Try finding a rock climbing gym or climb outside. Besides the obvious benefit building a strong core will have on your riding it is nearly impossible not to improve your anaerobic fitness. Though you will see toning and some muscle development in your upper body proper technique is climbing with your feet and using your naturally stronger legs to gain altitude. Who knows, you might just find a lady impressed with you being able to do pull-ups with one finger. Planches and one arm levers are cooler but still it is a good goal that tends to be more important to people with larger muscles. Long lean efficient muscles can do the same and you are more aero on the side of a cliff than this guy would be.