<p>Previous studies have suggested that trunk muscular strength is an important factor for the competitive ability of female judo athletes. The purpose of this study was to clarify the characteristics of lightweight, middleweight, and heavyweight class athletes with decreases in peak torque according to increases in angle velocity. The subjects were 61 female judo athletes consisting of 28 lightweight, 17 middleweight, and 16 heavyweight class athletes without lower back pain. We used the CYBEX 770-Norm System with a Trunk Extension / Flexion Unit to measure peak torque during trunk extension and flexion. The peak torque was measured at angle velocities of 30, 60, 90, 120, and 150 deg/s, according to the CYBEX TEF standard protocol.</p><p>The results we achieved are as follows.</p><p>1.Peak torque during trunk flexion at all angle velocities showed a tendency to be larger in the following order: heavyweight group, middleweight group, lightweight group. At an angle velocity between 30-120 deg/s, the differences among the 3 groups are significant (P < 0.05 or P < 0.01). At an angle velocity of 150 deg/s, the difference between the lightweight and middleweight groups, as well as the difference between the lightweight and heavyweight groups, is significant (P < 0.01). However, the difference between the heavyweight and middleweight groups is not significant.</p><p>2.Peak torque during trunk extension at all angle velocities showed a tendency to be larger in the following order: heavyweight group, middleweight group, lightweight group. At all angle velocities, the differences between the heavyweight and middleweight groups and the lightweight group is significant (P < 0.05 or P < 0.01). However, the difference between the heavyweight and middleweight groups is not significant.</p><p>3.In both cases of trunk flexion and extension, the index showing the change in gradient in peak torque according to the increase in angle velocity (the x coefficient of the regression line) lowered in the following order: heavyweight group, middleweight group, lightweight group. The difference between the heavyweight and lightweight groups is significant (P < 0.05 or P < 0.01).</p><p>These results suggested that heavyweight athletes have a higher trunk strength but also the possibility of having a larger decrease in trunk strength accompanied by an increase in movement speed, when compared with middleweight and lightweight female judo athletes.</p>