Thanks for the link.
It fits with what I had heard - lifting weights became popular after the war. American influence perhaps. So O Sensei did not get his muscular body from lifting weights. It also fits with the story I heard about his powerlifting student. It happened in the early sixties.
Looking around, I found that the first All Japan Weightlifting competition was held in 1936, and the first all Japan Weightlifting Association was formed at that time - so weightlifting must have been around for some time prior to that if it had already spread around the country.
Plus, there are plenty of similar resistance style exercises that would produce similar results, even if not in western fornat.
As an aside, I seem to remember Yukiyoshi Sagawa, who was a contemporary of Ueshiba, as being a big weight lifter at one point in his life.