Researchers commonly study arm movements to gain insight into the neural control of movement. However, quantitative descriptions of muscle architecture and moment arms needed to understand the force and moment-generating capacities of the elbow muscles are incomplete. The variation of muscle architecture and moment arms across the population is also unknown. The goal of this dissertation was to evaluate the functional capabilities of the elbow muscles based on measurements from anatomical specimens encompassing a large size range.

Biceps brachii, brachialis, brachioradialis, extensor carpi radialis longus, pronator teres, and triceps brachii were studied in ten upper extremity specimens, ranging in size from a 5'0" female to a 6'4" male. Flexion moment arm, musculotendon length, muscle length, fascicle length, sarcomere length, pennation angle, and mass were measured in each muscle. Muscle operating lengths and isometric moment-generating potentials were estimated by combining the muscle architectural parameters and moment arms of each specimen. Anthropometric dimensions were also measured, and muscle attachment sites and joint surfaces were digitized on each humerus, radius, and ulna. The accuracy with which elbow flexion moment arms can be estimated from musculoskeletal geometry was investigated using both linear regression analysis and specimen-specific biomechanical models created from digitized bone surfaces and magnetic resonance images.

Analysis of muscle architectural parameters showed that the elbow muscles encompass a wide range of force and excursion capacities. Despite substantial differences in muscle architecture and moment arms between specimens, there were clear distinctions in the functional capabilities of the individual elbow muscles. Linear regression analysis revealed that the shorter distance (Ds) between the elbow flexion axis and a muscle’s attachment sites explained 96% of the measured variation in peak moment arms. Bone length was not significantly correlated to peak moment arm unless bone length was also significantly correlated to Ds. Moment arms estimated from specimen-specific biomechanical models and from normalized elbow flexion moment arm curves scaled by anthropometric dimensions captured the salient features of elbow muscle moment arms. This work emphasizes the importance of both muscle architecture and moment arms in determining muscle function.