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June 9, 2008

Ballad of the Fatigued

The Effects of Long Innings

by Eric Seidman

Delivering to the dish with a 2-2 count, Wandy Rodriguez hit the outside corner with a 91 mph fastball with which Edgar Renteria could do nothing but whiff. This heater happened to be the 55^th pitch that Rodriguez threw in the inning on August 1, 2007. While the pitch brought the inning to a close, it simultaneously placed Rodriguez atop a list of the pitchers who had thrown the most pitches in a single inning. Compiled by Retrosheet’s David Smith and posted on the Inside the Book blog, the list is composed of the pitchers with the most pitches thrown in an inning from 2004-2007.

I decided to examine the Pitch F/X for Wandy’s game. Analyzing the velocity and movement of Rodriguez’s fastball, I was surprised to find that his fastball sustained its velocity and “bite” as he went deeper into the inning. However, during the rest of the game things changed a bit. In the second inning, his velocity lost three miles per hour, but his movement increased. It has been theorized before that some pitchers may throw with more movement when they tire due to a dropping of their arm angle; perhaps this happened here, as Wandy lost velocity but threw with more movement.

After several ideas were tossed back and forth in attempts to deduce causation, I decided to turn this into an extended study, looking at the 25-30 longest innings captured by the Pitch F/X system. First, though, we need to understand why this study matters from a mechanical and physiological standpoint; in other words, how throwing a baseball affects the body, and how throwing these long innings can cause even more problems for the pitchers who have to throw them.

The Science of Fatigue

To fully grasp the science behind fatigue, I turned to Will Carroll. He offered the following:

Baseball has conducted some internal studies on this, and it seems that there’s a point where pitchers really begin to see the effects of in-inning fatigue. Since pitchers do essentially the same activity, though in very different ways, one of the commonalities I expected to see was a common fatigue point for their specific skill. Elite marathoners all tire at the same level (the legendary “wall” at the 20-mile mark). Sprinters and weightlifters all have a narrow range of anaerobic capacity. Pitchers, it seems, have that same type of common fatigue point. It was actually a bit higher than I expected.