Fencing. With swords, not pickets, barbed wire, etc. I gave it up 25 years ago, then took it up again about 18 months ago. I now fence all three weapons, having started Sabre about six months ago. Fencing is a very aerobic sport, and participating in it has done wonders for my fitness and mobility over the past year or so.
Here are a couple of videos of me fencing foil in a Masters competition last year.