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The introduction of carbon fiber plate footwear has led to performance benefits in runners. The mechanism for these changes in running economy includes altered biomechanics of the foot and ankle. The association of this footwear with injuries has been a topic of debate clinically, but not described in the literature. In this Current Opinion article, illustrated by a case series of five navicular bone stress injuries in highly competitive running athletes, we discuss the development of running-related injuries in association with the use of carbon fiber plate footwear. While the performance benefits of this footwear are considerable, sports medicine providers should consider injuries possibly related to altered biomechanical demands affecting athletes who use carbon fiber plate footwear. Given the introduction of carbon fiber plate footwear into athletics and other endurance sports, strategies may be required to reduce risk of injury due to altered foot and ankle mechanics. This article is intended (1) to raise awareness on possible health concerns around the use of carbon fiber plate footwear, (2) to suggest a slow gradual transition from habitual to carbon fiber plate footwear, and (3) to foster medical research related to carbon fiber plate technology and injuries.
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Sports Medicine (2023) 53:1499–1505
Bone Stress Injuries inRunners Using Carbon Fiber Plate Footwear
AdamTenforde1 · TimHoenig2 · AmolSaxena3 · KarstenHollander4
Accepted: 31 January 2023 / Published online: 13 February 2023
© The Author(s) 2023
The introduction of carbon fiber plate footwear has led to performance benefits in runners. The mechanism for these changes
in running economy includes altered biomechanics of the foot and ankle. The association of this footwear with injuries has
been a topic of debate clinically, but not described in the literature. In this Current Opinion article, illustrated by a case series
of five navicular bone stress injuries in highly competitive running athletes, we discuss the development of running-related
injuries in association with the use of carbon fiber plate footwear. While the performance benefits of this footwear are con-
siderable, sports medicine providers should consider injuries possibly related to altered biomechanical demands affecting
athletes who use carbon fiber plate footwear. Given the introduction of carbon fiber plate footwear into athletics and other
endurance sports, strategies may be required to reduce risk of injury due to altered foot and ankle mechanics. This article
is intended (1) to raise awareness on possible health concerns around the use of carbon fiber plate footwear, (2) to suggest
a slow gradual transition from habitual to carbon fiber plate footwear, and (3) to foster medical research related to carbon
fiber plate technology and injuries.
Key Points
The benefits of carbon fiber plate footwear have been
documented in the scientific literature and are well
accepted in the track and field and road racing commu-
Prior reports of injuries using this technology have
been observed clinically; these concerns have not been
documented in the literature and limit knowledge among
medical providers concerning possible association with
development of injuries.
This Current Opinion article including a case series of
navicular bone stress injuries after using carbon fiber
plate footwear is intended to raise awareness that health
concerns around use of carbon fiber plate footwear
should be considered when athletes adopt this new
* Karsten Hollander
Adam Tenforde
1 Spaulding Rehabilitation Hospital, Department ofPhysical
Medicine andRehabilitation, Harvard Medical School,
Charlestown, MA, USA
2 Department ofTrauma andOrthopaedic Surgery, University
Medical Center Hamburg-Eppendorf, Hamburg, Germany
3 Department ofSports Medicine, Sutter-PAMF, PaloAlto,
4 Institute ofInterdisciplinary Exercise Science andSports
Medicine, MSH Medical School Hamburg, Am Kaiserkai 1,
20457Hamburg, Germany
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1500 A.Tenforde et al.
1 Background
The sport of running has seen recent changes in training
and competition with the use of an embedded carbon fiber
plate (CFP) within the midsole of footwear [1]. The CFP
spans and is embedded into the midsole inside a compliant
and resilient foam [1](see example in Fig.1). The early
prototypes were worn by elite marathoner Eliud Kipchoge
who ran a sub-2-h marathon using CFP footwear in arti-
ficial conditions including closed loop circuit and pace-
makers [2]. Concerns about fairness in sport were evalu-
ated by World Athletics and resulted in new rules stating
that the combination of a single CFP and responsive foam
midsoles was permissible for use if not exceeding 25mm
of sole thickness for track (≥ 800m) and 40mm for road
running (“Athletics Shoe Regulations”, effective from 1
January 2022) [3]. The footwear industry has continued
to incorporate this technology into running shoes. Since
the introduction of CFP shoes into competition starting
in 2016, every world record from 5000m to marathon
distance has been eclipsed by competitors using this new
technology [4]. Additionally, sports science has validated
the performance benefits of CFP combined with compres-
sive foam midsole compared to earlier footwear used for
training and competition [58].
2 Biomechanics ofCarbon Fiber Plate
The use of CFP footwear during training and competi-
tion has been shown to introduce novel biomechanical
demands on the foot and lower extremities. The biome-
chanical differences between a novel CFP footwear com-
pared to standard competitive running footwear have been
previously evaluated in competitive male runners [9].
In this investigation, runners using CFP footwear were
observed to have decreased cadence and correspondingly
longer steps as well as a longer flight time [9]. Further-
more, peak vertical ground reaction forces and the verti-
cal impulse per step were higher in runners using CFP
footwear. No changes in knee or hip mechanics but differ-
ences in ankle and metatarsophalangeal joint mechanics
were observed in runners using CFP footwear [9]. The
authors also described thatpeak ankle dorsiflexion dur-
ing stance, and peak ankle moments were reduced and
lower negative and positive ankle work were observed in
CFP over standard competitive footwear during running.
These results suggest that more energy was stored in the
midsole and less in the muscles and tendons of the ankle
[9]. A biomechanical explanation of these findings is that
the CFP increases longitudinal bending stiffness of the
footwear and, thus, is associated with reduced dorsiflexion
of the metatarsophalangeal joints before take-off accom-
panied by an altered energy storage and return [9]. This
suggests CFP footwear may store and return more energy
compared to prior standard footwear. Observed improve-
ments in running economy may result from energy return
from compression of cushioning material and the lever
effects of the ankle mechanics considering the curve of
the CFP and a higher toe spring [9, 10]. The CFP has
been proposed to create a “teeter-totter effect” that moves
forces anteriorly in the foot during thepropulsive phase
[10]. Importantly, this is not supported by experimental
data, which show no difference in the center of pressure
progression [9]. The midsole cushioning may also con-
tribute to improvements in running economy, as shown in
earlier work [11]. However, the compressive foam would
be expected to contribute to a return of energy in the form
of vertical displacement and, thus, may be dependent on
the footstrike pattern [12].
Fig. 1 Lateral X-ray of a run-
ner's left foot in a carbon-plated
running shoe. Red arrows
outline the embedded plate. The
green arrow shows the fulcrum
point of the plate. Note the
relation of the curvature of the
plate to the metatarsal locations
(metatarsal phalangeal joints)
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Bone Stress Injuries in Runners Using Carbon Fiber Plate Footwear
3 Biomechanical Inuences Associated
withBone Stress Injuries
The change in foot and ankle mechanics introduced by CFP
footwear may contribute to the risk of injury. Bone is an
adaptable tissue that responds to changes in demands includ-
ing those resulting from footwear. For example, a study
demonstrated that the gradual introduction of minimalist
footwear over 10weeks resulted in changes on magnetic
resonance imaging (MRI) concerning metatarsal bone stress
injury (BSI) in a population of runners previously habituated
to standard footwear [13]. By extension, the use of CFP foot-
wear could be expected to generate novel stress to bone. BSI
represents an overuse injury that is the result of localized
failure of bone from cumulative loading and can progress to
the development of stress fracture [14]. Navicular BSIs are
classified as a high-risk location for injury as some of these
injuries may not effectively heal with non-surgical meas-
ures [14]. While navicular BSIs are described in older pop-
ulations of collegiate and professional athletes [15], these
injuries have also been observed in youth athletes [1618].
Prior studies on biomechanical risk factors associated with
navicular BSI are retrospective and include reduced ankle
dorsiflexion and subtalar range of motion [18], higher peak
rearfoot eversion and range of motion [19], both cavus and
planus foot types [20], and plantar displacement of navicular
and cuneiforms with narrowing of the medial aspect of the
talonavicular joint [21]. The navicular bone receives une-
qual forces from the first and second metatarsocuneiform
joints [22] that create shear stress over the central third of
the bone, corresponding to a region of reduced blood supply
[23], and a common site for navicularBSI. A grading system
of navicular BSIs developed by Saxena and Fullem is com-
monly used to guide evaluation and management based on
CT findings and inform surgical decision making [20, 24].
4 Case Series ofNavicular Bone Stress
Injuries inRunners Using Carbon Fiber
Plate (CFP) Footwear
This case series reflects clinical observations in five patients
presenting with foot pain and diagnosis of navicular BSI
who were using CFP footwear at the time of injury. Given
the high rate of adoption of CFP footwear in track and field,
understanding potential associated health concerns is impor-
tant for athletes and healthcare providers.
4.1 Case 1
A 17-year-old male junior elite steeplechase runner was
using CFP shoes for interval sessions on the track prior to
a race. The athlete felt severe midfoot pain directly after a
3000m steeplechase race. He had no relevant history of BSIs
and had been using different types of carbon-plated shoes
for 2years (completing approximately 1000km of total run-
ning in this footwear). Plain radiographs were performed
immediately after the race and the athlete was cleared to
continue sports participation. Due to persistent pain over the
following 5weeks, he presented at an outpatient clinic and
was diagnosed with a navicular stress fracture. The injury
was managed by sports restrictions (no cast immobilization,
no weight-bearing restrictions). Six weeks later (at 11weeks
after the inciting race), a follow-up MRI was obtained and
did not demonstrate visible bony consolidation (Fig.2a–c).
However, the athlete was pain free and was allowed a grad-
ual return to sports. However, with persistent non-union of
the fracture, he was transferred to a specialist with advanced
knowledge in foot injuries and sports medicine. A weight-
bearing CT revealed a stable Type III navicular stress frac-
ture [20] with the absence of bony consolidation (Fig.2d–f).
After an interdisciplinary case conference with the patient,
shared decision-making was applied, and he completed a
gradual load buildup on an anti-gravity treadmill at 75% of
body weight, and he ultimately returned to land-based run-
ning. Despite a follow-up CT scan revealing that the fracture
line was still present, the athlete continued to run without
4.2 Case 2
A 17-year-old female junior elite middle-distance runner
was using CFP shoes exclusively for interval sessions on
the track. She had been using carbon-plated shoes for about
6months over 100km. She experienced pain in the midfoot
after a track session wearing CFP shoes. The runner had a
previous history of a navicular BSI in the same foot 2years
earlier that was treated conservatively. On evaluation, she
was noted to have bilateral pes planovalgus. An MRI after
the inciting event revealed a Type 0.5 (“stress reaction”)
of the navicular bone [20]. She was initially treated with
6weeks of non-weightbearing in an AirCast. Repeat MRI
obtained 6weeks after the initial diagnosis showed a reduc-
tion of edema but still a stress reaction leading to 2 more
weeks of non-weightbearing. After a total of 8weeks of
non-weightbearing the athlete started cross-training on an
Alter-G treadmill (initially with 70% of body weight) and
was back to normal and pain-free training 15weeks after
the initial diagnosis.
4.3 Case 3
An 18-year-old female elite 3000m steeplechase runner was
racing a 10km road race in CFP racing shoes. The race was
the first time that she had used the new CFPshoes. The
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1502 A.Tenforde et al.
week after the race she experienced foot pain localized at the
forefoot with associated minimal swelling and was unable to
walk pain-free in the following days. Without medical con-
sultation, she went back to running and experienced trauma
from acute supination in the same foot leading to medical
consultation. Resulting from this consultation at 4weeks
after the race and 1week following trauma, an MRI was
obtained that revealed a navicular BSI, and a subsequent
CT scan confirmed the presence of a Type III navicular
stress fracture (Fig.3). She was subsequently treated with
non-weightbearing for 4weeks in a walker. Afterwards, she
initiated strength exercises and cross training on a cycle
ergometer. Seven weeks from thetime of CT, she attempted
to run but experienced pain at level 4/10 on a numeric rating
scale. Following one additional week off from running, she
was able to return to running pain-free.
4.4 Case 4
A 38-year-old male elite triathlete competed in a half-
marathon (13.1 miles/21.1km) in CFP shoes. The shoe he
wore had not been used in any significant training or rac-
ing prior. Towards the latter portion of the race, he expe-
rienced midfoot pain, and upon completion, was unable to
walk pain-free. He had minimal swelling, pain localized to
the “N-spot” and experienced throbbing at night. He had a
previous history of a navicular BSI in the same foot, treated
non-operatively 18years prior as a collegiate steeplechaser.
He also had a history of a navicular BSI in the contra-lateral
foot treated operatively 6years prior. He had a stable foot
structure and normally did not wear foot orthoses. Due to his
prior history, a CT scan was obtained, which revealed a Type
II navicular BSI, and the patient underwent open reduction
and internal fixation, and went on to successful healing.
4.5 Case 5
A 36-year-old male elite triathlete ran a 22-mile training
run in preparation for a marathon race 4weeks later. He had
only run in the CFP shoes two to three times prior and for
much shorter distances. He developed midfoot pain imme-
diately after the inciting run, with similar symptoms to the
Fig. 2 Images from Case 1. Sagittal (a), coronal (b), and long axis
(c) on T2 fat-suppressed sequences on magnetic resonance imaging
demonstrate vertically oriented stress fracture. Corresponding views
on CT visualize the fracture orientation (df) and classify as navicu-
lar Type III stress fracture [20]
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Bone Stress Injuries in Runners Using Carbon Fiber Plate Footwear
case above (limping, pain at the “N-spot”, throbbing at night),
but no swelling. He had no prior history of a navicular BSI.
The athlete normally wore custom foot orthoses but did not
use these in his racing shoes. Due to the short time-span of
his upcoming race, a CT scan was ordered and was negative
for a fracture. He was diagnosed with a Type 0.5 navicular
BSI (“stress reaction”) and treated with a below-knee boot,
focused extracorporeal shockwave therapy (at 0.40mJ/mm2
for 2000 pulses at the “N-spot”) and electromagnetic transduc-
tion therapy (9000 pulses at power level 8, 8Hz). This treat-
ment was repeated 1week later, and since he was pain-free,
he discontinued the boot. He was allowed cross-training on
a stationary bike and swimming after diagnosis. He started
training on an anti-gravity treadmill 10days after initiating
treatment at 70% body weight. He was able to run on land
approximately 12days prior to his marathon, and he completed
the marathon pain-free.
5 Discussion
The purpose of this Current Opinion article is to describe
both running performance benefits and potential associa-
tions of BSI in runners using CFP footwear. We illustrate
this with a series of navicular BSIs in two discrete cohorts
including a population of junior elite track and field ath-
letes in Europe and two older athletes competing in endur-
ance events in North America. In all cases, athletes devel-
oped acute pain during or after running in CFP footwear.
Differences in time to diagnosis and management reflect
the relative experience of the healthcare providers who
initially evaluated each athlete. A prior study related that
the time to reach an accurate diagnosis for navicular stress
injuries is almost 9months [20]. Recognizing possible
associations of navicular BSI in runners presenting with
vague midfoot or ankle pain who use CFP footwear may
Fig. 3 Images from Case 3. Long axis (a), sagittal (b), and coronal
(c) on T2 fat-suppressed sequences on magnetic resonance imaging
demonstrate vertically oriented stress fracture. Corresponding views
on CT visualize the fracture orientation (df) extending through both
plantar and dorsal cortices and classify as navicular Type III stress
fracture [20]
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1504 A.Tenforde et al.
be important to identify this high-risk injury. A previous
study of 139 elite tennis players reported stress fracture
incidence of 12.9%, of which 27% were located in the
tarsal navicular [25]. A previous article reports navicular
stress fractures to be 35% of all stress fractures [26]. The
true incidence may be hard to estimate since many of these
injuries go undiagnosed for long periods (on average over
8months, as data from a large series and a systematic
review suggest [24, 26]).
Each case presented involved the use of CFP footwear
with a compressible foam midsole designed to improve run-
ning economy. The mechanism for injury in each case cannot
be determined due to limitations of a case report format and
lack of studies to describe the changes in lower extremity
biomechanics between forms of training and racing foot-
wear in both sexes [5].The athletes include a mix of sex,
age, use of CFP footwear and primary competition events.
Use of custom orthotics and prior history of BSI in athletes
could influence injury risk. Two athletes competed in the
steeplechase event and prior work has demonstrated higher
vertical ground reaction forces with hurdling and water jump
landings compared to treadmill running [27].
Based on prior studies describing risk factors for navicu-
lar BSI [18, 19, 22], it is plausible that shoes with a com-
pressive foam midsole may allow for increased plantar
displacement of the navicular and cuneiform bones and
modified forces to the hindfoot. As discussed earlier, multi-
ple biomechanical variables may change using CFP footwear
compared with other types of competition shoes. Behav-
iors of the athlete in their use of these shoes for training
and competition may also explain novel demands on the
foot, including training at faster velocities, which would be
expected to increase skeletal loading [28].
Currently, sports governing bodies permit the use of CFP
footwear, and many runners are using these shoes with the
aim of enhancing performance. Our case series is the first
published cohort to document the potential associated risk
of navicular BSI using this new footwear. Athletes choosing
to wear CFP footwear should recognize the development
of pain, particularly over the navicular bone, anterior ankle
or midfoot region, which may represent a more significant
injury that requires further evaluation to guide correct treat-
ment. Based on prior evidence of maladaptation following
rapid adoption of minimalist footwear use with metatarsal
BSI [13], one potential behavioral strategy for runnersmay
be to incorporate CFP footwear gradually into training and
While this is the first report to describe bone stress inju-
ries in association with novel CFP footwear, there are clearly
limitations to this work. The development of BSI is often
multifactorial [14] and retrospective chart review limits
understanding mechanisms for injury. The cases are from
two separate cohorts of junior and senior elite from different
geographic locations, and it is unclear whether similar inju-
ries have been observed in other populations. The diagnostic
testing is described using the Saxena and Fullem classifica-
tion to provide consistency in descriptors of injury [21].
6 Conclusion
This Current Opinion discusses a possible association of
BSIs with CFP footwear while recognizing the perfor-
mance benefits that have been described. Advances in the
evaluation and management of BSIs have been extensively
published, and highlight the need to identify multiple risk
factors for BSIs including those that are modifiable. We
recommend further research to better understand whether
the association of BSIs with CFP footwear is unique to the
described runners in this case series or applies to other
running populations. Prior experience with metatarsal BSI
with minimalist footwear led shoe companies to develop
a more gradual program for transitioning to minimalist
shoes; it is plausible that similar advances could be devel-
oped by shoe companies, researchers and clinicians to pro-
mote safety in sports when using CFP footwear. Further
discussions are expected, and both sports industry and
sports federations have a duty to respect the guidance and
advice of medical professionals. The excitement surround-
ing this new technology due to faster running times is pal-
pable for both athletes and the sports medicine community.
We hope this article helps to guide better recognition of
medical issues related to CFP footwear, appropriate use of
this new technology, and safety for our athletes.
Acknowledgements We would like to thank the runners who allowed
us to present their cases in this Current Opinion article.
Funding Open Access funding enabled and organized by Projekt
Funding No funding has been received in relation to this work.
Conflict of interest Adam Tenforde, Tim Hoenig, Amol Saxena, and
Karsten Hollander declare that they have no conflicts of interest rel-
evant to the content of this article.
Ethics approval Not applicable.
Consent to participate and publication All patients consented to the
use of their case for this purpose.
Availability of data and material Not applicable.
Author contributions All authors contributed equally to writing this
Current Opinion article. All authors read and approved the final manu-
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Bone Stress Injuries in Runners Using Carbon Fiber Plate Footwear
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... Currently, there is limited evidence that running footwear with stability and cushioning elements could reduce RRI rates [15]. However, drastic footwear modifications such as oversimplified designs (e.g., minimal shoes) or over-designed modifications, combined with insufficient habituation time, can result in the onset of RRI [16][17][18]. New approaches, e.g., the comfort filter, habitual motion path theory, and the preferred movement path theory, linking RRIs to uncomfortable perceived shoes, are becoming increasingly established in the running community and may serve as an opportunity to reduce injuries in the future [12,19,20]. These new concepts aim to enhance the subject-specific response to footwear. ...
... Eight articles found a reduction in the ground contact time [130,[133][134][135][137][138][139], and two found unchanged ground contact times [134,140] when running in midsoles with lower bending stiffness. Although studies found lower vertical GRF loading rates [140] and increased comfort perception [135] when athletes ran in more flexible than stiffer midsoles, the relationship between BRFs and injury development when altering the longitudinal bending stiffness has not been sufficiently studied yet, but first studies have evolved showing that bones stress injuries might increase when switching to footwear with carbon fibre plates [18]. ...
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Injury prevention is essential in running due to the risk of overuse injury development. Tailoring running shoes to individual needs may be a promising strategy to reduce this risk. Novel manufacturing processes allow the production of individualised running shoes that incorporate features that meet individual biomechanical and experiential needs. However, specific ways to individualise footwear to reduce injury risk are poorly understood. Therefore, this scoping review provides an overview of (1) footwear design features that have the potential for individualisation; and (2) the literature on the differential responses to footwear design features between selected groups of individuals. These purposes focus exclusively on reducing the risk of overuse injuries. We included studies in the English language on adults that analysed: (1) potential interaction effects between footwear design features and subgroups of runners or covariates (e.g., age, sex) for running-related biomechanical risk factors or injury incidences; (2) footwear comfort perception for a systematically modified footwear design feature. Most of the included articles (n = 107) analysed male runners. Female runners may be more susceptible to footwear-induced changes and overuse injury development; future research should target more heterogonous sampling. Several footwear design features (e.g., midsole characteristics, upper, outsole profile) show potential for individualisation. However, the literature addressing individualised footwear solutions and the potential to reduce biomechanical risk factors is limited. Future studies should leverage more extensive data collections considering relevant covariates and subgroups while systematically modifying isolated footwear design features to inform footwear individualisation. Supplementary Information The online version contains supplementary material available at 10.1186/s13102-023-00760-x.
... Along with midsole cushioning, a key component of advanced footwear technology is the increase in longitudinal bending stiffness (LBS) with an embedded carbon fibre plate (Ortega, 2021). Running in footwear with increased LBS from a carbon fibre plate has been associated with an increased risk of bone stress injuries (Tenforde, 2023), but the mechanisms behind this relationship are not fully understood. Therefore, measuring plantar pressure distributions while running in footwear with increased LBS can help us better understand the influence of carbon fibre plated shoes on performance and injury. ...
... The peak plantar pressures in both the stiff and stiffest conditions were greater than the control shoes, but interestingly there were no differences between the two experimental conditions. Running in shoes with carbon fibre plates to increase LBS can lead to bone stress injuries (Tenforde et al., 2023). Our results suggest that these injuries may be due to higher peak plantar pressures in the different foot regions. ...
... Additional analysis of recent performance trends in events which do not have superspikes available (for example, shot put and discus) would also provide insight into whether recent track performance improvements have been driven by technology or by more general sport-wide improvements in training methodology and competition opportunities, for example. Further, given recent commentary on the potentially enhanced risk of injury with AFT (Tenforde et al., 2023), the long-term ramifications of repeated exposure to AFT in sprint spikes should be investigated, especially in youth and developing athletes. ...
Background Elite track and field sprint performances have reached a point of stability as we near the limits of human physiology, and further significant improvements may require technological intervention. Following the widely reported performance benefits of new advanced footwear technology (AFT) in road-running events, similar innovations have since been applied to sprint spikes in hope of providing similar performance enhancing benefits. However, it is not yet clear based on current evidence whether there have been subsequent improvements in sprint performance. Therefore, the aims of this study were to establish if there have been recent year-to-year improvements in the times of the annual top 100 and top 20 athletes in the men’s and women’s sprint events, and to establish if there is an association between the extensive use of AFT and potential recent improvements in sprint performances. Methods For the years 2016–19 and 2021–2022, the season best performances of the top 100 athletes in each sprint event were extracted from the World Athletics Top lists. Independent t-tests with Holm corrections were performed using the season’s best performance of the top 100 and top 20 athletes in each year to identify significant differences between years for each sprint discipline. Following the classification of shoes worn by the top 20 athletes in each event during their annual best race (AFT or non-AFT), separate linear mixed-model regressions were performed to determine the influence of AFT on performance times. Results For the top 100 and top 20 athletes, there were no significant differences year-to-year in any sprint event prior to the release of AFT (2016–2019). There were significant differences between AFT years (2021 or 2022) and pre-AFT years (2016–2019) in eight out of 10 events. These differences ranged from a 0.40% improvement (men’s 100 m) to a 1.52% improvement (women’s 400 m hurdles). In the second analysis, multiple linear mixed model regressions revealed that the use of AFT was associated with improved performance in six out of ten events, including the men’s and women’s 100 m, women’s 200 m, men’s 110 m hurdles, women’s 100 m hurdles and women’s 400 m hurdles (estimate range: −0.037 – 0.521, p = <0.001 – 0.021). Across both analyses, improvements were more pronounced in women’s sprint events than men’s sprint events. Conclusion Following a period of stability, there were significant improvements in most sprint events which may be partly explained by advances in footwear technology. These improvements appear to be mediated by event, sex and potentially level of athlete.
... With the high amount of loading during the workouts of this intervention, it would be of interest to look at changes in bone marrow edema between runners using super shoes and a control group, such as the work of Ridge et al. (2013), over a longer period of super shoe use, or before and after prolonged downhill running or marathon completion. Injury data on super shoes is currently limited, with a recent collection of retrospective case studies linking super shoe use and navicular bone stress injuries (Tenforde et al. 2023), highlighting the importance of understanding the risks and benefits associated with transitioning to these shoes. Prospective research assessing the impact of regular super shoe use and injury risk at all ability levels is needed to help inform athletes, coaches, and footwear companies. ...
Conference Paper
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Lab testing with Nike Vaporflys (VP) has revealed running economy (RE) benefits of 2.5-4%. With runners also anecdotally reporting less sore calf muscles and less "beat up" legs after hard workouts, use of these shoes may cause runners to undergo physiological adaptations since their muscles may be aided during training by the shoe's energy returning technology. The purpose of this pilot study is to investigate the long-term effects of using VP in workouts by comparing training in VP versus traditional racing flats (FL) on race performance and explore physiological and biomechanical adaptations. Collegiate cross country runners (n=8) completed pre-and post-intervention testing in both VP and FL. They were assigned either VP or FL for an 8-week intervention. Metabolic and biomechanical data were collected and compared. FL-trained runners improved average running economy more than the VP-trained runners (FL: 5.61 ± 1.11%; VP: 0.97 ± 3.64%; p=0.077, ES (g)=1.409). Computing a "VP % benefit" by comparing the RE when running in VP compared to running in FL, the VP-trained runners increased VP % Benefit compared to FL-trained runners (VP: 0.21 ± 2.23%; FL:-0.38 ± 0.24%; p=0.433, g=0.148) In this pilot phase there were no significant correlations between biomechanical and metabolic measures. Heterogeneity of foot strike techniques likely prevented group biomechanical differences from being observed. We will use the effect sizes of these differences to power the next larger phase of the study. This pilot study suggests a specificity of training effect where participants improved relative RE more from PRE to POST when running in the shoe type they trained in. Overall, the FL group improved RE to a greater extent, suggesting that training in FL is more optimal for race performance despite decreasing the acute RE benefits incurred from super shoes.
... However, future studies should compare the wear process in shoes with PEBA midsole with a carbon fiber plate to increase LBS and without carbon fiber plate to analyze the influence of the element to increase the LBS (carbon fiber plate) on AFT wear. In addition, since there is recent discussion about the possible risk of injury when using AFT, 49,50 future studies should also investigate the influence of using AFT with EVA and PEBA midsole and their corresponding worn conditions on the risk of injury. ...
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Background Ethylene and vinyl acetate (EVA) and polyether block amide (PEBA) are recently the most widely used materials for advanced footwear technology (AFT) that has been shown to improve running economy (RE). This study investigated the effects of these midsole materials on RE and biomechanics, in both fresh and worn state (after 450 km). Methods Twenty‐two male trained runners participated in this study. Subjects ran four 4‐min trials at 13 km‧h⁻¹ with both fresh EVA and PEBA AFT and with the same models with 450 km of wear using a randomized crossover experimental design. We measured energy cost of running (W/kg), spatiotemporal, and neuromuscular parameters. Results There were significant differences in RE between conditions (p = 0.01; n² = 0.17). There was a significant increase in energy cost in the worn PEBA condition compared with new (15.21 ± 1.01 and 14.87 ± 0.99 W/kg; p < 0.05; ES = 0.54), without differences between worn EVA (15.13 ± 1.14 W/kg; p > 0.05), and new EVA (15.15 ± 1.13 w/kg; ES = 0.02). The increase in energy cost between new and worn was significantly higher for the PEBA shoes (0.32 ± 0.38 W/kg) but without significant increase for the EVA shoes (0.06 ± 0.58 W/kg) (p < 0.01; ES = 0.51) with changes in step frequency and step length. The new PEBA shoes had lower energy cost than the new EVA shoes (p < 0.05; ES = 0.27) with significant differences between conditions in contact time. Conclusion There is a clear RE advantage of incorporating PEBA versus EVA in an AFT when the models are new. However, after 450 km of use, the PEBA and EVA shoes had similar RE.
... In addition to longer single testing protocols, longitudinal studies could be beneficial with regard to understanding the long-term impact of using advanced footwear technology with respect to both improving performance (mechanical changes to the lower limb muscletendon units, for example) 13 and the risk of injury. 30 This would be particularly useful if in vivo testing of muscle-tendon units were used in conjunction with the modeled estimations 23 of leg stiffness. One limitation of our study, and other research on super shoes, is that the cost of the footwear and the sheer quantity of models available (>30 manufacturers have shoes approved by World Athletics) 19 preclude an evaluation of each shoe or a comparison with all others. ...
Purpose: Advanced footwear technology is prevalent in distance running, with research focusing on these "super shoes" in competitive athletes, with less understanding of their value for slower runners. The aim of this study was to compare physiological and biomechanical variables between a model of super shoes (Saucony Endorphin Speed 2) and regular running shoes (Saucony Cohesion 13) in recreational athletes. Methods: We measured peak oxygen uptake (VO2peak) in 10 runners before testing each subject 4 times in a randomly ordered crossover design (ie, Endorphin shoe or Cohesion shoe, running at 65% or 80% of velocity at VO2peak [vVO2peak]). We recorded video data using a high-speed camera (300 Hz) to calculate vertical and leg stiffnesses. Results: 65% vVO2peak was equivalent to a speed of 9.4 km·h-1 (0.4), whereas 80% vVO2peak was equivalent to 11.5 km·h-1 (0.5). Two-way mixed-design analysis of variance showed that oxygen consumption in the Endorphin shoe was 3.9% lower than in the Cohesion shoe at 65% vVO2peak, with an interaction between shoes and speed (P = .020) meaning an increased difference of 5.0% at 80% vVO2peak. There were small increases in vertical and leg stiffnesses in the Endorphin shoes (P < .001); the Endorphin shoe condition also showed trivial to moderate differences in step length, step rate, contact time, and flight time (P < .001). Conclusions: There was a physiological benefit to running in the super shoes even at the slower speed. There were also spatiotemporal and global stiffness improvements indicating that recreational runners benefit from wearing super shoes.
... Earlier studies have also reported higher injury incidence at the knee (30.7%) compared to the ankle (8.3%) or foot (14.6%) [42]. As exemplified in our study, it is plausible that foot injuries may be on the rise, which, while still speculative, may be related to the growing popularity of carbon-plated super shoes [45]. ...
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This study aimed to characterize running-related injuries (RRIs), explore their relationship with run and resistance training (RT) parameters, and identify perceived prevention measures among adult recreational runners. An anonymous online survey was designed and distributed via social media and email. Data were analyzed with chi-square, t-test, or analysis of variance (ANOVA), with significance accepted at p ≤ 0.05. Data from 616 participants (76.8% female, age: 42.3 ± 10.5 y) were analyzed. Most runners (84.4%) had an injury history, with 44.6% experiencing one in the past year. The most common RRI sites included the foot/ankle (30.9%) and knee (22.2%). RRI prevalence was higher in those running >19 miles weekly (48.4%, p = 0.05), but there were no differences based on RT participation status. Among those using RT, relatively more RRIs were observed in runners who trained the hip musculature (50.3%, p = 0.005) and did not include the upper body (61.6%, p < 0.001). A disproportionately high RRI prevalence was found for several of the other risk-reduction strategies. RRIs remain a substantial problem, particularly around the ankle/foot and knee. Higher run volume and performance motives were positively associated with RRIs. Most runners incorporated RRI risk-reduction techniques, with over half using RT. The current study did not determine whether preventative strategies were implemented before or after injury; therefore, prospective studies controlling for previous injuries are required to evaluate the effectiveness of RT in preventing future RRIs.
... Based on clinical observations and anecdotal evidence, concerns about running-related injuries have been raised. 2 However, we are yet to have a discussion about these risks guided by an evidence base. We hope that this editorial increases awareness of potential medical issues related to TARS and encourages a scientific process to determine how best to ensure safety for our athletes. ...
... 47,48 Typically, a high increase in frequency and/or intensity of training, a change of equipment or training surface may result in exceeding the bone's healing capacity. 11,49 Bone stress injuries can occur in any sport, but are more frequent in impact sports involving running or jumping (crosscountry running, ballet, track and field, gymnastics). 12 There are factors that may enhance the bone's healing capacity such as longer physical activity history, late sport specialization, adequate energy availability, and good vitamin D and calcium status. ...
The foot is a complex structure that plays a crucial role in all static and dynamic tasks associated with posture and locomotion. Foot injuries are common in youth athletes, especially in sports including running, kicking, and jumping. The foot is prone to acute and overuse injuries, such as fracture, tendon injury, apophysitis, plantar fasciopathy, avascular necrosis and bone stress injury. Diagnosis and treatment decisions need to be made on an individualized approach considering the age and development of the youth athlete. Preventive foot core training should focus on increasing the feet’s capacity to withstand the high load exposed to in sports.
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Background: Compared to conventional racing shoes, Nike Vaporfly 4% running shoes reduce the metabolic cost of level treadmill running by 4%. The reduction is attributed to their lightweight, highly compliant, and resilient midsole foam and a midsole-embedded curved carbon fiber plate. We investigated whether these shoes also reduce the metabolic cost of moderate uphill (+3°) and downhill (-3°) grades. We tested the null hypothesis that compared to conventional racing shoes, highly-cushioned shoes with carbon-fiber plates would impart the same ∼4% metabolic power (W/kg) savings during uphill and downhill running as they do during level running. Methods: After familiarization, 16 competitive male runners performed six 5-min trials (2 shoes × 3 grades) in 2 Nike marathon racing shoe models (Streak 6 and Vaporfly 4%) on a level, uphill (+3°), and downhill (-3°) treadmill at 13 km/h (3.61 m/s). We measured submaximal oxygen uptake and carbon dioxide production during Minutes 4-5 and calculated metabolic power (W/kg) for each shoe model and grade combination. Results: Compared to the conventional shoes (Streak 6), metabolic power in the Vaporfly 4% shoes was 3.83% (level), 2.82% (uphill), and 2.70% (downhill) less (all p < 0.001). The percent change in metabolic power for uphill running was less compared to level running (p = 0.04, effect size, ES = 0.561) but was not statistically different between downhill and level running (p = 0.17, ES = 0.356). Conclusion: On a running course with uphill and downhill sections, the metabolic savings and hence performance enhancement provided by Vaporfly 4% shoes would likely be slightly less overall, compared to the savings on a perfectly level race course.
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Every women’s and men’s world records from 5 km to the marathon has been broken since the introduction of carbon fibre plate (CFP) shoes in 2016. This step-wise increase in performance coincides with recent advancements in shoe technology that increase the elastic properties of the shoe thereby reducing the energy cost of running. The latest CFP shoes are acknowledged to increase running economy by more than 4%, corresponding to a greater than 2% improvement in performance/run time. The recently modified rules governing competition shoes for elite athletes, announced by World Athletics, that includes sole thickness must not exceed 40 mm and must not contain more than one rigid embedded plate, appear contrary to the true essence and credibility of sport as access to this performance-defining technology becomes the primary differentiator of sporting performance in elite athletes. This is a particular problem in sports such as athletics where the primary sponsor of the athlete is very often a footwear manufacturing company. The postponement of the 2020 Summer Olympics provides a unique opportunity for reflection by the world of sport and time to commission an independent review to evaluate the impact of technology on the integrity of sporting competition. A potential solution to solve this issue can involve the reduction of the stack height of a shoe to 20 mm. This simple and practical solution would prevent shoe technology from having too large an impact on the energy cost of running and, therefore, determining the performance outcome.
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Purpose We compared running economy (RE) and 3-km time-trial (TT) variables of runners wearing Nike Vaporfly 4% (VP4), Saucony Endorphin lightweight racing flats (FLAT), and their habitual running (OWN) footwear. Methods Eighteen male recreational runners (mean +/− SD, age: 33.5 ± 11.9 year (mean ± standard deviation), peak oxygen uptake (VO2peak): 55.8 ± 4.4 mL/kg·min) attended 4 sessions approximately 7 days apart. The first session consisted of a VO2peak test to inform subsequent RE speeds set at 60%, 70%, and 80% of the speed eliciting VO2peak. In subsequent sessions, treadmill RE and 3-km TTs were assessed in the 3 footwear conditions in a randomized, counterbalanced crossover design. Results Oxygen consumption (mL/kg·min) was lesser in VP4 (from 4.3% to 4.4%, p ≤ 0.002) and FLAT (from 2.7% to 3.4%, p ≤ 0.092) vs. OWN across intensities, with a non-significant difference between VP4 and FLAT (1.0%–1.7%, p ≥ 0.292). Findings related to energy cost (W/kg) and energetics cost of transport (J/kg·m) were comparable. VP4 3-km TT performance (11:07.6 ± 0:56.6 mm:ss) was enhanced vs. OWN by 16.6 s (2.4%, p = 0.005) and vs. FLAT by 13.0 s (1.8%, p = 0.032). 3-km times between OWN and FLAT (0.5%, p = 0.747) were similar. Most runners (n = 11, 61%) ran their fastest TT in VP4. Conclusions Overall, VP4 improved laboratory-based RE measures in male recreational runners at relative speeds compared to OWN, but the RE improvements in VP4 were not significant vs. FLAT. More runners exhibited better treadmill TT performances in VP4 (61%) vs. FLAT (22%) and OWN (17%). The variability in RE (–10.3% to 13.3%) and TT (–4.7% to 9.3%) improvements suggests that responses to different types of shoes are individualized and warrant further investigation.
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The footstrike pattern of an athlete is understood as the way the foot touches the ground. Over the years, several definitions and techniques to classify and quantify footstrike patterns have been described. Therefore, this narrative review summarizes the existing classifications of footstrike patterns, gives suggestions for further use of these classifications, and provides a summary of the relationship between footstrike patterns and the occurrence of overuse injuries. Footstrike patterns are classified by using nominal (e.g. forefoot strike, midfoot strike, rearfoot strike) or continuous variables (e.g. footstrike angle). Possible assessments include visual, video-based, 3D-biomechanical, force plate-based or inertial measurement unit-based analysis. Scientists, coaches, and clinicians can choose between different methods to analyze footstrike patterns in runners. All approaches to classify footstrike patterns have advantages and limitations. In certain situations, it might be beneficial to combine these methods. Despite great efforts in analyzing footstrike patterns, relationships between footstrike patterns and running-related injuries are mostly unclear at present. Based on the current literature, causal links to overuse injuries, recommendations to change running technique, and other simplifications solely based on the footstrike pattern must be considered critically.
Objective Bone stress injuries (BSIs) are classified in clinical practice as being at low- or high-risk for complication based on the injury location. However, this dichotomous approach has not been sufficiently validated. The purpose of this systematic review was to examine the prognostic role of injury location on return-to-sport (RTS) and treatment complications after BSI of the lower extremity and pelvis. Design Systematic review and meta-analysis. Data sources PubMed, Web of Science, Cochrane CENTRAL and Google Scholar databases were searched from database inception to December 2021. Eligibility criteria for selecting studies Peer-reviewed studies that reported site-specific RTS of BSIs in athletes. Results Seventy-six studies reporting on 2974 BSIs were included. Sixteen studies compared multiple injury sites, and most of these studies (n=11) described the anatomical site of injury as being prognostic for RTS or the rate of treatment complication. Pooled data revealed the longest time to RTS for BSIs of the tarsal navicular (127 days; 95% CI 102 to 151 days) and femoral neck (107 days; 95% CI 79 to 135 days) and shortest duration of time for BSIs of the posteromedial tibial shaft (44 days, 95% CI 27 to 61 days) and fibula (56 days; 95% CI 13 to 100 days). Overall, more than 90% of athletes successfully returned to sport. Treatment complication rate was highest in BSIs of the femoral neck, tarsal navicular, anterior tibial shaft and fifth metatarsal; and lowest in the fibula, pubic bone and posteromedial tibial shaft. Conclusion This systematic review supports that the anatomical site of BSIs influences RTS timelines and the risk of complication. BSIs of the femoral neck, anterior tibial shaft and tarsal navicular are associated with increased rates of complications and more challenging RTS. PROSPERO registration number CRD42021232351.
Bone stress injuries, including stress fractures, are overuse injuries that lead to substantial morbidity in active individuals. These injuries occur when excessive repetitive loads are introduced to a generally normal skeleton. Although the precise mechanisms for bone stress injuries are not completely understood, the prevailing theory is that an imbalance in bone metabolism favours microdamage accumulation over its removal and replacement with new bone via targeted remodelling. Diagnosis is achieved by a combination of patient history and physical examination, with imaging used for confirmation. Management of bone stress injuries is guided by their location and consequent risk of healing complications. Bone stress injuries at low-risk sites typically heal with activity modification followed by progressive loading and return to activity. Additional treatment approaches include non-weight-bearing immobilization, medications or surgery, but these approaches are usually limited to managing bone stress injuries that occur at high-risk sites. A comprehensive strategy that integrates anatomical, biomechanical and biological risk factors has the potential to improve the understanding of these injuries and aid in their prevention and management. Bone stress injuries, commonly referred to as stress reactions or stress fractures, result from repeated overloading of bone and are thought to involve an imbalance in microdamage formation and repair. This Primer provides an overview of the epidemiology, pathobiology, risk factors, diagnostic approaches, treatments and consequences of bone stress injuries.
Approximately 30% of tarsal navicular stress fractures are missed by physicians because plain radiographs often show no diagnostic clues. If early diagnosis and treatment are not obtained, such fractures will become refractory and the patient will no longer be able to actively participate as an athlete. We herein describe our experience treating a 14-year-old female track sprinter with persistent foot pain. Magnetic resonance imaging 6 months after the onset of pain showed a stress fracture of the tarsal navicular bone. Computed tomography showed the tarsal navicular stress fracture as well as sclerosis at the fracture edges. We diagnosed a refractory tarsal navicular stress fracture. Conservative management in the form of non-weight-bearing cast immobilization is the standard treatment for both partial and complete stress fractures of the tarsal navicular bone. However, surgical treatment is required in refractory cases. We treated the herein-described refractory case with 6 weeks of non-weight-bearing cast immobilization. We instructed the patient to perform quad muscle training at the same time as casting. Six weeks later, follow-up computed tomography showed callus formation and disappearance of the fracture line. The patient thus began full weight bearing with daily use of arch support equipment, and we allowed her to gradually return to sports. We gradually increased her activity intensity from jogging to running. She completely and successfully returned to sports after 3 months of treatment.
Purpose: Foot strike patterns (FSP) influence landing mechanics, with rearfoot strike (RFS) runners exhibiting higher impact loading than forefoot strike (FFS) runners. The few studies that included midfoot strike (MFS) runners have typically grouped them together with FFS. In addition, most running studies have been conducted in laboratories. Advances in wearable technology now allow the measurement of runners' mechanics in their natural environment. The purpose of this study was to examine the relationship between FSP and impacts across a marathon race. Methods: A total of 222 healthy runners (119 males, 103 females; age, 44.1 ± 10.8 yr) running a marathon race were included. A treadmill assessment was undertaken to determine FSP. An ankle-mounted accelerometer recorded tibial shock (TS) over the course of the marathon. TS was compared between RFS, MFS, and FFS. Correlations between speed and impacts were examined between FSP. TS was also compared at the 10- and 40-km race points. Results: RFS and MFS runners exhibited similar TS (12.24g ± 3.59g vs 11.82g ± 2.68g, P = 0.46) that was significantly higher (P < 0.001 and P < 0.01, respectively) than FFS runners (9.88g ± 2.51g). In addition, TS increased with speed for both RFS (r = 0.54, P = 0.01) and MFS (r = 0.42, P = 0.02) runners, but not FFS (r = 0.05, P = 0.83). Finally, both speed (P < 0.001) and TS (P < 0.001) were reduced between the 10- and the 40-km race points. However, when normalized for speed, TS was not different (P = 0.84). Conclusions: RFS and MFS exhibit higher TS than FFS. In addition, RFS and MFS increase TS with speed, whereas FFS do not. These results suggest that the impact loading of MFS is more like RFS than FFS. Finally, TS, when normalized for speed, is similar between the beginning and the end of the race.