Jake Arrieta has pitched a lot of innings dating back to the start of the 2015 MLB season. In fact, Arrieta has thrown far more innings with the Chicago Cubs than he ever did with the Baltimore Orioles.
Before joining the Cubs midseason in 2013, Arrieta was in his fourth season with the Orioles. In total, Arrieta threw just 358 innings from 2010-2013 with the Orioles. Those 358 innings all came during the regular season; in fact, Arrieta never pitched for the Orioles in the playoffs.
Since joining the Cubs, Arrieta has thrown 712 1/3 regular season innings, nearly doubling his total from his stint with the Orioles.