Patellar forces during isokinetic knee extension

Eight healthy male subjects performed isokinetic maximum knee extensions from 90 degrees flexion to full extension in a CYBEX n apparatus at two different speeds (30° and 180° s(-1)). Using a planar biomechanical model of the patellofemoral joint, the patellar forces in the sagittal plane were quantified. At the slower speed the patellofemoral compressive force and the suprapatellar tendon force reached values of about 12 bodyweights while the infrapatellar tendon force did not exceed 9 bodyweights. At the faster speed, the corresponding force magnitudes were 7.5 bodyweights and 5.5 bodyweights. The force peaks occurred at the beginning of the extension movement between 65° and 75° of knee flexion and were a function of knee angle and knee extension strength. The magnitude of the patellar forces during isokinetic knee extension of maximum effort were compared to other knee extending activities and were found to be considerably higher than during walking, jogging, and cycling.