In the interconnected network of the neuromuscular system, the size of the muscle seldom equates to the relative input to the nervous system. Many very large muscles have surprisingly little input into the nervous system, while quite a few very small muscles have disproportionately large impact. The reason for this is probably dependent upon location and function.
Much of this process can be counter-intuitive; I would suspect that few therapists would target these muscles based solely on palpation. Yet, the impact is great.
This is not unlike our social web. My good friend, Dr. Gene Robinson of the University of Illinois has done extensive (and world renowned) study of the social relationships of bees. By putting very small GPS trackers (yes, you read that correctly) on honeybees, it is clear that some bees have far more extensive social connections than others. If you want to influence the greatest amount of bees in the colony, these hyper-connected bees are the way to make that happen. Great marketers also know this principle- get your message to "connectors" and they will influence the greatest amount of people.
The human nervous system is no different- influence matters. Very large muscles with a relatively small capacity to impact the nervous system are not the "influencers" we are looking for. How exactly is that influence measured?
The science behind this is quite interesting, but the bottom line is to influence, one must have a wealth of neurotransmitter capacity. An excellent example of this capacity is the very small rectus capitis posterior minor (RCPM). This tiny muscle, hiding behind the semispinalis capitis, is richly endowed with neural capacity. For instance, the gluteus maximus has .7 muscle spindles per gram. The RCPM has 36! Small muscle, loud voice.