Check out your possible physical issues first, as you already know. If you are sure that there are none, then presume that this horse has never truly had “forward” installed, therefore is not “broke” to ride. IMO, every horse needs “forward” installed FIRST, he needs to learn to GO when he is told to GO. He needs to RESPOND accurately, first in his ground work, then later respond similarly under saddle. As his trainer, you can not accept a half response, he must strut forward and confidently on cue at each gait. He must respond accurately and adequately. He must understand what you are asking, and you respond to his efforts in a positive manner. THEN, and only then, you are communicating with each other, responding to each other, and “training” the horse is what is happening.
If he does not go forward and respond on the lead rope, or on the lunge line, he is not ready to ride. He needs to learn that on the ground FIRST, what is expected of him, and what brings him your acceptance and appreciation of his efforts. He must make an effort to please you, and you must respond to these efforts. Good horses want to do the right thing, always, if they understand what the right thing is. This is the relationship you are looking for when training/riding a horse.
Once he does walk, trot, canter and whoa on the lunge line in a forward and responsive manner, you move on to ground driving. This will teach him both “steering”, and “pressure on his mouth means whoa”, and link up pressure on his sides (with the long lines tapping his sides) with potential leg cues that he will equally respond to when you are on his back. You DRIVE him forward from walking and running along behind him. He GOES, he steers, he whoas. Together, you do walk and trot, circles, serpentines, etc in a contained area. You both walk over poles on the ground, and he learns to look where you are sending him, look after stepping over the poles correctly, and around barrels, jump standards, whatever you have. THEN, you strike out into the great outdoors, go out of the arena, and drive him forward around your barn area (if adequately safe), and look for things that he may have an opinion about, perhaps he is uneasy about something. You deal with that, you take his attention away from what he may be concerned about, and drive him forward, and steer. All this without being on his back. He learns to take his cues from you, and respond accurately and safely.
Then, you get on him. You move around in the saddle, and put your leg on his side. You do this in a contained area, a round pen or a large stall. You ask him to move forward from your leg, as you have already taught him to do on the long lines. He goes forward as asked. Don’t be shy, kick him forward, move your legs on his sides. Practice until you get the desired response from him, and congratulate him for his acceptance of these cues, and adequate responses. When you feel safe in a contained area, you strike out into the arena, and ride. You still expect the responses you have installed into the horse to be there adequately, because you made sure they were there before you got onto his back.
A horse who does not respond to these basic cues is simply not yet broke to ride. Being “broke” does not mean that you are simply allowed to sit on his back, it implies an understanding of cues and responses between both horse and rider, lines of communication are established and understood by both parties. A pack horse will usually allow a human to sit on it’s back, but a pack horse is not broke to ride. Teach him the language and the parameters of the relationship before you expect to have a conversation and a partnership with him, and show him the responses you require before expecting him to perform for you.
Good luck! Envision what you want him to do for you, and show him how to respond the way you want him to. And reward for good responses from him. Horse training. (Everything training, actually).
