Within in the past few months I have been building up my horses muscles and fitness enought to be able to start working in a frame, or "on the bit" (except I ride in a hackamore). Everything was going really nicely, he was soft, quiet, and responsive. I was very impressed! I broke him in when I was 7 so we had a lot of problems before.
Then there was a period of a few weeks where he was only schooled about 4 times. He was worked daily, but I was either on the ground or we were out on a trail.
Now that I've put him back into work, he is very heavy into the bridle. I've tried doing a lot of pressure and release with my hands and legs, and I changed nothing that I did before. His athleticism is not the problem because I gradually brought him back to this and he is fit enough to do what I'm asking.