Really there two things that are the crux of tendon changing (at least in the way it is taught in the HT Iron Shirt 2 system).

1) Movement is focused, or emphasized, in those parts of the body that have a high concentration of tendons.  For instance: the hands, the spine, the feet.  The theory is that all of the tendons in the body are connected.  If you activate the tendons in those high-concentration areas then, to some extent, you are going to activate the tendons in the rest of the body.

It's also easiest to learn a small portion of the body at first, and then build up.  Mantak Chia's instructional video starts by applying the movement to just the hands, and then gradually includes more and more of the body - by the end of the video he has a whole-body movement going.  In this essay I'm just going to specifically address the hands and feet, which you can still get a lot out of.

2) The movements have a quality as if you were smoothly, partially, stretching and relaxing a rubber-band; your tendons should feel that way when you're doing the exercise.  Partially, in that the stretch is far short of a maximum stretch, maybe just 20 - 30 percent, and then smoothly relax.  It's smooth and continuous.  There is no fast jerk to the stretch, no stop at the apex of the stretch, no sudden release: just a smooth partial stretch, and a smooth release back to relaxed.  A kind of undulation, really.

Go ahead and try it with just your hands, or even just one hand.  Concentrate on opening your palms with a gentle opening stretch and release of your fingers, in one smooth, almost undulating, movement.  Do that 3 or 4 times in succession.  It's the sort of movement that you can play around with, any time, any where, and I encourage you to: it's fun, and you'll discover things.  

(For instance, experiment with the difference between opening your palms by opening your hand from the finger-tips, versus from your inner most knuckles.)

After I studied the video, and worked with it some, I found that I wanted to incorporate my feet more than was shown in the video.  Rooting through the legs is so important, and my legs have always been somewhat under-developed compared to my upper body... This is what I came up with.

Basically, you're shooting for the same movement with you feet as you just did with your hands: You want to open up the sole of your foot by gently opening / stretching, then relaxing, the toes and joints of your feet.

I found that my feet were a lot more cumbersome than my hands, and needed some guidance.  So, I sat down on the floor, with my legs stretched out in front of me.  Then, I practiced my right hand and right foot at the same time, right in sync with each other.  My hand provided a familiar feeling, and sense of coordination, that my foot could sort of track along with.

Once you're somewhat comfortable with the hands and feet, in this way, you can start applying the movements to other practices that you already know.  For instance, while in a standing posture from Iron Shirt 1 you can do the tendon changing movements with your hands and feet simultaneously.  This really assists in opening the tendons to the energy flow of the Earth.

Additionally, you can expand the basic movement to various other muscle groups.  Experiment.

I used to take hatha yoga, a little, and know that stretching is important to maintain a smooth chi flow through my body.  I've found that if I apply a little of the tendon changing hands-and-feet movement to my standard stretches, it changes things immensely. Instead of just stretching, my limbs feel more connected, and I feel a spreading warmth of circulation with very little work.

For instance, in the two stretches below (forgive my stick figures).  In the one on the left ("downward dog") both hands and feet are on the floor.  I find that if I do the tendon changing movements to all four (both hands and feet) at the same time, a lot opens up.  In the position on the right, I do the tendon-changing movement to the extended right hand and left foot at the same time.

SQUATS, Squat Variations, and Leg-work in general.   

(NOTES & WARNING! :  

    Practice caution, awareness, responsibility towards your knees.  Some of the following exercises are very rigorous for the knees.  If you have knee problems, back off, consult your doctor.  Even if your knees are healthy, practice caution and go slow - especially if you are not warmed up or haven't done this sort of thing before.

    This section refers to body-weight only squats.  Weight-lifting, while it may be beneficial, is out of the scope of this website.)

Squats engage the power and volition of the lower tan tien, and are excellent for warming up and stretching the major muscles, tendons, ligaments, joints of the legs.  Very important for expressing and integrating the force that accumulates through qi gong, as part of root and power development, and especially important for those of us living a 'modern' lifestyle - which nearly entirely lacks lower body work.

          hands in prayer mudra

The Kneeling Exercise

ACTION: Gently, slowly, repeatedly, rhythmically, move in the small arc shown.  Not all the way up nor down.

PURPOSE: Gently flexes the lower-most lumbar.

CAUTIONS: You must completely discard weight-lifting mentality for this exercise.  Deep spinal tissues do not respond, grow, nor repair as muscles do.  Do not aspire to increased weight, speed, nor frequency.  Leverage inherent in the position focuses into the spine and potential injury is a concern: do this exercise gently.

    Though this may work your quadreceps, it's not the point of the exercise.  There are much better more conventional exercises for that.  Don't strain your knees. 

(Thanks! to Dragon Gate Sanctuary for the kneeling exercise.  If you are familiar w/ DGS's "Kwan Yin Magnetic Qigong" then it's easy to apply a little for the heart chakra during the kneeling exercise.  Afterwards, in order to balance chakra development: more extensive Kwan Yin Magnetic, plus perhaps other practice/s such as lower dan tien breathing while standing.  Once comfort is established, other simple KYMQ variations become possible.)

Squat: Hands Raised

This static position is indespensible for gently opening the lower back such that jing naturally rises.  Don't try to stretch in this position, just raise your hands and gently open the joints. 

(Thanks! to ZerosTao, to myself, and to bumbling luck.  This exercise was the happy result of misunderstood communication.)

Moving Squats, tendon-changing application:  

Start standing.  Extend your hands out in front of you, palms down, relaxed.  As you squat down, do the tendon-changing opening movement (as described above) with both hands and feet.  As you stand up, relax hands and feet.

Tips: 

  - Feet flat on the ground the whole time, shoulder-width, each foot pointed 45 degrees from your center-line.  

  - Don't bounce into~out-of the fully lowered position; be respectful of your knees.  Only squat as low as you are comfortable with, this is not a competition.

  - Move in tempo with your breath; the lower tan tien inhales as you squat, exhales as you rise.  The inhale and exhale should be of the same duration; the whole cycle of breath should be smooth.  

  - Allow yourself the safety valve of stopping, and breathing regularly, as you feel is appropriate. 

  - LATER: Occasionally experiment with brief pauses at the apexes of inhale and exhale.  I suggest doing this only after you've been doing the moving squats for a while, and have developed some familiarity with the mechanics.  Adding the pauses, on an occasional basis, adds a whole new dynamic (non-dynamic) to the process; its too much to learn all at once.

  - If any of the above breathing exercises is causing build-up of bound-up tension, back off from that breathing - and just do squats with no special breathing, for leg warm-up & tendon-changing.

This can progress to squats starting from a variation of 'embracing the tree': palms facing forward.  This assists with the hoop-like connection of hands, arms, around the back.  Be aware of your cervical and lumbar vertebrae alignment.  Again, hands & feet opening~relaxing in tempo with the down~up of squats.

(The rest of this section isn't re: tendon-changing, but variations of squats.)

Static Squat

Time simply spent down in a static squat position itself is helpful.  Many qi gong systems encourage slow relaxed lower tan tien breathing through a variety of postures; static squat is a standard.

  - If you tend to tip over in static squat, grab a-hold of some support (door-frame, pole, etc.).  CAUTION: If you pull too hard, the support can act as leverage and put excessive strain on knees, hips.

static squat, lower tan tien breathing

Want to take "breathing in a static squat" to a whole other level?

Vibration platform.

Combo Moving~Static Squat

Once some comfort is established with both the moving squat and static squat, they can be combined.  Several reps of moving squats, then stay at bottom for one or more cycles of breath in static squat, then continue on with moving squats.

Hindu Squats

Hindu squats are repetitions of squats with body-weight only.  Here's a discussion of hindu squats at theTaoBums.com, and here's an article at Testosterone Nation.  Hindu squats are part of Matt Furey's Combat Conditioning course.  Some people really get into doing high repetitions of hindu squats (Go Cameron!), which has gotta be great for circulation.

Lateral Squats   *best*, imo

While hindu squats are mostly about repetitions, lateral squats are mostly about root.  Go slow and smooth with these, and only so low as you can maintain integral root through all of the joints of both legs.  Never drop nor let go into a lateral squat.

- Warm up with something else (hindu squats are convenient), something that's easy on the knees; don't do this exercise cold.
- Wide stance.  Each foot out at 45 degrees.  Breathe, establish posture, root.
- Slowly squat to one side, only so low as you are comfortable with.  Depth might vary, depending on day, time of day, degree of warm-up, number of reps, etc.  Rise up to center.  Squat to the other side.  Repeat.
- Going low into a lateral squat works deeply into the hips, much better than hindu squats, but going lower than you are ready for can strain, injure, your knees.  Be sensitive to your level every time you practice - even to the point of putting your hands on the seat of a chair, for extra support, if you need to.  Maintain smooth integral control.

Vertical Jumping

Rep's of vertical jumping (from/to a fairly low position, though higher than a bottomed out squat) make a good body-weight exercise.  The repetitive explosive muscular work is very satisfying to the lower tan tien.

Prostrations

Prostrations are a sine wave of utter surrender and feet-on-the-ground umph.  Opens the channels, exercises upper and lower body.  A physical devotional practice of broad scope, at every level ... a staple.

            Thank you to Sean Omlor for the graphic!!

Lunges and Airborne Lunges - Easy intro to one-legged squats.  Re: this and the following exercises, one-legged work assists in opening the thrusting vessels.

Three-Dimensional Balance Training - by Scott Sonnon  (external link)

Works the hip joints, with body-weight, at a variety of angles.   One of the keys to getting the most out of this exercise is to do it slowly: explore one-legged root.  Maintain slow, steady, lower tan tien breathing.  

JOINT (HIP) ROTATIONS: Leg circles at each position.

Use Sonnon's positions as starting ideas, and apply the principles (posture, movement, yi, qi) of internal work.  All sorts of benefits beyond balance in this one!

Stadion.com 

Thomas Kurz's website.  Includes his dvd, Secrets of Stretching (easily worth the $50).  Kurz takes the approach that leg strength is a necessary complement to stretching in order to get good flexibility (splits), and so he includes a comprehensive set of leg strengthening exercises (squats and much much more), from many different angles, using a variety of modalities.  As you can see from Kurz's picture, his approach results in strength and stability leveraged deeply into the pelvic region.  Obvious benefits to jing gong.

Thomas Kurz demonstrating strength and flexibility.

Squats section wrap-up comment

Obviously, I'm not suggesting that you have to do all of the above, in a single routine, or ever, only indicating that there's variety and scope of practice that one might explore - over time - with leg work.  

RELATED TOPICS

FINISHING COMMENTS

I hope that I've conveyed some sense of the tendon-changing movement, as well as the fact that it can be experimented with, and applied, in a variety of ways.

Mantak Chia's Iron Shirt 2 video is a fair product, and worth getting for an introduction to tendon-changing movements (which are difficult to convey in text).  However, it is just an introduction: it doesn't compare to working with a good teacher of an authentic internal martial art in person, consistently, over a long period of time.