plausible to assume that
continuous changes over time between
high progression states (eg, 25%) may ultimately lead to an injury. But more work
is needed to validate this assumption.
9/16/2014 4:42:25 PM
The biomechanical rationale that explains the mechanisms leading to injury
development owing to a sudden increase
in weekly distance remains unknown.
Yet, it seems plausible to assume that
running longer distances than usual may
force runners to decrease running speed,
especially if they are fatigued. If running speed is decreased for a given running distance, the cumulative number
of steps increases considerably.9 This is
important, because the cumulative load
at the knee joint seems to be significantly
increased during slow-speed running
compared with faster running.29 A similar finding may be present at the lateral
part of the hip and at the medial part of
the lower leg. In contrast, another biomechanical rationale suggests a sudden
increase in running speed to be linked
with injuries like Achilles tendinopathy,
plantar fasciitis, tibial stress fracture,
hamstring injuries, iliopsoas injuries, and
calf injuries.3,9,29 This may be the reason
for the difference in the results across distance-related and pace-related injuries.
We strongly underline the importance of
this assumption because it seems crucial
to make such a categorization if the influence of training errors on injury development is to be investigated properly.
The strengths of the present study are
the number of individuals included and
the method used to gather information
about running exposure. Also, the statistical approach used, allowing for delayed
entry/time-dependent exposures and
competing risks, is a major strength. A
comprehensive tutorial of the strengths
and validity of time-to-event analysis, including a description of time-dependent
exposures in observational studies, is provided by Bull and Spiegelhalter.7 But important limitations should be taken into
account when interpreting the results.
First, nearly all novice runners included
in the study utilized a rearfoot strike.2
The results from the present study cannot
be generalized to runners utilizing other
foot-strike patterns, as other mechanisms
leading to injury may exist for those with
a midfoot- or forefoot-strike pattern.
TABLE 3
Observed and Expected Number
of Running-Related Injuries in Each
of the Exposure Groups*
<10%
10%-30%
All injuries (n = 202)
92 (85.6)
Distance injuries (n = 76)
32 (33.9)
Pace injuries (n = 58)
Other overuse injuries (n = 52)
Traumatic injuries (n = 16)
>30%
NA
P Value†
12 (13.2)
54 (53.3)
44 (53.0)
.36
4 (4.1)
26 (17.1)
14 (20.9)
.06
31 (26.8)
4 (3.8)
13 (13.5)
10 (13.8)
.60
24 (24.5)
2 (3.2)
10 (12.3)
16 (12.0)
.49
5 (8.0)
2 (1.0)
5 (3.8)
4 (3.2)
.45
Abbreviation: NA, not able to calculate a progression.
*Values are observed number of injuries (expected number of injuries). The injuries in the distance,
pace, other overuse, and traumatic groups are similar to those described in TABLE 2.
†
The P values correspond to the log-rank test for equality of survivor functions.
Second, it must be emphasized that the
present study is an observational study.
Because of this study design, the results
presented are vulnerable to confounding,
and the results must therefore be interpreted with caution. In TABLE 1, age, BMI,
fat percentage, and previous runningrelated injuries were found to be risk
factors for developing an injury. These
risk factors were included in an adjusted
analysis, but the adjustment had little
influence on the estimates. Still, various
unknown risk factors may confound the
results of the present study. To take into
account the risk of confounding, more
randomized controlled trials are needed.
In such studies, it is of great importance
to perform clinical examination of the
injured participants because different
training approaches (sudden change in
running distance versus sudden change
in running pace) are associated with development of different types of injuries.
Third, the results of the present study revealed that sudden progression of weekly
running distance was a risk factor for the
development of only 76 of 202 injuries
(37.6%). Therefore, work must be devoted to identifying the training errors
linked to the development of the remaining 126 injuries. For now, it seems plausible that excessive pace may be somehow
associated with Achilles tendinopathy,
plantar fasciitis, tibial stress fracture,
hamstring injuries, iliopsoas injuries,
and injuries to the triceps surae muscles
(n = 58, 28.7%).26 It would therefore be
of great interest to perform an analysis
to investigate whether progression in
running pace may be associated with
development of these injuries. Unfortunately, the measurement errors provided
by the nondifferential GPS watches used
to quantify the running pace were too
severe to perform such analysis based on
the DANO-RUN data set.
CONCLUSION
N
ovice runners increasing their
weekly running distance by greater
than 30% were more vulnerable to
distance-related injuries, such as patellofemoral pain, iliotibial band syndrome,
medial tibial stress syndrome, patellar
tendinopathy, gluteus medius injury,
greater trochanteric bursitis, and injury
to the tensor fascia latae, than runners
who kept their progressions in running
distance to less than 10%. These differences were not present for what we would
consider “pace-related” or “other overuse”
injuries. Due to the exploratory nature of
the present study, randomized controlled
trials are needed to confirm these findings, and more experimental studies are
needed to validate the assumption that
some structures are relatively more exposed to stress than other structures in
relation to an increase in running distance. Yet, novice runners may be well
advised to increase their weekly running
9/16/2014 4:42:26 PM
[
distance by less than 30% over a 2-week
period. t
KEY POINTS
FINDINGS: A sudden increase in weekly
running distance of greater than 30%
over a 2-week period may lead to the
development of patellofemoral pain,
iliotibial band syndrome, medial tibial
stress syndrome, patellar tendinopathy,
gluteus medius injury, greater trochanteric bursitis, and injury to the tensor
fascia latae.
IMPLICATIONS: Novice runners may be well
advised to increase their weekly distance
by less than 30% over a 2-week period.
Clinicians should pay particular attention to a runner’s progression in weekly
distance if they have patellofemoral
pain, iliotibial band syndrome, medial
tibial stress syndrome, patellar tendinopathy, gluteus medius injury, greater
trochanteric bursitis, or injury to the
tensor fascia latae.
CAUTION: Other training-related factors,
such as progression over several weeks
and intensity, should be taken into account when designing a program for
runners.
ACKNOWLEDGEMENTS: The authors greatly ac-
knowledge the contributions from employees
and students connected to the DANO-RUN
project during the data-collection period. Garmin and Adidas are greatly acknowledged
for making it possible to buy the watches and
shoes at a reduced price.
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@
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9/16/2014 4:42:27 PM
jospt perspectives for patients
Running
How to Safely Increase Your Mileage
J Orthop Sports Phys Ther 2014;44(10):748. doi:10.2519/jospt.2014.0506
D
o you want to start a running program? Are you already a runner and want to increase your miles? Are
you recovering from an injury and trying to return
to running? If you are working to accomplish any
of these goals, you have probably wondered how
to increase your running miles safely so that you are not hurt.
Running-related injuries are very common, and training errors
are the leading cause of preventable injuries. Most training injuries are the result of “too much, too soon, too fast, too quick.”
Although preventing running injuries is complicated and scientists still have a lot to discover, one rule familiar to many runners is the 10% rule, which states that you should not increase
running mileage more than 10% each week. A study published
in the October 2014 issue of JOSPT puts the 10% rule to the test.
NEW INSIGHTS
Gluteus medius injury
Greater trochanteric bursitis
Iliotibial band syndrome
Patellar tendinopathy
(jumper’s knee)
Injury to tensor fascia latae
Patellofemoral pain (anterior
knee pain, runner’s knee)
Medial tibial stress
syndrome (shin splints)
RUNNING-RELATED INJURIES. A sudden increase in weekly running distance by more than 30% over a 2-week
period may put runners at increased risk for developing patellofemoral pain (runner’s knee), iliotibial band syndrome,
medial tibial stress syndrome (shin splints), patellar tendinopathy (jumper’s knee), greater trochanteric bursitis, and
injury to the gluteus medius or tensor fascia latae.
For this and more topics, visit JOSPT Perspectives for Patients online at www.jospt.org.
This Perspectives article was written by a team of JOSPT’s editorial board and staff, with Deydre S. Teyhen, PT, PhD,
Editor, and Jeanne Robertson, Illustrator.
This JOSPT Perspectives for Patients is based on an article by Nielsen et al, titled “Excessive Progression in Weekly
Running Distance and Risk of Running-Related Injuries: An Association Which Varies According to Type of Injury,” J
Orthop Sports Phys Ther 2014;44(10):739-747. Epub 25 August 2014. doi:10.2519/jospt.2014.5164
Although runners, coaches, and health care providers
commonly use the 10% rule, more science is needed
to understand its role in injury prevention. Researchers
followed 873 new runners for 1 year; during this
period, 202 runners had a running-related injury. The
researchers compared runner injuries based on each
participant’s weekly increase in running distance: less
than 10%, 10% to 30%, and more than 30% in the
2 weeks prior to injury. Runners who increased their
mileage by more than 30% had a higher injury rate
than those who increased their mileage by less than
10%. Runners who ran farther faster were at higher
risk for patellofemoral pain (runner’s knee), iliotibial
band syndrome, medial tibial stress syndrome (shin
splints), patellar tendinopathy (jumper’s knee), greater
trochanteric bursitis, and injury to the gluteus medius
or tensor fascia latae (see illustration). However, other
types of injuries were not linked to the 10% rule, such
as plantar fasciitis, Achilles tendinopathy, calf injuries,
hamstring injuries, tibial stress fractures, and hip flexor
strains. The authors suggest that these injuries may be
related to other training errors.
PRACTICAL ADVICE
A sudden increase in weekly running distance by more
than 30% over a 2-week period may put runners at
increased risk for developing running-related injuries.
The lowest injury rates were found in new runners who
increased their weekly mileage by less than 10% over 2
weeks. However, other running injuries may be linked to
running pace, increasing running speed, sprint training,
or other training errors. If you are starting a running
program, your physical therapist can help customize a
safe running progression to meet your needs. For more
information on a personalized running program, contact
your physical therapist specializing in musculoskeletal
disorders and running-related injuries.
JOSPT PERSPECTIVES FOR PATIENTS is a public service of the Journal of Orthopaedic & Sports Physical Therapy. The information and recommendations
contained here are a summary of the referenced research article and are not a substitute for seeking proper health care to diagnose and treat this condition.
For more information on the management of this condition, contact your physical therapist or health care provider specializing in musculoskeletal
disorders. JOSPT Perspectives for Patients may be photocopied noncommercially by physical therapists and other health care providers to share with
patients. The official journal of the Orthopaedic Section and the Sports Physical Therapy Section of the American Physical Therapy Association (APTA),
JOSPT strives to offer high-quality research, immediately applicable clinical material, and useful supplemental information on musculoskeletal and
sports-related health, injury, and rehabilitation. Copyright ©2014 Journal of Orthopaedic & Sports Physical Therapy ®
44-10 Perspectives.indd 748
9/16/2014 4:43:17 PM
This article has been cited by:
1. Bryan Heiderscheit. 2014. Always on the Run. Journal of Orthopaedic & Sports Physical Therapy 44:10, 724-726. [Abstract]
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Excessive Progression in Weekly Running Distance and Risk of

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