At the trot and canter my legs swing and are in chair seat, and I can never sit it like I will bounce. I've just switched horses and my new horse is VERY slender. I'm used to riding slower, calmer, fatter horse and now I have a fast, hyper, skinny horse. So her canter is very racy, her trot to canter transitions are like she's trotting then I ask her to canter and she will just bolt into the canter. Could she just be in heat? She's not always like this. Anyways, since she's racy I can't stop my swinging lower legs because if I try to grip with my calf she will just go. It's usually the same with her trot to. The chair seat may be because of my saddle, as it's a courbette arosa. Any suggestions?
I've been doing stuff to build up my leg muscle as well :)