I had a couple of falls (non-kiting) which led to lower back pain and severe sciatica with numbness in my pinky toe. I had leg weakness in my dominant leg. Jump rope was helpful to train the nerve to fire again and build up strength. Riding skateboards or bikes is also good for building leg strength. It was a year-long recovery.
Numbness is irritation of the nerve, where the location of the numbness may hint where the path of the nerve is damaged/irritated in/to the spine.
I've experienced finger numbness. Be aware of carpal tunnel and educate yourself on proper movement. The nerves in your fingers go through the wrist, elbow, shoulder, neck. Improper movement/posture in any of these areas can lead to symptoms.
Things that helped me were:
https://www.amazon.com/Back-Mechanic-St ... 65&sr=8-1
#This book teaches movement tests where the results will guide you to movements you should avoid. My Dr. referred me to physical therapy which made my numbness worse, so I listened to my body and stopped going to a physical therapist.
https://www.amazon.com/Healing-Back-Pai ... 598&sr=8-2
#After getting checked out and getting a diagnosis, this book teaches you how to deal with the pain. Before this book I was maxed out on painkillers and miserable. After this book, I was off painkillers and the pain progressively got better. Stay mobile as motion is lotion.
https://www.amazon.com/True-Form-Founda ... 700&sr=8-4
Foundation training teaches you how to use your core muscles throughout the day to protect your back. I used to get lower back pain while kiting, but now I use my core muscles properly.
The other thing that has helped me is SUP. It tones up your core (shoulders, abs, glutes, legs). After taking up SUP my hips don't feel as stiff. Perfect for windless days.
The path I have taken with kitesurfing is smaller kites, more efficient boards. I find that when I am on a kite that is too big for the conditions, I can start feeling stress in my back.
I stretch and try to avoid movements that put me out of alignment (hips). I am lucky to have found an amazing chiropractor.
I am now of the opinion that strong legs are good for the back. It has been my new year's resolution to improve my leg work.