Yoga is terrific for flexibility, body awareness and core strength. I like to bike for aerobic fitness. Running made my calves outgrow my boots, and they muscled so heavily that they would actually cramp when I rode. I also do both free weights and regular weights for strength.
There are numerous ways you can torture yourself with an exercise ball, too!
Do you have access to a gym? There is no way to simulate riding, but I think with regular exercise (4-5x/week), your riding strength will return faster than you might think. I had to take a 4 month break after a knee injury which required surgery. My surgeon recommended cycling, walking, elliptical and swimming (I suppose you could run if you are inclined). He said that it's the best way to recover and build strength (my leg was pitiful, shrunken and weak), and then to maintain strength. For riding you need both aerobic fitness and endurance strength.
I swim 3x/week for 30 min, then do the elliptical trainer, without holding on, 2x/week for 30min. My whole body stays toned and I have strong abs with visible definition. I don't have time to spend doing much more than that, and there is recent research that says the ideal time to spend exercising is 150 min/week. I was overjoyed! The rower is also a good total body workout that I used before my injury when I didn't have access to a pool.
When I got back on the horse I did feel pretty weak, but there is something called muscle memory which is a wonderful thing! I did a lot of 2 point and some no stirrup work. My non-injured leg strength came back very quickly.
Agree with Nikki and Sing that yoga is absolutely wonderful. It really does improve your riding. DH is an athletic trainer, and was constantly telling me to stretch before and after I ride. After dutifully ignoring him for several years (what does he know about riding anyway?) I ended up going to ride right after a yoga class. I felt the difference, and my trainer immediately noticed my position was better. Now I always stretch before a ride.
Whenever I take a break from riding, I tend to keep up my muscle strength, but my cardio endurance plummets quickly. I will agree with Sing again, that serious running will bulk up your calves. I also love biking, because it's low impact on my delicate knees.
I bought a Pilates reformer recently to do toning and core strengthening exercises at home. If you look around, you can find them used for a reasonable price or buy a nice one on sale like I found for $299 (down from ~$800).
I really like it for doing core strengthening exercises and toning the muscles used for riding in a low/no impact way.
Trainer at the gym thought she was torturing us the other day with the following exercise on the ball. I just felt like I was riding without stirrups.
sit on ball with knees bent behind you. It will feel weird, even to riders. Then squeeze with thighs and "post" by squeezing the inner muscles. You will feel it in your inner thighs the next few days, but I really think it would be useful to riders. It is one of the few things I have ever done in the gym that really "felt" like I was using the same muscles as riding.
Honestly, I rode perhaps the best I have ever ridden when I was running 6 days a week...even though that was the point in my life where I was riding the least. Go figure. Running is great for cardiovascular health, core and overall strength, and endurance. I actually wish I had more time for running right now, because I know it would help my riding a lot. Ironically, I don't have much time for running because now I'm riding 5-6 days a week!
I love pilates and usually use http://poppilates.com. They are tough, but once you do them a few times they get a little easier I also love Tracy Anderson's workouts, especially her arm one (just youtube Tracy Anderson). I try to do these videos for an hour 3-4 days a week. Also, on the other 2-3 days (I work out 5-6 days a week depending on how much time I have), then I walk on the treadmill w/ a steep incline. This really forces you to use your core to keep you balance, plus it burns tons of calories (I usually burn about 1000 in a little over an hour).
Road cycling! Improves balance, aerobic capability, and is sooo fun, especially useful when you live somewhere with lots of hills. Not so useful in the winter but you can always do spin classes when it is crappy out.
Specialized Equine Rehabilitation and Fitness in the Wine Country
I do serious running and have not had a problem with bulking up to the point my boots don't fit. since I've started running they actually fit better and they are customs. I also do spin class, weights, and boot camp. I skip the yoga as I don't enjoy it one bit
If you belong or are close to a gym that offers the Les Mills classes (body pump, body combat, etc...) I highly recommend Body Attack! It's a "sports training" class, it's fun, and it has the added bonus of certain sections making you feel like you're Tommy Tune in a broadway musical! (I am the LEAST coordinated person on the planet, so if *I* can do it... lol!)
Great over all strengthener and really builds your stamina as well.
The ninja monkeys are plotting my demise as we speak....
Kickboxing!!! Amazing core, strength and endurance!! Also a great way to blow off steam after a stressful day/week. I'm also doing brazilian jiu jitsu. All the self defence stuff is good to know and gets you in shape plus it's a blast.
Core and cardio would be the best thing to stay on top of as well as some leg strength. Most things (sit ups, planks, air squats, lunges) can be done at home without anything more than an exercise mat. Add in a ball and the possibilities are almost endless. I also agree that stretching is key.
I do not use weights... and I run between 3 and 6 miles a day. It really has been the best thing for *me* to keep the weight off. Well, that and watching what I eat. Oy... the holidays. *sigh* For me, yoga is torture. I am such a dunce when it comes to "getting it"...
The ninja monkeys are plotting my demise as we speak....
Any yoga DVD recommendation so we can do it at home?
I love Jillian Michaels "Yoga Meltdown" DVD. It incorporates yoga with movement so it burns more cals. It is my fav workout DVD ever. I get bad workout ADD, but this one I've enjoyed for about two years now. Not too long (about 40 mins), moves quickly through the exercises without too much repetition, gives a good stretch and a little burn without making me feel like I am going to keel over. Some traditional yoga DVDs can make me a little sleepy if there is too much focus on breathing & relaxation.