Carina Price

The effect of unstable sandals on instability in gait in healthy female subjects.

Unstable footwear generally lacks thorough peer-review published research to support concepts and marketing claims. The purpose of this study was to investigate the instability induced by four (FitFlop, Masai Barefoot Technology, Reebok Easy-Tone and Skechers Tone-Ups) commercially available unstable sandals and one stable control sandal (Earth) in walking in 15 females (mean±SD age was 29±6.7 years, mass 62.6±6.9kg and height 167.1±4.2cm). Three-dimensional motion with synchronised electromyography and kinetic data were collected. Walking speed and step length remained consistent between conditions, however double support time decreased in Masai Barefoot Technology. Centre of pressure data identified no consistent difference between the stable control and the unstable sandals, however Masai Barefoot Technology reduced the anterior-posterior range of centre of pressure. Muscle activity differed significantly at the ankle in the unstable footwear. FitFlop, Reebok and Skechers increased peroneal activity during pre-swing, whereas Masai Barefoot Technology increased medial gastrocnemius and decreased tibialis anterior activity in loading response and mid-stance. The larger rocker sole of the Masai Barefoot Technology altered gait and muscle activation with regard to braking and progression in the sagittal plane. Reebok, Skechers and FitFlop, with softer, less stable foreparts increased evertor action at toe-off, having their effect in the coronal plane. The study highlighted that any instability induced by the shoes is design-specific.

Validity and repeatability of three in-shoe pressure measurement systems

In-shoe pressure measurement devices are used in research and clinic to quantify plantar foot pressures. Various devices are available, differing in size, sensor number and type; therefore accuracy and repeatability. Three devices (Medilogic, Tekscan and Pedar) were examined in a 2 day×3 trial design, quantifying insole response to regional and whole insole loading. The whole insole protocol applied an even pressure (50-600kPa) to the insole surface for 0-30s in the Novel TruBlue™ device. The regional protocol utilised cylinders with contact surfaces of 3.14 and 15.9cm(2) to apply pressures of 50 and 200kPa. The validity (% difference and Root Mean Square Error: RMSE) and repeatability (Intra-Class Correlation Coefficient: ICC) of the applied pressures (whole insole) and contact area (regional) were outcome variables. Validity of the Pedar system was highest (RMSE 2.6kPa; difference 3.9%), with the Medilogic (RMSE 27.0kPa; difference 13.4%) and Tekscan (RMSE 27.0kPa; difference 5.9%) systems displaying reduced validity. The average and peak pressures demonstrated high between-day repeatability for all three systems and each insole size (ICC≥0.859). The regional contact area % difference ranged from -97 to +249%, but the ICC demonstrated medium to high between-day repeatability (ICC≥0.797). Due to the varying responses of the systems, the choice of an appropriate pressure measurement device must be based on the loading characteristics and the outcome variables sought. Medilogic and Tekscan were most effective between 200 and 300kPa; Pedar performed well across all pressures. Contact area was less precise, but relatively repeatable for all systems.

A comparison of plantar pressures in a standard flip-flop and a FitFlop using bespoke pressure insoles

Purpose: The study was undertaken to compare plantar pressures in a Havaiana flip-flop to a FitFlop, a flip-flop with a multi-density midsole designed to induce instability. It was hypothesised that in the Havaiana the toes are used to ‘grip’ the shoe in swing and the loose upper and thin sole provide limited protection to the foot, producing higher plantar pressures than the FitFlop. Methods: Twenty female subjects walked in the footwear conditions while a bespoke instrumented insole quantified plantar pressures. Data analysis grouped sensors into regions for the heel, 1st metatarsophalangeal joint and hallux to isolate pressures that have been linked to comfort and symptoms reportedly alleviated in the FitFlop. Additional analysis was undertaken to measure hallux ‘gripping’ during swing. Results: Significant reductions in plantar pressures in the FitFlop, particularly in peak pressure in the heel (3.6%) and pressure-time integral in the 1stmetatarsophalangeal joint (12.0%) were identified. These findings were attributed to the thicker midsole with different ethylene vinyl acetate (EVA) construction and a redistribution of load to the midfoot where contact area increased by 19.9% compared to the Havaiana. Also evident were reductions in anterior-posterior centre of pressure velocity in the FitFlop, attributed to its softer midfoot delaying progression. Hallux variables identified reductions in time spent ‘gripping’ as well as the magnitude of force applied by the hallux in swing in the FitFlop. Conclusions: Findings from the study identify that the FitFlop reduces pressure in key areas of the foot which are associated with walking comfort as well as clinical conditions. The ‘gripping’ mechanism postulated to hold flip-flops on is lessened in the FitFlop, potentially reducing the likelihood of overuse injuries.

Validity and repeatability of three commercially available in-shoe pressure measurement systems

In-shoe pressure measurement devices are commonly used in research and clinical settings to quantify pressure on the plantar foot. Various in-shoe pressure measurement devices are currently available and they differ in their size, number of sensors, sensor type and therefore their loading response and accuracy. Previous comparisons focus on pressure plates [1]. An in-shoe study highlighted that the F-Scan system became erroneous at pressures over 200kPa and the repeatability of the Novel device was high [2]. However the long loading durations (11 minutes) studied has limited application to a real-life setting. The validity and repeatability of each system effects their appropriateness for applications within clinical and research test settings. This abstract, therefore aims to establish the suitability of each device to test protocols with differing loading magnitudes and durations.

Does flip-flop style footwear modify ankle biomechanics and foot loading patterns?

BackgroundFlip-flops are an item of footwear, which are rubber and loosely secured across the dorsal fore-foot. These are popular in warm climates; however are widely criticised for being detrimental to foot health and potentially modifying walking gait. Contemporary alternatives exist including FitFlop, which has a wider strap positioned closer to the ankle and a thicker, ergonomic, multi-density midsole. Therefore the current study investigated gait modifications when wearing flip-flop style footwear compared to barefoot walking. Additionally walking in a flip-flop was compared to that FitFlop alternative.MethodsTesting was undertaken on 40 participants (20 male and 20 female, mean ± 1 SD age 35.2 ± 10.2 years, B.M.I 24.8 ± 4.7 kg.m-2). Kinematic, kinetic and electromyographic gait parameters were collected while participants walked through a 3D capture volume over a force plate with the lower limbs defined using retro-reflective markers. Ankle angle in swing, frontal plane motion in stance and force loading rates at initial contact were compared. Statistical analysis utilised ANOVA to compare differences between experimental conditions.ResultsThe flip-flop footwear conditions altered gait parameters when compared to barefoot. Maximum ankle dorsiflexion in swing was greater in the flip-flop (7.6 ± 2.6°, p = 0.004) and FitFlop (8.5 ± 3.4°, p < 0.001) than barefoot (6.7 ± 2.6°). Significantly higher tibialis anterior activation was measured in terminal swing in FitFlop (32.6%, p < 0.001) and flip-flop (31.2%, p < 0.001) compared to barefoot. A faster heel velocity toward the floor was evident in the FitFlop (-.326 ± .068 m.s-1, p < 0.001) and flip-flop (-.342 ± .074 m.s-1, p < 0.001) compared to barefoot (-.170 ± .065 m.s-1). The FitFlop reduced frontal plane ankle peak eversion during stance (-3.5 ± 2.2°) compared to walking in the flip-flop (-4.4 ± 1.9°, p = 0.008) and barefoot (-4.3 ± 2.1°, p = 0.032). The FitFlop more effectively attenuated impact compared to the flip-flop, reducing the maximal instantaneous loading rate by 19% (p < 0.001).ConclusionsModifications to the sagittal plane ankle angle, frontal plane motion and characteristics of initial contact observed in barefoot walking occur in flip-flop footwear. The FitFlop may reduce risks traditionally associated with flip-flop footwear by reducing loading rate at heel strike and frontal plane motion at the ankle during stance.

Foot dimensions and morphology in healthy weight, overweight and obese males

BACKGROUND Overweight and obesity are increasing in prevalence. However, despite reports of poor foot health, the influence of obesity and overweight on adult foot morphology has received limited attention. The objective of this work is to accurately and appropriately quantify the foot morphology of adults who are overweight and obese. METHODS The foot morphology of 23 healthy weight (BMI=22.9kg.m(-2)), overweight (27.5kg.m(-2)) and obese (32.9kg.m(-2)) age (60years) matched males was quantified using a 3D scanner (all size UK 9). Data analysis computed normalised (to foot length) standard anatomical measures, and widths, heights and circumferences of 31 evenly spaced cross-sections of right feet. FINDINGS Anatomical measures of foot, ball and heel width, ball and heel circumference and ball height were all greater in the obese group than the healthy weight (P<0.05). Cross-sectional measures were significantly wider than the healthy group for the majority of measures from 14 to 67% (P=0.025-1.000) of heel-to-toe length. Also, the obese group had significantly higher midfoot regions (P=0.024-0.025). This increased foot height was not evident from anatomical measures, which were not sensitive enough to detect dimensional differences in this foot region. INTERPRETATION Feet of obese adults differ from healthy and overweight individuals, notably they are wider. Data needs to avoid reliance upon discrete anatomical landmarks to describe foot morphology. In the obese, changes in foot shape do not coincide with traditional anatomical landmarks and more comprehensive foot shape data are required to inform footwear design.

Testing a mechanical protocol to replicate impact in walking footwear

Impact testing is commonly undertaken to quantify the shock absorption characteristics of footwear. The current widely reported mechanical testing method mimics the vertical heel velocity at touchdown and effective mass of the lower limb recorded in running. This therefore results in a greater impact energy than would be expected at touchdown in walking. Despite this mismatch, the methodology is utilised to quantify the shock absorption properties of running and walking footwear alike. The current work modifies the mechanical testing methodology to replicate the kinematics, specifically the vertical heel velocity, identified in walking footwear. Kinematic and kinetic data was collected for 13 subjects walking in four different styles of footwear used for walking (trainer, oxford shoe, flip-flop and triple-density sandal). The kinematic data was utilised to quantify heel velocity at touchdown and accelerometer and force plate data was utilised to estimate the effective mass of the lower limb. When walking in the toe-post style footwear significantly faster vertical heel velocity toward the floor was recorded compared to barefoot and the other footwear styles (Figure ​(Figure11 for example flip-flop: 0.36±0.05m.s-1 compared to trainer: 0.18±0.06m.s-1). The mechanical protocol was adapted by altering the mass and drop height from 10.6-17.3 kg and 2-7 mm, compared to the original protocol of 8.45 kg dropped from 50 mm. As expected, the adapted mechanical protocol produced significantly lower peak force and accelerometer values than the ASTM protocol (p <.001). These values more closely resembled those recorded in walking. The mean difference between the human and modified protocol was 12.7±17.5% (p<.001) for peak acceleration and 25.2±17.7% (p=.786) for peak force values. The timing of peak force and acceleration variables was less representative of the real-life data with larger mean differences. This pilot test has demonstrated that the altered mechanical test protocol can more closely replicate loading on the lower limb in walking. Further research should consider more variables related to the shock absorption properties of footwear. The results also demonstrate that testing of material properties of footbeds not only needs to be gait style specific (e.g. running versus walking), but also footwear style specific due to the differences in heel touch-down velocity in footwear styles. Figure 1 Vertical heel velocity towards the floor in the human testing for the four footwear conditions. Triple-density sandal = SA, flip-flop = FF, shoe = SH and trainer = TR and Barefoot (BF). Error bars denote standard deviation across the 13 subjects tested. ...

The effect of unstable sandals on single-leg standing

Purpose: Unstable footwear lacks peer-review published research to support concepts and claims. The present study was therefore undertaken to quantify and compare the effect of commercially available unstable sandals on single-leg balance in a healthy female population. Methods: Fifteen participants stood on their right-leg in one control sandal (Earth) and four sandals that are marketed as unstable footwear (FitFlop, Masai Barefoot Technology, Reebok Easy-Tone and Skechers Tone-Ups). Centre of pressure trajectory, lower limb kinematics and lower limb muscle activation were recorded as participants undertook three 30 second trials in each sandal. Results: The unstable sandals altered parameters related to stability in participants. Namely Masai Barefoot Technology increased centre of pressure range in the anterior-posterior direction and concurrently increased sagittal ankle motion. Reebok Easy-Tone had a similar effect in the coronal plane at the ankle. Muscle activation increased in the unstable sandals, with significant differences apparent in the medial gastrocnemius, soleus and rectus femoris, predominantly in Masai Barefoot Technology. Findings were attributed to the large rocker sole on the Masai Barefoot Technology sandal and more subtle outsole designs in the other sandals. Conclusions: Overall minimal differences from the control sandal were evident and it is expected that dynamic tasks may elicit greater differences in stability. The instability imposed by the sandals is design-specific and consideration should be given to this when the footwear is recommended to specific individuals.

Single-leg balance in “instability” footwear

Background The concept of instability footwear is to reduce stability, increase muscle activation and “tone”. Recently numerous brands have developed instability footwear for significant sales. Despite extensive marketing claims there are few empirical studies quantifying effects of instability footwear on muscle activity or motion in healthy individuals aside from Masai Barefoot Technology (MBT) [1,2]. The aim of the study was to quantify instability in single-leg standing in a variety of commercially available instability sandals.

Big issues for small feet: developmental, biomechanical and clinical narratives on children’s footwear

The effects of footwear on the development of children’s feet has been debated for many years and recent work from the developmental and biomechanical literature has challenged long-held views about footwear and the impact on foot development. This narrative review draws upon existing studies from developmental, biomechanical and clinical literature to explore the effects of footwear on the development of the foot. The emerging findings from this support the need for progress in [children’s] footwear science and advance understanding of the interaction between the foot and shoe. Ensuring clear and credible messages inform practice requires a progressive evidence base but this remains big issue in children’s footwear research.