Balance or the lack there of is the key issue here with the falling on the fore or the leaning on the bit. Now whether he is falling because he himself is not balanced enough to do the transition or if you are not balance and that he can not do the transition in balance. Lunge without side reins or any other gadget or lunge line assistance (preferably free lunging) and see how he does the transition. Does he do it smoothly or does he trip and fumble to do the down ward trans.

If he does it skillfully by himself then it’s time to work on you :) . If you have a round pen or an arena - an enclosed area, then ride totally with out rein contact before you do the down transition and on into the transition. If your body talks to him then he will do the down transition. The worst mistake is to rein him into a down transition. He will only fall on to the fore which to compensate he will have to lean on the bit to try and not fall on his face. Thus he will also learn that it’s ok to rely on your "support" of the rein when he goes into a down transition. He thinks that’s the way you want him. And from that point on he will seek you carrying his head and neck instead of carrying himself like he does when he is free in the pasture. The first goal from the start should be that the rider communicate with the horse with the least amount of leg and the least amount of rein. Thus the communication is with the body , above the knees and through the torso. As explained in the Riders Body Awareness category under "Detaching the body from the use of muscle constriction" . And when the leg or rein is needed for an aid it will always be clear.

If he does not do it well then he is not balanced enough to be at that stage. Go back and make sure he is balanced in the stages before that. Here’s another example. We have someone who can walk good , but he starts to run and he runs faster and faster with his head and upper body more forward than it should be. He is trying to catch up to himself so he doesn’t fall on his face. I’m sure we have all run at one point and then felt like we were going to trip over ourselves. And to not trip over ourselves we try to have the legs catch up to the angle of the upper body and head but what happens the upper body is still in front of the legs and the legs can’t catch up. In order to save ourselves from falling we grab on to anything that is next us to so we can get the upper body to come back up to slow down so the legs can catch up to the upper body. Be we’re totally off balance and the body was totally out of control. Now lets say we put a coach into the scenario. The coach that wants to build an athlete will see that the person can’t start off being unbalance at the sprit and think that it will improve. Why because the persons body is not in shape or aware of how to be at that sprinting stage. So it is difficult to start unbalanced and then try to be balanced down the road. You are always picking yourself up rather than starting where you have a balance and build upon that each step. Balance equals the heart of future building steps.

Lets put that into horse terms. The horse goes from the walk to the trot. He is going along in a mediocre gait but the rider wants to go to a canter. The rider asks for a canter. The horse trots faster and faster, the rider starts holding on to the reins to slow the horse down. And manages to go into a canter. The horse had to use the riders reins to avoid from falling on his face so to speak. But the contradiction of it all is the expression "ride him more forward". So what happens worse to the horse is not only is he way out in front of his center of balance, but now the rider gives him an aid with the legs to go faster. Or in theory to bring his hind more under him. This is like trying to get that person that was running in the above paragraph to run faster yet to get his legs caught up to his upper body. The off center of balance with the forward movement means a momentum that is uncontrollable with out holding on to the reins as if you were trying to lift your horse from the cliff below.

The horse was from the start unbalanced. It all started in the beginning of the trot. Rather than perfecting the working on the mediocre trot that the rider thought was good enough the rider pressed for a great canter. The equation of good (walk), to mediocre (trot) to awful (canter) is obviously a negative process.  How can a horse have balance with an equation as negative as this.  It a work process that is unessential.

I’ve got  bad shoulders for the past 6 years from a horse accident and there is no way that I’m going to sacrifice ripping my shoulders again just to hold the reins to keep him from falling and taking me off balance in the process. Which is uncalled for if the balance foundation is solid. If anyone has a body that is not optimal and not have the full use of some of the body they certainly have limited use of muscles and can not hold or carry the horse. One learns that there is a easier way using the horses inborn balance, then the fall on the fore that the rider caused and bring up and hold the horses head and try to press with the legs to keep him "forward". To much going on for the horse and rider that is unnecessary