Why do the leg and pelvic muscles play such an important role in our Qigong exercises with the horse-riding stance?

Why do the leg and pelvic muscles play such an important role in our Qigong exercises with the horse-riding stance?
One of the main reasons is the muscle endocrine function.
A study shows leg resistance exercises pump out more testosterone than elbow flexor exercises do, where  elbow flexor exercises almost do nothing significantly. Quantitatively, the leg resistance exercise men produce 2 times more testosterone than the elbow flexor exercise ones do during the experiments, as shown in
“Resistance exercise-induced increases in putative anabolic hormones do not enhance muscle protein synthesis or intracellular signalling in young men”
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2790261/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2790261/pdf/tjp0587-5239.pdf

Our Qigong exercises are inspired by Wudang Snake, Cheng Style BaguaZhang Mother Palm 八卦掌母掌(low body and leg movements, such as crouching step) , Bioelectricity/Qi , and Kundalini Chakras Awakening
https://www.youtube.com/watch?v=8Up2Mnq7JSM
https://www.youtube.com/watch?v=z12uQY4RTGQ
https://www.youtube.com/watch?v=msbYQOg42zk
The pelvic floor and adductor muscle stretch and gluteus muscle contraction with a load of body weight in a horse-riding stance are highly resistance exercises. BaguaZhang’s low body and leg movements energize the Kundalini  snake in the root Chakras/下丹田/會陰/長強 (the pelvic floor, gluteus, tailbone, and adductor muscles)

Qigong – the Emulation of the Electric Eel’s Bioelectric Generation via the Cyclic Stretching of Epithelial Cells in the Linings of Body Cavities and Organ Surface

Qigong – the Emulation of the Electric Eel’s Bioelectric Generation via  the Cyclic Stretching of Epithelial Cells in the Linings of Body Cavities and Organ Surface

Qigong’s deep breathing (stepwise/digital inhaling and holding) exerts mechanical stimuli  that are transduced into intracellular signals in lung alveolar epithelial cells (AEC) .  The mechanical stress is an important regulator of cell growth  and because extracellular signal-regulated kinase 1/2 (ERK1/2)  are believed to be vital components of proliferative pathways
http://ajplung.physiology.org/content/282/5/L883

Qigong deep breathing pumps the main body’s three cavities – the thoracic, abdominal and pelvic cavity to stretch the epithelial cells in the cavity linings and the internal organs, resulting in bioelectric generation via the piezoelectric effect and the cellular ion-channel depolarization.  The generated bioelectric pulses thus charge the dopamine nervous system via the vagus nerves.  The Qigong effectiveness on the brain and nervous function is better than drugs’.

Qigong stretching exercises stretch cells and provide a general means of altering protein conformation to generate signals.  Force-induced effects on conformation trigger the muscular endocrine mechanism in which enzymatic activity or protein interactions chemically mediate bioelectric signaling, in addition to depolarizing the afferent neuron producing an action potential with sufficient depolarization.
http://www.sciencedirect.com/science/article/pii/S153458070500482X
http://en.wikipedia.org/wiki/Stretch-activated_ion_channel#cite_note-Purves.2C_p.207-209-1
More information on stretch-activated ion channel –
http://www.nature.com/scitable/topicpage/ion-channel-14047658 (this article describes the basic of ion channel.)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1193237/pdf/jphysiol00593-0701.pdf
http://ajpheart.physiology.org/content/262/4/H1110.short
http://link.springer.com/article/10.1007/BF00582635
http://jap.physiology.org/cgi/pmidlookup?view=long&pmid=10642367
http://jap.physiology.org/content/94/6/2475
http://www.ncbi.nlm.nih.gov/pubmed/15298539
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1474216/
Stretch-Activated Ion Channels: What Are They?
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2924431/