Are we avoiding the Elephant (descending behind us) In The Room here?
Humans aren't very well designed for descending (monkeys climb down trees); running downhill seems like a massive increase in load on the joints, even done slowly. Not being competitive, and already suffering from running gently on the flat, I'm therefore
inclined to descend very steadily indeed.
<\boring old fart>
p.s. a mate of mine left me for dead by running straight down this (in walking boots):
Maps of the world, street map search - powered by Multimap(descent SE off Great Gable - at least 300m down)
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Edit: Just remembered the business about eccentric* contractions etc.
Normal running:
you supply a small force to cushion your landing, then
a LARGE force to spring away.
Descending:
LARGE force to cushion each landing, then
fairly small force to spring away (cos gravity does all the work)
IIRC training your muscles will give them strength in the 1 direction you use most
i.e. until you've descended a lot, your muscles won't be strong in that kind of work. This may make you very injury-prone.
[*I've forgotten all the right jargon to use here
]