Yup! I dealt with that for the longest time. Pony (fjord) is as most ponies tend to be, just a bit less angulation through the stifle than the anywhere horse.
It wasn’t bad, and he never locked up, mostly it was that flat tire feeling. But add his fitness progressed, things got worse before they got better. That’s perfectly normal, you are building up all the muscles that help support the stifles, and the obvious outcome of that program is that the muscle groups are tired and sore before they become strong and supple. Also, that loss of stability (slipping) in the stifle is not comfortable for the pony, and in the beginning, you need to do more work. More work = more instances of UFP. The more this happens, the more the stifle becomes inflamed and sore while you are increasing fitness. You get caught in a little bit of a vicious cycle before you come out on the other side. I usually give bute (1gr pm) when I feel like I’m dealing with a little bit more discomfort than just muscle soreness.
But the part that surprised me was how MUCH fitness it took for my pony. He was doing lower level CDEs and 1st level dressage, so a) he was FIT going up and down hills and b) he was schooling collected trot/canter. There was a lot less of it, but it was still shows up mildly in once or twice in a ride.
As he went into his intermediate cde season I added estradiol cypoate to the mix and that worked wonders for him (worked better than injecting his stifles) although who knows if it had much effect after the first few injections, because at that point his fitness level was exceptional and he was well along in collection work, so at the very least, it was a combination of both. By this time last year he was solid in second level, mostly solid in third and preparing for his FEI CDE divisions in winter, so I discounted the estrogen in early summer. He’s been absolutely fine since then with the only flat tire instances happening when he is bone tired, typically the second day after a CDE (day after is an off day, but the next day is just a long walk day).
I will say that as a former hj person, who took fitness a lot more seriously than many of my fellow competitors, since I’ve started combined driving I realize I only thought I took fitness seriously before.
