Acoustic reflex contraction of the stapedius muscle stiffens the middle-ear, thus decreasing middle-ear admittance; this can be measured thanks to tympanometry. The acoustic stapedius reflex can also be recorded by means of extratympanic manometry (ETM). As the stapedius muscle is innervated by the facial nerve, a measurement of the reflex can be used to locate the injury on the nerve. If the injury is distal to the stapedius muscle, the reflex is still functional. A measurement of the reflex can also be used to suggest a retrocochlear lesion (e.g., vestibular schwannoma, acoustic neuroma). The acoustic reflex normally occurs only at relatively high
In vitro muscle testing the level which ensures maximal motor unit recruitment. The servomotor can be programmed to maintain a given force while allowing the muscle to change length, vice versa, or the muscle may be subject to more complex testing, such as in work loops. When pennate muscles are used, sonomicrometry is often used to accurately determine fiber length during the test. "In vitro" muscle testing can be done on any scale of muscle organization - entire groups of muscles (provided they share a common insertion or origin, as in the human quadriceps), a single muscle, a "bundle" of muscle fibers, a single