I think it varies tremendously in terms of how the horse is kept, its body type and temperament, and even age. Also, fitness for 1st level is not going to be sufficient for 4th.
I have a crossbred gelding who is naturally very fit and strong - gets fit, and stays fit, more easily than any other horse I have had. Heāll come home from a day hunting first field sweaty when everyone else is lathered - that kind of fit.
He lives out on 70 hilly acres, has a natural engine, and never spends more than 3 days a week schooling dressage. He hacks out (at some speed, on hills, over logs, etc.) usually twice a week and jumps once a week. I donāt think heād be as happy, healthy, or amenable to the work if he spent all his under saddle time doing dressage. Plus we like doing other things!
We are prepping for our 3rd level move up and my coach says he could do PSG in time. I never, ever worry about his fitness for what Iām asking of him now.
I was pleased at how well he kept his fitness during quarantine - we werenāt allowed at the barn for just over 2 months, and he got ridden 20 mins a day 3 times a week by my eventing coach - correctly ridden but not really working on 2nd or certainly 3rd level stuff. It took me over a month (Iām over 50) to get my riding fitness back, but by the time I did he felt terrific just being back in his regular schedule.
I think the living out on hills, hacking out on hills, and cross training helps a lotā¦but he is also a phenomenal natural athlete (I donāt mean super talented, I mean just by build and genetics he is very athletic - makes everything else easy, except sometimes directing all that energy. He can be spicy!).
The issue of training time is very different. I have limited access to my coach (every 2 weeks at the moment), and obviously weād be a lot further along if I rode with her more. But that is reflected in the pace of our progress - how quickly we go up the levels - not in our ability to progress period. Even if I could, however, I donāt think Iād want to ride more than once a week with my coach. Sheās amazing but intense, and I find I need some rides on my own to process and begin to feel and replicate what we do in lessonsā¦and if I cut out the hacking and jumping Iād have a much less willing - and possibly less sound - partner.