Sexual dimorphism in the mechanical advantage of the biceps brachii muscle

The force generated by a muscle may be influenced by the length of its lever arm, the distance between its insertion and the point of resistance. Shorter lever arm length contributes to greater force as the effort (muscle contraction) is brought closer to the point of resistance. This study tested whether strength differences between males and females in flexion of the elbow are related to sexual dimorphism in the mechanical advantage of the biceps brachii muscle utilizing the ratio of lever arm to resistance arm lengths. The lever arm was quantified as the distance from the radial biceps brachii insertion on the radial tuberosity to the radiohumeral joint while the resistance arm length was defined as the distance from the distal‐most point on the ulna to the superior‐most point on the ulnar olecranon process. A mixed sex sample (n=24; 12 males and 12 females) of left arms was measured. Results show that the male values (.1653 – .2189) are slightly greater than those of the females (.1475 – .1948). However, this difference was not statistically significant (p=0.086). It appears that, despite a slight tendency toward sexual dimorphism, the length of the lever arm of the biceps brachii muscle is functionally constrained among humans. Strength differences between males and females may instead be attributable to cross‐sectional thickness of the biceps brachii and brachialis muscles. Grant Funding Source : None