During their 2016 playoff run, the Cleveland Indians were unexpectedly aided by the bat of veteran outfielder Coco Crisp. The 5’10”, 185-pound Crisp homered in each of Cleveland’s first two series-deciding games to help the Indians reach the World Series. While the power outburst from someone like Crisp (who has just 130 career home runs over 15 major league seasons) was quite a surprise, the fact that he was in the lineup was not.

There’s a growing trend in baseball to fill the outfield with smaller and more athletic players than those who have manned the position in the past. Lumbering power hitters (think Manny Ramirez, Joe Carter, or a 43-year-old Barry Bonds) are not as likely to be outfielders as they used to be.

A recent analysis from FanGraphs’ Eno Sarris notes that runs created and slugging percentages from outfielders have been dropping steadily in relation to overall MLB averages. Sarris also put together this figure, which shows the average weight of outfielders over time vs. the league norm for all players:

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The evidence suggests that outfielders are leaner and more athletic than ever before, particularly in comparison to infielders. Data from our WHOOP MLB Performance Study supports that theory.

Last season, 230 minor league players from 28 teams and 9 different organizations were outfitted with WHOOP straps. One of the many things WHOOP does is measure heart rate variability (HRV), a metric that is becoming more and more popular as a training tool for tracking cardiovascular fitness in elite athletes.

We examined the heart rate variability of the players using WHOOP over the course of the study, then broke it down by position. On average, outfielders had much higher HRV than infielders:

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While outfielders appear to be more physically fit than infielders, pitchers were found to have the highest average HRV.

At any given moment in a baseball game, the pitcher is usually the player undergoing the most strenuous athletic workload, so it should come as no surprise that they are the ones most equipped to handle it. However, it’s hard to view pitchers from the same perspective as infielders and outfielders considering they don’t play on a daily basis. The fact that pitchers get more rest than other players could play a significant role in the HRV differences.

WHOOP uses HRV, resting heart rate and Sleep Performance to calculate daily Recovery. Results of the study showed that starting pitchers usually required three days to fully recover after taking the mound. Unlike players at other positions who compete on a daily basis, pitchers are actually given the time needed (four days off is the accepted norm between starts) to recover. This is likely a major factor in why pitchers have the highest HRV.

Come back tomorrow for Part 3 of our Special Report on the The Locker detailing the findings of the WHOOP MLB Performance Study.

Introduction: WHOOP and MLB Conduct Largest Performance Study Ever in Pro Sports

Part 1: Effects of Travel