You could try the followinging articles for a start (then have a look at their references) -
1: Changgeng Yi Xue Za Zhi. 1998 Mar;21(1):20-7.
Effects of silicon-insole socks on pressure distribution and shear force of the
Wong PY, Chen MD, Hong WH, Chen HC, Wong MK, Tang FT.
Department of Rehabilitation Medicine, Chang Gung Memorial Hospital, Taipei,
BACKGROUND: Many problems of the foot are due to abnormal plantar pressure and shear force, but until now shear force could not be accurately measured. Different methods can be used to reduce foot pressure, such as foot orthosis or shoe modification. The purposes of our study were to propose a method for measuring the maximum shear force of the foot and also to investigate the effect of silicone-insole socks in reducing the peak plantar pressure and shear stress of the foot. METHODS: Twenty-two healthy subjects were included in this study, each subject underwent 2 kinds of experiments to study the peak plantar pressure, the horizontal shear reaction force, and the maximum shear force under 3 conditions: barefoot, wearing 100% cotton socks, and wearing silicone-insole socks. RESULTS: Our results showed a significant decrease in midfoot peak plantar pressure while walking, and a decrease in horizontal shear reaction force and maximum shear force while wearing cotton socks and silicone-insole socks in walking and pulling. Silicone-insole socks were more significant in decreasing horizontal shear reaction force than cotton socks. CONCLUSION: Silicone-insole socks are better than cotton socks in reducing horizontal shear reaction forces and their friction coefficients. Because only normal subjects have been tested, further study is required to prove the efficacy of silicone-insole socks on different kinds of foot pathology.
2: Clin Infect Dis. 2004 Aug 1;39 Suppl 2:S87-91.
Mechanical loading and off-loading of the plantar surface of the diabetic foot.
van Deursen R.
Research Centre for Clinical Kinaesiology, University of Wales College of
Medicine, Heath Park, Cardiff, United Kingdom. firstname.lastname@example.org
During weight-bearing activities, the feet are exposed to large forces, particularly when the activity is dynamic, such as walking. The pressure under the plantar surface during walking varies per foot area because of a number of factors related to the normal rollover during the stance phase of gait. Diabetes mellitus often results in loss of protective sensation and in structural changes that make the feet more susceptible to injury. Increased plantar pressure is an important factor in the development and maintenance of diabetic foot ulceration.
Increased plantar pressures and associated ulcers need to be treated by off-loading of the plantar surface. Useful off-loading mechanisms include reduction of walking speed, alteration of foot rollover during gait, and transfer of load from affected areas to other areas of the foot or the lower leg. These plantar off-loading mechanisms could result in an optimization of treatment, but clinical effectiveness must be demonstrated.
3: Iowa Orthop J. 2004;24:72-5.
Plantar foot surface temperatures with use of insoles.
Hall M, Shurr DG, Zimmerman MB, Saltzman CL.
Orthopaedics and Rehabilitation Bioengineering, University of Iowa, IA, USA.
PURPOSE: Patients with diabetes are often prescribed foot orthoses to help prevent foot ulcer formation. Orthotics are used to redistribute normal and shear stress. Shear stresses are not easily measurable and considered to be responsible for skin breakdown. Local elevation of skin temperature has been implicated as an early sign of impending ulceration especially in regions of high shear stress. The purpose of this study was to measure the effects of commonly prescribed insole materials on local changes in plantar foot temperature during normal gait. METHODS: Six commonly used foot orthosis materials were tested using the Thermo Trace infrared thermometer to measure foot temperature. Ten healthy adult volunteers without any history of diabetes or abnormal sensation participated in the study. During each trial the subject walked on a treadmill with the test material in the dominant foot's shoe, for six minutes at a speed of four miles per hour and rested for six minutes between trials. Four locations on the foot (hallux, first and fifth metatarsal heads, and heel) and the contralateral bicep temperatures were measured at 0, 1, 3, 5 minutes during the rest period. The order of material and skin location testing was randomized. RESULTS: Significant differences were found between baseline temperatures and foot temperatures for all materials. However, no differences were found between materials for any location on the foot. CONCLUSION: Previous studies have attempted to characterize materials based on laboratory and clinical testing, while other studies have attempted to characterize the effect of pressure on skin temperature. However, no study has previously attempted to characterize foot orthosis materials based on foot temperatures. This study compared foot temperatures of healthy adults based on the material tested.
Although this study was unable to distinguish between materials based on foot temperatures, it was able to show a rise in foot temperature with any material used. This study demonstrates a need to a larger study on a population with diabetes.
4: Clin Biomech (Bristol, Avon). 2003 Jul;18(6):S17-24.
Effects of total contact insoles on the plantar stress redistribution: a finite element analysis.
Chen WP, Ju CW, Tang FT.
Department of Biomedical Engineering, Chung Yuan Christian University, Chungli
320, Taiwan, ROC. email@example.com
OBJECTIVE: To investigate the effects of total contact insoles on the plantar
stress redistribution using three-dimensional finite element analysis. DESIGN:
The efficacies of stress reduction and redistribution of two total contact insoles with different material combinations were compared with those of a regular flat insole used as a baseline condition. BACKGROUND: Many specially designed total contact insoles are currently used to reduce the high plantar pressure in diabetic patients. However, the design of total contact insoles is mostly empirical and little scientific evidence is available to provide a guideline for persons who prescribe such insoles. METHODS: To use three-dimensional finite element models of the foot together with insoles to investigate the effects of total contact insoles on the foot plantar pressure redistributions. Nonlinear foam material properties for the different insole materials and the contact behavior in the foot-insole interface were considered in the finite element analysis. RESULTS: Results showed that the peak and the average normal stresses were reduced in most of the plantar regions except the midfoot and the hallux region when total contact insoles were worn compared with that of the flat insole condition. The reduction ratios of the peak normal stress ranged from 19.8% to 56.8%. CONCLUSIONS: Finite element analysis results showed that the two sets of total contact insoles used in the current study can both reduce high pressures at regions such as heel and metatarsal heads and can redistribute the pressure to the midfoot region when compared with the flat insole condition. RELEVANCE: It is possible to simulate foot deformities, change in material properties, different ambulatory loading conditions, and different orthotic conditions by altering the finite element model in a relatively easy manner and these may be of interests to the medical professionals who treat foot-related problems.
5: Clin Biomech (Bristol, Avon). 2000 Jan;15(1):46-53.
A study of in-shoe plantar shear in normals.
Hosein R, Lord M.
King's College School of Medicine and Dentistry, Bessemer Road, London, UK.
OBJECTIVE: To quantify features of in-shoe plantar shear in asymptomatic adult gait. DESIGN: In order to standardize footwear conditions and facilitate later comparison to patient groups, measurement is made in a group of adults walking freely in stock orthopaedic footwear. BACKGROUND: Better data on plantar shear is required to complement well-documented pressure data for an overall picture of plantar stress. METHODS: Measurements were made locally beneath the medial four metatarsal heads and heel using biaxial transducers mounted flush into an inlay. Pressure distribution was also measured. RESULTS: The shear data revealed common features in the shear pattern occurring at defined phases of gait, with good inter-step reliability. For the five sites of interest, these values ranged from 24 kPa to 70.4 kPa, and 31 kPa to 86.5 kPa for individuals wearing nylon hose or hose-free respectively. Maximum shear occurred more laterally than maximum pressure. CONCLUSIONS: Features of plantar shear were not always as expected; for example the forward thrust at push-off was not reflected in the anteroposterior shear stress. Because of the inter-subject variability, study of a larger group is indicated. RELEVANCE: Mechanical stress at the plantar interface between foot and shoe is of particular clinical relevance to the formation and management of ulcers in diabetic neuropathy. It is also of relevance to shoe and orthotic design for various foot pathologies. This study provides reliable data on the shear component of plantar stress for which, unlike the well-documented pressure component, there is only sparse data so far available.
6: J Am Podiatr Med Assoc. 2000 Jul-Aug;90(7):346-53.
Effectiveness of various materials in reducing plantar shear forces. A pilot
Curryer M, Lemaire ED.
Sandy Hill Community Health Centre, Ottawa, Ontario, Canada.
Vertical plantar forces are known to be a major precipitating factor in the development of foot pathology. It is also postulated that shear forces are important in the pathogenesis of foot ulcers in patients with diabetes mellitus.
Various materials are used in insoles designed to reduce forces on the foot.
While many foam materials have been tested for their ability to dissipate vertical forces, few studies have tested the effect of these materials on shear forces. This study assessed the effectiveness of five different materials in reducing plantar shear forces and compared two new gel materials with three of the more conventional foam materials. Four subjects were tested while walking over a force platform with one of the five materials taped to the surface. Peak force, impulse, and resultant shear force data were analyzed. The gel materials were significantly better than the foam materials at reducing shear forces. Thus the use of gel materials in insoles may be indicated for the reduction of plantar shear forces on the diabetic foot.
Also, you might want to google statements such as 'in shoe shear'