title: Morphology of the brachial biceps muscle and elbow flexion in man.
abstract: This study was undertaken to determine whether skeletal muscle fibre characteristics could be demonstrated to be of significance for muscle function in voluntary contraction in man. 4 male and 4 female adult subjects were studied. During elbow flexion force and velocity was measured at the hand with the forearm in a 100 degree position. A motor-driven heavy flywheel guaranteed a constant velocity or movement at the time of measurement. Force was registered by a straingauge dynamometer, and velocity by two sets of photocells. Cross-sectional area of the brachial biceps muscle was determined by computerized tomography scanning. Muscle fibre composition and fibre cross-sectional areas were assessed histochemically on needle biopsy samples obtained superficially from the brachial biceps muscle, the more superficial of the two large elbow flexor muscles. At contraction velocities from 2 to 7 radians per second (rad/s) a close relationship existed between the relative force output and the relative area of fast-twitch fibers (p less than 0.01). Maximal voluntary isometric contraction force averaged 189 N (120 to 309 N), and showed a close relationship with total cross-sectional area of the brachial biceps muscle. The specific tension (maximal isometric tension) of the muscle averaged 33 N/cm2 with no demonstrable difference between subjects of widely different fibre compositions, suggesting that maximal tetanic tension is similar in fast- and slow-twitch fibres in man.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000328:Adult; D004550:Elbow / Q000502:physiology*; D005260:Female; D006651:Histocytochemistry; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D009210:Myofibrils / Q000201:enzymology; D012737:Sex Factors; D014057:Tomography, X-Ray Computed
chemical_list: D000251:Adenosine Triphosphatases