Biomechanical Properties of the A2 Pulley in Rock Climbers

Abstract

Rock climbers prefer and often use the crimp grip position which enables the athlete to hold smallest ledges. Force transmission of the flexor tendon to the distal edge of the A2 pulley is maximal and the load to it about 4 times as high as at the fingertip. Use of crimp grip may lead to tendosynovitis, partial or complete ruptures of the pulley particularly if the warm up procedure has not been conducted properly, which involves at least 100 climbing moves. Under maximal load, friction between flexor tendons and pulleys is responsible for up to 18% of the holding force. Friction shows a clear correlation with the degree of flexion of the PIP (proximal interphalangeal) joint being maximal at 90°. There is also an interdependence of friction on the speed of movement. At high speed friction is considerably higher (37% strength deficit) than at low speed (15% strength deficit, which is in the range of normal muscular eccentric/concentric strength deficit). These findings explain why pulley injuries often occur during crimp grip (PIP joint flexed >90°) and happen during a sudden high eccentric load to the PIP joint. Friction has to be taken into account as an important factor in the biomechanics of finger modelling in sport climbing and the explanation of the pathophysiology of pulley injuries.