Or other activities. As a kid (about 4), some of us decided to try to climb to the top of a neighbor's barn type garage door. On me it fell, pinning me and fracturing my skull. Around the same or lesser age, I discovered that I could run and jump on the back of my tricycle and if I did it right, lean forward and grab the handle bars and coast forward some. If you missed and tried to do a breakfall on your arm only, it was possible to produce a long break of the ulna (BTW, I am not old, but the local family doctor washed the x-ray film in the tank of the toilet).
I learned some lessons, but as I grew older in wisdom, while in high school, I jumped over a mud puddle, slipped on rocks and broke both the ulna and radius at the wrist.
Realizing I had something going, while in AIT in the army, I skillfully placed by right foot under an about 550 pound bailey bridge panel as it fell off the roadway of the bridge. It buried my foot in the ground, breaking the first bone in my big toe in three places, and crushing joints in the big toe and the next two for good measure.
Feeling somewhat expert by now, I went on to break my right ankle, once in Vietnam (not in combat, but in stupidity), and again during a racket ball game in the USA. Little toes have been dislocated more times than I can remember.
Come to think some on it, Martial Arts training is the safest thing I have done.
