Isolated effects of footwear structure and cushioning on running mechanics in habitual mid/forefoot runners.

The true differences between barefoot and shod running are difficult to directly compare because of the concomitant change to a mid/forefoot footfall pattern that typically occurs during barefoot running. The purpose of this study was to compare isolated effects of footwear structure and cushioning on running mechanics in habitual mid/forefoot runners running shod (SHOD), barefoot (BF), and barefoot on a foam surface (BF+FOAM). Ten habitually shod mid/forefoot runners were recruited (male = 8, female = 2). Repeated measures ANOVA (α = 0.05) revealed differences between conditions for only vertical peak active force, contact time, negative and total ankle joint work, and peak dorsiflexion angle. Post hoc tests revealed that BF+FOAM resulted in smaller vertical active peak magnitude and instantaneous vertical loading rate than SHOD. SHOD resulted in lower total ankle joint work than BF and BF+FOAM. BF+FOAM resulted in lower negative ankle joint work than either BF or SHOD. Contact time was shorter with BF than BF+FOAM or SHOD. Peak dorsiflexion angle was smaller in SHOD than BF. No other differences in sagittal joint kinematics, kinetics, or ground reaction forces were observed. These overall similarities in running mechanics between SHOD and BF+FOAM question the effects of footwear structure on habituated mid/forefoot running described previously.

Effects of footwear cushioning on leg and longitudinal arch stiffness during running.

During running, humans increase leg stiffness on more compliant surfaces through an in-series spring relationship to maintain constant support mechanics. Following this notion, the compliant midsole material of standard footwear may cause individuals to increase leg stiffness while running, especially in footwear with very thick midsoles. Recently, researchers have also proposed that footwear stiffness can affect the stiffness of the foot's longitudinal arch (LA) via a similar mechanism. To test these ideas, we used 3D motion capture to record 20 participants running on a forceplate-instrumented treadmill while barefoot, and while wearing three types of sandals composed of materials ranging an order of magnitude in Young's modulus: ethylene vinyl acetate (EVA), and two varieties of polyurethane rubber (R30 and R60). We calculated leg stiffness using standard methods, and measured LA stiffness based on medial midfoot kinematics. While there was an overall significant effect of footwear on leg stiffness (P = 0.047), post-hoc tests revealed no significant differences among individual pairs of conditions, and there was no effect of footwear on LA stiffness. However, participants exhibited significantly greater LA compression when barefoot than when running in EVA (P = 0.004) or R30 (P = 0.036) sandals. These results indicate that standard footwear midsole materials are too stiff to appreciably affect leg stiffness during running, meaning that increasing midsole thickness is unlikely to cause individuals to alter their leg stiffness. However, use of footwear does cause individuals to restrict LA compression when compared to running barefoot, and further research is needed to understand why.

Barefoot Running: Between Fashion and Real Way to Prevent Joint Osteo Lesions?

BACKGROUND AND OBJECTIVES: Running has gone from a vital necessity for the man to a playful sport. Different rheumatic and orthopedic pathologies have appeared, in front of which the shoe industry has reacted by creating reinforced shoes that are supposed to overcome the induced lesions. Several years later, the trend toward reinforcement has gone toward minimalism, which is the absence of reinforcement, that is, a more natural race. METHOD: We observed variations of kinetics and kinematics in young, unprofessional, healthy runners during a shoe race and a shoeless race, which is the form of maximum minimalism. We then correlated minimalism variations with the variables of the race and the joint angles. RESULTS: We observed significant difference (P < 0.01) in the cycle rate, the cycle length, the step rate, and the angle of attack between running with and without shoes. A small variation of the minimalism index is associated with an increase in knee angle (r 2> 0.5). Conversely, a large variation in the minimalism index is related to a decrease in the knee angle (r 2> 0.5). The minimalism index has no impact on the angulation of the ankle and hip (r 2< 0.3). CONCLUSION: Slow transition will bring gains in terms of decreasing the length of the stride, which limits the load on the shin. Greater flexibility can be achieved by decreasing the flexion angle of the knee, which decreases the demand for quadriceps muscles and the risk of knee injury with a greater risk of injury at the tibial level.

Will the Foot Strike Pattern Change at Different Running Speeds with or without Wearing Shoes?

Runners strike their feet with three different patterns during running: forefoot, midfoot, and rearfoot. This study aimed to investigate whether runners maintain consistent patterns while running speed and foot condition change. The foot strike patterns of runners when running on a treadmill at paces ranging from slow to fast were recorded from twenty healthy male regular runners, with and without shoes, in random order. A high-speed camera was used to observe the strike patterns, which were then categorized by an experienced physical therapist. Linear-log and Pearson chi-square analysis with a significance level of α = 0.05 was performed to examine the correlation between foot strike pattern, running speed, and shoe conditions. The results suggest that runners strike with different patterns when running with and without shoes (χ2 = 99.07, p < 0.01); runners preferred to adopt heel strike regardless of running speeds when running with shoes. While running barefoot, only 23.8% of landing strikes were rearfoot, and the strike pattern distribution did not change significantly with the running speed (χ2 = 2.26, p = 0.89). In summary, the foot strike preference of runners is correlated with the foot condition (barefoot or shod) rather than running speed. For runners who intend to change their strike patterns for any reason, we recommend that they consider adjusting their footwear, which may naturally help with the foot strike adjustment. Future studies should attempt to use advanced techniques to observe further foot biomechanics in order to discover if changing strike pattern is directly correlated with lower limb injuries.

Review of Terms and Definitions Used in Descriptions of Running Shoes.

OBJECTIVE: Our study aim is to identify and describe the definitions used for different types of running shoes. In addition, we highlight the existence of gaps in these concepts and propose possible new approaches. Methods: This review was undertaken in line with the guidelines proposed by Green et al., based on a literature search (until December 2019) of the PubMed, Web of Science, Scopus, SPORTDiscus and Google Scholar databases. A total of 23 papers met the inclusion criteria applied to identify the definition of running shoes. RESULTS: Although there is a certain consensus on the characteristics of minimalist footwear, it is also described by other terms, such as barefoot-style or barefoot-simulating. Diverse terms are also used to describe other types of footwear, and in these cases, there is little or no consensus regarding their characteristics. CONCLUSIONS: The terms barefoot-simulated footwear, barefoot-style footwear, lightweight shoes and full minimalist shoes are all used to describe minimalist footwear. The expressions partial minimalist, uncushioned minimalist and transition shoes are used to describe footwear with non-consensual characteristics. Finally, labels such as shod shoes, standard cushioned running shoes, modern shoes, neutral protective running shoes, conventional, standardised, stability style or motion control shoes span a large group of footwear styles presenting different properties.

Measurement of intrinsic foot stiffness in minimally and traditionally shod runners using ultrasound elastography: A pilot study.

Running is an activity with a consistently high injury rate. Running footwear design that mimics barefoot running has been proposed to reduce injury rate by increasing the strength of foot structures. However, there is little evidence to support this. The purpose of the current study is to use shear wave ultrasound elastography to examine material properties (shear modulus) of intrinsic foot structures in experienced minimally and traditionally shod runners. It is hypothesized that minimalist runners will exhibit increased stiffness compared to controls demonstrating the strengthening of these structures. Eighteen healthy runners (8 minimalist and 10 traditionalist), running a minimum of 10 mi · wk-1, participated. Elastography scans were performed on the left foot of each participant. There is no apparent stiffening of foot structures associated with wearing minimalist shoes. Only the FHB tendon is different between shoe types and, contrary to the hypothesis, was stiffer in traditionalist compared to minimalist runners (257.26 ± 51.64 kPa vs 160.88 ± 27.79 kPa, respectively). A moderate positive (r = 0.7) relationship between training load and tendon stiffness suggests strengthening of tendon when running in traditional shoes. If running in minimalist shoes increases loading on these structures without resulting in stronger tissues, it is possible that minimalist footwear may increase injury risk.

Plantar support adaptations in healthy subjects after eight weeks of barefoot running training.

BACKGROUND: Although the studies of barefoot running have intensified, it is still missing longitudinal work analyzing the effects of barefoot running on the phases of plantar support. The objective of this research was to analyze the modifications undergone by the Total Foot Contact (TFC) phase and its Flat Foot Phase (FFP) in subjects beginning the practice of barefoot running, in its acute and chronic effects. METHODS: A total of 28 subjects were divided into the Barefoot Group (BFGr) (n = 16) and the Shod Group (SHGr) (n = 12), evaluated before (Baseline) and after running for 20 min at 3.05 m·s-1 (Post 20 min Running), and at the end of a running training protocol with an 8-week long progressive volume (Post-8-week Training). The dynamic plantar support was measured with a baropodoscope. The duration of TFC (ms), the moment at which the FFP occurred, the maximum surface of TFC (MSTFC) (cm2), the FFP surface (SFFP) (cm2), the peak pressure of TFC (PP°TFC) (kg·cm-2), and the peak pressure of FFP (PP°FFP) (kg·cm-2) were recorded. The 3 × 2 ANOVA analysis was made to determine the effects and interactions that the condition produced (Shod/Barefoot), and the time factor (Baseline/Post 20 min Running/Post-8-week Training). RESULTS: The condition factor caused more significant effects than the time factor in all the variables. Duration of TFC in BFGr showed significant differences between the Baseline and Post-8-week Training (p = 0.000) and between Post-20-min Running and Post-8-week Training (p = 0.000), with an increasing trend. In the moment at which the FFP occurred a significant increase (p = 0.029) increase was found in Post-20 min Running (48.5%) compared to the Baseline (42.9%). In MSTFC, BFGr showed in Post-8-week Training values significantly higher than the Baseline (p = 0.000) and than Post-20-min Running (p = 0.000). SHGr presented a significant difference between the Baseline and Post-8-week Training (p = 0.040). SFFP in BFGr modified its values with an increasing trend (p = 0.000). PP°TFC in BFGr showed a significant decrease (p = 0.003) in Post-8-week Training (1.9 kg·cm-2) compared to the Baseline (2.4 kg·cm-2). In PP°FFP significant decreases were recorded in BFGr and between Post-8-week Training and Baseline (p = 0.000), and Post-8-week Training and Post 20 min Running (p = 0.035). CONCLUSIONS: The adaptation took place after the 8-week training. The adaptations to running barefoot were characterized by causing an increase of the foot's plantar support in TFC and in FFP, as well as a decrease of the plantar pressure peak in both phases. Also, there is an increased duration of the TFC and FFP, which may be related to an acquired strategy to attenuate the impacts of the ground's reaction forces.

Adaptation of Running Biomechanics to Repeated Barefoot Running: A Randomized Controlled Study.

BACKGROUND: Previous studies have shown that changing acutely from shod to barefoot running induces several changes to running biomechanics, such as altered ankle kinematics, reduced ground-reaction forces, and reduced loading rates. However, uncertainty exists whether these effects still exist after a short period of barefoot running habituation. PURPOSE/HYPOTHESIS: The purpose was to investigate the effects of a habituation to barefoot versus shod running on running biomechanics. It was hypothesized that a habituation to barefoot running would induce different adaptations of running kinetics and kinematics as compared with a habituation to cushioned footwear running or no habituation. STUDY DESIGN: Controlled laboratory study. METHODS: Young, physically active adults without experience in barefoot running were randomly allocated to a barefoot habituation group, a cushioned footwear group, or a passive control group. The 8-week intervention in the barefoot and footwear groups consisted of 15 minutes of treadmill running at 70% of VO2 max (maximal oxygen consumption) velocity per weekly session in the allocated footwear. Before and after the intervention period, a 3-dimensional biomechanical analysis for barefoot and shod running was conducted on an instrumented treadmill. The passive control group did not receive any intervention but was also tested prior to and after 8 weeks. Pre- to posttest changes in kinematics, kinetics, and spatiotemporal parameters were then analyzed with a mixed effects model. RESULTS: Of the 60 included participants (51.7% female; mean ± SD age, 25.4 ± 3.3 years; body mass index, 22.6 ± 2.1 kg·m-2), 53 completed the study (19 in the barefoot habituation group, 18 in the shod habituation group, and 16 in the passive control group). Acutely, running barefoot versus shod influenced foot strike index and ankle, foot, and knee angles at ground contact (P < .001), as well as vertical average loading rate (P = .003), peak force (P < .001), contact time (P < .001), flight time (P < .001), step length (P < .001), and cadence (P < .001). No differences were found for average force (P = .391). After the barefoot habituation period, participants exhibited more anterior foot placement (P = .006) when running barefoot, while no changes were observed in the footwear condition. Furthermore, barefoot habituation increased the vertical average loading rates in both conditions (barefoot, P = .01; shod, P = .003) and average vertical ground-reaction forces for shod running (P = .039). All other outcomes (ankle, foot, and knee angles at ground contact and flight time, contact time, cadence, and peak forces) did not change significantly after the 8-week habituation. CONCLUSION: Changing acutely from shod to barefoot running in a habitually shod population increased the foot strike index and reduced ground-reaction force and loading rates. After the habituation to barefoot running, the foot strike index was further increased, while the force and average loading rates also increased as compared with the acute barefoot running situation. The increased average loading rate is contradictory to other studies on acute adaptations of barefoot running. CLINICAL RELEVANCE: A habituation to barefoot running led to increased vertical average loading rates. This finding was unexpected and questions the generalizability of acute adaptations to long-term barefoot running. Sports medicine professionals should consider these adaptations in their recommendations regarding barefoot running as a possible measure for running injury prevention. REGISTRATION: DRKS00011073 (German Clinical Trial Register).

Running ground reaction forces across footwear conditions are predicted from the motion of two body mass components.

Although running shoes alter foot-ground reaction forces, particularly during impact, how they do so is incompletely understood. Here, we hypothesized that footwear effects on running ground reaction force-time patterns can be accurately predicted from the motion of two components of the body's mass (mb): the contacting lower-limb (m1 = 0.08mb) and the remainder (m2 = 0.92mb). Simultaneous motion and vertical ground reaction force-time data were acquired at 1,000 Hz from eight uninstructed subjects running on a force-instrumented treadmill at 4.0 and 7.0 m/s under four footwear conditions: barefoot, minimal sole, thin sole, and thick sole. Vertical ground reaction force-time patterns were generated from the two-mass model using body mass and footfall-specific measures of contact time, aerial time, and lower-limb impact deceleration. Model force-time patterns generated using the empirical inputs acquired for each footfall matched the measured patterns closely across the four footwear conditions at both protocol speeds (r2 = 0.96 ± 0.004; root mean squared error = 0.17 ± 0.01 body-weight units; n = 275 total footfalls). Foot landing angles (θF) were inversely related to footwear thickness; more positive or plantar-flexed landing angles coincided with longer-impact durations and force-time patterns lacking distinct rising-edge force peaks. Our results support three conclusions: 1) running ground reaction force-time patterns across footwear conditions can be accurately predicted using our two-mass, two-impulse model, 2) impact forces, regardless of foot strike mechanics, can be accurately quantified from lower-limb motion and a fixed anatomical mass (0.08mb), and 3) runners maintain similar loading rates (ΔFvertical/Δtime) across footwear conditions by altering foot strike angle to regulate the duration of impact. NEW & NOTEWORTHY Here, we validate a two-mass, two-impulse model of running vertical ground reaction forces across four footwear thickness conditions (barefoot, minimal, thin, thick). Our model allows the impact portion of the impulse to be extracted from measured total ground reaction force-time patterns using motion data from the ankle. The gait adjustments observed across footwear conditions revealed that runners maintained similar loading rates across footwear conditions by altering foot strike angles to regulate the duration of impact.

Do Strike Patterns or Shoe Conditions have a Predominant Influence on Foot Loading?

This study aimed to explore the effects of strike patterns and shoe conditions on foot loading during running. Twelve male runners were required to run under shoe (SR) and barefoot conditions (BR) with forefoot (FFS) and rearfoot strike patterns (RFS). Kistler force plates and the Medilogic insole plantar pressure system were used to collect kinetic data. SR with RFS significantly reduced the maximum loading rate, whereas SR with FFS significantly increased the maximum push-off force compared to BR. Plantar pressure variables were more influenced by the strike patterns (15 out of 18 variables) than shoe conditions (7 out of 18 variables). The peak pressure of midfoot and heel regions was significantly increased in RFS, but appeared in a later time compared to FFS. The influence of strike patterns on running, particularly on plantar pressure characteristics, was more significant than that of shoe conditions. Heel-toe running caused a significant impact force on the heel, whereas wearing cushioned shoes significantly reduced the maximum loading rate. FFS running can prevent the impact caused by RFS. However, peak plantar pressure was centered at the forefoot for a long period, thereby inducing a potential risk of injury in the metatarsus/phalanx.

Kinematic characteristics of barefoot sprinting in habitually shod children.

BACKGROUND: Anecdotally, a wide variety of benefits of barefoot running have been advocated by numerous individuals. The influence of the alterations in the properties of the shoe on the running movement has been demonstrated in adults at submaximal jogging speeds. However, the biomechanical differences between shod and barefoot running in children at sprinting speeds and the potential developmental implications of these differences are still less examined. The purpose was to determine the potential differences in habitually shod children's sprint kinematics between shod and barefoot conditions. METHODS: Ninety-four children (51 boys and 43 girls; 6-12 years-old; height, 135.0 ± 0.12 m; body mass, 29.0 ± 6.9 kg) performed 30 m maximal sprints from standing position for each of two conditions (shod and barefoot). To analyze sprint kinematics within sagittal plane sprint kinematics, a high-speed camera (300 fps) was set perpendicular to the runway. In addition, sagittal foot landing and take-off images were recorded for multiple angles by using five high-speed cameras (300 fps). Spatio-temporal variables, the kinematics of the right leg (support leg) and the left leg (recovery leg), and foot strike patterns: rear-foot strike (RFS), mid-foot strike (MFS), and fore-foot strike (FFS) were investigated. The paired t-test was used to test difference between shod and barefoot condition. RESULTS: Barefoot sprinting in habitually shod children was mainly characterized by significantly lower sprint speed, higher step frequency, shorter step length and stance time. In shod running, 82% of children showed RFS, whereas it decreased to 29% in barefoot condition. The touch down state and the subsequent joint movements of both support and recovery legs during stance phase were significantly altered when running in condition with barefoot. DISCUSSION: The acute effects of barefoot sprinting was demonstrated by significantly slower sprinting speeds that appear to reflect changes in a variety of spatiotemporal parameters as well as lower limb kinematics. It is currently unknown whether such differences would be observed in children who typically run in bare feet and what developmental benefits and risks may emerge from increasing the proportion of barefoot running and sprinting in children. Future research should therefore investigate potential benefits that barefoot sprinting may have on the development of key physical fitness such as nerve conduction velocity, muscular speed, power, and sprinting technique and on ways to minimize the risk of any acute or chronic injuries associated with this activity.

Foot internal stress distribution during impact in barefoot running as function of the strike pattern.

The aim of the present study is to examine the impact absorption mechanism of the foot for different strike patterns (rearfoot, midfoot and forefoot) using a continuum mechanics approach. A three-dimensional finite element model of the foot was employed to estimate the stress distribution in the foot at the moment of impact during barefoot running. The effects of stress attenuating factors such as the landing angle and the surface stiffness were also analyzed. We characterized rear and forefoot plantar sole behavior in an experimental test, which allowed for refined modeling of plantar pressures for the different strike patterns. Modeling results on the internal stress distributions allow predictions of the susceptibility to injury for particular anatomical structures in the foot.

The Influence of Running Shoes and Foot-Strike Patterns on Running Injuries / 医用生物力学

Long distance running is a popular sport with a high risk of getting musculoskeletal injuries, which is closely related to running shoes and foot-strike patterns. Biomechanical researches on relationship of running shoes and foot-strike patterns with running injuries were searched on the chain cloud library and Google academic database, and a total of 42 papers published from 1981 to 2016 were reviewed. There is not enough evidence to prove that running shoes have an effective cushioning and motor controlling function as what they claim, while barefoot running as a kind of more natural running pattern should be encouraged. Generally speaking, the forefoot strike has a lower injury risk on the knee, but increases the load on ankle and metatarsal bones. On the contrary, the rear foot strike always has a higher injury risk on the knee while a lower load on ankle and metatarsal bones. Therefore, runners should choose a suitable running method depending on their own conditions. The influence of running method transformation on biomechanical characteristics of lower limbs is not clear, and researches in such area may give more effective suggestions for runners to change their running methods.

The Influence of Footwear on the Modular Organization of Running.

For most of our history, we predominantly ran barefoot or in minimalist shoes. The advent of modern footwear, however, might have introduced alterations in the motor control of running. The present study investigated shod and barefoot running under the perspective of the modular organization of muscle activation, in order to help addressing the neurophysiological factors underlying human locomotion. On a treadmill, 20 young and healthy inexperienced barefoot runners ran shod and barefoot at preferred speed (2.8 ± 0.4 m/s). Fundamental synergies, containing the time-dependent activation coefficients (motor primitives) and the time-invariant muscle weightings (motor modules), were extracted from 24 ipsilateral electromyographic activities using non-negative matrix factorization. In shod running, the average foot strike pattern was a rearfoot strike, while in barefoot running it was a mid-forefoot strike. In both conditions, five fundamental synergies were enough to describe as many gait cycle phases: weight acceptance, propulsion, arm swing, early swing and late swing. We found the motor primitives to be generally shifted earlier in time during the stance-related phases and later in the swing-related ones in barefoot running. The motor primitive describing the propulsion phase was significantly of shorter duration (peculiarity confirmed by the analysis of the spinal motor output). The arm swing primitive, instead, was significantly wider in the barefoot condition. The motor modules demonstrated analogous organization with some significant differences in the propulsion, arm swing and late swing synergies. Other than to the trivial absence of shoes, the differences might be deputed to the lower ankle gear ratio (and the consequent increased system instability) and to the higher recoil capabilities of the longitudinal foot arch during barefoot compared to shod running.

Kinetic changes during a six-week minimal footwear and gait-retraining intervention in runners.

An evaluation of a six-week Combined minimal footwear transition and gait-retraining combination vs. gait retraining only on impact characteristics and leg stiffness. Twenty-four trained male runners were randomly assigned to either (1) Minimalist footwear transition Combined with gait-retraining over a six-week period ("Combined" group; n = 12) examined in both footwear, or (2) a gait-retraining group only with no minimalist footwear exposure ("Control"; n = 12). Participants were assessed for loading rate, impact peak, vertical, knee and ankle stiffness, and foot-strike using 3D and kinetic analysis. Loading rate was significantly higher in the Combined group in minimal shoes in pre-tests compared to a Control (P ≤ 0.001), reduced significantly in the Combined group over time (P ≤ 0.001), and was not different to the Control group in post-tests (P = 0.16). The impact peak (P = 0.056) and ankle stiffness reduced in both groups (P = 0.006). Loading rate and vertical stiffness was higher in minimalist footwear than conventional running shoes both pre (P ≤ 0.001) and post (P = 0.046) the intervention. There has a higher tendency to non-rearfoot strike in both interventions, but more acute changes in the minimalist footwear. A Combined intervention can potentially reduce impact variables. However, higher loading rate initially in minimalist footwear may increase the risk of injury in this condition.

Shoes alter the spring-like function of the human foot during running.

The capacity to store and return energy in legs and feet that behave like springs is crucial to human running economy. Recent comparisons of shod and barefoot running have led to suggestions that modern running shoes may actually impede leg and foot-spring function by reducing the contributions from the leg and foot musculature. Here we examined the effect of running shoes on foot longitudinal arch (LA) motion and activation of the intrinsic foot muscles. Participants ran on a force-instrumented treadmill with and without running shoes. We recorded foot kinematics and muscle activation of the intrinsic foot muscles using intramuscular electromyography. In contrast to previous assertions, we observed an increase in both the peak (flexor digitorum brevis +60%) and total stance muscle activation (flexor digitorum brevis +70% and abductor hallucis +53%) of the intrinsic foot muscles when running with shoes. Increased intrinsic muscle activation corresponded with a reduction in LA compression (-25%). We confirm that running shoes do indeed influence the mechanical function of the foot. However, our findings suggest that these mechanical adjustments are likely to have occurred as a result of increased neuromuscular output, rather than impaired control as previously speculated. We propose a theoretical model for foot-shoe interaction to explain these novel findings.

An Exploratory Study Investigating the Effects of Barefoot Running on Working Memory.

The aim of the present study was to compare the potential cognitive benefits of running barefoot compared to shod. Young adults (N = 72, M age = 24.4 years, SD = 5.5) ran both barefoot and shod on a running track while stepping on targets (poker chips) and when not stepping on targets. The main finding was that participants performed better on a working memory test when running barefoot compared to shod, but only when they had to step on targets. These results supported the idea that additional attention is needed when running barefoot to avoid stepping on objects that could potentially injure the foot. Significant increases in participant's heart rate were also found in the barefoot condition. No significant differences were found in participants' speed across conditions. These findings suggested that working memory may be enhanced after at least 16 minutes of barefoot running if the individual has to focus attention on the ground.

Individual Responses to a Barefoot Running Program: Insight Into Risk of Injury.

BACKGROUND: Barefoot running is of popular interest because of its alleged benefits for runners, including reduced injury risk and increased economy of running. There is a dearth in understanding whether all runners can gain the proposed benefits of barefoot running and how barefoot running may affect long-term injury risk. PURPOSE/HYPOTHESIS: The purpose of this study was to determine whether runners can achieve the proposed favorable kinematic changes and reduction in loading rate after a progressive training program that included barefoot running. It was hypothesized that not all individuals would experience a decrease in initial loading rate facilitated by increased ankle plantar flexion after a progressive barefoot running program; it was further hypothesized that relationships exist between changes in initial loading rate and sagittal ankle angle. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 26 habitually shod runners completed an 8-week, progressively introduced barefoot running program. Pre- and postintervention barefoot and shod kinematics, electromyography, and ground-reaction force data of the lower limb were collected. Ankle and knee kinematics and kinetics, initial loading rates, spatiotemporal variables, muscle activity during preactivation, and ground contact were assessed in both conditions before and after the intervention. Individual responses were analyzed by separating runners into nonresponders, negative responders, and positive responders based on no change, increase, and decrease in barefoot initial loading rate, respectively. RESULTS: No biomechanical changes were found in the group after the intervention. However, condition differences did persist during both preactivation and ground contact. The positive-responder group had greater plantar flexion, increased biceps femoris and gluteus medius preactivation, and decreased rectus femoris muscle activity between testing periods. The negative responders landed in greater barefoot dorsiflexion after the intervention, and the nonresponders did not change. An overall change in ankle flexion angle was associated with a change in initial loading rate (r(2) = 0.345, P = .002) in the barefoot but not shod condition. CONCLUSION: Eight weeks of progressive barefoot running did not change overall group biomechanics, but subgroups of responders (25% of the entire group) were identified who had specific changes that reduced the initial loading rate. It appears that changes in initial loading rate are explained by changes in ankle flexion angle at initial ground contact. CLINICAL RELEVANCE: Uninstructed barefoot running training does not reduce initial loading rate in all runners transitioning from shod to barefoot conditions. Some factors have been identified that may assist sports medicine professionals in the evaluation and management of runners at risk of injury. Conscious instruction to runners may be required for them to acquire habitual barefoot running characteristics and to reduce risk of injury.

Lower Extremity Biomechanics and Self-Reported Foot-Strike Patterns Among Runners in Traditional and Minimalist Shoes.

CONTEXT: The injury incidence rate among runners is approximately 50%. Some individuals have advocated using an anterior-foot-strike pattern to reduce ground reaction forces and injury rates that they attribute to a rear-foot-strike pattern. The proportion of minimalist shoe wearers who adopt an anterior-foot-strike pattern remains unclear. OBJECTIVE: To evaluate the accuracy of self-reported foot-strike patterns, compare negative ankle- and knee-joint angular work among runners using different foot-strike patterns and wearing traditional or minimalist shoes, and describe average vertical-loading rates. DESIGN: Descriptive laboratory study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 60 healthy volunteers (37 men, 23 women; age = 34.9 ± 8.9 years, height = 1.74 ± 0.08 m, mass = 70.9 ± 13.4 kg) with more than 6 months of experience wearing traditional or minimalist shoes were instructed to classify their foot-strike patterns. INTERVENTION(S): Participants ran in their preferred shoes on an instrumented treadmill with 3-dimensional motion capture. MAIN OUTCOME MEASURE(S): Self-reported foot-strike patterns were compared with 2-dimensional video assessments. Runners were classified into 3 groups based on video assessment: traditional-shoe rear-foot strikers (TSR; n = 22), minimalist-shoe anterior-foot strikers (MSA; n = 21), and minimalist-shoe rear-foot strikers (MSR; n = 17). Ankle and knee negative angular work and average vertical-loading rates during stance phase were compared among groups. RESULTS: Only 41 (68.3%) runners reported foot-strike patterns that agreed with the video assessment (κ = 0.42, P < .001). The TSR runners demonstrated greater ankle-dorsiflexion and knee-extension negative work than MSA and MSR runners (P < .05). The MSA (P < .001) and MSR (P = .01) runners demonstrated greater ankle plantar-flexion negative work than TSR runners. The MSR runners demonstrated a greater average vertical-loading rate than MSA and TSR runners (P < .001). CONCLUSIONS: Runners often cannot report their foot-strike patterns accurately and may not automatically adopt an anterior-foot-strike pattern after transitioning to minimalist running shoes.

Eight weeks gait retraining in minimalist footwear has no effect on running economy.

PURPOSE: To evaluate the effects of an eight week combined minimalist footwear (MFW) and gait-retraining intervention on running economy (RE) and kinematics in conventional footwear runners. METHODS: Twenty-three trained male runners (age: 43 ± 10 years, stature: 177.2 ± 9.2 cm, body mass: 72.8 ± 10.2 kg, V̇O2max: 56.5 ± 7.0 mL min(-1) kg(-1)) were recruited. Participants were assigned to either an intervention group (n = 13) who gradually increased exposure to MFW and also implemented gait-retraining over an eight week period. RE and kinematics were measured in both MFW and conventional running shoes (CRS) at pre-tests and eight weeks, in a random order. In contrast the control group (n = 10) had no MFW exposure or gait retraining and were only tested in CRS. RESULTS: The MFW and gait re-training intervention had no effect on RE (p < .001). However, RE was significantly better in MFW (mean difference 2.72%; p = .002) at both pre and post-tests compared to CRS. Step frequency increased as a result of the intervention (+5.7 steps per minute [spm]; p < .001), and was also significantly higher in MFW vs. CRS (+7.5 spm; p < .001). CONCLUSION: Whilst a better RE in MFW was observed when compared to CRS due to shoe mass, familiarization to MFW with gait-retraining was not found to influence RE.