A force sensor for detecting at least a force acting in a longitudinal direction of a catheter or guide wire, the force sensor comprising a force pick-up for detecting the force, wherein the force pick-up comprises: a base body with an end face, wherein the base body includes at least one cutout, wherein the cutout causes an asymmetry of the base body relative to the longitudinal direction of the catheter or guide wire upon flexing of the base body upon force Fz loading thereon from an axial direction, wherein the end face includes a surface area that is substantially greater than the cross-sectional area of the base body in the region of the cutout, but not substantially smaller than the cross-section of the rest of the base body. A method for using this force sensor is also disclosed.