Overview of running injuries of the lower extremity(uptodate

Training suggestions to reduce injury risk — Despite the dearth of high-
quality evidence to determine best practice [25], we have found the training
tips listed below to be helpful and to reduce the risk of injury for many
runners:

Beginning runners:

    Inexperienced runners often progress best using a combination of running
and walking for a set time, and gradually increasing the percentage of time
spent running.
    Beginning runners should start with no more than 20 minutes of total
training time per day and increase training time no more than 5 minutes
every 14 days.
    Most beginners do best on an every other day training program, which
enables gradual improvement of their aerobic and musculoskeletal fitness.

Mileage and rest guidelines:

    With the exception of elite runners, most individuals develop fewer
injuries by limiting their total mileage to 40 miles (65 km) per week. (See
'Training variables' above.)
    Runs longer than 13 miles (20 km) are best done no more frequently than
once every 14 days
    Most individuals do best running no more than four or five days per week
, with at least one rest day and one to two days doing other activities (ie,
cross-training)
    Runners should limit themselves to two to three marathons per year

Warm-up:

    Ease into training with a dynamic warm-up or light jog.
    Stretching before runs does not appear to reduce injuries; runners may
do better stretching after their run or improving their strength and
flexibility using other techniques, such as Yoga or Pilates. (See '
Stretching and warm-ups' above.)

Training variables:

    Runners who experience frequent injuries are likely to benefit from
running on a treadmill or a soft surface. Older athletes reduce their injury
risk by running on soft surfaces. (See 'Training variables' above.)

Training techniques:

    Runners need a solid base of aerobic fitness before adding speed work.
    Speed work is generally less risky if runners begin with the “Fartlek”
(speed play) approach for 20 to 30 percent of their continuous runs for at
least one month, before progressing to interval training (alternating fixed
activity and rest periods) or timed repeat speed distances (eg, 10 sets of
200 M runs). Fartlek training consists of running at a faster pace at random
times of variable duration during an otherwise standard distance run.
    Most runners need to limit the total mileage for interval or repeat
distance speed training to 3 miles (5 km) or less.
    Fast downhill runs increase impact and injury risk and should be avoided.

Footwear:

    Athletes should select a running shoe that feels extremely comfortable
and is well-suited to their foot structure (eg, high arch). (See 'Shoes and
orthotics' above.)
    Barefoot running, while it may help to improve the biomechanics of some
runners, probably only benefits those with sound running biomechanics at
baseline and a foot structure that does not increase their injury risk, and
should be limited to softer surfaces. Many running clinics are seeing an
increase in metatarsal stress fractures in individuals new to this approach.

Nutrition and recovery:

    Runners should maintain adequate hydration and increase their salt
intake if they tend to sweat heavily.
    Carbohydrate and protein intake soon (within about 30 minutes) after an
intense workout speeds recovery. (See 'Nutrition and supplementation' above.)

Supplemental strength training:

    Many runners have disproportionately strong hamstrings. Cross training
with a road or stationary bicycle or other equipment that develops
quadriceps strength helps to balance the hamstring dominance of runners.
    Many runners have weak hip flexors and hip abductors. Performing
supplemental strength exercises for these muscles may reduce the risk of
injury.
    Achilles tendon flexibility wanes with age. Regular performance of
eccentric strength exercises for the calf complex may help prevent injury. (
See "Achilles tendinopathy and tendon rupture", section on 'Eccentric
exercise rehabilitation'.)

All topics are updated as new evidence becomes available and our peer review
process is complete.
Literature review current through: Feb 2012. | This topic last updated: Oct
20, 2011.

INTRODUCTION — Running is one of the world’s most popular forms of
exercise, with millions of regular participants. In the United States alone,
up to 40 million people run regularly, with more than 10 million running at
least 100 days a year [1]. Although running is an effective way to achieve
many health benefits, it is associated with a high risk of injury; yearly,
up to half of runners report an injury [2]. Although some injuries are
traumatic, most are due to overuse.

Given the popularity of running and the high rate of associated overuse
injuries amenable to nonsurgical management, the primary care physician is
likely to manage many injured runners and should be familiar with the
diagnosis and treatment of the more common problems. The diagnosis and
management of common lower extremity injuries associated with running are
reviewed here. Detailed discussions of some specific injuries are found
separately. (See "Ankle sprain" and "Patellofemoral pain syndrome" and "
Hamstring injuries" and "Stress fractures of the metatarsal shaft".)

GENERAL EPIDEMIOLOGY — The incidence of lower extremity injuries in runners
ranges from 19.4 to 79.3 percent [3]. The knee is the most commonly injured
body part. The most common diagnoses include: patellofemoral pain syndrome,
medial tibial stress syndrome (shin splints), Achilles tendinopathy,
iliotibial band syndrome, plantar fasciitis, and stress fractures of the
metatarsals and tibia [3-6]. According to a 2009 survey of more than 11,000
year-round runners, more than 10 percent experienced hip and/or low back
pain in the previous 12 months [7]. Among marathon runners, men report more
hamstring and calf problems, whereas women report more hip complaints [8].

One retrospective survey of 2886 runners reported an overall injury rate of
46 percent, but found a higher incidence of soft tissue injuries to the calf
, Achilles tendon, and hamstring among masters runners (>40 years), who
comprised 34 percent of the participants [9]. Injured runners were more
likely to be male and to run six days per week and more than 30 miles each
week.

RISK FACTORS — Despite the popularity of running and the prevalence of
related injuries, few studies have successfully identified the individual
factors most responsible, suggesting that many running injuries are
multifactorial. A history of prior injury is one of the few variables that
has consistently been shown to increase the risk of incurring a subsequent
running injury [2,4]. Therefore, every injured runner seeking medical
attention should be questioned about prior injuries, including treatments.
Incomplete rehabilitation and failure to address potential risk factors
associated with a prior injury increases the likelihood of recurrence.
Greater mileage is another factor that is consistently associated with
increased injury risk [10].

Multiple risk factors are likely to contribute to running injuries. These
can be stratified into intrinsic risk factors (eg, anatomic and other
individual variables, including gender and BMI) and extrinsic risk factors (
eg, training variables and equipment).

Intrinsic risk factors

Anatomy — Running injuries have been attributed to a number of anatomic
variables, but the literature does not support many of these commonly held
beliefs. A prime example is patellofemoral pain syndrome, a common cause of
knee pain in runners. Lower extremity alignment that results in a greater Q
angle at the knee (common in women) has often been cited as a cause of
patellofemoral pain, but the large majority of studies refute this assertion.

Foot type is another purported risk factor, but most studies of runners have
not found consistent relationships between foot structure and specific
injuries. One group studying collegiate cross country runners failed to
identify any association between structural variations and the likelihood of
developing exercise-related leg pain [11,12]. One notable exception is
cavus foot (high arch), which is associated with myriad injuries [2,13].
Specific injuries implicated in one or more studies include tibial stress
fractures, patellofemoral pain syndrome, plantar fasciitis, and Achilles
tendinopathy. (See "Stress fractures of the tibia and fibula" and "
Patellofemoral pain syndrome" and "Plantar fasciitis and other causes of
heel and sole pain" and "Achilles tendinopathy and tendon rupture".)

Some researchers have proposed that limb asymmetry (ie, leg length
discrepancy) may increase injury risk, including stress fracture, [14,15],
but not all studies support this conclusion. These conflicting results
suggest that anatomy alone is not sufficient to explain the high risk of
injury among runners. Many experienced sports medicine clinicians believe
that the important issue is whether the difference in leg length affects
gait, rather than whether some measurement threshold is reached.

Gender and age — Gender and age may play a role in some running injuries,
but the literature is conflicting in this regard:

A prospective study of 844 male and female runners following a training
program in preparation for a 10 km race reported an increased risk of injury
among women age 50 or older and a lower risk among those 30 or younger [16].
A prospective study of 532 novice runners participating in a 13 week
training program noted that higher BMI was a risk factor for male but not
female runners (HR 1.15; 95% CI, 1.05-1.26) [17]. Conversely, navicular drop
was associated with injury in females but not males (HR 0.85; 95% CI, 0.75-
0.97).
A longitudinal study of former high school cross country runners over a
15 year period reported that girls had significantly higher injury rates
than boys (16.7 versus 10.9 injuries per 1000 athletic exposures) [18].

Studies consistently report an association between female gender and stress
fracture risk, particularly among females with lower bone density, menstrual
disturbances, and dietary deficiencies, as seen in the female athlete triad
. The risk factors for stress fracture are discussed separately. (See "
Overview of stress fractures", section on 'Risk factors'.)

While not consistently identified as a risk factor for running injury, age
has been associated with a number of injuries in several observational
studies. In contrast to the prospective study described above [16], a
retrospective study of more than 2000 runners found that age under 34 was
associated with an increased risk for patellofemoral pain syndrome in both
men and women and an increased risk for iliotibial band syndrome, patellar
tendinopathy, and tibial stress syndrome among men [5]. These findings may
reflect that master runners (>40 years) are primarily those with low injury
rates, while runners who sustain multiple injuries are more likely to give
up the sport.

Extrinsic risk factors — Studies have not consistently supported many
traditional beliefs about the association between anatomic variations and
injury risk. This has led many researchers to focus both on the effects of
extrinsic factors on running injury and on the combination of intrinsic and
extrinsic variables.

Training variables — Measures to reduce running injuries often include
modifying training variables, such as mileage and intensity. A systematic
review concluded that reducing the distance, frequency, and duration of
running may be effective in preventing soft tissue injuries in runners [19].

In male runners, excessive mileage is associated with higher injury rates.
Multiple observational studies report that training volumes of 65 kilometers
(40 miles) or more per week increase the risk of injury [2,3,9,10]. While
most sports medicine practitioners believe excessive mileage also affects
female runners, well designed clinical studies have not been performed. It
is unclear if more experienced runners are less susceptible.

Abrupt changes in training regimens can contribute to running injuries.
Studies of military recruits report that sudden increases in training volume
or changes in the type of training (eg, adding hill running) increase
injury rates [20]. Although many sports medicine physicians advocate the 10
percent rule (ie, increase training volume by no more than 10 percent per
week), a randomized trial of this approach in 532 novice runners reported no
reduction in injuries (20.8 versus 20.3 percent with standard training) [21
]. Nevertheless, common sense would suggest that gradual increases in
training volume are less likely to cause injury than sudden increases.

Some types of training may be protective. As an example, one research group
found that regular interval training is protective against knee injury [22].
Running surface probably affects injury rates. Running on concrete is
associated with increased risk, while running on a treadmill reduces the
stresses placed on the tibia and may thereby reduce the risk of tibial
stress fractures [23].

Stretching and warm-ups — It is hard to draw firm conclusions about the
effectiveness of stretching for reducing the risk of running injuries due to
the large number of variables involved. These variables include a runner’s
baseline flexibility, the timing of stretching (pre-exercise, post-exercise
, or not in conjunction with exercise), and the method of stretching (eg,
dynamic, static, or proprioceptive neuromuscular facilitation). Despite a
dearth of convincing evidence, many sports medicine physicians, running
coaches, and runners believe that stretching is beneficial. However, further
research is needed to determine which runners benefit and what methods to
use.

Multiple studies question the benefit of stretching, long a piece of injury
prevention advice given to runners [24,25]. A systematic review of
randomized trials that assessed multiple interventions designed to prevent
running injuries included six studies involving 5130 runners that looked at
stretching exercises and concluded that stretching regimens do not protect
against soft tissue injury [25]. The stretching regimens included in these
studies varied in the muscle groups targeted, the timing of the intervention
(eg, before or after training), whether a warm-up was also performed, and
other factors. Another review that included both randomized trials and
cohort studies investigating the effect of stretching on injury reduction
during sports also concluded that stretching was not associated with a
reduction in total injuries (OR 0.93; CI 0.78-1.11) [24].

Stretching may have other benefits. As an example, in a study of 900
military recruits, those who stretched regularly experienced lower rates of
low back and soft tissue pain [26]. Stretching may also play a useful role
in the management of other injuries, such as plantar fasciitis and Achilles
tendinopathy. (See "Plantar fasciitis and other causes of heel and sole pain
" and "Achilles tendinopathy and tendon rupture".)

There is insufficient high-quality research in runners to determine whether
warming up reduces injury rates. One randomized trial involving 421 runners
found that an educational intervention regarding warm-up, cool-down, and
stretching did not significantly reduce the risk of injury [27].
Nevertheless, many clinicians advocate a dynamic warm-up or light jogging
before engaging in strenuous running and we concur with this approach.

Shoes and orthotics — Debate continues about the role running shoes and
orthotics may play in reducing the risk of injury. Based on limited evidence
and clinical experience, we suggest using the running shoe that feels most
comfortable and is well suited to the shape of the runner’s foot [28].

There are three basic types of running shoes:

Shoes for runners with a low foot arch (overpronators) that are designed
to minimize foot motion and maintain the foot in a neutral position
Shoes for runners with a neutral foot shape
Shoes with extensive cushioning for runners with a cavus foot (
oversupinators)

Many clinicians and runners believe that selecting the shoe best suited to
the runner’s foot type prevents injury; however, this concept is not well
supported by the literature.

The most robust studies of running shoes come from the military. Studies of
recruits in the United States Marine Corps and Air Force undergoing basic
training found that assigning shoes to recruits based on foot type did not
significantly reduce injury rates [29,30]. In addition, a systematic review
did not find sufficient evidence to support the prescription of running
shoes based upon foot type [31]. However, one crossover randomized trial
found that some popular, neutral-cushioned running shoes reduced plantar
pressures in the cavus foot, theoretically reducing injury risk [32]. It is
possible that particular shoe types reduce the risk of injury in particular
subpopulations of runners (eg, runners with cavus feet), but further study
is needed to determine if this is so.

Regardless of shoe type, several studies of the shock absorption properties
of running shoes have shown that new shoes lose up to half their cushioning
after 250 to 500 running miles [33]. Therefore, most sports medicine
practitioners counsel runners to change their running shoes every 350 to 500
miles.

Orthotics may reduce the risk of some injuries. A randomized controlled
trial of 400 military officer trainees found a significant reduction in
lower extremity overuse injuries in the trainees given customized orthotics
[34], while systematic reviews performed prior to this study concluded that
orthotics “probably” reduce the risk of stress fracture [35,36]. Other
reports have found that orthotics reduce the pain associated with
patellofemoral pain syndrome and cavus foot, both common issues in runners [
37-39].

Although running with “minimalist” shoes (eg, Vibram fivefingers®) is
gaining popularity, no controlled study to date has found evidence that
such shoes have negative or positive effects upon performance or injury
rates [40].

Gait, strength, and biomechanics — Many laboratory and observational
studies have tried to determine the role of running biomechanics, vertical
load, and plantar pressures in the development of running injuries. However,
it is difficult to draw firm conclusions because many such studies involve
small numbers and multiple factors are likely to contribute to the risk of
injury. The following studies are illustrative:

A systematic review identified 13 articles comparing ground reaction
forces (GRF) and vertical load in runners with and without stress fractures
and found no significant difference in GRF between the two groups, but did
find a significant difference in vertical loading rates [41].
A study of 46 college students with running-related lower extremity
injuries reported that specific components of gait, including increased
pronation associated with increased pressure under the medial side of the
foot, increased the risk of injury [42].
A study of 45 healthy recreational runners found that subtle increases
in step rate reduce the loads placed on the hip and knee during running

Nutrition and supplementation — Little data exists to confirm or refute
associations between nutritional factors and running injuries, with the
important exception of stress fractures in female runners. Multiple studies
report that inadequate vitamin D, calcium, and calorie intake increases the
risk of stress fracture in female military recruits and runners. In addition
, a prospective study of 86 female runners found that low-fat intake
increased the risk of sustaining a low extremity injury [44]. (See "Overview
of stress fractures", section on 'Risk factors'.)

While there is little high-quality evidence to support any particular diet
to prevent running injuries, optimal nutrition does enhance performance and
recovery; common sense suggests that runners should eat a balanced diet that
includes adequate lean protein and all essential vitamins and minerals. A
position paper on nutrition and performance authored jointly by Dietitians
of Canada, the American College of Sports Medicine, and the American
Dietetic Association makes the following recommendations for athletes [45]:

Consume adequate calories. Insufficient calories can lead to reduced
muscle mass and bone density, cessation of menses, and delayed recovery, and
can increase fatigue and the risk of injury and illness. In general, fewer
than 1800 to 2000 kcals/day is inadequate for an exercising individual,
although many female runners restrict calories to this level. Several tools
are available to estimate calorie needs, including the Dietary Reference
Intakes and the Dietary Guidelines from the United States Department of
Agriculture (available at fnic.nal.usda.gov/interactiveDRI/).
Consume adequate carbohydrates. Runners need approximately 6 to 10 grams
/kg body weight of carbohydrates daily. Carbohydrates are critical for
maintaining blood glucose during exercise and replenishing muscle glycogen.
(See "Dietary carbohydrates".)
Consume adequate protein. Endurance athletes need 1.2 to 1.7 grams/kg
body weight of protein daily.
Consume adequate healthy fats. Healthy fats are a source of energy and
provide essential fatty acids and fat-soluble vitamins, and should comprise
20 to 35 percent of total calorie intake. (See "Dietary fat".)
Stay hydrated. Water loss of as little as 2 percent body mass can
decrease performance [45]. Runners should drink before, during, and after
exercise. An easy rule of thumb is to weigh yourself before and after
running, and drink 16 to 24 ounces (450 to 675 mL) of fluid for every pound
(0.5 kg) lost during exercise. For long or intense exercise (eg, marathon),
it is also important to replace electrolytes. (See "Exercise-associated
hyponatremia".)

The timing of nutrient intake is important [45-47]. A snack high in
carbohydrate, moderate in protein, and low in fat and fiber is generally
well-tolerated prior to exercise, whereas a snack higher in fat and fiber
may cause gastrointestinal cramping or other distress. During exercise that
lasts more than one hour, the athlete needs fluids and small amounts of
carbohydrate, such as that found in sports drinks. The runner should be
encouraged to replenish glycogen stores by consuming carbohydrate, 1.0 to 1.
5 gram/kg of body weight, within 30 minutes of exercise, and to continue “
refueling” every two hours for four to six hours. These goals can be met
with relatively small amounts of food.

Some researchers suggest adding protein to post-training snacks to aid
muscle recovery; this is likely most beneficial to the runner who does not
take in adequate carbohydrate following exercise [48]. Regardless of the
specific approach, it is helpful for runners to become familiar with the
concepts of “grams” and to learn how to apply this to their preferred
foods.

Although an adequate, well-rounded diet provides the majority of vitamins
and minerals needed by athletes, special mention should be made of iron.
Iron requirements are greater in endurance runners than in nonendurance
athletes [49]. Iron is lost through sweat, the gastrointestinal tract, and
menstruation. Thus, iron depletion is particularly common among
premenopausal female runners. Any runner complaining of fatigue and
decreased performance, especially females, should have a serum ferritin
measured. If low, iron levels can be increased through diet and
supplementation, but dietary replacement appears to be more effective [46].

Although muscle adapts to regular exercise, some exercise-induced muscle
damage occurs, mediated in part by the production of reactive oxygen species
(ROS). As antioxidants reduce ROS, some athletes take high doses of the
antioxidants (eg, vitamins C and E) hoping to attenuate muscle damage.
However, there is little evidence to support this practice, and there is
some evidence that interfering with ROS signals may impair muscle
performance [50]. Runners should be informed of the potential risks
associated with taking high doses of antioxidants [51,52].

Psychology — There is little evidence that psychological factors play an
important role in running injuries. One study of 30 runners found that those
with type A personality traits did not have higher injury rates than others
, but did have a higher risk of multiple injuries [53]. General studies of
athletes have found a weak association between injury risk and such
psychological factors as aggressiveness, exhaustion, and stressful life
events [54].

EVALUATION OF THE INJURED RUNNER — Evaluation of the injured runner begins
with a thorough history, which should include inquiries about:

    Prior injuries and related treatments (including the runner’s
compliance with treatment)
    Current training patterns, including mileage, frequency, and training
methods (eg, hill running); Inquire about changes in training that preceded
the injury
    Shoe and orthotic use, including any recent change in shoes
    Training surface, including any recent change
    Injury details (eg, what provokes and reduces symptoms, duration of
symptoms)
    Athletic activities other than running
    Detailed training history, including running and racing experience
    Medical conditions; prior surgeries
    Medication and supplement use

Examination of the injured runner includes assessment not only of the
injured area but of all related structures (ie, the runner’s entire “
kinetic chain”), noting any imbalances or deficits in structure (eg, leg
length discrepancy), strength, flexibility, or motion. Discrepancies may
exist between legs or between muscle groups of the same leg (eg, quadriceps
disproportionately stronger than hamstrings). One way to organize each
element (eg, observation, strength testing) of the physical examination is
to begin with proximal structures (eg, spine and pelvis) and work distally.
Careful observation of the patient’s walking and running gaits helps to
confirm that the anatomic problems identified during a stationary
examination affect biomechanical performance.

Begin your assessment by asking the injured runner to stand in front of you,
noting their posture and lower extremity alignment. Observe the legs from
hip-to-foot looking for symmetry. Note the structure of the knee, especially
genu varum (which may be associated with iliotibial band syndrome or medial
meniscal pathology) or valgus (often seen in women with patellofemoral pain
). Note the position of the patella and any apparent muscular asymmetry. Ask
the patient to stand on one foot and then the other, watching for balance,
control, and posture. Does the unsupported hip sag (ie, a positive
Trendelenberg test)? A positive Trendelenberg test suggests weakness of the
gluteus medius, a common finding in runners with hip and knee pain. Make
note of foot structure and position. Does the runner have a normal, high, or
flat arch? Ask the patient to walk and to squat. Watch for a limp,
stiffness of one limb, and a tendency to shift weight off one limb.

Screen for tenderness and altered mobility of the spine, pelvis (including
sacroiliac joints), hips, knees, ankles, and feet before turning your
attention to the area of complaint. Be sure to assess muscle strength and
neurovascular status throughout the lower extremity. Weakness of the hip
musculature (particularly hip abductors) is common among novice runners,
frequently contributing to lower extremity pain, especially patellofemoral
pain syndrome. (See "Patellofemoral pain syndrome".)

The following findings may be noted during the examination:

    Hip flexion, rotation, or abduction weakness is present with many lower
extremity injuries, particularly those affecting the hip or knee.
    Increased lumbar lordosis suggests weak anterior core muscles, a common
condition in runners with hip weakness.
    Vastus medialis atrophy or asymmetry can occur with patellofemoral pain
syndrome (PFPS), or in athletes who have had knee surgery.
    Tenderness along the medial tibial border bilaterally is often present
with medial tibial stress syndrome (MTSS), or “shin splints.”
    Loss of normal lumbar lordosis (with or without back pain) is often
present with tight hamstrings.
    Loss of internal rotation of the hip occurs with femoral neck stress
fracture.
    Asymmetry of the quadriceps muscles is common in runners with
osteoarthritis of the hip.
    Pain and/or a sense of “catching” in the groin with the knee flexed to
90 degrees suggests a labral tear, but also may be seen with iliopsoas
tendinopathy.
    Localized tenderness and a positive hop test suggest a tibial stress
fracture.
    Achilles tendon thickening or nodules suggests Achilles tendinopathy.
    Tenderness at the medial insertion of the plantar fascia into the
calcaneus suggests plantar fasciitis.
    Hallux limitus or hallux rigidus and reduced ankle dorsiflexion can
develop with plantar fasciitis or calf muscle injuries.
    Splayed toe sign and forefoot widening can occur with metatarsalgia.
    Leg length inequality may be present with stress fractures, and possibly
with iliotibial band syndrome and lower back and pelvic injuries.


Diagnostic imaging, including plain radiographs, ultrasound, magnetic
resonance imaging (MRI), computed tomography (CT), and bone scan may be
necessary in some cases to make a definitive diagnosis. However, the
clinician should have a clear differential diagnosis in mind before ordering
such studies.

Once a diagnosis is made and a treatment plan established, the clinician and
athlete should work together to uncover and eliminate potential
contributing factors, as many running injuries appear to be multifactorial.
The mainstay of treatment for the vast majority of running injuries is “
relative rest,” which means stopping running, or at a minimum significantly
reducing mileage, while the injury heals. Depending upon the injury, most
runners can maintain reasonable conditioning by performing non-impact
exercises in a pool or on a bike, or by using other equipment (eg, rowing
machine).

SPECIFIC INJURIES

Hip injuries

Overview and approach — Hip injuries are less common in runners than
injuries to the lower extremity and they can be difficult to diagnose.
Nevertheless, during jogging, the hip joint is subjected to loads up to
eight times body weight and both acute and chronic injuries can occur [55].
In runners, the differential diagnosis of hip pain includes gluteus medius
tendinopathy, piriformis syndrome, stress fracture of the femoral neck,
labral tear, and, less often, radicular pain from the lumbar spine. Better
understanding of the functional anatomy of the hip suggests a correlation
between hip muscle weakness and injury to the low back or lower extremity in
athletes, including runners [56-58].

Gluteus medius weakness and tendinopathy and piriformis syndrome — The
gluteus medius originates along the external surface of the ilium and runs
distally and laterally to its attachment on the greater trochanter of the
femur (picture 1). The gluteus medius abducts the hip and assists with
pelvic stability during running. Weakness of the muscle typically causes
pain with hip abduction and rotation. Pain generally increases when the
muscle is stretched and there may be focal tenderness at the muscle’s
insertion, just medial and superior to the greater trochanter. Difficulty
maintaining a level pelvis while standing on one leg (positive Trendelenburg
sign) may be noted.

The piriformis muscle is a small but important external rotator of the hip
that crosses the sciatic nerve and is believed by some to cause sciatica-
type pain when it compresses the nerve [59,60]. However, the existence of
this so-called “piriformis syndrome” remains controversial and diagnosis
is difficult [61-63]. Piriformis syndrome in the runner may be associated
with foot overpronation, weakness of the gluteal muscles and other hip
abductors, and tightness of the hip adductors.

The mainstay of treatment for both gluteus medius tendinopathy and
piriformis syndrome is physical therapy and correction of biomechanical
abnormalities. Orthotics and massage therapy may be useful; acetaminophen
and nonsteroidal antiinflammatory drugs may be used for analgesia. There are
reports of using injections of local anesthetics, glucocorticoids, and
botulinum toxin (Botox) to treat piriformis syndrome [64].

Femoral neck stress fracture — Stress fractures of the femoral neck are an
uncommon but important cause of hip or groin pain in the adult runner
because of the relatively high risk of nonunion. (See 'Stress fractures'
below.)

Labral tear — The acetabular labrum is a ring of fibrocartilage and dense
connective tissue attached to the bony rim of the acetabulum. It is thought
to be largely avascular. Although the labrum’s function is not fully
understood, it is thought to provide stability and decrease the stress
placed on the hip joint. Therefore, a significant tear in the labrum can
increase stress on the hip joint, decrease stability, and ultimately lead to
damage of the articular cartilage.

Labral tears are reported in sports that require frequent hip rotation, such
as soccer and hockey, and in runners, especially female runners. Runners
with a labral tear typically complain of pain in the anterior hip or groin.
They may have mechanical symptoms, including clicking, locking, catching, or
giving way (so-called “snapping hip”). Other hip injuries that may
produce such mechanical symptoms include iliopsoas tendinopathy.

Labral tears are complex and often frustrating to treat. Physical therapy
has mixed results. Arthroscopic surgery is often helpful, but the recovery
can be prolonged. Runners diagnosed with labral tears should be counseled
carefully regarding the paucity of evidence for determining the best
treatment and the benefits and risks of each approach.

Iliopsoas tendinopathy — Iliopsoas tendinopathy produces symptoms similar
to a labral tear but presents more often as anterior hip pain in younger
athletes, especially after a rapid growth spurt, and is more easily treated.
Athletes who repeatedly engage in forceful flexion of the hip, including
track and field athletes (eg, hurdlers, jumpers), are at greatest risk.
Examination usually reveals tight, painful hip flexors (picture 2).
Iliopsoas tendinopathy typically responds within a few weeks to activity
modification, acetaminophen and nonsteroidal antiinflammatory drugs, and
physical therapy.

Knee and thigh injuries

Knee pain (patellofemoral pain syndrome) — Knee pain is among the most
common complaints from runners. Most such runners are diagnosed with
patellofemoral pain syndrome (PFPS) [5,65]. Despite the prevalence of this
diagnosis, no consensus exists about its etiology or the factors most
responsible for causing pain. Overuse and malalignment are commonly cited
causative factors. In addition, runners (especially females) with PFPS often
have decreased strength in hip abduction, external rotation, and extension
compared to healthy controls [66,67]. Patients with PFPS typically complain
of anterior knee pain that worsens with squatting, running, prolonged
sitting, or when ascending or descending steps. Pain is often poorly
localized "under" or "around" the patella. Details about the diagnosis and
management of PFPS are provided separately. (See "Patellofemoral pain
syndrome".)

Iliotibial band syndrome — The iliotibial band (ITB) consists of connective
tissue that runs from the ilium to the anterolateral aspect of the proximal
tibia (picture 3). It is involved in hip abduction and internal rotation,
knee extension and flexion, and helps to stabilize the knee during running.

The iliotibial band syndrome (ITBS), which occurs primarily in runners, is
characterized by an aching or burning pain at the site where the ITB courses
over the lateral femoral condyle; occasionally the pain radiates up the
thigh toward the hip. Runners often complain of such lateral knee pain while
running, but pain may persist after training, especially with activity that
requires repetitive flexion and extension of the knee, such as ascending or
descending stairs or standing from a seated position. The diagnosis of ITBS
is clinical; no imaging is typically needed.

The ITB does not attach to bone between the hip and knee, and for years many
clinicians believed that repeated flexion and extension of the knee caused
the band to rub back and forth over the lateral femoral condyle, creating
friction and inflaming the tissue beneath the band. However, subsequent
investigations suggest that the ITB moves very little and that the pain of
ITBS results from compression of a layer of innervated fat and connective
tissue between the ITB and lateral femoral epicondyle [68].

Biomechanical studies and our clinical experience suggest that the
underlying causes of ITBS are multifactorial but that patients often fall
into two major categories [69-71]. One group (usually less experienced or
female runners) demonstrates weak hip abduction, increased hip adduction,
and internal rotation of the knee (genu valgum); the other group (often
advanced runners) manifests decreased hip adduction and external rotation of
the knee (genu varum). Physical therapy for the first group should
emphasize strengthening the hip abductors; therapy for the latter group
should include stretching exercises to improve hip adduction. Other risk
factors for ITBS include excessive running mileage, worn shoes, repetitive
running on uneven terrain, and continually running in only one direction on
a track [72].

Ice, analgesics (eg, acetaminophen and nonsteroidal antiinflammatory drugs),
and a short period of rest are usually effective at reducing acute
discomfort. Glucocorticoid injections may be helpful for symptomatic relief
in refractory or severe cases, or when there is associated bursitis, but
there is little evidence supporting such treatment [73]. Once inflammation
is reduced, the patient begins stretching and strengthening exercises to
correct identified deficits [74,75]. A study comparing three common
stretches for the ITB found all to be effective [76]. In one limited
randomized trial, deep transverse friction massage was not beneficial [77].

Hamstring injuries — Hamstring injuries are typically acute; the injured
runner complains of developing a sudden, sharp pain in the posterior thigh
while running at high speed or up hills. Examination findings depend upon
the severity of injury and may include a limping gait (due to the inability
to fully extend the knee); ecchymosis; a visible or palpable defect in the
hamstring muscle; focal tenderness; and pain or weakness with muscle
contraction. Details about the diagnosis and management of hamstring muscle
injuries are provided separately. (See "Hamstring injuries".)

Knee OA — Exercise is recommended for most patients with OA of the hip or
knee. Although water-based exercise is often suggested, multiple studies
confirm the value of regimens involving full weightbearing exercise. (See "
Nonpharmacologic therapy of osteoarthritis", section on 'Exercise'.)

Despite this evidence, many clinicians subscribe to the traditional teaching
that patients with osteoarthritis (OA) of the knee should not run because
it exacerbates the condition. The medical literature, however, does not
support the contention that running contributes to the degeneration of
articular cartilage in the knee [78]. Examples of such studies include:

    A prospective cohort study followed 45 runners and 53 controls over 18
years and, using a validated score to assess for OA, found no difference
between the two groups in the progression or the number of severe cases of
knee OA [79].
    Another prospective study of 16 runners and 13 nonrunners found no
evidence that running predisposes to OA of the lower extremities [80].
    Multiple retrospective studies have found no evidence of premature
damage of articular cartilage or increased risk for OA among long-distance
runners [81-83].
    Small clinical and laboratory studies using MRI to evaluate the knees of
long-distance runners report no significant damage to articular cartilage
following a race and no major differences when images were compared to those
of active nonrunners [84-86].

Stress fractures — Stress fractures in runners occur most often in the
tibia, but can develop in any bone of the lower extremity, including the
metatarsals, navicular, and femoral neck [87]. Detailed discussions of
stress fractures, including a description of those at high risk for nonunion
, appear separately; a brief description and information of particular
importance for runners is provided here. (See "Overview of stress fractures"
and "Stress fractures of the tibia and fibula" and "Stress fractures of the
metatarsal shaft".)

When evaluating the runner with a suspected stress fracture, the clinician
should ask for a description of the pain, running patterns and recent
changes in training, shoe and orthotic wear, and prior injuries. Information
about the patient’s nutrition and menstrual history, and any family
history of metabolic bone disease, are also important.

Typically, the runner with a stress fracture complains of focal pain that is
insidious in onset, increases as a run progresses, and improves with rest.
Over time, if the athlete persists in running despite such symptoms, pain
occurs with less strenuous activity and ultimately at rest. Some runners
present with acute onset of severe pain, which may result from a complete
fracture at the site of a preexisting stress fracture.

Important risk factors for developing stress fractures include a history of
prior stress fracture, increasing volume and intensity of training, poor
running biomechanics, female gender and menstrual irregularity, a diet poor
in calcium, and poor bone health. The management of stress fractures in
runners is discussed separately. (See "Overview of stress fractures",
section on 'Treatment concepts'.)

The clinician should be aware that stress fractures at high risk for
nonunion (eg, femoral neck and navicular) are more common in runners than in
other athletes. If a high-risk stress fracture is suspected, an aggressive
work-up is warranted and immediate orthopedic consultation should be
obtained if the diagnosis is confirmed. A history of recurrent stress
fracture or a fracture in cancellous bone suggests that the runner’s bone
mineral density may be low and should be measured.

Femoral neck stress fractures should be suspected in any distance runner
with groin pain of insidious onset, especially female distance runners at
risk for the “female athlete triad” (eating disorder, amenorrhea, and
osteoporosis). The female athlete triad is reviewed separately. (See "
Amenorrhea and infertility associated with exercise".)

Navicular stress fractures occur more often in male athletes participating
in track and field events (eg, hurdlers, jumpers, sprinters) and middle
distance runners [87]. The athlete with a navicular stress fracture often
presents with insidious pain in the midfoot or arch that increases with
jumping.

Medial tibial stress syndrome (shin splints) and tibial stress fractures —
Clinicians confronted by runners with shin pain must distinguish between
stress fractures of the tibia and medial tibial stress syndrome (MTSS),
often referred to as “shin splints.” Although the history may be similar,
a focal, palpable area of tenderness is present in most patients with stress
fractures, whereas tenderness is much more diffuse and there are no
discrete palpable lesions in those with MTSS. Imaging may be necessary in
some cases to rule out a stress fracture. Plain radiographs are normal in
patients with shin splints, but may also be unrevealing early in the course
of a stress fracture. (See "Stress fractures of the tibia and fibula",
section on 'Clinical presentation and examination' and "Stress fractures of
the tibia and fibula", section on 'Radiographic findings'.)

Distinguishing between the two diagnoses affects treatment: a runner with a
stress fracture should avoid running and pursue non-impact activities like
swimming or cycling while the stress fracture heals, while the runner with
MTSS can continue running but should reduce the total mileage. A systematic
review found that shock-absorbing insoles may reduce symptoms and prevent
recurrence of MTSS [88].

Chronic exertional compartment syndrome — Chronic exertional compartment
syndrome (CECS) occurs when increased pressure within a muscle compartment
reduces blood flow, leading to muscle ischemia and pain when metabolic
demands cannot be met. The patient with CECS is often a young runner who
describes gradually increasing pain in a specific muscle region (usually the
lower leg) during exertion. The pain may be described as aching, squeezing,
cramping, or tightness. Pain generally begins within several minutes of
starting a run, often at a specific point in training. Runners can often
describe the time or distance required for symptoms to develop. Pain
resolves completely with rest, although not immediately upon stopping
exercise. The diagnosis and management of CECS is discussed in detail
separately. (See "Chronic exertional compartment syndrome".)

Foot and ankle injuries — Foot and ankle injuries account for up to 20
percent of running injuries, and are the most common injury reported by
distance runners and marathoners [89]. This is not surprising given that the
ground reaction forces the foot must absorb with each stride are several
times body weight. The most common foot injuries in runners are overuse
injuries of soft tissues, including tendons and fascia.

Plantar fasciitis — Plantar fasciitis (PF) is the most common cause of
rearfoot pain in runners. The predominant symptom of PF is pain in the
plantar region of the foot that increases when initiating push-off while
walking or running. The hallmark for diagnosis is focal point tenderness.
The etiology of PF remains unclear but the condition is often attributed to
training errors, biomechanical problems, and excessive foot pronation or
supination, and is more common in older and heavier runners [89-91]. The
biomechanical abnormality most often associated with PF is decreased
dorsiflexion of the foot and toes and thus stretching is an important part
of treatment. Another common biomechanical problem is weakness of the
plantar flexors, which some clinicians believe is best treated with
eccentric strengthening exercises. The diagnosis and management of PF is
reviewed separately. (See "Plantar fasciitis and other causes of heel and
sole pain", section on 'Plantar fasciitis'.)

Tendon injuries — Runners are susceptible to tendon injuries at a number of
sites, the Achilles being most common. Others include the peroneal,
posterior tibial, and anterior tibial tendons (picture 4).

Achilles tendinopathy occurs in up to 10 percent of elite runners annually [
92]; runners with more than 10 years of experience are at higher risk [93].
Among former elite male distance runners, the lifetime risk is reported to
be as high as 52 percent [94]. The biomechanical factors that predispose
runners to Achilles tendinopathy remain unclear but are the subject of
research [95-97]. Poor flexibility of the Achilles tendon, overpronation,
and valgus or varus deformity of the calcaneus all affect rear-foot
mechanics, possibly increasing torque on the Achilles. Some clinicians
advocate using a heel pad or orthotic in runners to counteract this effect.

Patients with Achilles tendinopathy typically complain of pain or stiffness
2 to 6 cm above the posterior calcaneus. The pain is frequently described as
burning, increases with activity, and is relieved by rest. Runners with the
condition often have recently increased their training intensity or have
been training rigorously for a long time. A history of excessive foot
supination, increased speed work or hill training, or improper (eg, poorly
fitting shoes, tennis instead of running shoes) or worn out footwear may be
found. The diagnosis and management of Achilles tendinopathy is discussed
separately. (See "Achilles tendinopathy and tendon rupture".)

Peroneal tendon injury may be traumatic, usually from a lateral ankle sprain
, or related to overuse and associated with excessive foot pronation and
weak foot plantar flexors [98]. Examination reveals tenderness along the
course of the tendon posterior or inferior to the lateral malleolus, which
increases with resisted eversion.

Posterior tibial tendinopathy is typically an overuse injury that develops
following an abrupt increase in training intensity, and is associated with
poor foot and calf flexibility and excessive foot pronation. Examination
findings include tenderness along the course of the posterior tibial tendon
posterior or inferior to the medial malleolus, which increases with resisted
inversion.

Anterior tibial tendinopathy is a common cause of anterior ankle pain in
runners, and often develops following abrupt increases in training,
particularly hill running. Examination often reveals tenderness, and
possibly swelling, of the tendon as it crosses the ankle joint. Pain
increases with resisted dorsiflexion.

The treatment of overuse tendinopathies is discussed separately. (See "
Overview of the management of overuse (chronic) tendinopathy".)

First metatarsal phalangeal joint — Running generates substantial forces
across the forefoot and thus can aggravate hallux rigidus or hallux valgus (
bunion) of the metatarsal phalangeal (MTP) joint of the great toe (ie, first
MTP joint). The sesamoid bones located on the plantar surface of the MTP
joint can become inflamed from running and may cause discomfort.

Hallux rigidus and hallux valgus (bunion) — There is little high-quality
evidence to provide insight into the causes and guide the management of
hallux rigidus. Hallux rigidus is presumed to be a degenerative condition of
the first MTP joint associated with either an acute injury (eg, forced
hypertension of the great toe, so-called “turf toe”) or repetitive
microtrauma, as would occur with running [99,100]. Genetic predisposition
may play a role. The result is limited dorsiflexion of the first MTP joint;
approximately 60 degrees of dorsiflexion is needed for normal gait.

Runners with hallux rigidus are typically older than 30 and complain of pain
at the dorsum of the great toe. However, some runners may present with
vague lateral forefoot pain. This presentation is likely due to runners
shifting their body weight to the lateral foot during the foot-strike phase
of running to reduce the load on the great toe. It remains unclear whether
running is a cause of hallux rigidus or aggravates symptoms elicited by
other factors. Shoes with a toe box that is too small or pointed may
contribute.

Hallux valgus (ie, bunion) deformity is defined as a lateral deviation of
the hallux (great toe) on the first metatarsal. The etiology of hallux
valgus is multifactorial and likely involves abnormal mechanics and anatomy.
Patients generally complain of a deformed and painful great toe. (See "
Hallux valgus deformity (bunion)".)

In runners with either of these conditions, mechanically limiting first MTP
joint motion by using appropriate shoes and unloading techniques can be
helpful. We suggest walking shoes with a wide toe box, stiff soles, rocker
bottoms, and low heels. Comfortable running shoes with a wide toe box
combined with techniques to reduce the impact on the first MTP joint, such
as custom orthotics or cushioned insoles, reduce symptoms in many runners.
Acetaminophen or nonsteroidal antiinflammatory drugs may be used for short-
term pain relief. Ice can be applied following running. Glucocorticoid
injections may provide short-term pain relief for those with mild hallux
rigidus [101]. Consultation with a foot surgeon should be obtained for
severe or recalcitrant cases, although there is little high-quality evidence
to guide decisions about surgery or conservative care.

Sesamoiditis — The sesamoids are pea-sized bones that function as pulleys
for tendons (just as the patella does for the knee extensors) and assist
with weightbearing. Inflammation or injury of the sesamoid bones located on
the plantar surface of the first MTP joint can cause focal pain in runners,
particularly sprinters (picture 5 and figure 1). The runner with
sesamoiditis typically complains of pain at the area of the MTP joint with
weightbearing that is exacerbated by walking, and even more so by running.
Exquisite tenderness of the sesamoids is present, and is exacerbated by
dorsiflexion of the great toe. Imaging is required to differentiate between
sesamoiditis and a stress fracture.

Both sesamoiditis and sesamoid stress fractures are notoriously difficult to
treat and may require a short period of immobilization followed by
prolonged rest from running. Runners can use alternative, nonweightbearing
forms of exercise to maintain fitness. Treatment with custom orthotics, soft
pads cut to relieve pressure on the sesamoids, and in severe cases
glucocorticoid injections may be helpful, but there is little evidence to
guide treatment. Women runners should avoid wearing high heels; shoes with a
stiff sole (eg, clog) are often helpful. Consultation with a foot surgeon
is reasonable in recalcitrant cases.

Treatment of sesamoiditis does not differ significantly from that for
sesamoid fractures. The evaluation and management of sesamoid fractures is
discussed separately. (See "Sesamoid fractures of the foot".)

Metatarsalgia — Pain in a runner’s forefoot that is not due to a
metatarsal stress fracture is likely due to metatarsalgia or an interdigital
neuroma. (See 'Stress fractures' above.)

Metatarsalgia is a general term for pain that occurs along the ball of the
foot. Most runners with metatarsalgia complain of pain in the forefoot
during running; the examiner will find tenderness along the plantar surface
just proximal to the metatarsal heads. The condition is often associated
with overpronation and/or collapse of the transverse arch. A metatarsal pad
placed proximal to the area of tenderness often relieves symptoms; in more
severe cases, a custom orthotic may be needed.

(Mortons) neuroma — Interdigital neuromas (often referred to as Mortons
neuroma) are thought to be due to swelling and scar tissue formation on the
small interdigital nerves. They most commonly involve the third webspace,
but may also be seen in the second and fourth.

The runner with a neuroma may complain of numbness of the involved toes or
pain that increases with activity and is usually felt in the interspace
between the third and fourth toes (figure 2) [102]. The diagnosis can be
confirmed by noting a clicking sensation (Mulders sign) when palpating this
interspace while simultaneously squeezing the metatarsal joints.
Overpronation and tight shoes are often associated with the condition.

An intermetatarsal bursitis can cause a similar pain. The use of magnetic
resonance imaging (MRI) to diagnose Morton's neuroma is problematic because
features consistent with neuroma may appear in as many as one-third of
asymptomatic individuals [103,104].

Conservative treatment should precede expensive diagnostic procedures. This
approach involves decreasing pressure on the metatarsal heads by using a
metatarsal support or bar or padded shoe insert. Several studies have
measured the loading pressures placed on metatarsals before and after use of
metatarsal pads, bars, orthotics, and specialized orthopedic shoes [105-110
]. In all reports, pain relief correlated with reduction in pressure. Proper
placement of the inserts just proximal to the metatarsal head is important.
Strength exercises for the intrinsic foot muscles are often part of
conservative treatment. No randomized controlled studies have been performed
to assess these interventions.

Treatment inserts are often placed in both shoes, even when symptoms are
unilateral, to ensure that the patient walks evenly, but bilateral pads are
not always needed. Symptomatic relief often begins within a few days of
insert use and pain may completely subside over several weeks.

A broad-toed shoe that allows spreading of the metatarsal heads may be
helpful. Proper shoe width should be determined while standing, using a
professional shoe fitting device. If width has changed, older shoes should
be discarded.

If conservative measures fail to relieve symptoms, a single injection of a
local anesthetic and glucocorticoid into the site of tenderness can be
performed using a dorsal, not plantar, approach [111,112]. A plantar
approach is more likely to cause complications. A combination of
methylprednisolone (20 mg, or 0.5 mL) and one percent lidocaine (0.5 mL) may
be used.

Ultrasound guided injection is preferred by many practitioners although
studies are limited. Ultrasound can distinguish neuroma from adjacent joint
synovitis or bursitis. The majority of patients experience some relief with
ultrasound-guided injection according to three case series involving a total
of 113 patients [113-115]. Complications are rare; metatarsal fat pad
atrophy can be debilitating but may occur less often if a dorsal injection
is used. No randomized controlled trials of ultrasound guided injection have
been published.

Surgical removal of the neuroma and nerve may be necessary in patients who
remain symptomatic after 9 to 12 months of nonoperative therapy. Surgical
success rates of up to 80 to 90 percent have been reported in uncontrolled
studies [111,116-118]. Surgery performed using a dorsal approach resulted in
more timely weightbearing, return to work, and less painful scarring [119].
No randomized trials of surgery for plantar neuroma have been reported.
Rarely, a neuroma may recur following surgery. Experience with injections of
alcohol, phenol, and other substances and with nerve transplants is limited.

Tarsal tunnel syndrome — Tarsal tunnel syndrome (TTS) is an uncommon source
of foot pain in runners due to entrapment of the posterior tibial nerve (
PTN) or one of its branches as it courses behind the medial malleolus. The
most common causes include an acute injury and its sequelae (eg, scar tissue
) or repetitive microtrauma, as occurs with running, particularly in runners
who overpronate. Runners with TTS complain of numbness or burning pain,
usually along the plantar surface of the foot, although complaints may be
localized to the medial plantar surface of the heel, mimicking plantar
fasciitis. TTS typically worsens with running or at night. Findings are
almost always sensory; muscle weakness is uncommon. A positive Tinel sign
may be present. As in carpal tunnel syndrome, a positive sign occurs when
symptoms are elicited by tapping over the path of the nerve. TTS is
discussed in detail separately. (See "Overview of lower extremity peripheral
nerve syndromes", section on 'Tarsal tunnel syndrome'.)



INFORMATION FOR PATIENTS — UpToDate offers two types of patient education
materials, “The Basics” and “Beyond the Basics.” The Basics patient
education pieces are written in plain language, at the 5th to 6th grade
reading level, and they answer the four or five key questions a patient
might have about a given condition. These articles are best for patients who
want a general overview and who prefer short, easy-to-read materials.
Beyond the Basics patient education pieces are longer, more sophisticated,
and more detailed. These articles are written at the 10th to 12th grade
reading level and are best for patients who want in-depth information and
are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We
encourage you to print or e-mail these topics to your patients. (You can
also locate patient education articles on a variety of subjects by searching
on “patient info” and the keyword(s) of interest.)

    Basics topic (see "Patient information: Achilles tendinopathy (The
Basics)")

SUMMARY AND RECOMMENDATIONS

    Up to half of regular runners report an injury each year. Some injuries
are traumatic, but most are due to overuse and many of these involve the
knee. The most common diagnoses include: patellofemoral pain syndrome,
medial tibial stress syndrome (ie, “shin splints”), Achilles tendinopathy,
iliotibial band syndrome, plantar fasciitis, and stress fractures of the
metatarsals and tibia. (See 'General epidemiology' above.)
    A number of intrinsic and extrinsic risk factors are associated with
running-related lower extremity injuries. Perhaps the most important and
most easily changed are training variables, such as mileage and intensity.
The role of other factors, such as shoes, stretching, and biomechanics, is
less clear. Training suggestions to reduce the risk of injury are provided
in the text. (See 'Risk factors' above and 'Training suggestions to reduce
injury risk' above.)
    A careful history and physical examination are essential for determining
the differential diagnosis and the need for diagnostic imaging. Guidance
about how best to evaluate the injured runner is provided in the text. (See
'Evaluation of the injured runner' above.)
    Descriptions of important and common causes of running-related lower
extremity injuries, organized anatomically, are provided in the text, along
with links to more detailed discussions. (See 'Specific injuries' above.)