Qigong Principle:  Use somatic motor nervous control to stretch and contract muscles and neurons to generate bioelectric currents to charge the vagus and spinal nerves via  stretch-activated ion channels.
http://www.nature.com/ki/journal/v48/n4/pdf/ki1995397a.pdf
This means Qigong electrically charge the nervous system and brain in Three (3) ways:
1. piezoelectric effects of biomass;
2. activation of ion channels;
3. hormone production from LDL via the muscle neuroendocrine function with the liver cytochrome P450 enzymes – http://en.wikipedia.org/wiki/Cytochrome_P450#mediaviewer/File:Steroidogenesis.svg

Qigong uses the somatomotoring nerves, aka mind control and movement, to generate piezoelectric , mechanical, thermomatic somatosensory and vagus / autonomic nervous responses via the coupling interneurons of the local spinal cord discs, and to cause the stretch-activated ion channel for depolarization and thus bioelectric generation,  in addition to the induction of the endocrine function in the vibrating (stretching and contracting) muscles. You use somatomotoring nerves to move your mind from cerebral cortex (百會穴, on the top of your head) to your thorasis, andomen and pelvic cavities (http://droualb.faculty.mjc.edu/…/chapter_10%20Fall%202011.h… ), and then contract the gluteus muscles against the tailbone (followed by squeezing/contracting the shoulder blades toward/ against the spine) to complete the somatic nervous action. Under the somatomotoring muscular and nervous stimulation, the somatosensory pathway transmits information from the local thermoreceptors and nociceptors in response to heat generated by the piezoelectric pulse and androgen hormone release in the tailbone and pelvic area, so that you can feel you are circulating Qi ! It is worthwhile to learn the somatic nervous circuit although the vagus and autonomic response circuits are another story to tell next. In fact, I use the the somatosensory stimulation on the periaqueductal gray (PAG) and nucleus raphe magnus (NRM) of the brainstem to initiate the endorphine and serotonin release to achieve the ejaculation /orgasmic control with the nociceptors in the pelvic floor (including prostate and seminal vesicles) for endorphine and serotonin nervous targeting while using both the bulbocavernosus( penile/clitoral S2-S4 nerve) <=> sacral reflex arc and the pubis => medulla oblongata => bulbocavernosus(penile/clitoral/uterine) vagus reflex arc to power enhance erection. You can prolong sex for 1-2 hours when endorphine and serotonin are releasing from PAG and NRM, as well as local erectile tissues (with an extremely erectile  ballooning effect), under nervous stimulation of central dopamine (oxytocinergic nervous pathway),  Nitric Oxide (parasympathetic-NOnergic nervous erectile mechanism) , norepinephrine (androgenic beta receptors – the sympathetic nervous erectile mechanism) and  epinephrine (androgenic beta receptors) – (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2993853/pdf/nihms245416.pdf ). I have trained midnight cowboys to take care of 10 ladies in one night by this way. In this regard, you have to last for 3 hours without back down. I means you must have sufficient dopamine in the hypothalamus to burn for 3 hours. Once the brain’s dopamine is burned out (that is a low dopamine with excessive norepinephrine and epinephrine), the pituitary gland releases prolactin to constrict your penile arteries, and then. your erection will go limp, that is the sympathetic nervous flight. Hereafter, your fun is over for a while. Some useful references: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2993853/pdf/nihms245416.pdf ; http://neuroscience.uth.tmc.edu/toc.htm; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2682726/pdf/nihms-106342.pdf; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3104618/pdf/hmj6903_0070.pdf; http://www.ncbi.nlm.nih.gov/pubmed/197601; http://press.endocrine.org/doi/pdf/10.1210/en.2003-1287

The principle of the Anal Breathing Qigong for ejaculation control or prolonging sex is based upon the trained cerebellar-tailbone reflex arc where the input sensory nerve can be from the eyes (visual sexual stimulation) , ears (audio sexual stimulation), penis, prostate, seminal vesicles or pelvic floor muscles. This trained reflex arc directs the response motoring efferent to the tailbone, instead of the prostate and the seminal vesicles, to prevent semen emission and ultimate ejaculation. It also activates the sacral => bulbocavernosus reflex arc for more powerful erection via the tailbone and anal muscles contraction.

OK. Let me outline Practices of Dr. Lin’s Aquila Anal Breathing QiGong- For Vagus And Spinal Nervous Stimulation (打通奇經八脈的天鷹牛郎迷走神功):

The horse-riding stance is the essential posture for Qigong practice.  This is becaues the horse-riding stance naturally expands or stretches the perineum (pelvic floor muscle) with groin pull or adductor muscle stretching, and relax the scrotum (hanging and moving freely), to allow Qi (somatomotor nervous flow) to sink (pulse) into the effectors testicles and glans penis (or clitoris, for women). In Tantra Yoga, it is called “Open the root Chakra.” In Qigong, it is named “Sink Qi to DanTien,” where DanTien is referred to the pelvic cavity that includes the organs inside and the testicles which was inside too in the fetus. 
Perform an elliptic rotation of your pubic bone ( http://action.love/PelvicEllipticMotions.wmv )with the following sequence: inhale into the pelvic cavity (sink Qi into DanTien); exert a light pressure against your bladder (focus Qi toward your pubis to activate the vagus nerve to the glans penis or glans clitoris); Sink your torso slightly (about 6 inches or so); Move your pubis forward (for pubic expansion and penile/clitoral vagus nerve stimulation) and then upward while contracting your gluteus maximus against your tailhone (for S1-S5 and Co nervous stimulation with a mild stimulation on L1-L5): Simultaneously expand your chest contract your shoulder blades against your spine (full spinal nervous stimulation from your tailbone (coccygeal) Co upto your cervical nerves C1,http://en.wikipedia.org/wiki/Spinal_cord… ) further bend your neck/head backward to compress your cervvical nerves and expand your thyroid gland when moving your pubis upward and continuously contracting your gluteus maximus against your tailbone, where you can repetitively perform the pelvic inhaling and pubic expansion and contract the gluteus and the shoulder blades against the tailbone and spine, respectively, for 5-20 cycles, at a rate of 1.25 second per cycle (or 0.8 Hz); Finally, return your pubis and torso back to the originally position with exhaling. Practice it for 20-30 minutes 2-3 times a day. Why should you practice 30 minutes? http://action.love/…/how-does-aquila-anal-breathing…/

The elliptic movement of the pubis and pelvic bones with horse-riding stance is the piezoelectric and sex-hormone generator for charging central dopamine- thalamus / hypothalamus-pituitary axis via the electrifying and hormonal stimulation of the vagus and peripheral nervous system – somatic nervous system and the autonomic nervous system with sensory nerves.