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Shore hardness (SH) is a cost-effective and easy-to-use method to assess soft tissue biomechanics. Its use for the plantar soft tissue could enhance the clinical management of conditions such as diabetic foot complications, but its validity and reliability remain unclear. Twenty healthy adults were recruited for this study. Validity and reliability were assessed across six different plantar sites. The validity was assessed against shear wave (SW) elastography (the gold standard). SH was measured by two examiners to assess inter-rater reliability. Testing was repeated following a test/retest study design to assess intra-rater reliability. SH was significantly correlated with SW speed measured in the skin or in the microchamber layer of the first metatarsal head (MetHead), third MetHead and rearfoot. Intraclass correlation coefficients and Bland–Altman plots of limits of agreement indicated satisfactory levels of reliability for these sites. No significant correlation between SH and SW elastography was found for the hallux, 5th MetHead or midfoot. Reliability for these sites was also compromised. SH is a valid and reliable measurement for plantar soft tissue biomechanics in the first MetHead, the third MetHead and the rearfoot. Our results do not support the use of SH for the hallux, 5th MetHead or midfoot.

Abstract This proof-of-concept study demonstrates that repetitive loading to the pain threshold can safely recreate overloading-induced soft tissue damage and that localised tissue stiffening can be a potential marker for injury. This concept was demonstrated here for the soft tissue of the sole of the foot where it was found that repeated loading to the pain threshold led to long-lasting statistically significant stiffening in the overloaded areas. Loading at lower magnitudes did not have the same effect. This method can shed new light on the aetiology of overloading injury in the foot to improve the management of conditions such as diabetic foot ulceration and heel pain syndrome. Moreover, the link between overloading and tissue stiffening, which was demonstrated here for the first time for the plantar soft tissue, opens the way for an assessment of overloading thresholds that is not based on the subjective measurement of pain thresholds.

Identifying areas in the sole of the foot which are routinely overloaded during daily living is extremely important for the management of the diabetic foot. This work showcases the feasibility of reliably detecting overloading using a low-cost non-electronic technique. This technique uses thin-wall structures that change their properties differently when they are repeatedly loaded above or below a tuneable threshold. Flexible hexagonal thin-wall structures were produced using three-dimensional printing, and their mechanical behaviour was assessed before and after repetitive loading at different magnitudes. These structures had an elastic mechanical behaviour until a critical pressure (Pcrit = 252 kPa ± 17 kPa) beyond which they buckled. Assessing changes in stiffness after simulated use enabled the accurate detection of whether a sample was loaded above or below Pcrit (sensitivity = 100%, specificity = 100%), with the overloaded samples becoming significantly softer. No specific Pcrit value was targeted in this study. However, finite-element modelling showed that Pcrit can be easily raised or lowered, through simple geometrical modifications, to become aligned with established thresholds for overloading (e.g. 200 kPa) or to assess overloading thresholds on a patient-specific basis. Although further research is needed, the results of this study indicate that clinically relevant overloading could indeed be reliably detected without the use of complex electronic in-shoe sensors.

The aim of this study is to investigate whether exercise can reverse some of the adverse effects of high-fat-diet-induced obesity on lipid metabolism and bone biomechanical properties. A total of 26 adult male C57bl/6J mice were randomly assigned into three groups: (A) Control group (n=6), (B) High-fat diet group (n=10), (C) High-fat diet and exercise group (n=10). Body mass and relevant biochemical parameters were measured for the duration of the experimental protocol (37 weeks). Mechanical strength of both femurs of each animal was assessed in-vitro based on three point bending tests. It was re¬vealed that exposure to high-fat diet led to significant increase of body mass and cholesterol levels and also to substantial changes in bone mor-phology and strength. Ultimate stress for the animals exposed to high-fat diet and those exposed to high-fat-diet and exercise was 25% and 24% lower compared to control, respectively. Exercise increased bone thickness by 15% compared to animals that were not exposed to exer¬cise. It was concluded that high-fat-diet ap¬pears to have a detrimental effect on bone biomechanics and strength. Exer¬cise reversed the reduction in bone thickness that appears to be induced by high-fat diet. However no statistically significant increase in bone strength was observed.