Ninja work requires strength, especially upper body strength. That is obvious to any who watch Ninja Warrior games, and I concentrated on upper body strength at every session with my trainer. But there is something else. When I began my ninja training, my bone tests showed mild osteoporosis, not atypical for my age. After a couple of years of strength training as part of my "ninja training, my bone density tested normal. The strength training added to the density of my leg and upper body bones. Walking took care of the spine. I used to think that walking was boring, and that walking was simple. You just put one step in front of the other over and over again, and soon you are striding along, losing weight and gaining health. Then, I learned about High-Intensity Interval Training , varying speed over time. My cup of tea. I could mis things up on an outdoor walk and distract myself from boredom by playing with the controls on the treadmill at the gym: fast, slow, almost-running, st
