The complex relationship between musculoskeletal architecture and muscle function is an intriguing one:​ Are animals born with immutable muscle and joint structure characteristics, or is musculoskeletal architecture dictated by functional demands? Classic research in comparative functional morphology suggests that the musculoskeletal architectural parameters (such as muscle fascicle length, pennation angle, muscle thickness, and moment arm) of many animals allow them achieve maximal performance. This correspondence of form and function has been demonstrated in animals such as the cheetah, the fastest running animal, and the frog, one of nature’s best jumpers,

While muscle architecture and joint structure have been shown to influence function in animals, the relationships between musculoskeletal architecture and muscle function are not well established for many human movements. Previous investigations have established that fascicle length, pennation angle, and muscle thickness influence muscle function through the force length and force velocity properties of muscle. Muscle moment arm, however, has received less attention. Muscle moment arm affects the force-, moment-, and power-generating capacity of a muscle such that a muscle with a smaller moment arm may operate on more favorable regions of the force length and force velocity curves, although mechanical advantage may be sacrificed to do so.

Human locomotor performance is often evaluated using gait analysis, but the influence of musculoskeletal architecture on variables measured in the gait laboratory has received little attention. The overall goal of this dissertation was to investigate the link between musculoskeletal architecture and locomotor performance in sprinters and older adults, populations that have obvious functional demands. In vivo measurements of lateral gastrocnemius muscle and ankle joint structure were made, as well as assessments of locomotor performance through gait analysis. Our findings suggest that sprint performance may be enhanced by shorter plantarflexion moment arm and longer toes as demonstrated by in vivo measurements using ultrasonography and a simple computer simulation of the sprint push-off. Those two musculoskeletal architecture parameters permit generation of greater forward impulses which is essential during the acceleration phase at the start of a sprint race.

Reductions in ankle plantarflexor function with advancing age, in the form of decreases in strength and power, have been shown to correlate with slower gait in the elderly. Our findings show that plantarflexor moment arm is a strong predictor of gait velocity in elderly individuals who walk slowly. In addition, several musculoskeletal architectural parameters of the lateral gastrocnemius were found to correlate with ankle kinematic, kinetic, and spatiotemporal gait parameters during gait at slow, preferred, and fast speeds in elderly individuals. These specific results suggest that age-related changes in muscle and joint architecture may be associated with declines in mobility, specifically walking, through their influence on plantarflexion rangle of motion and plantarflexor moment and power. The studies of sprinters and older adults in this thesis provide insight and understanding into the influence of musculoskeletal architecture on plantarflexor function. It is hoped that these findings will lead to targeted training protocols that will improve locomotor performance and quality of life for the elderly.