Force and repetition in cycling: possible implications for iliotibial band friction syndrome.

This study examined force and repetition during simulated distance cycling with regard to how they may possibly influence the on-set of the overuse injury at the knee called iliotibial band friction syndrome (ITBFS). A 3D motion analysis system was used to track lower limb kinematics during cycling. Forces between the pedal and foot were collected using a pressure-instrumented insole that slipped into the shoe. Ten recreational athletes (30.6+/-5.5 years) with no known history of ITBFS participated in the study. Foot-pedal force, knee flexion angle and crank angle were examined as they relate to the causes of ITBFS. Specifically, foot-pedal force, repetition and impingement time were calculated and compared with the same during running. A minimum knee flexion angle of approximately 33 degrees occurred at a crank angle of 170 degrees. The foot-pedal force at this point was 231 N. This minimum knee flexion angle falls near the edge of the impingement zone of the iliotibial band (ITB) and the femoral epicondyle, and is the point at which ITBFS is aggravated causing pain at the knee. The foot-pedal forces during cycling are only 18% of those occurring during running while the ITB is in the impingement zone. Thus, repetition of the knee in the impingement zone during cycling appears to play a more prominent role than force in the on-set of ITBFS. The results also suggest that ITBFS may be further aggravated by improper seat position (seat too high), anatomical differences, and training errors while cycling.