Baseball Arm Injury Overview

Arm injuries are the most common issue in major league baseball accounting for 40% of incidents and over 50% of days on the injured list IL) from 1998-2015. Elbow and shoulder issues are split fairly evenly over the period studied, but elbow problems have become more frequent recently. The findings are similar for NCAA baseball injuries.

Since prior injuries are the most significant predictor of future injuries, early prevention is critical. Medical research by Samuel Olsen and others shows that overuse and fatigue are the primary drivers of arm injuries in adolescents including pitching a high volume of months per year, games per year, innings per game, pitches per game, pitches per year, and warm-up pitches before a game. It also shows that injured pitchers were more likely to be starters, pitch in more showcases, throw with higher velocity, and pitched more often with arm pain and fatigue. Other research has shown that pitchers that are taller and throw harder are at greater risk. Additionally, injuries skew earlier in the season as the acute workload or stress on a player’s body may be more than he’s level of chronic workload or fitness is prepared to handle at that point in time. Southern high school pitchers have a higher injury rate than northern. Is it true at the collegian level as well.

Baseball has tried to remedy the arm injury epidemic by monitoring workload through pitch counts, but the vast majority of throws are missed including pre-game warm-up, bullpens and warm-ups between innings. Additionally not all pitches create the same risk. Fastball velocity (see Hardball Times as well) was found to be the biggest predictor of future injuries in the MLB according to research by Matt Manocherian & John Shirley. Rany Jazayerli has studied injury risk as well and call out three principles:

  1. While pitching is an inherently unnatural motion, throwing a pitch does not necessarily do permanent damage to a pitcher’s arm. It’s only when fatigue sets in (and a pitcher’s mechanics start to waver) that continued pitching can result in irreversible injury.
  2. There is a certain number of pitches that a pitcher can throw before that fatigue sets in.
  3. Once a pitcher is fatigued, each additional pitch causes more damage, and results in more additional fatigue, than the pitch before.

At the MLB level, he created a fatigue metric called Pitcher Abuse Points (PAP) to track overuse above 100 pitches a game, which is the average threshold when injury risk escalates. A score is created by taking the number of pitches above 100 and cubing it. For example, 105 pitches is worth 125 points (5^3), 110 pitches is 1,000 points and 115 pitches is 3,375 points. This means that the risk of injury is exponential rather than linear such that throwing 5 pitches above 105 is eight times worse (1,000 / 125), than the five pitches above 100 and pitches 111-115, 27x worse (3,375 / 125). A comprehensive 2002 study based on this methodology was completed by Keith Woolner, where he showed that high PAP pitchers were three times more likely than low PAP pitchers to be injured. Early sports specialization and age can also play a significant factor in arm injuries at the pro level significant factor with pitchers under 25 at higher risk than those over that point with the highest risk at ages 21 and 22.

These studies triangulate on the key risks of fastball velocity, prior injury history and fatigue as drivers of future injuries. Better discipline and tracking is needed through workload tracking technology like Driveline’s Pulse.

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