Minimalist Shoes Research Articles

Minimalist Shoes Walking for Children

Minimalist Shoes Walking for Children

Effect of mechanically aged minimalist and traditional footwear on female running biomechanics

The purpose of this study was to improve the understanding of human–material interactions by combining polymer engineering and biomechanical approaches. The forefoot and heel of traditional shoes and minimalist running shoes were degraded using a mechanical aging protocol to quantify (1) the effect of subject-specific degradation and (2) human biomechanical effects due to decreased material properties. Four recreational-level female participants ran in the shoes pre-mechanical aging to determine the aging protocol input parameters and post-mechanical aging to evaluate the effect of degradation on kinematics and kinetics. Initial biomechanics translated into different mechanical aging input parameters among conditions: 500 greater number of impact cycles for minimalist shoe, 430 N higher peak force for forefoot, 75 kPa greater peak stress for the heel, 3.1 and 13.7 kN/s greater loading rates for minimalist shoe and the heel, and recovery time 220 ms greater for the heel. From mechanical aging, the shoe types and regions lost 1.2–1.8 mm thickness and 38%–54% energy absorption overall, while drop decreased 0.6 mm for traditional shoe only. Samples degraded at different rates depending on runner-specific input parameters. Human kinematics and kinetics were affected by both shoe type and aging. Aging of the shoes decreased knee flexion velocity (1°/s; p = 0.01), decreased ankle dorsiflexion during stance (3°, p = 0.01), and increased the vertical loading rate (4 BW/s, p = 0.01). The results support previous findings that different footwear influence running biomechanics and concurrently advance footwear science to show running biomechanics are also influenced by shoe degradation rates, such that unique and intuitive human–material interactions are apparent.

Lower extremity stiffness when running in minimalist, traditional, and ultra-cushioning shoes

Differences in running mechanics between minimalist (MIN) and traditional (TRAD) running shoes have been the subject of much research in the last decade. More recently, ultra-cushioning (ULTRA) shoes featuring oversized midsoles have emerged and are growing in popularity. However, relatively little is known regarding how ULTRA shoes effect running mechanics. Therefore, the purpose of this study was to compare foot strike, leg stiffness, joint stiffness, and negative joint work when running in MIN, TRAD, and ULTRA shoes. Fifteen recreational runners ran on an instrumented treadmill in each shoe while their whole body kinematics were recorded using a 12-camera motion capture system. Foot strike pattern was quantified using the strike index (SI) and foot strike angle (FSA). Leg stiffness was calculated using a spring-mass model. Joint stiffness was calculated as change in joint moment relative to change in joint angle during the absorption period. Negative joint work was calculated by integrating the negative portion of the joint power curve. Differences between shoes were evaluated using a one-way repeated measures ANOVA. Results showed there were no differences between MIN and TRAD shoes for any of the dependent variables. In the ULTRA shoe, participants used a more pronounced rearfoot strike pattern. There were no differences in leg stiffness between shoes. Compared to the MIN and TRAD shoes, in the ULTRA shoes the ankle was stiffer and performed less negative work while the knee and hip were less stiff and performed more negative work. These findings suggest a reorganization of the neuromuscular control of the limb when running in ULTRA compared to MIN or TRAD shoes. This reorganization may have implications for running performance or injury prevention.

Comparison of in-shoe plantar loading forces between minimalist and maximalist cushion running shoes

While several published studies have evaluated the biomechanical responses to minimalist (MIN) footwear, little has been reported on maximalist (MAX) shoes. The purpose of this study was to compare in-shoe plantar loading parameters between MIN and MAX running footwear. Researchers recruited 15 recreational runners who ran in a minimalist (New Balance Minimus Hi-Rez) and maximalist (Hoka One One) footwear conditions. Data were collected through PEDAR® insoles. A paired t-test was conducted comparing plantar loading variables during stance: contact time (CT), maximum mean pressure (MMP), peak pressure (PP), pressure time integral (PTI) and force time integral (FTI) with further evaluation of the total foot, forefoot, midfoot and rearfoot. Statistically significant decreases were seen in all plantar loading variables under the total foot and forefoot in the maximalist shoe when compared to the minimalist shoe (p < .003). On average, the following decreases were seen in the maximalist shoe in the total foot when compared to the minimalist shoe: MPP 11.6%, PP 30.6%, PTI 29.8%. Larger differences were seen in the forefoot and less so in the rearfoot when the plantar surface was evaluated in thirds. The findings suggest that maximalist cushion footwear decreases plantar loading under the total foot and forefoot during running. Maximalist shoes may be considered when the aim is to reduce forces and pressures under the foot during running activities.

Walking in Minimalist Shoes Is Effective for Strengthening Foot Muscles.

Weakness of foot muscles may contribute to a variety of loading-related injuries. Supportive footwear may contribute to intrinsic foot muscle weakness by reducing the muscles' role in locomotion (e.g., absorbing forces and controlling motion). Increased stimulus to the foot muscles can be provided through a variety of mechanisms, including minimalist footwear and directed exercise. To determine the effect of walking in minimalist footwear or performing foot strengthening exercises on foot muscle size and strength. Fifty-seven runners were randomly assigned to one of three groups-minimalist shoe walking (MSW), foot strengthening (FS) exercise, or control (C). All groups maintained their prestudy running mileage throughout the study. The MSW group walked in provided footwear, increasing weekly the number of steps per day taken in the shoes. The FS group performed a set of progressive resistance exercises at least 5 d·wk. Foot muscle strength (via custom dynamometers) and size (via ultrasound) were measured at the beginning (week 0), middle (week 4), and end (week 8) of the study. Mixed model ANOVA were run to determine if the interventions had differing effects on the groups. There were significant group-time interactions for all muscle size and strength measurements. All muscle sizes and strength increased significantly from weeks 0 to 8 in the FS and MSW groups, whereas there were no changes in the C group. Some muscles increased in size by week 4 in the FS and MSW groups. Minimalist shoe walking is as effective as foot strengthening exercises in increasing foot muscle size and strength. The convenience of changing footwear rather than performing specific exercises may result in greater compliance.

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Prediction of ground reaction forces in level and incline/decline walking from a multistage analysis of plantar pressure data

Knowing the ground reaction forces (GRFs) during walking has various biomechanical applications in injury prevention, gait analysis, as well as prosthetic and footwear design. The current study presents a method for predicting the GRFs in level and incline/decline walking that may be used in various outdoor biomechanics studies geared towards the above applications. The method was developed to predict the complete set of GRFs at walking inclinations of 0°, ±5°, ±10°, ±15°, and ±20°. Plantar pressure insoles were used to obtain inclination-specific, linear regression models based on three periods of gait stance phase, and the model-determined GRFs were compared with those measured from a forceplate. The three periods were determined based on the observed shifting of load-bearing insole sensors from heel to forefoot during walking, i.e., heel-strike, midstance, and toe-off. Six subjects wearing minimalist shoes fitted with plantar pressure insoles containing 99 pressure sensors performed ten walking trials at each of the aforementioned inclinations on an adjustable ramp with an embedded forceplate. Data from contact of the instrumented shoes with the forceplate were used to create linear regressions to transform insole pressure data into a complete set of GRFs. The root mean square error (RMSE) over peak recorded values were on average 10%, 3%, 21% for level walking and 11%, 4%, 23% for ramp walking in the respective anteroposterior, vertical, and mediolateral directions. The multistage linear regression model developed in the current study may be an acceptable option for estimating GRFs during walking in various environments without the restraint of a forceplate.

Longer-term effects of minimalist shoes on running performance, strength and bone density: A 20-week follow-up study

This study investigated whether male runners improve running performance, running economy, ankle plantar flexor strength, and alter running biomechanics and lower limb bone mineral density when gradually transitioning to using minimalist shoes for 100% of weekly running. The study was a planned follow-up of runners (n = 50) who transitioned to minimalist or conventional shoes for 35% of weekly structured training in a previous 6-week randomised controlled trial. In that trial, running performance and economy improved more with minimalist shoes than conventional shoes. Runners in each group were instructed to continue running in their allocated shoe during their own preferred training programme for a further 20 weeks while increasing allocated shoe use to 100% of weekly training. At the 20-week follow-up, minimalist shoes did not affect performance (effect size: 0.19; p = 0.218), running economy (effect size: ≤ 0.24; p ≥ 0.388), stride rate or length (effect size: ≤ 0.12; p ≥ 0.550), foot strike (effect size: ≤ 0.25; p ≥ 0.366), or bone mineral density (effect size: ≤ 0.40; p ≥ 0.319). Minimalist shoes increased plantar flexor strength more than conventional shoes when runners trained with greater mean weekly training distances (shoe*distance interaction: p = 0.036). After greater improvements with minimalist shoes during the initial six weeks of a structured training programme, increasing minimalist shoe use from 35% to 100% over 20 weeks, when runners use their own preferred training programme, did not further improve performance, running economy or alter running biomechanics and lower limb bone mineral density. Minimalist shoes improved plantar flexor strength more than conventional shoes in runners with greater weekly training distances.

Minimalist shoes running intervention can alter the plantar loading distribution and deformation of hallux valgus: A pilot study

BackgroundHallux valgus (HV) is one common deformity of the human foot. Metatarsal pain, gait deviation and foot function disorder may occur when HV is severe.Research question: It was hypothesized that a 12-week minimalist shoes running intervention among mild and moderate hallux valgus males may alter foot morphology and plantar pressure distribution during walking and running. MethodsThe foot morphology and plantar pressure data, in this study, were collected from eleven participants using the Easy-Foot-Scan (EFS) and Novel EMED force plate. ResultsCompared to pre-intervention sessions, the hallux abductus angle and forefoot width decreased significantly with increased metatarsal waist girth in the post-intervention session. The peak pressure, maximum force and force time integral in the first metatarsal reduced significantly due to the distribution of plantar pressure to the central foot regions. SignificanceThe findings suggest that minimalist shoes may deform forefoot morphology and neutralize loading concentration for mild and moderate hallux valgus.

Midfoot Angle Changes During Running After an 8-week Foot Strengthening Program

Category: Other Introduction/Purpose: The arch has been referred to as the core of the foot. The arch’s structure, movement, and integrity during running gait largely depends on the function of intrinsic and extrinsic foot muscles. There are many injuries that can be associated with a dysfunctional medial longitudinal arch. Improving the strength of the foot muscles could help improve arch function during running. The purpose of this study was to compare changes in arch deformation after eight weeks in a foot strengthening exercise group (FS), a group walking in minimalist shoes (MSW), and a control group (C). Methods: 24 healthy runners (average of 15-30 miles/week, no experience with minimalist footwear) were randomly assigned to FS (n=9), MSW (n=7) or C (n=8). FS subjects followed a series of progressive exercises designed to strengthen the intrinsic and extrinsic foot muscles. MSW subjects walked in minimal footwear, increasing from 2,500 to 7,000 steps/day over an 8 wk period. All runners maintained their pre-study mileage in conventional running shoes throughout the 8-week study Three-dimensional motion analysis data was collected at the beginning of the study and after week 8. Passive-reflective markers were placed according to the Oxford Foot Model. Subjects ran at a self-selected pace on a treadmill while data were collected for at least 10 strides. Peak midfoot angles were extracted and averaged within each trial. Group means at week 0 and week 8 were compared using paired t-tests with alpha set at 0.05. Results: While all groups experienced a decrease in midfoot angle, only the FS group experienced a significant change (see table). These results suggest that the foot exercise intervention resulted in more arch control during running than the progressive walking in minimal shoes. Greater changes may have been found if the subjects progressively ran in the minimal shoes which would have placed greater demands on the arch musculature. Conclusion: Based on these data, it seems possible for patients to reduce the amount of arch deformation during running by using targeted foot exercises. This could help with patients who have overuse injuries associated with increased arch deformation. These results also suggest that foot strengthening may be an effective way to prepare for minimal footwear running.

A Comparison of Foot Strengthening versus Minimal Footwear Use on Intrinsic Muscle Size and Strength

Category: Other Introduction/Purpose: The intrinsic muscles of the arch have been classified as the core of the foot. Intrinsic foot muscles (IFM) work as local stabilizers and extrinsic foot muscles (EFM) work as global movers to help control the pronation of the foot. These muscles prevent excessive strain of the MLA. Previous research has shown that strengthening IFM may reduce pain and improve function in people with plantar fasciitis. Additionally, habitual use of minimal shoes that lack support of the arch require greater demand on the intrinsic muscles. The purpose of this study was to determine the effectiveness of two different strengthening interventions on IFM and EFM size and strength. Methods: 57 healthy runners (avg 15-30 mpw) were randomly assigned to a foot strengthening (FS, n=19), a minimal shoe walking (MSW, n=19), or a control group (C, n=19). Baseline cross-sectional areas of abductor hallucis, quadratus plantae, flexor digitorum brevis, and flexor digitorum longus, and thickness of the flexor hallucis brevis, tibialis posterior, and tibialis anterior were obtained with ultrasound using a 10 MHz linear probe. Doming, great toe flexion and lateral toes flexion strength were also measured using a custom-built dynamometer. The FS group then underwent an 8 wk foot and ankle strengthening program. The MSW group progressively walked in minimal footwear from 2,500-7,000 over the course of 8 wks. All groups, including C, maintained normal running mileage in conventional footwear throughout the 8 wks. Size and strength measures were then repeated. A repeated measures ANCOVA with a post-hoc test was used to determine differences in size and strength between groups. Results: All muscles measured in the FS and MSW groups increased significantly in size from weeks 0-8. There were no changes in muscle size in the C group. The FS group experienced significantly greater size changes for the flexor hallucis brevis than the MSW group. All other changes in muscle size were not significant between the FS and MSW groups. The FS and MSW groups showed significant increases in strength in all 3 tests from week 0-8. Strength of the control group did not change at any time. The increases in strength in the FS and MSW groups were not significantly different than each other. Conclusion: Exercises that target the intrinsic and extrinsic foot muscles are effective in increased strength and size of the muscles. However, similar increases in strength and size can be obtained by progressive walking in minimal footwear. Combining both these approaches may have an even greater effect. Stronger feet may offer greater protection against overuse injuries such as plantar fasciitis.

Changes in the foot strike pattern and pressure distribution when running in minimalist and traditional sport shoes

Changes in the foot strike pattern and pressure distribution when running in minimalist and traditional sport shoes

Improving Running Economy by Transitioning to Minimalist Footwear: A Randomised Controlled Trial

ObjectivesOngoing debates about benefits and risks of barefoot- and minimally-shod running have, to date, revealed no conclusive findings for long-term effects on physical performance. The purpose of this study was to examine the effects of an 8-week transition to minimalist footwear (MFW) on running economy (RE). DesignRandomised controlled trial. MethodsThirty-two male, habitually-shod runners were assigned randomly to an 8-week training intervention either in minimalist (=intervention group) or conventional running shoes (=control group). The intervention consisted of a gradual increase in use of the new footwear by 5% of the individual weekly distance. Before and after the intervention, a VO2max test was followed by a submaximal RE test at 70% and 80% of vVO2max in both shoe conditions 7days later. RE was measured at the submaximal tests and expressed as caloric unit cost (kcalkg−1km−1) and oxygen consumption (mlkg−1km−1). ResultsRE improved in the intervention group over time compared to the control group with small to moderate effect sizes (ES) in both shoe conditions: Effects on RE (kcalkg−1km−1) in conventional running shoes: ES vVO270%: 0.68 (95% CI: −0.14 to 1.51), ES vVO280%: 0.78 (95% CI: 0–1.56). In minimalist footwear: ES vVO270%: 0.3 (95% CI: −0.54 to 1.14), ES vVO280%: 0.42 (95% CI: −0.41 to 1.25). These effects were not statistically significant (p>0.05). The repeated-measures ANOVA also showed no group by time interactions for all submaximal RE testing conditions (p>0.05). ConclusionsAlthough not reaching statistical significance, training in MFW compared to CRS resulted in small to moderate improvements in RE.

Immediate and short-term adaptations to maximalist and minimalist running shoes

Biomechanical response to running footwear has been studied with regard to traditional shoes and, more recently, minimalist (MIN) shoes. Maximalist (MAX) shoes have grown in popularity as a highly-cushioned counterpoint to MIN shoes. However, little is known about the influence of MAX shoes on running biomechanics alone or in comparison to a MIN shoe design. Because many features of the MIN and MAX shoe are similar (low heel-to-toe drop, minimal stability) with one distinguishing characteristic (cushioning), the primary purpose was to contrast immediate and short-term adaptations to these extreme footwear types. Thirty runners were randomly assigned either the MIN or MAX shoe and ran for four weeks in their assigned shoe. Spatiotemporal measures, vertical ground reaction forces (GRF), lower leg and foot accelerations, and foot strike angle were assessed in the runners’ native shoes and both experimental shoes prior to and following the four-week exposure period. Foot strike angle was significantly more plantarflexed and vertical GRF loading rates were significantly higher in both experimental shoes. Running in MIN shoe resulted in higher shank accelerations and lower heel accelerations. Changes from the native shoe were not uniform between the MIN and MAX shoe. No further adaptation was noted at four weeks for either shoe. However, over half the runners using the MIN shoe became injured. Runners appear to immediately respond to changes in heel-toe drop and level of cushioning when running in an unfamiliar shoe. Initial response does not appear to change over a four-week period of running in the unfamiliar shoe. Choosing a MAX shoe may be less risky than MIN shoes when shifting from traditional running footwear, particularly in the initial month of exposure.

Heel impact forces during barefoot versus minimally shod walking among Tarahumara subsistence farmers and urban Americans.

Despite substantial recent interest in walking barefoot and in minimal footwear, little is known about potential differences in walking biomechanics when unshod versus minimally shod. To test the hypothesis that heel impact forces are similar during barefoot and minimally shod walking, we analysed ground reaction forces recorded in both conditions with a pedography platform among indigenous subsistence farmers, the Tarahumara of Mexico, who habitually wear minimal sandals, as well as among urban Americans wearing commercially available minimal sandals. Among both the Tarahumara (n = 35) and Americans (n = 30), impact peaks generated in sandals had significantly (p < 0.05) higher force magnitudes, slower loading rates and larger vertical impulses than during barefoot walking. These kinetic differences were partly due to individuals' significantly greater effective mass when walking in sandals. Our results indicate that, in general, people tread more lightly when walking barefoot than in minimal footwear. Further research is needed to test if the variations in impact peaks generated by walking barefoot or in minimal shoes have consequences for musculoskeletal health.

Foot strength and stiffness are related to footwear use in a comparison of minimally- vs. conventionally-shod populations

The longitudinal arch (LA) helps stiffen the foot during walking, but many people in developed countries suffer from flat foot, a condition characterized by reduced LA stiffness that can impair gait. Studies have found this condition is rare in people who are habitually barefoot or wear minimal shoes compared to people who wear conventional modern shoes, but the basis for this difference remains unknown. Here we test the hypothesis that the use of shoes with features that restrict foot motion (e.g. arch supports, toe boxes) is associated with weaker foot muscles and reduced foot stiffness. We collected data from minimally-shod men from northwestern Mexico and men from urban/suburban areas in the United States who wear ‘conventional’ shoes. We measured dynamic LA stiffness during walking using kinematic and kinetic data, and the cross-sectional areas of three intrinsic foot muscles using ultrasound. Compared to conventionally-shod individuals, minimally-shod individuals had higher and stiffer LAs, and larger abductor hallucis and abductor digiti minimi muscles. Additionally, abductor hallucis size was positively associated with LA stiffness during walking. Our results suggest that use of conventional modern shoes is associated with weaker intrinsic foot muscles that may predispose individuals to reduced foot stiffness and potentially flat foot.

Does neuromuscular electrostimulation have the potential to increase intrinsic foot muscle strength?

PurposeThe purpose of this study was to investigate the effect of an eight-week neuromuscular electrostimulation program on the intrinsic foot muscle strength. The results were compared with those from a passive and an active control group. Methods74 healthy participants were recruited and divided into three groups: a neuromuscular electrostimulation group (n=19), a passive control group (n=15) with no further intervention, and an active control group following a running protocol with minimal shoes (n=40). The electrostimulation and running groups followed a training protocol consisting of two sessions per week over a period of eight weeks. Three characteristics of intrinsic foot muscle strength were investigated: cross sectional area of the abductor hallucis muscle, longitudinal arch stability, and intrinsic foot muscle fatigue. ResultsAfter eight weeks of intervention, the cross sectional area increased by 16.3% for the running group with a large effect size (0.801) according to Cohen’s d. The electrostimulation group showed no such effect. The increase in the cross sectional area had no impact on longitudinal arch stability or intrinsic foot muscle fatigue results. ConclusionThis study investigated neuromuscular electrostimulation as a prevention and rehabilitation strategy. The results indicate that, compared to minimally shod running, the effects of electrostimulation on healthy participants might be too small to be detected. Further, the results provide evidence that the static navicular drop test is not sensitive enough to indicate intrinsic foot muscle strength. This appears clinically relevant, as this test is often used by therapists to evaluate patients’ longitudinal arch function.

8-week training in partial minimalist shoe reduces impact force during running

PurposeExcessive external load is a likely cause of running injuries. Although minimal running has been suggested as a possible approach to reduce impact and injury risk, an abrupt transition from conventional shoes to minimal running is also related to injuries. Therefore, the partial minimalist shoe has been suggested as a training strategy for a safe transition to minimal running. The study investigated if 8 weeks of training in partial minimalist shoe could improve impact control of shod and barefoot running.MethodsRecreational runners (12 men, 2 women), inexperienced in minimal running, performed 3 training sessions/week in partial minimalist shoes for 8 weeks. Before and after the intervention, the participants ran on a treadmill at 2.5 m/s under two conditions: in their habitual shoes and barefoot. Vertical ground reaction force (VGRF) was recorded.ResultsAfter the intervention, reduced values of the first peak (16.7% for shod, 36.7% for barefoot), time to reach the first peak (7.7% for shod, 30.2% for barefoot), and the load rate of the first peak (9.8% for shod, 9.5% for barefoot) were observed for both conditions (&lt;i&gt;p&lt;/i&gt; &lt; 0.001). Six subjects dropped out from the intervention.ConclusionsPartial minimalist training improved VGRF variables related to shock attenuation. Thus, the 8-week running training program with partial minimalist shoes was an effective approach to increase impact control. The intervention reduced the impact force in both shod and barefoot running, arising as a feasible option to progressively transition to minimal running.

The relationship between immediate comfort and plantar foot sensitivity during running in cushioned versus minimal shoes

In addition to footwear characteristics, it has been hypothesised that plantar foot sensitivity influences the perception of footwear comfort during running. This study examined the relationship between plantar foot sensitivity to light tough, mechanical pain, vibration and pressure pain and footwear comfort rankings of cushioned and minimal shoes during running. Seventy-five participants (Females = 39, Age 35 (SD 8.9) years, BMI 23.7 (3.6) kg/m2), who identified as regular recreational runners, underwent a standardised protocol of quantitative sensory measures. They then ran on a pre-specific 900 m, outdoor track in each shoe. At the completion of both runs, participants were asked to rank the shoes in order of comfort. Participants were grouped based on their top comfort ranking. The 47 individuals who ranked the cushioned shoe as most comfortable were significantly more sensitive to mechanical pain at their heel (mean difference 109.2 mN, 95% confidence interval 9.6 to 208.7; p = 0.032) and lateral midfoot (87.7 mN, 13.2 to 162.2; p = 0.022). They were also significantly less sensitive to vibration at their medial forefoot (mean difference −2.33 s, 95% CI −4.43 to −0.23; p = 0.03) and lateral midfoot (−1.76 s, −3.51 to −0.2; p = 0.048). This study demonstrates that there is an association between plantar foot sensitivity profiles and immediate footwear comfort. This may have implications when advising individuals who prefer cushioned shoes to run in minimal shoes. It may expose them to potentially painful stimuli with detrimental effects on soft tissue.

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.