Shear stress measured on beds and wheelchairs.

Local shear is understood to be one of the principal risk factors for the development of pressure sores. There is a need for a small deformable sensor that can measure the shear force between skin and deformable materials without disturbing the shear phenomenon. In the present study a new shear sensor is introduced with a contact area of 4.05 cm2. A series of validation experiments was performed with ten healthy young subjects. It was demonstrated that with a forward-tilted seat, the sum of the local shear forces between skin and sensormat is equal to the resultant shear force measured with a force plate. This result serves as a validation of the new sensor. The shear values recorded are 4.8 kPa in the longitudinal direction and 8.5 kPa in the transversal direction while sitting in a wheelchair, and 5.6 kPa in the longitudinal direction and 3.1 kPa in the transversal direction on a mattress of a hospital bed, while in sitting position in bed.