The effects of heel height, shoe volume and upper stiffness on shoe comfort and plantar pressure
, PhD thesis, University of Salford.
The research in this thesis investigated the independent effects of changing heel height, forefoot shoe volume and upper material stiffness on plantar pressures and comfort in ladies raised heel shoes. Plantar pressure is widely associated with comfort and foot pain including conditions such as subchondral bone microfractures, cartilage degeneration, osteoarthritis, hallux valgus, plantar calluses, metatarsalgia, morton’s neuroma, and hammer toe. Reducing peak plantar pressure at localised foot regions is therefore an aspiration of footwear manufacturers and health professionals alike.
As a precursor to the primary investigations, protocols for measuring plantar pressure were investigated. Specifically, how long it takes for a participant to acclimatise to new footwear and how many steps must be measured to provide valid plantar pressure data are research design issues not thoroughly resolved by prior research. In the first study within this thesis it was found that 166 steps per foot were required to acclimatise to unfamiliar footwear. Also, that data from 30 steps should be collected to ensure sufficient data for a representative step could be accurately calculated (within error of +/-2.5%) assumed
The second study investigated the effects of incremental increases in heel height and upper material stiffness on comfort and plantar pressure. It was found that an increase in heel height of 20mm was required for a significant 19% increase in plantar pressure at MTP1 in shoes which have a heel height under 55mm. A significant increase in pressure was observed with just a 10mm increase in heel height for shoes over 55mm. Similar, though smaller, effects were observed for perceived comfort in different heel heights.
The third study investigated the effects of shoe volume and upper stiffness on comfort and plantar pressure. It was found that an increase in shoe volume increased the pressure at the MTP1 and reduced it at the heel. There was also a volume, the medium volume shoe, which clearly produced the significantly lowest pressure at the MT24 (275kPa medium shoe compared to 289kPa and 305 kPa in the smallest and largest volumes respectively). A significant interaction between shoe volume and material stiffness was also observed: when the material stiffness is changed the amplitude of the effect due to volume is magnified.
Of the three footwear features investigated heel height has the greatest significant effect on both comfort (74% increase in overall discomfort for 35mm to 75mm heel height) and plantar pressure (33% increase at MTP1 between 35 and 75 mm heel height), followed by shoe volume then upper stiffness. There was a clear relationship between plantar pressure and comfort and the results suggest that shoes with an effective heel height over 55mm should be considered different from those with heel height less than 55mm. This serves to define a “high heeled“shoe.
To ensure that set measurements could be defined investigations into the effects of heel height were completed with only one shoe size. Thus for other shoe sizes scaling may be required. The results of this thesis will improve the quality of future investigations because it has provided guidelines on the required number of steps to acclimatise to unfamiliar footwear, and the number of steps required to produce an average representative step. Also, to the benefit of researchers, the results of this thesis have highlighted the difficulty in controlling features of footwear such as the stiffness of the upper material whilst simultaneously demonstrating the importance of controlling this feature. For both shoe manufactures and research these results have shown the effect of a systematic increase in heel height which has enabled the first pressure and comfort based definition of a high heeled shoe. From this information designers will have a greater understanding of how their designs will have an effect on the plantar pressure and comfort experienced by the wearer.
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