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April 16, 2003

Testing the Nexus

Pitcher Age and Workload Effects

by Lee Sinins and Will Carroll

One of the glaring weaknesses in the injury analysis game is the lack of data. As the injury database is built and populated, we are left with spotty research and anecdotal knowledge, especially when it comes to the crossroads of sports medicine and pitcher workloads. Adding to the problem is the lack of data for both minor league and college pitching. Since pitching is pitching, opponents of workload limitations often bring this up.

In one of the first systematic studies of early pitching workload, Lee Sinins, creator of the Sabermetric Baseball Encyclopedia, studied 135 pitchers who threw 175 innings or more before the age of 22. Age 22 is equivalent to the age-point found in Nate Silver's study on pitcher injury and age--the Injury Nexus--but was selected by Lee prior to the publication of Nate's study. Lee selected the pitchers from The Sporting News 1997 Baseball Register, giving us a distant enough perspective on many of the pitchers and allowing objective analysis on the possible effects of heavy workloads at such a young age. Unfortunately, innings thrown in winter leagues or in spring training could not be counted in this study as the data were not available. Innings were not adjusted for level and the totals are a sum for all levels in a season.

There were a few basic theories being tested in this study. First, the injury nexus would be tested. Despite the strong correlations between age and injury found by Nate Silver, real world numbers should match up closely. Second, while somewhat arbitrary, the 175-inning threshold seems to be a point where fatigue sets in for almost all pitchers. Young pitchers usually have not reached this threshold in their careers and the first test of this level often results in injury, massive failure, or a survivor effect.

Of the players included in the study, a large percentage went on to have severe injury problems or lost their effectiveness early in their career. Unfortunately, this loss of effectiveness cannot always be clearly tied to an injury, but it is a safe assumption in most cases. There appears to be an interesting pattern. Of those pitchers in the study that were able to absorb the workload without immediate damage, there was an ability to pitch into their early 30s before breakdown. Again, there is no clear cause and effect between early workloads and later injuries, but the pattern appears to imply that this would be the case. It should be noted that according to major league data, the breakdown of older pitchers begins around age 34; for pitchers in this study, it appears to begin at ages 30 and 31.

There are also two generalizations to be made regarding the pitchers in this study. In order to pitch such a high amount of innings in the minor leagues, these pitchers were being used as starters and organizations appeared to have high expectations for these "prospects." Few, if any, of these pitchers were not expected to be at least major league-average starters and most were able to reach the majors in some capacity.

As with any study, there are exceptions. Pitchers such as Roger Clemens, Greg Maddux, and Tom Glavine were included yet show no problems and have had what could be called successful careers. Clemens, to be noted, did have early arm problems, but overcame them to continue what will become a Hall of Fame career. Others, such as David Cone, Doug Drabek, and Dennis Eckersley, had quite successful careers, but perhaps did not reach their full potential due to early usage patterns. This, however, is impossible to prove with available data, and few if any teams would be dissatisfied with their results. Several others, including Doug Jones, John Wetteland, and Randy Myers, had successful careers in the bullpen. It is unclear if or how early workload impacted their careers, or if a switch to the bullpen might have been effective for some of the other pitchers in the study.