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)