The mechanics.
When you sit down on to a chair, you automatically, and without forcing it, do a pelvic tilt. If you don’t, you run the slight risk of hurting your spine.
The same thing should be true in tai chi and qigong when you move your weight from the front leg to the rear leg of a Bow stance; you need to do a pelvic tilt (see previous blog).
Forcing it.
Without repeating the previous blog, I’ve noticed that quite a few people force the pelvis under 
rather than allowing it to roll under by releasing the back and the neck. If you don’t release the muscles in the back, you’re just creating further tension and the movement won’t function as effectively if someone were to push or pull you at the same time.
This relates to the question that people sometimes ask – How do you relax the gluteus muscles in the buttocks at same time as tucking under?
Stretching or releasing?
If you force the pelvic tilt, you are deliberately trying to stretch the lower back muscles by contracting the abdominal muscles. Forcing it means that the movement is coming from only one place, and the back isn’t joining in the game – or only slightly.
If you force the pelvis under, the neck doesn’t release, and the tension within the pelvis may even cause the chin to lift because the entire back, including the back of the neck, contracts.
In fact, to go a stage further, when tucking the pelvis under, your neck should release at precisely the same moment.
Feeeeeel……
When you release the back, as opposed to ‘forcing’ it, the sensation of release occurs throughout the entire back – the waist, the ribcage (sides and back), the armpits, the shoulder blades, the neck, and even in the back of the head and up to the crown of the head. Your back should feel like a compressed spring releasing.
Should you release the neck or the back first? Both; it’s all one and the same.
How does the front of the body behave?
When you release the back, the muscles at the front feel as though they are being drawn upwards and inwards, rather than tensed.
What happens is that the back ‘opens’ – not exactly a bowing backwards, more a sensation of the cellular structure undoing and opening, and the front of the body ‘closes’, – a feeling of the front drawing in, compressing. These events happen simultaneously so that one reinforces the other.
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James Drewe teaches Taijiquan and qigong in both London and in Kent. Details of weekly classes can be found on the website, and there are classes for 2-person Taijiquan one Saturday a month.
CONTACT:
http://www.taiji.co.uk
http://www.qigonghealth.co.uk
Email: taijiandqigong@gmail.com
Phone: 07836-710281 or 020-8883 3308
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Taiji & Qigong (classes with James Drewe) 
Dear James
I just wanted to say thanks for your blog, which I only fairly recently discovered. I have found the articles really helpful in my ongoing practice of taiji and qigong (I am still only a relative beginner, having been practicing here for just over 3 years now), particularly those to do with “sinking” and “relaxing”. I will gradually work through your archives!
Warm regards
JS
Brisbane, Australia
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Is this release not a subtle awareness of the relaxing quality of reciprocal inhibition, James?
In order for smooth movement to happen at a joint – or joints – the resisting muscles (antagonists) have to relax so that the shortening muscles (agonists) can contract.
For example, steady bending of the elbow requires the triceps to release as the biceps contract.
This balance of contraction and release, creates a steady ‘reciprocal inhibition’.
In this case, are we not feeling the release in the muscles of the lower back (antagonists) as a response to a subtle contraction of the hamstrings and abdominals (agonists)?
The back of the pelvis is drawn down by the hamstrings.
The front of the pelvis is drawn up by the abdominals.
Both occur very subtly.
And, to allow this to happen, the lower back releases and the lumbar spine lengthens.
Similar actions and reactions – reciprocal inhibitions – happen to paired muscles along the spine, allowing it to lengthen right up to the base of the skull.
Learning to feel which ‘contracting’ muscles trigger their corresponding ‘releasing’ muscles, and how to subtly engage them, allows us to experience the consciousness of ‘letting go’.
This has been my experience in Taiji and elsewhere.
Simon
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Yes, over all I agree with you, but the problem that I have is that I can’t explain in in those terms in a class; I just don’t think that people can relate to it that way.
The only part of your comment that I am unsure about is: “The back of the pelvis is drawn down by the hamstrings.” I’m not sure that this is right – in fact I think I’d go further to say that I think this might be ‘wrong’ (N.B. the hesitancy here!), and that there is actually a release of the hamstrings. Tightening the hamstrings actually restricts the pelvic tilt – it seems to stop it halfway.
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