Abstract des Autors

The physiological cross-sectional area (PCSA) of knee extensors (KE) and flexors (KF) was determined using magnetic resonance imaging (MRI) in humans. Twenty-two healthy male volunteers were assigned to the subjects and MRI was taken to obtain 41-52 consecutive axial images (slice thickness; 10 mm, interslice gap; 0 mm) from right-leg thigh. From these images, anatomical cross-sectional area (ACSA) of KE and KF was determined. Muscle volume was calculated from the summation of each ACSA and the distance between each section. Muscle length was determined as the distance from most proximal to most distal images in which the muscle was visible. The PCSA of each muscle was calculated as muscle volume times the cosine of the angle of fiber pennation divided by fiber length, where published fiber length:muscle length ratio were used to estimate fiber length. The isokinetic knee extension and flexion (angular velocity; 30, 60, 180, 300, 450 deg/sec) was measured to estimate the muscle force at KE and KF. Specific tension of KE and KF was calculated as muscle force divided by PCSA. The mean muscle volume of KE and KF was 2178, 1141 cm**3. The ratio of KE:KF was 2.6. The mean fiber length in KE was 7-8 cm, and in KF was 6-42 cm. Peak torque during knee extension was significantly higher than knee flexion at all angular velocities. The specific tension of KF was higher than that of KE at all tendon velocities. Moreover, in relationships between specific tension and tendon velocity/fiber length, KF was still higher than KE. These results suggest that the capacity of tension development differ between KE and KF under the same shortening velocity per unit of sarcomere. Verf.-Referat