Foot blisters are related to excessive frictional forces experienced on or under the foot. For this reason, they are common in competitive sports and in military service.
This study sought to reveal the distribution of plantar shear forces in athletic individuals and its relevance to foot blisters.
Thirty-three volunteers were recruited and divided into three groups – one group with 11 active runners suffering from frequent blisters; a second group of 11 moderately active adults with no history of frictional blisters; and a third group of 11 physically active paediatric individuals.
Local barefoot forces were collected using a custom-built shear and pressure platform consisting of 80 sensors.
The forefoot region was of primary interest because athletic blisters most frequently occur in this area.
A custom-written Matlab code was used to mask five regions of the foot: the hallux, lessor toes, first metatarsal head, central metatarsal head region and lateral metatarsal head region.
Six parameters were determined for each of these five regions: peak pressure, peak resultant shear stress, peak-to-peak anteroposterior shear, peak-to-peak mediolateral shear, peak resultant shear-time integral, and peak anteroposterior shear-time integral.
Upon quantifying plantar shear stress distribution in athletic individuals, it was found that their shear forces were elevated compared with those of the control groups.
This increase in the shear parameters occurred despite the fact that athletic individuals walked 16% slower than the paediatric control group and at approximately the same speed as the adult control group.
This finding may be due to different frictional properties of the skin, intrinsic muscle activity, or increased pressure magnitudes.
The authors suggest further investigating whether foot blisters develop in areas with high shear stress. They also encourage studying increase in local temperature under the foot due to kinetic friction, as this may be relevant to blister formation.
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