Monitoring body kinematics and joint flexion has fundamental relevance in orthopedics and rehabilitation. The used sensing element is prepared from a highly-deformable polymer composite composed of a network of entangled electrically-conductive carbon nanotubes embedded in elastic polyurethane. The composite is prepared by an innovative procedure in which the non-woven polyurethane filtering membrane and the carbon nanotube cake are integrated by compression molding. As an example of the composite use as a strain sensor, human knee flexion and its cyclic movement is monitored, that may be applicable in athletic training as well as in orthopedics and rehabilitation.