To maintain a reasonable level of fitness, I have been using a cross trainer. It's very convenient as it's at home, so can use at any time (so far have been on it at 7am and 9:30pm). But it is so *boring* compared to being out in the countryside running!
I have also been doing some fitness training for karate - mainly press-ups and sit-ups. Could also maintain leg strength by doing squats, but see above for boredom factor. Hoping to get out on the bike this week as that should hit the spot.