Does this mess your back up? There are some large BMXs.
I raced BMX growing up and feel like it set me up well to become a runner later in life. We'd ride 3-7 miles to some of the local parks that had BMX jumps / practice tracks, spend an hour or so there sprinting at jumps / racing around the tracks. Then we'd ride home. My dad built me a starting gate to practice on, Usually once or twice a week, I'd do 10-20 starts with a maybe 40 yard sprint to top speed. This was a daily thing for me for years.
Most of the big air jumps you see people doing these days have nice, sloped landings. Actually, that's part of the skill of the sport is to make sure you land on the down slope of the jump, set of doubles, etc....