The application of b-mode ultrasonography for analysis of human skeletal muscle

Skeletal muscles control the joints of the skeletal system and they allow human movement and interaction with the environment. They are vital for stability in balance, walking and running, and many other skilled motor tasks. To understand how muscles operate in general and specific situations there are a variety of tools at the disposal of research scientists and clinicians for analysing muscle function. Strain gauges for example allow the quantification of forces exerted during joint rotation. However, skeletal muscles are multilayer systems and often different muscles are responsible for the overall force generated during joint rotation. Therefore, strain gauges do not reveal the extent of the contribution of individual muscles during muscle function. The most widely-used and accepted muscle analysis tool is electromyography (EMG), which can measure the activation level of individual muscles by measuring the electrical potential propagating through muscle resulting from local activations of motor units. However, EMG does not linearly relate to any real physical forces, meaning that without prior knowledge of the force exertion on the level of the muscle, force cannot be estimated. EMG can measure superficial layers of muscle non-invasively by attaching surface electrodes (surface EMG) to the skin over the belly of the muscle. To measure the activity of individual muscle beneath the superficial muscle, a needle or thin-wire electrode must be inserted through the skin and into the muscle volume (intramuscular EMG), which is invasive and not practical in many situations. Furthermore, intramuscular EMG can only provide measurement of a very small volume (