Jin Series #2 (by Mike Sigman)
The Essence of What Jin Is, in Practical Usage.
I'm going to keep this short/truncated so that the meaning gets through more clearly without getting too far into the weeds.
Stand up and either imagine slipping a 30-pound backpack/rucksack onto your shoulders or imagine putting a 10-pound bag of beans on the top of your head like a primitive porter might do. Feel the weight. Now, mentally try and arrange your body so that the weight of whichever you imagined goes down through your bones to the soles of your feet and therefore the weight has "gone through your body" and is now resting on the ground. There is a very different feeling when you have allowed a weight to go straight through your structure to the ground. Learn to relax and let forces go through you to the ground at your feet.
Do the same process two or three times and notice what happens when you "change" your body inside and "let the weight go straight through your structure to the ground".
When you let the weight go through your structure and rest on the ground, rather than holding the weight somewhere in your body, you will be using less muscular effort because you're now letting the ground hold most of the weight. So suddenly you have a bit more spare muscular strength to play with. A quick test that I suggest for people to use when they feel like they've let the load through their body to the ground is to wriggle/gyrate the hips a little bit: the hips should wiggle freely and, most of all, the lower-back should be relaxed. Always keep the lower-back relaxed because that aids in letting the support of the ground up through your body to hold the weight on back or head. Tension in the lower-back reduces the purity of the ground forces coming back up through the body and therefore forces you into a more muscular-strength-demanding mode.
The tissues and micro-muscles that are changing where forces are coming from (whether the sole of the foot or somewhere in the body) are the qi and if you notice, if you were able to shift the weight down to the soles of the feet, you couldn't directly just bring those muscles into play: you had to visualize the effect you wanted and those micro-muscular arrangements were shifted/changed accordingly by the subconscious. So you can think of your "qi", in this case, as being some involuntary-muscle-tissues that are mostly controlled by subconscious, not the conscious, direct mind.
Exercise #1
There is a very good, basic exercise where you hold a small weight/ball in your right hand (or left hand) and arrange yourself inside so that the weight of your body and the weight in your hand are resting directly on the soles of your feet: your foot-sole accepts the full weight from above. Try to keep the weight from your hand and body always resting on the soles of your feet while you make the weight/hand go around in a small circle. At all points in the circle, the weight should be resting as much as possible on the ground at the soles of your feet. You are now doing a basic jin/movement exercise.
If you want to utilize the body most efficiently while making the circle, keep the weight on the ground through your body, but make your middle/waist the pivot point for how the body is moving the hand circularly. If you're more comfortable just using the shoulder, that's fine for the moment. If you're going to start learning to use the dantian/hara, you're going to have to move your pivot to the middle of the body someday.
Exercise #2
This is a variant of Exercise #1, but in this case hold your right arm horizontally out in front of you, right foot forward, with your palm facing forward. Start off with your weight slightly forward onto the front/right foot. Let a partner push into your palm with about 3-5 pounds of force and you sink back and down into your foot. Imagine a straight line from your back/left foot-sole going straight to the point where your partner is pushing into your palm. Even though your body is bent at the shoulder/arm, the actual force should be imagined as going straight from the palm of the hand to the foot. The foot does all the holding work; rest into it completely and let it be the foot that stops/holds the incoming push from partner.
If you're successfully letting the sole of your foot accept the incoming push, you should be able to easily wriggle/gyrate your hips a bit. Keep the lower back relaxed, always!
If you're doing Exercise #2 correctly, you should be able to focus on keeping the incoming force in the back foot while you do a slow, small circle of your arm/hand while keeping the weight/force comfortably in your back foot. Once again you're doing a fairly basic jin exercise if you do this correctly.
Think about what is going on, for a moment. This post is to give you an idea about what Jin actually is: we'll get deeper into how to use it and ways to use it, later. Jin is a way of setting up force paths by imagining them: your subconscious and your involuntary-muscle system do the aiming of the force direction. Most of your jin forces will come from the ground, but some of them can come from the down-pull of weight or some combination of the two mechanisms. Some jin usages can be pretty complex and take some practice to use, but essentially jin comes from the way the qi-tissues and subconscious align forces in the body (a largely autonomic process). So the mind leads the qi and the qi configures itself ahead of the jin being present. Jin is called "the physical manifestation of the qi": what could be more accurate than that?
If you let the ground hold most of the weight/forces, the ground does most of the work. If you let your weight pulling down provide most downward force, gravity is again doing most of the work.