Time - well over time - for a new post!
I have been gadding around America teaching clinics, and have seen a number of long term pupils who have over-used the 'slingshot' idea. Any good idea when taken to the extreme can become a bad idea, just as any cake cannot be successfully baked when one ingredient is out of proportion with the others. My plan was to write about the antidote for the slingshot, but I think I need to save that for another post and start by explaining how the slingshot works.
When a rider needs to move further back in the saddle, we usually suggest that she thinks of her thighs like the elastic in a slingshot, imagining that her knees are at the ends of the stick that would form the 'Y' of the slingshot, and that her pelvis is the stone. When the thigh muscles elongate and come under tension they form a longer, narrower 'V', just as the elastic does when you pull out a slingshot. The knees and the seat bones move further apart through being pulled in opposite directions.
The easiest way to access this is to put the heels of both hands on the pommel, and to make a sustained push back off them. The trick is to do this with your seat bones continuing to point straight down, so that they slide back over the flesh of your backside and do not point forward or back in a way that makes you round or hollow backed.
I am of course assuming that you are in 'neutral spine' with your seat bones pointing straight down as you begin this, which is a big assumption, given how many riders either lean forward or lean back, often whilst also either rounding or hollowing their back! Sitting in vertical and neutral cannot be taken for granted, and once there you might still find that your first response to the slingshot idea is to lift your seat bones within your backside, or to point them somewhere other than down. If you can, halt your horse sideways on to a mirror so you can check that you remain vertical and neutral as you push off your hands.
If you are sitting reading this with a table in front of you, try finding neutral and pushing back off the edge of the table. Experiment until you can feel your seat bones move back over your flesh and your front firm up. This should make your torso feel stronger.
As your seat bones slide back you are bringing your whole torso and your centre of gravity back. This may become necessary on a horse who delights in pulling the rug out backwards from under your feet. He is the lethargic or even nappy type, who attempts to get you 'in front of him'. You can then find yourself sweating away to no avail, as you are no longer in the place where your aids have meaning. You can kick and flail about all you want, but he will take no notice of you until your centre of gravity moves back over his.
Is it difficult, but very effective, to 'slingshot back' instead, using your energy to keep yourself still and firm, with narrow elongated thighs. If you then kick from that further-back-place you will find the 'go' button, as your aids suddenly work. On this kind of horse, you are unlikely to overdo the slingshot - in fact it is far more likely that you will not some far enough back, and that feeling weird will stop you from making an adjustment that is as extreme as the situation
This may sound paradoxical, but on easier horses, the idea of the slingshot can also help you move the horse's centre of gravity back. As your thighs elongate back and your torso moves back, you need to think of the horse's insides moving back within him (as opposed to you moving back relative to him). Some of the riders who have been doing this for a while are the ones who have reached overkill. They needed to change tactics and find a way to draw the back of the horse towards the front of the horse. But more of that in the next post!