Frictional Behaviour of Running Sock Textiles Against Plantar Skin

Friction blisters on feet are a common dermatological injury among long-distance runners which can result from repeated shearing of the skin. Previous studies have shown that an increase in moisture level between the sock - skin interface tends to increase the friction and hence the likelihood of blister formation. For the past few decades, many new sock technologies have been developed based on the principle of friction reduction to prevent blisters such as ‘friction-free’ and double layer running socks. However, there have been very few published results on their frictional performance.Five different running sock materials were selected based on the variations of their knit pattern and fibre composition. The frictional behaviour of these sock materials against whole plantar skin was then assessed in dry condition. All tests were conducted using a bespoke rig that was developed at the University of Sheffield for studies on foot friction. 26 subjects were recruited for this purpose and friction was measured for a range of normal loads. Subjects’ feet were kept at their natural level of hydration, monitored at specific intervals using the Corneometer® CM 825 device.It was observed that there was a positive correlation (p<0.05) between foot hydration and friction force. However, no particular trend can be seen in the friction coefficient values between the tested sock types. This suggests that the properties of the subject's foot had more prominent effect on the friction levels than the knit pattern and composition of sock materials under dry contact conditions.Outcomes from this study indicate that the natural variations in the plantar skin and level of moisture present had a more substantial impact on friction behaviour than any changes in knit pattern or sock material, suggesting the control of moisture levels within the shoe environment is a key factor of concern.