The most common thing I hear when I speak about the benefits of yoga is "I'm not good at yoga, I'm not flexible, I'm not strong enough, I wasn't patient enough" The list goes on and on. Like anything, it is a practice but the best part of this practice is it is one that you simply cannot fail.
The beautiful thing about yoga is there are no goals, no expectations, no way to not succeed. Not only do equestrians need this wonderful break in their life but so does everybody.
Yoga accepts you where you are, and you need to find an instructor that does the same. Finding an instructor that makes you comfortable is one of the most important parts because yoga is about compassion for yourself and others.
Every time I touch my mat I remind myself that for me this is fun. I used to take my equestrian errors onto my mat and get frustrated if I wasn't getting something "right". Then I made a vow to myself that I would not get on my mat without a smile on my face, this would be my fun. That translated into the saddle (any sport that one does) and my riding became less stiff and forced.
Over time great benefits will follow, it takes time, the best part is the process. Remember to be thankful for all of the wonderful things your body does for you, yoga is just something you can do for it.