I would recommend yoga for balance, and I personally have taken up krav maga. It's for self defense, but I have noticed some improvement in my riding, believe it or not. I also run when I can, and I do light work-outs 6 days a week- I alternate between two, the first consists of push-ups, planks, side-planks/ plank twists, backwards sit-ups, wall-sits, pilates, seated russian twists, and isolations. The second focuses on arms/ shoulders/ upper body and legs, with 5-10 lb weights/ kettle bells, and some lunges and stretches for my legs- overall, I focus on flexibility with my legs and leave riding/ running / krav maga for strength. I usually exercise for about forty minutes to an hour, although I would like to do more, as I want to be fit and know a form of self- defense for next year, when I turn 18, because I plan on traveling.