Effects Of Bicycle Crank Length On Hip And Knee Joint Kinematics And Compressive Forces

Abstract

PURPOSE: Crank length (CL) on a bicycle may affect knee and hip joint compressive forces and range of motion (ROM). The relationship between knee/hip joint forces, moments, and ROM can have an influence on hip and knee joint health (i.e. osteoarthritis, patellofemoral disorder, ligament damage, etc.). The purpose of this study was to examine the effects of four different CL (155, 165, 175, and 185 mm) on ROM and resultant compressive forces on the hip and knee. METHODS: 12 non-cyclists (4M, 8F, aged 18-55) participated in a single blind randomized cross-over experiment with four CL. An Enhanced Helen Hayes marker protocol was used to place 32 retroreflective markers on anatomical landmarks to track kinematic data using a 12-camera 3D motion analysis system with Cortex software (Motion Analysis Corp., CA, USA). Kinetic data were collected using a stationary bike (SRM IndoorTrainer, Germany) retrofitted with custom pedals containing 6-axis load cells (AMTI, MA, USA). A 3 minute warm-up for each CL was performed at 1.5 W/kg and 70 rpm. 4x1 minute trials were conducted at 2 W/kg. The first two trials were at a constant cadence of 70 rpm and the second two trials were at a constant pedal speed (PS) of 1.47 m/s. There were 10 seconds of rest between trials and 5 minutes of recovery between each condition. Kinematic data was processed using Cortex software and filtered (4th order Butterworth, cutoff 6 Hz). Kinetic data was filtered using MATLab (MathWorks, MA, USA). All data was averaged from 30 seconds of each trial. RESULTS: During submax cycling, the 155 mm CL had a significantly smaller hip ROM (42 deg vs. 49 deg; p<0.05) and a significantly smaller knee ROM compared to the 185 mm CL (72 deg vs. 80 deg, p<0.05). No significant differences were found at a cadence of 70 rpm: 155 mm CL peak hip compressive force (1.3 N/kg) vs. 185 mm CL (0.9 N/kg); 155 mm CL peak knee compressive force (2.8 N/kg) vs. 185 mm CL (2.6 N/kg). No significant differences were found at a PS of 1.47 m/s: 155 mm CL peak hip compressive force (0.6 N/kg) vs. 185 mm CL (0.7 N/kg); 155 mm CL peak knee compressive force (2.3 N/kg) vs. 185 mm CL (2.5 N/kg). CONCLUSION: Hip and knee ROM was significantly greater with a longer CL. There are no significant differences in hip or knee peak compressive forces. Implementation of a shorter CL at a PS of 1.47 m/s may minimize peak hip and knee joint compressive forces.