Applied mechanics for humans: challenges in sports engineering

Abstract

This paper describes some of the challenges encountered when applying mechanical principles to human biomechanical problems, using examples from the author’s experience in sports-related research and product development. As a mechanical system, the human body is unlike any man-made machine or mechanism. Its framework adapts to support habitual loads. Its actuators rely heavily on elastic properties and appear to regulate the stiffness of limbs rather the applied force or displacement. Its motion control systems can appear chaotic, with the consequence that even repetitive, cyclic movements patterns (e.g. walking and running) are highly variable. A speed suit development project illustrates the contribution a biomechanical perspective can bring to a sports engineering project. In this case, kinematic analyses of sprinters and speed skaters were used to document the continually varying velocities and orientations of the body’s segments relative to the air flow. This information allowed the aerodynamicists to test suit materials under appropriate conditions and to select different materials for different parts of the suit. As a second example, the selection of materials for American Football helmets begins as a classical cushioning design problem. Empirical descriptions of the impact tolerance of the head constrain the possible solution but helmets can be engineered to prevent skull fractures and traumatic brain injuries. The prevention of mild traumatic brain injury (concussion) remains an unsolved problem, however, and a mechanical solution may not exist. In comparison to a helmet, athletic shoe cushioning systems are required to handle relatively low forces and impact energies. Designing a running shoe that attenuates impact shock is, mechanically speaking, a relatively trivial task. The mechanical processes underlying some other important, related functions of the sports shoe are less well defined. “Comfort” and other perceptual responses, for example, are harder to measure than impact shock, and consequently more difficult to engineer. The application of mechanical principles to human biomechanical problems can generate some unique problems, but the paths taken in an effort to find innovative, practical solutions will be familiar to engineers working almost any field.