BACKGROUND: Disruption of the finger flexor tendon pulleys are the most often occurring injury in rock climbers due to bowstringing of tendons during crimp grip position. The aim of this study was to quantify friction between the flexor tendons and pulleys and the influence of high load and speed of movement as a potential factor of pulley disruption. METHODS: Friction between the flexor tendons and pulleys of eight human cadaver fingers was indirectly determined using an isokinetic movement device. During flexion and extension movement with rotational speed from 30 to 210 deg/s in the proximal interphalangeal joint and with load from 20 to 100 N to the flexor tendons the flexion force at the tip of the finger was measured. FINDINGS: With 40 N loaded flexor tendons the force at the fingertip was 14.5 N (SD1.5) during extension and 12.6N (SD1.3) during flexion movement. Corresponding force difference of 12.9% and 3.77 N (SD0.6) force of friction can be calculated. Friction peaked at 85.8 degrees (SD2.05) of flexion of the proximal interphalangeal joint. Different speed of motion and load to the flexor tendons did not influence force difference other than linear. INTERPRETATION: Considerable friction between flexor tendons and pulleys is apparent and therefore may have an influence on pulley injuries. Particularly during the crimp grip position where the proximal interphalangeal joint is flexed about 90 degrees shows the greatest amount of friction. However there was no change of friction during high speed motion and no other than linear increase during high load.