During the years that I rode steeplechase races, I would run 5, 6 or more miles four days a week.
Sometimes students—or parents of younger students—will ask me what they can do to practice their riding or to improve their riding fitness. My short answer is always the same: "Ride more."
Unfortunately, that simple solution isn’t always practical or even possible.
But it's an issue with which I'm quite familiar. For the 24 years that I worked at The Chronicle of the Horse, as a staff member and as the editor, I always wanted to ride more. But usually I simply couldn't, sometimes because of time and sometimes because I didn't have any other horses to ride.
So, yes, I used to do other non-mounted exercises to be confident in my riding fitness. I ran three to five days (mostly nights) a week; at one point I did quite a bit of bicycling to ease the strain running put on my legs; for about 12 years I swam two to three days a week; and for awhile I worked out in a gym on the days I swam. During the years that I rode steeplechase races, I would run 5, 6 or more miles four days a week, both for fitness and for weight control.
I haven't run, swam laps or bicycled in more than seven years now, because I don't need to and don’t have the time, since I'm riding four or five horses a day, have farm work to do, and a young son to raise. But I do practice yoga three or four times a week, for strength and flexibility. As I've discovered at age 54, you really do lose both of those qualities as the years start to pile up.
So I speak from experience when I say that non-riding exercise is beneficial to riding, but only to a degree. Certainly anything you do to increase your strength and your endurance helps you in any physical activity, and riding is no exception. If you're out of breath or exhausted after trotting a couple of times around the ring or cantering over a small course, then anything you can do to improve your overall fitness can substantially improve your ability to stay on, and to influence, your horse.
And the more you want to do on your horse, the fitter you need to be. Running serious mileage definitely helped me to be able to ride two- or three-mile steeplechase races and to finish physically within myself, but running didn't make me a better steeplechase rider. Running didn't improve my ability to judge when it was the right time to move or make me brave enough to send a horse at the last fence in order to win. I don't think I ever became more than about halfway good at either of those decisive abilities, but what improvement I did make was from riding horses at speed over jumps and from riding races.
So my longer answer to the question is always this: If you want to get fitter (which is always a good idea)—then undertake a serious and consistent exercise routine. But if you want to become a better rider, then you need to ride more. Ride as often as you can, on whatever horses you feel confident riding. Yes, do what you can to ride horses besides your own.
Here's an observation that I offer as an example of how riding improves riding: I've just returned from working in the media center at the Hampton Classic Horse Show on the eastern end of New York's Long Island. I spent eight days watching some of the best jumper and hunter riders in the country jump a lot of jumps. And my biggest observation was the same this year as when I've worked here in the past: Man, those guys and gals can really find the fences.
Of course, that's especially true of the pros, but even some of the amateurs and most of the juniors who show in top shows like this are really good at finding the fences on the right stride.
Why? Because they practice jumping almost all the time, so they can instinctively and immediately adjust their horses' stride to meet the jumps at the correct distance.
As an eventer, I'm envious of the time they can spend working on the basics and the fine points of jumping. Sure, flat work is important to improve jumping, but flat work for hunters and jumpers really is a means to en end, not an end in itself. They practice leg-yields and shoulder-ins strictly for gymnastic, strength-building reasons. They don't have to worry about how correct the bend is or how long the strides remain through the exercise, because no judge is gong to score them on it. Even transitions aren't as big a deal for them—they have to be obedient and soft, but that’s really all that matters.
The hunter people do an astounding job of teaching their horses to canter around in the prescribed rhythmic self-carriage with a rounded frame, on a loopy rein. The jumpers don’t have to go in a prescribed manner between the jumps, but the more responsive and rideable the horse is, the more likely he’ll be to keep the rails up. They can allow a jumper to go in almost any frame he wants, as long as he responds correctly to his rider's aids.
My point is that the hunter/jumper people are better at jumping than we eventers because they practice it far more than we can. The dressage riders are better than we are for the same reason.
The simple truth is that if you want to be good at jumping, you have to jump a lot. If you want to become better at dressage, you have to spend a lot of time riding with your horse truly on the bit.
The key to both—and to riding well in any discipline—is practice, practice, practice.