The bulk of the muscle you are using for an acoustic window is the brachioradialis muscle.
It makes a lovely window allowing a high resolution view of the tendons.
It is interesting that we don’t ever really think about brqchioradialis as it is never really injured and we are very rarely asked to assess it. But it is a really big muscle. The design features of brachioradialis mean that it is rarely pathological.
It also provides excellent protection to the superficial branch of the radial nerve in the forearm.
It is an unsung hero !!
Steve.