Kawakami Y, Nakazawa K, Fujimoto T, Nozaki D, Miyashita M, Fukunaga T

Eur J Appl Physiol 1994;68(2):139-147

Series cross-section images of the upper extremity were obtained for four men by magnetic resonance imaging (MRI) andanatomical cross-sectional areas (ACSA) of elbow flexor muscles [biceps brachii (BIC), brachialis (BRA), brachioradialis(BRD)] and extensor muscles [triceps brachii (TRI)] were measured. Physiological cross-sectional area (PCSA) was calculatedfrom the muscle volume and muscle fibre length, the former from the series ACSA and the latter from the muscle lengthmultiplied by previously reported fibre/muscle length ratios. Elbow flexion/extension torque was measured using an isokineticdynamometer and the force at the tendons was calculated from the torque and moment arms of muscles measured by MRI.Maximal ACSA of TRI was comparable to that of total flexors, while PCSA of TRI was greater by 1.9 times. Within flexors,BIC had the greatest contribution to torque (47%), followed by BRA (34%) and BRD (19%). Specific tension related to theestimated velocity of muscle fibres were similar for elbow flexors and extensors, suggesting that the capacity of tensiondevelopment is analogous between two muscle groups.