NOTE: A's sign Ben Sheets to a one-year deal. See fanpost for discussion.
As Dusty Baker or Bruce Bochy won't tell you, carrying a starting pitcher's workload through a full season is really, really difficult. It's a little easier for veteran starters, but young arms seem to be more susceptible to pitching-related injury and loss of effectiveness as a result of a large pitching workload. A few years back, Tom Verducci of Sports Illustrated hypothesized that the safe limit, or magic number if you will, is around 30 innings. More specifically, he theorized that pitchers who are 25 or younger that experience workload increases of 30 innings or more from year to year will pay for it in the next season. Of course, it's not a strict rule, but a guideline that managers should generally follow. In his words,
Why can't [young pitchers] throw 200 innings? Simply put, they're not conditioned for it yet. It's like training for a marathon. You need to build stamina incrementally. The unofficial industry standard is that no young pitcher should throw more than 30 more innings than he did the previous season. ...Pitchers generally feel the effects of abusive increases in workload the next year, not the season in which they were pushed. In other words, you might be able to finish that marathon for which you didn't properly train, but your body will have hell to pay for it. I call it the Year After Effect.
Verducci isn't arrogant enough to name the effect after himself. Rather, Will Carroll of Baseball Prospectus did his own research independently which seemed to corroborate Verducci's hypothesis. Carroll named the effect after Verducci, a name which Tom apparently refrains from using.
In either case, which Oakland pitchers fall under possible Verducci Effect candidacy? We've got enough young arms to move a Coliseum-sized tarp (on second thought, maybe not), but which ones are at risk because of getting overworked?
Dallas Braden (2008: 124.3 IP, 2009: 136.2 IP)--Dallas is fine. He's 25, at the upper edge of the Verducci Effect's age range anyway, and a 12 inning increase isn't going to hurt. Also, that 2009 figure isn't his career high.
Brett Anderson (2008: 105.0 IP, 2009: 175.1 IP)--Yikes. A 70 inning jump in workload can't be good. On the bright side, he pitched 120 innings in 2007, but a 55 inning increase over his previous career high still spells trouble. If it's any consolation, Anderson's average fastball velocity remained at 93 mph in the second half of the season, without any decline. I'm just not sure if fastball velocity is a good measure of year-after fatigue.
Gio Gonzalez (2008: 157.0 IP, 2009: 159.2 IP)--Nothing to worry about here. He actually pitched 150 innings in 2007. Oddly consistent.
Trevor Cahill (2008: 124.1 IP, 2009: 178.2 IP)--Another red flag. That 54 inning increase just might be another problem Cahill will have to deal with in his already ten-story "Things to Work On" pile.
Vin Mazzaro (2008: 171.0 IP, 2009: 147.3 IP)--Yes, that's right, Vin pitched 171 innings as a 22-year old split between AA and AAA. And believe it or not, but that wasn't even a 30 inning increase from 2007. He should be good to go for 2010.
Again, remember that the Verducci Effect isn't a sure thing, just a rule of thumb. Brett Anderson and Trevor Cahill aren't guaranteed to suffer next season, but Geren may want to think about treating them with extra care.