Muscle contractions are composed of an electrical event associated with motor unit activation through the nervous system from the brain (i.e. intention) and subsequent mechanical events due to the interaction of the contractile proteins. An in-vivo study of muscle function often involves recording the action potentials of motor units and measuring the net force produced by agonist and antagonist muscles around a joint. In some studies, the measurements also include the transverse displacement of the skin surface over the contracting muscle which has been termed the surface mechanomyogram (MMG). The skin displacement can be deduced from measuring acceleration.