Koshiba: ...Because my father was an army officer, I was told to enter the military school during the war. Luckily or unluckily, one month before the entrance examination I got polio, which made my right arm numb. It's still numb.
DeVorkin: But you have full control of it.
Koshiba: Well, I don't have any strength. That made me exempt from military service during the war.
Later in the interview, Koshiba mentions that he had been fairly athletic, especially at kendo, before he contracted polio and diphtheria at age 13. Afterwards, he took up building working model airplanes, from bamboo and paper and rubber bands.
Now here's the odd way I came to this: I took my daughter to Anime Expo over the weekend, and we went to a panel on kendo. The expert speaker on the topic, it turned out, was a polio survivor, who took up kendo partly because his martial arts teacher pronounced it "too difficult" for someone with his disabilities. So, while hearing about kendo, the audience of several hundred (mostly) young anime fans also got some disability memoir too. I can't find the name of that speaker, but while I was trying to track him down, I came across Professor Koshiba instead.