I am big on cross-training. I'm so big on it, I wrote a whole book about it: Runner's World Guide to Cross-Training. Recently I've gotten into a new type of cross-training that is not mentioned in that book: slideboarding. A slideboard is a long, narrow, thin, rectangular sheet of plastic that you lay on the floor and "skate" on from side to side while wearing fabric booties. They are mainly used by hockey players, speedskaters, and skiers for off-season training, but I have a hunch that slideboarding might be hugely beneficial for runners.
Why? Because it's highly complementary to running. On the one hand, slideboarding provides an excellent cardiovascular and muscle conditioning workout for the legs, just like running. On the other hand, slideboarding is a non-impact activity, so it provides an extra fitness boost without increasing injury risk. More important, unlike running, slideboarding is a lateral motion activity, so it strengthens lots of important lateral stability muscles that are crucial to minimizing stress on the joints during running but are not really strengthened by running itself. Slideboarding is particularly good for the muscles of the outer hips and buttocks, which tend to be especially weak in runners who are especially injury-prone, like me.
I just started using my slideboard this week. While I am confident it will prevent injuries in the long run, it will only cause an injury in the short run if I do too much of it too soon, as it is taxing muscles that my body had more or less forgotten even existed. At present I'm doing just a few minutes each night (I run in the late morning). I will eventually build up to 20-30 minutes per session, 4-5 times per week. I will give you a progress report down the road.