Guys like CC and King Felix are different cases because they're built like dump trucks. (I assume you meant) James Shields isn't a power pitcher (ave 92.3 mph fastball in 2012, a career high and 90.9 career) who's best pitch is a changeup which is much less stressful to throw.
Innings limits on younger pitchers and pitch counts for individual games are a major part of pitching now due to the high attrition rate of young pitchers, especially when compared to position players.
Here is a favorite article of mine from
Baseball Prospectus