I've been reading more about N'Djamena and discovered that there are some tennis courts and a 9-hole golf course as well! Looking at satellite photos of N'Djamena it looks like the water isn't always as brown as when I was there so perhaps I should bring my fishing pole along. However, it may be carefully regulated as it was illegal to take pictures without a permit. Even if you had a permit your camera could be confiscated.
My friends in N'Djamena warned me there isn't a good gym available and it wasn't safe to run outside so I plan on shipping a treadmill, trainer for my bike, and a small home gym. If I can't exercise I will swell up and go nuts! I guess I could try boating too...