Caroline:

Training every third day is under-training - you're spending more of your
week resting! Attempts to reconstruct Paleo life as a robust hunting or
scavenging trip followed by several days of lounging around the condo made
of stone-a (thanks, Steve Martin) seem to forget life in the primitive was
not blessed with the labor saving luxuries of post-indutrial revolution
Western civilization. Compared to most of us, those folks worked (as in
workout) most of the time. What's more, they played. So I just don't get how
we can assume 'rest' days so much as a spectrum of light, medium and high
intensity. As such, 'surfing the curve' of various components of strength
(the filled in version of Hill's force/velocity curve) provides ways of
training making use of all three conditions.

Early human's possessed a degree of conditioning rendering the imbued with
'readiness' in a world in which they were not merely hunter but just as
often the one being hunted. Once you get over the hump from living a
'resting' week to training a minimum of four out of seven days, then you'll
be in an exercising week mode, with a degree of fitness more akin to early
man.