There is always something new on here !!

I can think of Steve Moneghetti as a good example of a low arm hang action.
Others I have watched seem to keep the forearm below horizontal, and an angle open above 90 deg ( never get to an L shape or more closed than that).
My guess is that tighter arm action causes fatigue and also lifts the body's centre of gravity, so more energy is needed to keep the loss/restore balance rhythm sequence. (did a CofG Running style analysis in Yr4 of PE course)
Some African marathoners may not meet this criteria, but the lean body mass they have and their ectomorph body type mean that arm angle is less of a factor.
For me, its arm slung low as well. This is a good topic- some may say who cares, but in the last 5k of a marathon every little bit makes a difference.
cheers
rowey
