A friend of mine has got me interested in doing a duathlon. There are two events, the Fun Run (5K run, 5K cycle, 5K run) and the Challenge event (10K run, 20K cycle, 5K run). I'm seriously thinking about entering the latter.
Last night I ran about 11.5K and then cycled 20K (in about 2 hours 20 minutes) before collapsing at home. About half way around the run I got caught in the periphery of a thunderstorm, so got a proper soaking (thankfully no hail in this one!) but nicely cooled down too. At the end of all that, I really had nothing left at all. Even now, after sleeping it off I still feel exausted. This really does require an extreme amount of exercise, of which I'm respectfully scared.