ADDITION : There has been great discussions over this blog, I've loved it... To add on what I missed out. When we come higher in the move, and the hips start to extend - then the glutes will be used as they are hip extensors and it assists opening the front body.
My aim was to talk through baby swan, low extension. I've found squeezing the glutes when the person is staying low in the extension unnecessary for many, although for some it can help. If someone tends to always squeeze their butt, I'd ask them not to as it is their default way to stabilise and I'd prefer them to be in their deep body not the superficial.
It's hard to get everything across and the comments have helped me see I need to be a bit more thorough with some of the moves I talk about.
Every body is different and what works for one doesn't for another and as trainers and movers it's great to explore and see what helps the individual move with ease.
In (most) movement disciplines thoracic extension exists, we just all call it different things but basically it is the movement of the upper spine (including the head) in a backward way rather than going forward (flexion).
If we look at our lives today, we sit - A LOT... Often hunched forward over a computer, driving, texting, playing computer games, drawing, sewing to name a few. If we let ourselves go under gravity we get pulled forward into a hunched position, our heads drop forward, shoulders rounded, chest tight, our organs get squished and our breathing becomes shallow.
Sitting this way for hours on end is not good for us and one hour at the gym a day doesn't reverse the effect. Plus gym exercises often add to our body's woes - push ups, chest press, sit ups....... (depending on how you train).
To undo the forward body posture we need to do the reverse- i.e extension.
You'll see in the video and from my stick man, how to do extension. Often what happens is people feel their lower back work first, what we are aiming for is a smooth work from the neck muscles, into the mid back and then if you come higher the lower back muscles will also feel it too and that's ok. It's when the lower back is the first thing to feel it that we need to address your movement patterns.
It can also be tricky to understand how to 'draw the core' in when lying on your front. This is where the deep muscles need some engagement, if you tighten too hard and your '6-pack' muscles gets tensed then you are fighting your body.
See this video - I use Human Anatomy Atlas - excuse the quality... You'll see the rectus at the front will move us into that forward flexed position - so if we tighten that, how are the back muscles meant to work? We need to let go of the front to use the back. This is what happens all over the body - (triceps/biceps - quads/hamstrings) so if you brace your core you can't effectively come into extension, and your lower back might take the brunt. You can however engage the deep core (inner unit, pelvic floor, transversus etc) as the muscles wrap around and can be lengthened as you extend; they don't hold you back.
Another way to think about, it's like tug of war - one side has to slacken off to move...
Hope all that makes sense - there are of course other muscles involved in the movement - but these are the things I've seen over the years that help.
Extension is vital for us - a strong back keeps us upright, strong bones help prevent osteoporosis, upright postures reduces the strain on our discs. Please try and if you need some help - be in touch!!