The sense of position and movement of one’s body is referred to as ‘proprioception’, and is particularly important for sensing limb position (stationary proprioception) and limb movement (kinaesthetic proprioception). Proprioception relies on special mechanoreceptors in muscle tendons and joint capsules. In muscles there are specialized stretch receptors (muscle spindles) and in tendons there are Golgi tendon organs, which sense the contractile force. In addition, stretch sensitive receptors signalling postural information are in the skin. This cutaneous proprioception is particularly important for controlling movements of muscles without bony attachment (lips, anal sphincter). By these means of afferent input the functional status of a striated muscle (or rather: a certain movement) is represented in the brain. Indeed, muscle awareness reflects the amount of sensory input from various sites. Typically, feedback to awareness on limb muscle function (acting at joints) is derived not only from their input from muscle spindles, and receptors in tendons, but also from the skin, and from visual input, etc. The concept of the ‘awareness’ thus in fact overlaps with the ability to voluntarily change the state of a muscle
In contrast to limb muscles, the PFM (and sphincters) lack several of the above mentioned sensory input mechanisms and therefore the brain is not ‘well informed’ on their status. Additionally, there may be a gender difference, inasmuch as pelvic floor muscle awareness in females seems to be in general less compared to males. (The author concludes this on the basis of long personal experience with PFM EMGs in both genders; there seems to be no formal study on PFM activation patterns in man apart from ejaculation.)
Healthy males have no difficulties in voluntarily contracting the pelvic floor, but up to 30% of healthy women cannot do it readily on command. The need for ‘squeezing out’ the urethra at the end of voiding and the close relationship of penile erection and ejaculation to PFM contractions may be the origin of this gender difference. The primarily weak awareness of PFM in women seems to be further jeopardized by vaginal delivery.