Shuping Xiong

Foot arch characterization: a review, a new metric, and a comparison.

BACKGROUND The medial longitudinal arch of the foot is important because it helps protect the foot from injury. Researchers have developed many measures to quantify the characteristics of the arch, and there is ongoing debate about the suitability of these different metrics. This article compares the various measures related to the foot arch, including a new metric, the midfoot dorsal angle, and then investigates the differences in the dimensional measures among various foot types. METHODS The right feet of 48 healthy individuals (24 men and 24 women) were measured, and various metrics, including the arch height index, the navicular height to arch length ratio, the arch index, the footprint index, the subjective ranking, the modified arch index, the malleolar valgus index, and the midfoot dorsal angle, were determined. RESULTS Correlation analyses showed that the arch index obtained from the inked footprint has a moderate to high correlation (Pearson correlation coefficients >0.50) with all measured foot-type metrics except for the malleolar valgus index. There were no differences in participant age, stature, weight, body mass index, foot length, foot width, and midfoot height among high, normal, and low foot arches. However, the high-arched group had significantly shorter arch lengths but larger navicular heights and higher midfoot dorsal angles compared with the low-arched group. There were differences in force distributions and peak pressures as well. The rearfoot had more loading and greater peak pressure whereas the midfoot had less load in the high-arched group compared with the low-arched group. CONCLUSIONS The midfoot dorsal angle may be an appropriate metric for characterizing the foot arch because it is quick and easy to measure, without the tedious procedures associated with area calculations and dimension measurements.

Modelling foot height and foot shape-related dimensions

The application of foot anthropometry to design good-fitting footwear has been difficult due to the lack of generalised models. This study seeks to model foot dimensions so that the characteristic shapes of feet, especially in the midfoot region, can be understood. Fifty Hong Kong Chinese adults (26 males and 24 females) participated in this study. Their foot lengths, foot widths, ball girths and foot heights were measured and then evaluated using mathematical models. The results showed that there were no significant allometry (p > 0.05) effects of foot length on ball girth and foot width. Foot height showed no direct relationship with foot length. However, a normalisation with respect to foot length and foot height resulted in a significant relationship for both males and females with R2 greater than 0.97. Due to the lack of a direct relationship between foot height and foot length, the current practice of grading shoes with a constant increase in height or proportionate scaling in response to foot length is less than ideal. The results when validated with other populations can be a significant way forward in the design of footwear that has an improved fit in the height dimension.

Computerized girth determination for custom footwear manufacture

Good fitting footwear requires matching not just the linear dimensions of feet but their girths as well. Footwear fitters have been using manual measurements for a long time, but the development of computerized techniques and scanner technologies have now made automatic determination of different foot dimensions feasible. The resistance to using such computer measurements has been the lack of trust in the accuracy of the data. This paper proposes an approach to obtain the necessary girths of feet in order to customize footwear. The proposed approach attempts to simulate the manual measurement procedures, and its effectiveness is assessed through an experiment with 15 foot castings. The results show that the simulated measurements can be within 5mm of the manual measurements if the measuring locations can be correctly identified. Linear regressions show that the differences between the manual measurements and the simulated measurements can be modeled with the addition of a systematic error term of less than 4mm. The computerized acquisition of foot dimensions is a useful way forward for custom shoe manufacturers.

Pressure thresholds of the human foot: measurement reliability and effects of stimulus characteristics

Information related to reliable values of discomfort thresholds can help to improve the designs of various products. This study aimed to investigate the measurement reliabilities associated with pressure thresholds, while determining the effects of stimulus characteristics (stimulus area, indentation speed) of the human foot. An indentation apparatus was used with four sizes of indentation probes and three indentation speeds. In total, 13 locations on the right foot of 10 male and 10 female participants were tested to determine the pressure discomfort thresholds (PDT) and pressure pain thresholds (PPT). Results show that the tests had very good measurement reliability with intra-class correlations (ICC) greater than 0.8 for the PPT measurements and acceptable reliability (most ICC > 0.75, with a few between 0.5 and 0.75) for the PDT measurements, demonstrating that participants are capable of judging their pain and discomfort thresholds. Pressure sensitivity differs across locations of the foot, with the medial plantar arch of the foot being the most sensitive, followed by the dorsal surface of the foot. The heel area was the least sensitive. PPT and PDT are dependent on the stimulus characteristics of the area and the speed of indentation. A smaller area has a higher PPT and PDT, indicating significant effects of spatial summation. The increase of PDT and PPT at higher speeds may be partially explained by the increase in stiffness because foot tissue exhibits viscoelastic properties. The findings can have a significant impact on the design of footwear and other accessories for improved foot health and comfort. Statement of Relevance: This study investigated the threshold measurement reliability while determining the pressure sensitivity on the surface of the foot with varying stimulus characteristics. The findings may be very useful in the design of footwear and other accessories for improved comfort and reduced injuries.

Footbed shapes for enhanced footwear comfort

A shoe wearers comfort is related to the shape of the footbed of a shoe. Even though the footbed shape is important in footwear design, there exists no methodology to evaluate the existing guidelines used in last making. Thirty-two females participated in an experiment where heel seat length, heel seat inclination and heel height were investigated using the profile assessment device. The dependent variables were plantar pressure and perceived feeling of each participant. The results show that perceived feel is best for wedge angles of 4° and 5° at a heel height of 25 mm, 10° and 11° at a heel height of 50 mm and 16° and 18° at a heel height of 75 mm. A regression model was derived and this explained approximately 80% of the variation of perceived feeling with the contact area, peak plantar pressure and percentage of force acting on the forefoot region. Both heel wedge angle and heel seat length play an important role in the perceived feel of high-heeled shoes. This study, in relation to the load-bearing heel part of a shoe, highlights the importance of good footbed design. The findings can be used to design footwear with enhanced comfort.

An indentation apparatus for evaluating discomfort and pain thresholds in conjunction with mechanical properties of foot tissue in vivo

The mechanical properties of human foot tissue in vivo as well as discomfort and pain thresholds are important for various applications. In this study, an apparatus for measuring the discomfort and pain thresholds and the mechanical properties of human tissues is presented. The apparatus employs a stepper motor that controls the indentation speed, as well as a load cell and potentiometer that determine the corresponding reaction force and tissue deformation (displacement), respectively. A LabVIEW program (LabVIEW 8, National Instruments Corporation; Austin, Texas) was developed to control the indentation via a data acquisition card. The apparatus can accommodate indentor displacements up to 35 mm and can impart forces up to 150 N at a controlled indentation speed in the range of 0 to 10 mm/s. Tests showed that the displacement measurement error is <0.17 mm in the nominal range (0.5% in the full scale) and the measurement error of force is <1.6 N in the nominal range (1.1% in the full scale). Experimental results indicate that the apparatus is reliable and flexible for measuring the mechanical properties of foot tissue in vivo in conjunction with pain and discomfort thresholds.

Effects of high heeled shoes wearing experience and heel height on human standing balance and functional mobility

This study aimed to examine the effects of high heeled shoes (HHS) wearing experience and heel height on human standing balance and functional mobility. Thirty young and healthy females (ten experienced and twenty inexperienced HHS wearers) participated in a series of balance tests when they wore shoes of four different heel heights: 1 cm (flat), 4 cm (low), 7 cm (medium) and 10 cm (high). Experimental results show that regardless of the wearing experience, the heel elevation induces more effort from lower limb muscles (particularly calf muscles) and results in worse functional mobility starting at 7 cm heel height. While the heel height increased to 10 cm, the standing balance also becomes worse. Experienced HHS wearers do not show significantly better overall performance on standing balance and functional mobility than inexperienced controls, even though they have better directional control (76.8% vs. 74.4%) and larger maximum excursion (93.3% vs. 89.7%). To maintain standing balance, experienced wearers exert less effort on tibialis anterior, vastus lateralis and erector spinae muscles at the cost of more intensive effort from gastrocnemius medialis muscle. Practitioner summary: Many women wear high heeled shoes (HHS) to increase female attractiveness. This study shows that HHS induce more muscular effort and worse human standing balance and functional mobility, especially when heel height reaches 10 cm. HHS wearing experience only provides certain advantages to wearers on limits of stability in terms of larger maximum excursion and better directional control.

Load distribution to minimise pressure-related pain on foot: a model

The optimal force distribution to minimise pain or discomfort at the foot–shoe interface is still not known. Most shoe-related products attempt to distribute the load uniformly without much consideration to the bony and soft tissue regions. An experiment was conducted to first determine the pressure pain threshold (PPT) and tissue deformation on the plantar surface of the foot. Circular probes of areas 0.5, 1.0 and 2.0 cm2 at indentation speeds of 0.5, 1 and 2 mm/s showed that PPT depends on the location stimulated, area of stimulation and the indentation speed. The results also showed that tissue stiffness is quite low for small deformations ( < 4 mm), but significantly higher at large deformations (>4 mm). The stiffness at the larger deformation region was positively correlated with PPT (r = 0.63, p < 0.001). The data were further used to develop a model with PPT, deformation and stimulated area. Practitioner Summary: Pressure at which there is an onset of pain is higher when a larger area of soft tissue is stimulated. Bony areas may be better suited to bear load on smaller areas to minimise pressure-related pain. Thus, manipulating supporting surface stiffness and surface contours can help minimise pain.

A new region growing algorithm for triangular mesh recovery from scattered 3D points

A novel region growing algorithm is proposed for triangular mesh recovery from scattered 3D points. In our method, the new principle is used to determine the seed triangle considering both maximum angle and minimum length; the open influence region is defined for the active edge under processing; positional element is added into the criterion to choose the most suitable active point; geometric integrity is maintained by analyzing different situations of the selected active point and their corresponding treatments. Our approach has been tested with various unorganized point clouds, and the experimental results proved its efficiency in both accuracy and speed. Compared with the existing similar techniques, our algorithm has the ability to recover triangular meshes while preserving better topological coherence with the original 3D points.

An automatic method of measuring foot girths for custom footwear using local RBF implicit surfaces

Three-dimensional point cloud data of a foot are used to determine the critical dimensions for making custom footwear. However, automatic and accurate measurement of dimensions, especially girths, is an issue of concern to many designers and footwear developers. Existing methods for measuring girths are primarily based on points or generated triangles, but their accuracy is heavily dependent on the density of the point cloud data. In this paper we present the use of the Radial Basis Function (RBF) surface modelling technique for measuring girths as it has the advantage of being able to operate on unorganised three-dimensional points, so that the generated surface passes through every scanned point, while repairing incomplete meshes. To overcome the high computational expense of the RBF method, local surface recovery, octree division and combination, inverse power method and improved Cholesky factorisation are used. The girth measurements obtained from adopting these approaches are compared against the existing measurement methods. Experimental results demonstrate that the local RBF implicit surface can provide more stable and accurate measurements using relatively less time, proving its value in custom footwear manufacture.