An outsole sample is mounted in the clamps of the flexing machine with the flexing line positioned over the centre of the flexing roller. The operator adjusts the device to ensure that the test piece is at maximum flex position and always aligned with the axis of the mandrel, then pierces the test piece at a specified position with a cutting tool. After switching on the machine to bend the test piece at a constant rate between 135 cycles per min and 150 cycles per min through an angle of（90 ± 20）° about the axis of the mandrel for the given number of flexes, the cut growth or initiation of cracks in the outsole may occur. The length of the cut is measured with a measuring device and compared with the length before flex to determine the flex resistance of the sample outsole.
Because this flex resistance method is only applicable to the outsoles having an upper limit of 30 N longitudinal rigidity, a machine for the measurement of the longitudinal rigidity of outsoles, named Outsole Bending Stiffness Tester, is indispensable to help in completing the outsole flex resistance test.