Techniques are disclosed of constructing a computer-based musculoskeletal model physically representing bones and muscles of a human body. These techniques include: defining as a first pivot-axis-direction for a selected joint, a direction of an axis about which selected bone models are pivoted relative to each other in response to expansion/contraction of a selected muscle model; defining as a second pivot-axis-direction, a direction of an axis about which the selected bone models are pivoted relative to each other in response to a specified motion imparted to the human body; and redefining the first pivot-axis-direction, as a function of a relative angle of the first pivot-axis-direction to the second pivot-axis-direction.