Going out for a run.

[Bierzo Baggie]

I concur. Running over rain-slick flint and slithery mud you have to stay light on your feet. The only way for a 'heafty chap' to do that is to move 'his' feet as fast as 'he' can. I guess if you set it to music you might come up with an amusing YouTube clip. Riverdance would probably do it.

Hang on though - surely "hefty chaps" get greater purchase? I avoid slippery surfaces (especially downhill ones) because my lighter frame doesn't get purchase and I end up arse-over in a most un-dancer like fashion.

No real science as far as I know. There are big muscular guys who descend well and small guys with glass ankles. So many different factors come into play which of course makes it sort of interesting...