The Risks and Benefits of Running Barefoot or in Minimalist Shoes: A Systematic Review

Abstract

Context:
The popularity of running barefoot or in minimalist shoes has recently increased because of claims of injury prevention, enhanced running efficiency, and improved performance compared with running in shoes. Potential risks and benefits of running barefoot or in minimalist shoes have yet to be clearly defined.

Objective:
To determine the methodological quality and level of evidence pertaining to the risks and benefits of running barefoot or in minimalist shoes.

Data sources:
In September 2013, a comprehensive search of the Ovid MEDLINE, SPORTDiscus, and CINAHL databases was performed by 2 independent reviewers.

Study selection:
Included articles were obtained from peer-reviewed journals in the English language with no limit for year of publication. Final inclusion criteria required at least 1 of the following outcome variables: pain, injury rate, running economy, joint forces, running velocity, electromyography, muscle performance, or edema.

Study design:
Systematic review.

Level of evidence:
Level 3.

Data extraction:
Two reviewers appraised each article using the Downs and Black checklist and appraised each for level of evidence.

Results:
Twenty-three articles met the criteria for this review. Of 27 possible points on the Downs and Black checklist, articles scored between 13 and 19 points, indicating a range of evidence from very limited to moderate. Moderate evidence supports the following biomechanical differences when running barefoot versus in shoes: overall less maximum vertical ground reaction forces, less extension moment and power absorption at the knee, less foot and ankle dorsiflexion at ground contact, less ground contact time, shorter stride length, increased stride frequency, and increased knee flexion at ground contact.

Conclusion:
Because of lack of high-quality evidence, no definitive conclusions can be drawn regarding specific risks or benefits to running barefoot, shod, or in minimalist shoes.

Full text

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Sports Health: A Multidisciplinary
http://sph.sagepub.com/content/6/6/475
The online version of this article can be found at:
DOI: 10.1177/1941738114546846
2014 6: 475 originally published online 8 August 2014Sports Health: A Multidisciplinary Approach
Kyle P. Perkins, William J. Hanney and Carey E. Rothschild
The Risks and Benefits of Running Barefoot or in Minimalist Shoes: A Systematic Review
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475
SPORTS HEALTHvol. 6 • no. 6
[ Sports Physical Therapy ]
The popularity of running in the United States has grown
considerably in the past decade.21 While many enjoy
running as a recreational activity, others participate to
maintain and improve cardiovascular-pulmonary health, body
composition, and overall fitness.34 As participation in running
has grown, so has the number of reported running-related
injuries (RRIs).36 The overall incidence of RRI is estimated to be
between 19.4% and 79.3% annually.36 Despite efforts to reduce
the incidence of RRI, injury rates have yet to decline.7 The
modern running shoe may have a negative effect on foot
546846SPHXXX10.1177/1941738114546846Perkins et alSports Health
research-article2014
The Risks and Benefits of Running
Barefoot or in Minimalist Shoes:
A Systematic Review
Kyle P. Perkins,† William J. Hanney, PhD, PT, DPT, ATC,†
and Carey E. Rothschild, PT, DPT, OCS, SCS, CSCS*†
Context: The popularity of running barefoot or in minimalist shoes has recently increased because of claims of injury
prevention, enhanced running efficiency, and improved performance compared with running in shoes. Potential risks and
benefits of running barefoot or in minimalist shoes have yet to be clearly defined.
Objective: To determine the methodological quality and level of evidence pertaining to the risks and benefits of running
barefoot or in minimalist shoes.
Data Sources: In September 2013, a comprehensive search of the Ovid MEDLINE, SPORTDiscus, and CINAHL databases
was performed by 2 independent reviewers.
Study Selection: Included articles were obtained from peer-reviewed journals in the English language with no limit for
year of publication. Final inclusion criteria required at least 1 of the following outcome variables: pain, injury rate, running
economy, joint forces, running velocity, electromyography, muscle performance, or edema.
Study Design: Systematic review.
Level of Evidence: Level 3.
Data Extraction: Two reviewers appraised each article using the Downs and Black checklist and appraised each for level
of evidence.
Results: Twenty-three articles met the criteria for this review. Of 27 possible points on the Downs and Black checklist,
articles scored between 13 and 19 points, indicating a range of evidence from very limited to moderate. Moderate evidence
supports the following biomechanical differences when running barefoot versus in shoes: overall less maximum vertical
ground reaction forces, less extension moment and power absorption at the knee, less foot and ankle dorsiflexion at ground
contact, less ground contact time, shorter stride length, increased stride frequency, and increased knee flexion at ground
contact.
Conclusion: Because of lack of high-quality evidence, no definitive conclusions can be drawn regarding specific risks or
benefits to running barefoot, shod, or in minimalist shoes.
Keywords: barefoot; minimalist; running
From the †Department of Health Professions, University of Central Florida, Orlando, Florida
*Address correspondence to Carey E. Rothschild, PT, DPT, OCS, SCS, CSCS, Department of Health Professions, University of Central Florida, 4364 Scorpius Street, Orlando,
FL 32816-2205 (e-mail: carey.rothschild@ucf.edu).
The authors report no potential conflicts of interest in the development and publication of this article.
DOI: 10.1177/1941738114546846
© 2014 The Author(s)
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function despite added cushion and stabilizing features.28
Hence, the efficacy of the modern-day running shoe has been
called into question.
Barefoot running has recently increased because of claims of
injury prevention, enhanced running efficiency, and improved
performance.16,18,19,32 Advocates of barefoot running suggest that
humans should run with bare feet as ancestors did thousands of
years ago.23 The development of “minimalist” footwear has
evolved with the barefoot running movement as a way to mimic
barefoot running yet offer foot protection.19 These newer
running practices have prompted researchers to investigate
injury mechanisms, physiological effects, biomechanical
differences, and performance effects of running barefoot versus
in shoes.19
Much of the recent literature is anecdotal and unclear as to the
specific risks and benefits of running barefoot or in minimalist
shoes.19 A related systematic review investigated the influence
of stride frequency and length on running mechanics; however,
it did not consider the effects of footwear and potential
outcomes that may ensue.33 Sustaining an RRI is multifactorial
and may not result from shoe wear alone; demographic
characteristics must be considered.36 Furthermore, there is no
single factor such as shoe design that will explain more than a
fraction of RRIs.22 Physicians, physical therapists, and athletic
trainers may face difficulties in advising a patient to run with or
without shoes.
Methods
Data Sources
In August and September 2013, Ovid MEDLINE, SPORTDiscus,
and CINAHL databases were searched to identify studies
examining running barefoot or in minimalist shoes using the
following keywords independently and in combination:
barefoot, running, and minimalist. The search was restricted to
articles from peer-reviewed academic journals, published in the
English language, and conducted with human subjects. Reviews,
commentaries, case studies, and case series were excluded from
the review.
Study Selection
Studies were initially included if the keywords were found in
the title or abstract and the article met the inclusion criteria.
Criteria for final selection included reporting on at least 1 of the
following outcome variables: pain, injury rate, running
economy, joint forces, running velocity, electromyography
muscle performance (EMG), or edema. A consensus meeting
between the 2 reviewers was held to determine whether the
study met the predetermined criteria. Should the 2 reviewers
disagree on article selection, a third reviewer would be
consulted for mediation. The 2 reviewers fully agreed on the 23
articles included in the systematic review for quality assessment;
therefore, arbitration by a third reviewer was not required
(Figure 1).
Quality Assessment
The methodological quality of each study was independently
assessed by the reviewers using the Downs and Black checklist.
The checklist includes 4 categories of assessment: reporting,
external validity, internal validity/bias, and internal validity/
confounding. The checklist has good interrater (r = 0.75) and
good test-retest (r = 0.88) reliability, as well as high internal
consistency (KR-20 = 0.89).11 Each study was further evaluated
for significant results (P < 0.05) in the outcome categories of
kinetics, kinematics, EMG, and running economy. These results
were pooled, and overall quality of evidence for each outcome
grouping was further classified by “level of evidence” (see
Appendix 1, available at http://sph.sagepub.com/content/
suppl).37
Results
The initial search of Ovid MEDLINE, SPORTDiscus, and CINAHL
resulted in 656, 343, and 110 publications, respectively. After
applying the inclusion criteria and omitting duplicates, 23
articles were identified, from which all articles investigated
kinetic, kinematic, running economy, or EMG differences or a
combination of these 4 variables (see Appendix 2, available at
http://sph.sagepub.com/content/suppl).
Quality Assessment
With a maximum total score of 27 points on the Downs and
Black checklist, all articles scored between 13 and 19 points
(mean, 17.4 points), indicative of moderate methodological
quality among the included studies (see Appendix 3, available
at http://sph.sagepub.com/content/suppl). The appraisal of
level of evidence in the outcome categories of kinetics,
kinematics, EMG, and running economy yielded evidence
ranging from conflicting to moderate (Table 1).
Under the reporting section of the Downs and Black checklist
(Table 1), at least 26 of 27 articles scored points from all items
except 3, 8, and 10. In the external validity section, all articles
scored zero points. Items 16 through 20 of the internal validity
(bias) section scored points to all 27 articles, while items 14 and
15 scored none. Finally, items 21, 22, and 26 of the internal
validity (confounding) section scored points to all articles, items
23 and 27 scored partial points, and items 24 and 25 scored
none.
discussion
The differences between barefoot and shod running have been
increasingly studied in the literature.2,6,9,18,20,23,25,28,31 Runners
typically contact the ground with the heel first: a rear foot strike
(RFS). In contrast, barefoot runners tend to display a midfoot
strike (MFS) or a forefoot strike (FFS), which may allow for
absorption of collision forces with the ground and avoidance of
excessive pressure at the heel.23 The difference in strike patterns
may be related to potential kinetic and kinematic changes in
ground reaction forces (GRFs), loading rates, joint moments and
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SPORTS HEALTHvol. 6 • no. 6
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powers, joint range of motion, muscle activation patterns, and
running economy. These alterations in biomechanics and joint
forces while barefoot or in minimalist shoes may protect against
RRI20,29-31 and/or enhance running performance.13,26
Kinetics
Moderate evidence suggests an association between barefoot
running and lowered maximum vertical GRFs.5,6,8,9,17,20,23 This
decrease in peak vertical GRF at initial contact may be
associated with the FFS pattern observed while running
barefoot.8,23 Kinetic analysis of the vertical GRF during the 3
running strike patterns revealed that an RFS yields a defined
impact peak on contact with the surface.6 Forefoot striking
eliminated this impact by loading the posterior calf
musculature.6 Added cushioning found in the modern running
shoe serves to attenuate shock and reduce impact forces;
however, this may influence RFS pattern and ultimately increase
forces to the lower extremity.23,28 Moreover, the length and
direction of the GRF moment arm may be altered by the
geometry of the modern shoe and the thickness of the foot-
ground interface by compression of the midsole.5 Further
kinetic analysis reveals a decrease in the moment arm of both
the vertical and mediolateral GRFs when forefoot striking,
which reduces the tendency to evert during RFS.2
Related to impact force is the impulse, which is equal to the
force times the duration of the collision with the ground.
Impulse represents the effective mass times its change in
velocity over the duration of the impact.23 Very limited evidence
suggests higher braking and pushing impulses as well as higher
preactivation of the triceps surae in forefoot strike runners.9
Very limited evidence also confirms a difference in peak vertical
or medial-lateral impulses while barefoot.27 There is moderate
evidence to support that a runner may experience lower peak
GRFs during barefoot running.18 Whether the absence of an
impact peak in barefoot running correlates with a benefit of
decreased injury rate is not known.
The limited evidence indicating a decreased extension
moment and increased power absorption at the knee when
Figure 1. Summary of search and selection process.
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barefoot may have implications for knee injuries because of the
increased length of the GRF moment arm.3,5,20,39,40 As a tradeoff
to less knee extension, limited evidence shows an increase in
power generation and absorption at the ankle in barefoot
running3,39 may be associated with ankle overuse injuries such
as Achilles tendinopathy.15 Hence, the alterations in joint
moments and power may be considered a possible risk factor in
ankle overuse pathology.
Table 1. Level of evidence for outcome categories
Studies Included Conclusion/Level of Evidence
Kinetics
Ground reaction forces 5,6,8,9,17,20,23 Moderate evidence suggestive of lowered maximum vertical GRF
when barefoot
8,17 Limited evidence suggestive of lowered max vertical GRF only during
barefoot FFS
20 Very limited evidence suggesting decreased medial-lateral and
increased anterior-posterior GRF when barefoot
Impulse 9,27 Very limited evidence suggesting greater breaking and pushing
impulses of plantar flexors during FFS
Very limited evidence suggestive of differences in peak vertical or
medial-lateral impulses while barefoot
Rate of loading 1,6,40,41 Very limited evidence suggestive of differences in loading rates when
running barefoot, in minimalist shoe, or shod
Joint moments and power 3-5,20,39 Limited evidence suggesting less extension moment and power
absorption at the knee when barefoot
3,39 Limited evidence suggesting increased power generation and
absorption at the ankle when barefoot
Kinematics
Foot-strike pattern 8,17,26,27,39,41 Limited evidence suggesting FFS is associated with barefoot running
Stride 3-6,10,13,
20,24,26,38,41
Moderate evidence suggesting barefoot running is associated with
increased stride frequency, shorter stride length, and less ground
contact time
Joint range of motion 3,18,39,41 Moderate evidence suggestive of decreased foot and ankle
dorsiflexion at initial contact when barefoot
41 Very limited evidence suggesting decreased ankle eversion at ground
contact
5,6,18,28 Moderate evidence suggesting increased knee flexion at ground
contact and less knee flexion during stance when barefoot or in
minimalist shoes
Running economy 10,13,16,27,35,38 Very limited evidence suggestive of significant difference in running
economy between barefoot, shod, and minimalist shoes
EMG 1,26,39 Limited evidence suggests decreased peak tibialis anterior activity
when barefoot FFS
EMG, electromyography; FFS, forefoot strike; GRF, ground reaction force.
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SPORTS HEALTHvol. 6 • no. 6
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Kinematics
Limited evidence supports a forefoot strike pattern when barefoot,
resulting in a flatter foot placement at contact25 and a more
plantarflexed ankle position.18 Moderate evidence does support
decreased foot and ankle dorsiflexion at initial contact when
barefoot. Runners may adopt this position during barefoot
running3,4,18,39,41 to reduce local pressure underneath the heel.6 In
the shod condition, this local pressure is eliminated by cushioning
through an elevated heel, which enables runners to land with a
dorsiflexed ankle.23 The resulting increase in ankle plantarflexion
moment during barefoot running implies the need for increased
eccentric work of the triceps surae muscles.4 Ultimately, this could
lead to an increased risk for pathology in the Achilles tendon and
may be considered a risk of running barefoot.
At the knee, moderate evidence shows an increase in knee
flexion at ground contact and a decrease in knee flexion during
stance when barefoot or in minimalist shoes. An increased knee
flexion angle at ground contact5,6,23,28 and less knee flexion
during stance3,4,27,41 may reduce the resultant knee extension
moment arm and perhaps lessen the stress across the
patellofemoral joint. Running barefoot with a forefoot strike
pattern may therefore be beneficial for runners suffering from
knee pain and injury.
Other kinematic differences that have been observed with
barefoot running include an increased stride frequency
(cadence), a shorter stride length, and less ground contact
time.3-6,10,13,20,24,26,38,41 Even though the decreased contact time
with the ground may influence a reduction in force, the
increased cadence may actually have a cumulative effect of joint
forces over time. Very limited evidence suggests a decrease in
stride length may reduce the probability of a stress fracture by
3% to 6%.12
Running Economy
For every 100 grams of mass added to the shoe, the volume of
oxygen in the body increases by approximately 1%.14 Other studies
suggest that the additional weight of the shoe is irrelevant and that
other significant factors such as barefoot running experience and
shoe construction may affect the metabolic cost of barefoot and
shod running.13 Limited evidence suggests that barefoot running
may result in lower metabolic demand (Vo2, heart rate, and rating
of perceived exertion) when barefoot or in minimalist shoes.16 This
may be because of the longitudinal arch of the foot permitting
more elastic energy storage and recoil.27 The longitudinal arch
stretches until the heel makes contact with the ground, and then it
recoils until take off.27 An RFS, however, does not stretch the
longitudinal arch until both the rear foot and forefoot make contact
with the ground.27 The foot then recoils until take off.27 Whether
running barefoot benefits running economy and potentially
improves performance is unknown.
Electromyography
Limited evidence suggests decreased peak tibialis anterior
activity in the barefoot FFS condition. Very limited evidence
associates preactivation of the gastrocnemius and soleus when
barefoot.9 The preactivation of these muscles supports the
reduction of heel impact by switching to the FFS technique.9
The resultant increase in muscle activity required by the plantar
flexors may be considered a risk of barefoot running.
Methodological Limitations
The low scores from the quality assessment using the Downs
and Black checklist suggest that improved methodological
quality is necessary to provide strong evidence for minimalist
and shod running.
Common attributes were identified in each of the rated articles
that yielded low scores. First, each study failed to report all
adverse events that may be a consequence of the intervention.
Second, subjects were not randomly selected and therefore
were prone to selection bias. With regard to the internal validity
bias section, subjects and examiners were not blinded except in
1 case.28
Only 10 studies reported actual probability values for their
data.3,4,6,16,17,20,26,35,40,41 Since all of the studies had a relatively
small sample size (between 9 and 68), finding statistically
significant results is less likely.
Clinical Relevance
Changing the foot-ground interface (eg, shoes, no shoes, heel
heights, lateral flares, rocker soles) changes the kinematics and
kinetics of runners in different ways and might also change the
direction of the GRF vector and therefore, the moment arm
length of the GRF.5 Whether this change is beneficial or
increases risks depends on the subject.
conclusion
The mechanisms underlying the modification of stride
frequency, stride length, foot strike pattern, lower extremity
mechanics, and how they relate to running performance and
injury are not yet fully understood.39 Despite the different
technologies available, minimalist shoe designs cannot entirely
replicate barefoot running, possibly because of differences in
mechanics and economy in barefoot running. No definitive
conclusions can be drawn on the risks or benefits to running
barefoot, shod, or in minimalist shoes.
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