(1) From now on there will be much less litter. People will value every trip to the bin as part of their training routine.
(2) There will be less crime, and for the same kind of reason; everyone will be so busy training. Who would even think of a robbery, to say nothing of a (says nothing of it)?
(3) There will be a huge step forward towards social equality. This is because everyone will be so attached to the idea of a level playing field that they'll think of themselves lying down on one next to their very rich or very poor compatriots, and feel they are all of similar height.
(4) The homeless will no longer be with us. Give everyone a bicycle and they'll spend their nights cycling around. Their bikes will be their homes.
(5) Flooding will cease to be a problem. Why? On account, you suggest, of the increase in swimming? Forget about it; the Olympics have been far more radical than that in their transfomative influence. Those whose homes are flooded will simply pole-vault out of them on to the high ground.