From motor unit to whole muscle properties during locomotor movements

Over the last century, progress has been made in understanding the basic structure and function of muscle. The emphasis on muscle research has become increasingly focused at the molecular level, and startling advances have been made. Surprisingly, at the whole muscle level significant questions remain unanswered. The details of how muscles are actually used in locomotion are lacking. The foregoing sections have discussed some basic muscle properties and then reviewed instances in which they have been directly measured during locomotor movements. Although most of the basic functional properties of muscle are known, some simple questions such as what the preferred operating point is on the F-L and F-V curves remain unanswered. Design principles of muscle structure and their control by the CNS have yet to be illuminated. Most in vivo techniques to study muscle function are difficult to use. This precludes their use on all but a small number of specialized muscles. With the exception of photography and electromyography, at best a small number of muscles can be studied at a time. The technique of measuring some muscle properties in vivo and then duplicating the conditions in an isolated muscle for further measurements seems promising. Combinations of mathematical models and careful experimental verification will also be necessary.