The boys did a ninja class at Cape Cod Gymnastics last summer. John also practiced with their ninja warrior team there (Cape Cod Gym-ja Warriors). It's a growing thing now, with actual ninja gyms across the country and a national ninja league and everything. Way to make it big, American Ninja Warrior!
The owner of the gym recorded John doing some of the obstacles.
Every summer I get them enrolled there now, and they love it!