The promise post about energy. This is just to start. I´m not going to make the connection to the practice, by writing, I will leave that task to you… I will keep my research!
One possible definition…
1. The capacity for work or vigorous activity; vigor; power.
2. The capacity of a physical system to do work.
Etymology: Gk, energia
The capacity to do work or to perform vigorous activity. Energy may occur in the form of heat, light, movement, sound, or radiation. Human energy is usually expressed as muscle contractions and heat production, made possible by the metabolism of food that originally acquired the energy from sunlight. Chemical energy is that released as a result of a chemical reaction, as in the metabolism of food.
(in Mosby’s Medical Dictionary, 8th edition. © 2009, Elsevier)
About the muscles work:
“Energy doesn’t flow through tight muscles […]. Stretching and flexibility are about more than being able to kick high.”
“When a muscle is tight it can’t move and you have to relax it before you can do anything with it. The more loose and relaxed you can be on a moment to moment basis the faster and more easily you’ll be able to move. When your muscles are loose and relaxed your energy flows better also because it doesn’t have to overcome the resistance of the tight muscles, which leads into the next concept.”