of the medial femorotibial joint cartilage were assessed using a 3T MR system (Verio; Siemens). The whole and superficial (half of the whole cartilage) cartilage in the medial knee joint were assessed. The study was approved the Ethics Committee, and the nature of the study was explained to all participants, and written informed consent was obtained. Results: The peak knee adduction moment (external) and angle between the 20s (4.8 10z 1.9 10 z) and 40s (5.8 10z 1.7 10 z) during free gait was not significantly different (Fig. 2). Although the first peaks of knee flexionmoment in the 40s (5.7 10z 1.7 10 z) were significantly larger than the values in the 20s (3.2 10z 2.6 10 z) (Fig. 3, P < 0.05), the knee flexion angle between the 20s and 40s was not significantly different. T2 values of the femoral superficial cartilage in the 40s (34.0 1.8 msec) were significantly higher than the values in the 20s (32.2 1.4 msec) (P < 0.01). The first peak of the knee flexion moment and the T2 in the 40s were not significantly correlated (r 1⁄4 0.21). Conclusions: Knee flexion moments in the 20s were higher than the moment in the 40s during free gait. Kinematic and kinetic change of the knee joint during gait due to the ages might start on the sagittal plane. Although T2 mapping values at the medial superficial femoral cartilage in the 40s were higher than the values in the 20s, the knee flexion moment is not related to T2 mapping values of knee joint cartilage. We could not conclude that the increased knee flexion moment is the preceding knee kinetic change of the early knee OA from this crosssectional study.