My 17 year old tb has various issues that have contributed to uneven muscling .the club foot ,the infamous LLD ( or at least what LOOKS like different leg lengths ,let’ s not go into this dicsussion ) slightly dropped pelvis ,one shoulder more forward,one hind leg slightly shortsteps ---- the works. all of this has been noted,checked and worked on with help of vet - who confirmed all these issues are managable and that the kind of work i am doing with him is beneficial ( light and basic dressage in the ring ,some trail )- the farrier ,vet\chiro and massage therapist.
the horse for various reasons( unrelated to his issues ) had a 2 year break and has now come back to work ,very gradually,since may,mostly lunge work ,with and without side reins,pessoa system, sometimes just off the halter,he has been handwalked pretty much daily and only lately backed again.it is very noticable now that his left front side is visibly less muscled ( hind end looks good and is almsot even) and while he always had this because of above mentioned issues,i assume that the 2 year time off made this worse.
i have read many older threads addressing this and have come across the advice to * work him more on the weaker side * — i am not sure i understand what that means or if that is even possible.
The best advice for uneven muscling is to find what is causing it and address it. If it is old injuries that have compounded and caused other injuries, you may be pushing a stone uphill. There are a lot of bodily complaints you have mentioned, some more serious than others.
Full, 24/7 turnout would be my advisement, given this thread and your other thread about this horse. Followed by continued walking as you have done. I would start serious hacks on hills, and when in the ring, consider putting 6-8 walk poles on one side of the ring and going over them every time you walk by. After a few weeks of doing this start adding cavalettis on the opposite side of the ring. Walk poles and hill work are good antidotes to uneven muscling - provided the underlying issue that caused the uneven muscling has been addressed and healed.
You’ve provided a good start, with therapies and conservative work. It’s time to build on that work by adding things that challenge his proprioception and ability to lift his legs up. I am not a fan of targeting the weaker side specifically - I’ve had better luck building an overall strength program using hill work, turnout, and cavalettis.
Is he shod? It does help in rehab since so often, most horses have some undiagnosed bilateral foot soreness that makes things worse. Something to keep in mind is that a horse in undiagnosed or subtle pain, won’t be able to work correctly or well, so you will not see the same favorable results or improvement in condition.
Trail riding is great as long as it is up and down hills, negotiating tree roots and rocks, etc. Just flatwork in straight lines is not as helpful.
Cavelletti (trot poles) can be a huge help in getting a horse to use himself evenly. On the longe line there are many gymnastic exercises that you can set up that will be beneficial.
I don’t like the “work a horse more on the weak side” approach because they learn to compensate for their weakness and sometimes this makes it worse. Horses have 4 legs to compensate with, and they do!
I’ve schooled horses with uneven musculature and some of them will turn around quite quickly, just by doing things like making them use both leads. If it is hard to get one lead, then I would ask for more transitions and set the horse up in the corner to do that more easily.
Some horses that have spine issues, for example, may always be weaker on one side. I have tried using weights on the hoof that drags, and other techniques, but really just trail riding and cavelletti were what helped the most.
@beowulf yes i have posted several threads about him but also about my very senior mare which recently passed at age 34 … the underlying issue will remain a mystery.we do not know anything about his history ,the dealer who dropped him off at the barn had no info other than that he came from the tracks at 4 years old.i am sure though the horse sustained an injury durng his racing career since he has the scars to prove it,3 high on his forehead ,maybe a trailer accident or at the starting gates.hard to say if that caused the asymmetrie or if it was his natural posture from the beginning,we have debated which came first the club foot or the high low shoulder etc …just saying that the why will have to remain unknown and all i can address is the what to do with this.you are very right in pointing to the hooves ,they ceratinly play a role in this and he has been sore footed on and off .my previous farrier did an excellent job over the course of many years to keep them well balanced as best as possible and never recommended shoes but lately,since he is now in a very regular if light working schedule,he is wearing hoof boots.as for your suggestions how to work him,i am happy to read this since it is what i have been doing 
@Eclectic_Horseman so far only ground poles,i have a couple of cavalettis and may put them up again.2 years a go he hated them LOL .i am hoping this season i can take him out on more trails,it is what i feel will be best for both of us and the plus is that going out and coming back will involve a long long hill !
A good body worker in conjunction with some dressage work with a skilled trainer who can see the imbalances and know how to use exercises to work the less developed areas. All the fundamental/foundational exercises are useful, it’s a matter of which ones at a given point.
It’s about whether he needs to be more supple here, or stronger there
You CAN start by simply doing basic schooling movements and keeping your sessions catered to how long he can properly work his stiffer and weaker areas. You won’t develop the stronger/more supple areas for a while, but as the areas that need work start to catch up, you’ll be able to ride each thing, and each session longer.
There’s a time and place for, say, doing 8 leg yields to the right and only 3 to the left, but I would want a good trainer calling that shot.
i think a good body worker is what i have.she has done great work for my senior mare in the past and knows this horse in question well,too.as for a coach,would be GREAT !! but no such luck,i have my horses at home and we live remote ,that and the fact that good dressage coaches are rare around here,the ones we have are way too busy and do not have the time.so i am on my own.
so far it sounds you all confirm that working ONE side is not a good idea ( like i thought) but work the whole horse properly .
we are early days,baby steps actually .had just 6 rides ,up to 15 min by now since i try my best to listen to the horse and feel when he is done (without letting be the boss,still undecided when he is playing lazy and when he starts getting uncomfortable ).just changed to a western saddle - took some time to get used to THAT - but i suppose the basics can be done this way
Is there someone who can do a tele-training session? Maybe you can explain the issue, ask them for a starting point for some exercises, warm your horse up well, and then video those exercises. It’s not immediate feedback, but it can help give you some direction and let them see better what’s going on
55 Corrective Exercises for Horses by Jec Aristotle Ballou https://www.jecballou.com/store/p/55-corrective-exercises-book
It’s a fantastic book, I’ve used many of her exercises for rehabing and just to change up our routine. Not sure why the above is in bold lettering. Too early in the am to figure out why. 
that is not a bad idea !
I came on to post this! Love this book and she splits the exercises down into programs for different things (young horses, rehab etc). Lots of the exercises have video tutorials on her YouTube channel too.
Here is another book with some great tools! Core strength will help with balancing him out as well.
All of this assuming the base issue has been addressed. If it’s a mystery and hasn’t worked itself out by now, you may be facing an uphill/unwinnable battle. But you can give it a good effort and see what he can handle!
while i think he will never turn into a show dressage prospect 
i am fairly hopeful he can become a trustworthy trail horse for my remaining years as a senior rider .and i would think he will be fine with that.the base issue is manifold as is with many horses and since it is all connected and one thing leads to another,at his age all i am striving for is to have him in decent physical and mental shape.which he is at the moment although with room to improve.i still think his 2 year hiatus ,just being a horse on 24/7 turn out has done him some good in some ways but also contributed to the uneven muscling since he quite likely favoured his weak side.
thank you for recommending another interesting book !!
I don’t think of it so much as working on only/mostly the weak side, as addressing weaknesses with more focus.
If I find the horse has more difficulty in one direction/side than the other, as I pinpoint the issue(s), I will focus specific exercises for the weaker area even as I do them in both directions. I’ll also be cautious about overdoing the movement on the stronger side. The stronger side may not be correctly strong, but strongly able to create a different kind of evasion (evasion in this sense means trying to do both what you ask but do it in the way that is easiest for the horse). But overdoing is not “doing more physical work” but rather how you do the movement.
An example is my fjord, he is overall shockingly even but his weak point is his right hind leg, which mostly shows up (as one would expect) with less activity in the left lead canter and left haunches in (HI). His right HI is D R A M A T I C because he is quite bendy and he’s got less weight/activity on the left hind. His left HI is actually quite correct, but it’s still harder work for him. I do about the same amount of haunches in both ways although I’ll never do more to the right than left. Mostly what I do to the right is never more than 3 tracks, focusing more on the bend in the rib cage and his nose squarely in from of his chest, and I deliberately keep the minimum amount of acceptable bend in his body, because his overbendy ability is also an evasion, when he gets on 4 tracks it’s super easy for him to slightly evade the bend around my leg and get to slightly less HI, more leg yield along the wall or the exact opposite, more bendy into a half assed half pass for a few steps before I reel it back in. But to the left he needs to work up to the 4 tracks and it’s a lot of pushpushpush to get him there, hard enough that it takes all his focus and his only evasion is to not do it enough, it’s never about the overdoing the bend.
Every bit of me pushing him more to the left EQUALS the same result as me asking for a little less to the right. And I think a lot of people lose that part in the equation. Working more on one movement does not equal doing it more times!! If you watched me work my pony you would probably think he looked the same both ways. If you ask me or Xan which side had more of a workout, we would have a different opinion. I think this approach in most exercises is finding that balance between left and right work and tailoring each side to at some point become balanced and equal. But that rarely means doing more laps, more circles or more time on one side or another.
I’m going to plug RideIQ here as I keep my horses at home and struggle with coming up with different things.
While in person is best, the app has been invaluable when I get stuck and my instructor can’t get out for a couple weeks do to life. They have some good basic lessons on getting a horse balanced and coming back from injury.
