It's a good question - with a very complex topic. There are many levels of 'depth' you can go into it... There are many contexts - jing in qigong is one context, jing in Chinese medicine is another, jing in alchemy yet another...   So I'll try my best relate the fundamentals as best I can - mostly at the context of medicine or development in the human body...   Dwai put it quite nicely - Jing, Qi and Shen exist along a spectrum of vibration. They are discussed as separate things, but in fact, they're aspects of the same thing, just at different stages of the spectrum - from the most ethereal to the most corporeal... Jing is at the densest end of the spectrum - before it becomes matter. It is not matter. It is not fluids. It isn't sperm. It's not a substance...   You can think of jing in two ways - as a 'fuel' and as a 'blueprint' for the unfoldment of life processes...   Jing is also split into two major categories: Post-natal jing and Pre-natal jing.   Your prenatal jing conditions much of your constitution on a blueprint level. It is informed by many aspects - everything from karma to your bloodline - your parents, and the generations before... it's also strongly informed by astrological factors at the moment of conception and birth... and it is strongly informed by the 9 months spent in the womb - so your mother's quality of postnatal jing at that time - her qi, her mind and emotional state.   Jing manifests into the body at the area of the Ming Fire (in the area between the kidneys, ming men etc.) The "fire" aspect of Ming Fire is that spark of life created at the moment of conception and is the catalyst of moving jing into the process of unfoldment of life... The "ming" part is the unfoldment of life and its circumstances - to put it far too simplistically - your 'destiny'.   Some issues people find are often the result of a malfunction of the ming fire - meaning that jing isn't properly expressed into the life unfoldment process and you're unable to follow the path of your ming - so life becomes difficult and precarious and you feel lost. The ming fire is often damaged by a strong emotional trauma - usually in the form of some sexual assault or by being forced or dominated in a way that diminishes your sense of self. You can often see this manifesting in a person's body, where it seems that the growth of the body is halted at the stage of development when that trauma occurred. Not that you 'look young' - but your bone structure and body mechanics are frozen at an earlier developmental stage.   Anyway...   The kidneys are the root of prenatal jing. They're like the physical manifestation of prenatal jing - and they control the process of growth and decline - ageing - as well as the natural cycles of change as a result of ageing - such as puberty, menopause etc... there is a lot of interesting theory about these cycles, the numerology around them and so on - all in the yellow emperor's classic - so I won't go into more details here.   Postnatal Jing is rooted in the spleen and stomach! So here's a clue on how to improve postnatal jing... Another clue is that the spleen and stomach are in charge of creating qi in the body... also in charge of building muscle and 'solidity' of the body... and the Yi - or the mind...   Improving postnatal jing is the focus of Yang Sheng Fa - basically the healthy living protocols... and it's not surprising what they talk about considering the clues above.   Diet is the major contributing force to both postnatal jing and normal people's Qi (spleen and stomach are in charge of digesting and processing food to turn into 'energy'). Along with diet - it's about exercise (muscles), rest, sleep, and the quality of one's mind. This is the fundamentals - good sleep, enough rest, enough exercise, a good diet, no over thinking or too much mental stress (breathing is related to that) as well as moderating sexual activity (for men in particular) and harmonising the menstrual period with the moon cycle for women. Beyond this, we have other ways of working with postnatal jing for specific practices - such as stilling one's desires and breaking habitual patterns of thinking and acting - but attempting this before having a solid foundation is not only pointless but potentially hazardous.   Jing travels through the 8 extraordinary channels (not so much the organ meridians) - it moves to Guan Yuan point (bellow belly button) where it enters the uterus and is lost through periods for women. In women, it also travels up to a point in between the breasts and fills the breasts (particularly during lactation). In men, it converts to sperm and sexual fluid and is lost through orgasm and ejaculation.   Jing will also travel to the Hui Yin - the perineum where it transforms into base desires. A lot of systems and practices use the perineum because that's where jing descends to. But a very important piece of the puzzle is often left out - and that's that one must still the base desires before working with the perineum. Because without stilling the base desires through meditative practice, you can inflame base desires and turn them into psychological issues as well as unethical behaviour... who's seen unethical behaviour and sexual deviancy in the spiritual arts?   Back to kidneys. Jing also controls the kidney Qi system - Kidney Yin and Kidney Yang - these are the manifestation of Yin and Yang principles in the body. Kidney yin governs the cooling of the body, the creation of fluids etc. Kidney yang governs the warmth of the body and sexual desire. The balance between kidney yin and yang are behind a lot of the problems we find in the body. Too much yang, the body becomes fiery, hot, quickly burns up, strong desire. Too much yin - the body becomes cold, damp, slow sluggish low will. These, in turn, affect the other organ systems (heart palpitations, heated liver with out of control kidney yang - damp stagnated spleen, contracted, phlegmy lungs with too much yin).   The kidneys are the root of your constitutional health - low vitality and energy and 'lust for life' as well as a weak immune system are all usually rooted in a kidney issue.   Kidney jing also grows into the 'marrow' and the brain... if kidney jing is weak - bones get weak (osteoporosis, teeth falling out etc), back (spine) hurts, the brain doesn't get nourished and you develop mental fog, fuzzy thinking, dementia, Alzheimer's etc.   Sooo... I wonder how the horse stance relates to any of that