I don't know. But it is what I did this lunchtime. 8x400m (roughly - it's two fields worth of effort) with 1 minute rests between them.
It was a slog from the word go. As they do, they got progressively harder until it got so embarrassing I stopped. Not the most technically advanced way of training, but I'd recently watched the film about Graeme Obree, the Scottish cyclist; his home-made approach worked pretty well, so I'm optimistic mine will work for me.
Whisper it quietly, but I'm thinking very seriously of entering a fell race. Somehow, running with a number pinned wonkily to my chest seems strangely alluring. It's probably the endorphins talking. The runner's equivalent of drinking too much beer and taking on the world.
Smileyrating 4/10 for the effort, 10/10 for the conditions