Exactly, and there is, in TWIST. I did mention the principle of diminishing returns, and just as skills and stats develop and improve automatically when a character devotes time, attention, and practice to them, they fade and reduce automatically when that character fails to devote time, attention, and practice to them. The rules for this exist in a couple of systems out there, but GMs rarely enforce them or even require any player attention to them, somewhat like the rules for encumbrance or material components in D&D.

grogthing  wrote:A dynamic "improve as you do" type system needs to
take into account improvement limits and atrophy.

You may work hard and practice (x number of hours) to
become a better weight lifter. You improve from
mediocre lifting ability to fair lifting ability. It
take it takes even greater effort and dedication to go
from fair to good (maybe 2 to 3 times the amount of
time). Even more effort to get from good to great.
Most professionals would be at the great level and
that is all they do. All of their available time is
taken up in training one or two related skills.
And if he stopped his level of dedication and training
the ability will slowly atrophy and begin to slide
back down to lower levels. Say the weight lifter stops
lifting for six months, he probably slips from great
down to good. High level skills and abilites need
dedicated use and intense practice to maintain. 

Greg
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