I've been thaught that to collect a horse means to get his head on the bit. I've been taught to do this with much pressure on horses mouth. So when I get my own horse I didn't do it. That's been for 3 years...
Some time ago I was riding up the hill and I was actually holding reins in my hands because she was a bit 'ful of energy' that day. I wasn't pulling or anything, just holding the reins, I'm used to having them long all the time. A car drove behind us and I wanted to go a little bit faster so we could move off the road. My mare collected herself, it was a different feeling, riding her, like she put her back up and she dropped her head a bit, but still not as much as my extrainer always wanted.
Then I was injured and couldn't ride for 3 weeks. I did research on the net and found out collecting a horse isn't only being on the bit.
I tried to collect her today again, on that hill, but succed only once from 4 times (I went up and down, up and down, lol). I'll keep trying. She doesn't have any muscles on her topline and I want them.