MLB Players Packing on Muscle: Analysis of 144 years of reported weight of players

After looking at some notable players over time, I noticed that some were bigger in their 40s that they were in their 20s. And I’m not talking about fat. This was pure muscle. This got me to wondering, “Do the historical numbers show that players are packing on muscle?”

Sean Lahman has graciously compiled detailed historical data for Major League Baseball games dating from 1871–2015 (I assume that 2016 is coming soon). In that data set, the player’s weights are listed.

Caveats:

- The weight of the players are reported not measured by an independent observer. So, it could be self-reported by the player or by the team’s intern or whoever. It’s not scientific…sorta like you self-reporting your weight on your driver’s license :D
- Unfortunately, the player’s reported weights are not by year. There is only one weight listed on the player’s profile just like one home town or one last name. If a player plays for 10 years and is listed as 180lbs, it is unlikely that he was 180lbs every year. But the data set is very large and I am looking for big trends not trends for individuals.

It’s not scientific. But there are enough data points in the set to look for trends. “Are the reported weights of players increasing?”

The short answer is: YES! Players are getting bigger…especially since the early 1990's

You can use my interactive visualization here if you want to see for yourself.

Weighted Average Reported Weight of All MLB Players from 1871–2015

Weighted Average Weight

What is the “Weighted Average Weight” and why is it “Weighted”?

I didn’t just take the total weight of the players and then divide by the number of players. I felt that an outlier like a 320lb guy who only played 10 games shouldn’t have the same influence on the average as a 170lb guy who played 100 games. So, I weighted the averages (pun intended). So, using the Number of Games played at a position, I weighted the averages then

Average Weighted Weight = Avg(Sum(Weight x Games) / Sum(Games))

This way, the outliers wouldn’t skew the data.

The trend is definitely there!

Let’s look at the modern era of baseball from 1970 forward:

Weighted Average Reported Weight of All MLB Players from 1970–2015

Get this: From 1970–1992, the weighted average weight was between 184 and 186lbs. That’s sorta remarkable. Then something even more remarkable happens: The average weight rises steadily from 187 to 211 over the next 18 years!

The Speedy Guys

Let’s look at the Speedy Guys. Typically, the Shortstops, Second Basemen, and Center Fielders are the fastest guys on the team. They wouldn’t get bigger…would they?

Weighted Average Reported Weight of 2B, SS, & CF Players from 1970–2015

Wow. They are!

What’s more is that Center Fielders and Shortstops are bigger now than Catchers were from from 1871 into the 1990s:

Weighted Average Reported Weight of C, SS, & CF Players from 1970–2015

Note: Before the mid-1950’s, there was no distinction between Left, Center, and Right Field. They were all lumped in as “Outfield”.

Pitchers and Catchers

The growth of Pitchers and Catchers has almost been in lock-step:

Weighted Average Reported Weight of Pitchers & Catchers from 1970–2015

The Big Boys

Who are the “Big Boys” on the team? Pitchers, Catchers, Right Fielders, First and Third Basemen:

Weighted Average Reported Weight of P, C, RF, 1B, & 3B Players from 1970–2015

Biggest size differential? First and Second Basemen:

Weighted Average Reported Weight of First and Second Basemen from 1970–2015

All on one chart:

Weighted Average Reported Weight of all players from 1970–2015

“But, Baseball players are just fat!”

Before you associate weight with fat, let me remind you that at 207lbs, fleet-footed Usain Bolt weighs more than the average Outfielder or Middle-Infielder.

It’s well-known that muscle is more dense than fat, it’s really difficult to declare than anyone over a certain weight is “fat”. These are some of the top athletes in the world with every incentive to stay at the top of their sport. It’s fairly safe to assume that the increasing weight over time is due to muscle mass as training and diets have improved. We must remember to differentiate between functional muscles that athletes need from “beach muscles”.

Prince Fielder as shown in ESPN Magazine

Conclusions

This was really enlightening to me. I’ll leave it up to you folks to speculate as to why this is occurring or why clubs are choosing bigger players. Is it weight training, diet, supplements, programming, strength, power…?

Baseball is an anaerobic “sprint” sport with short, powerful bursts of activity. It’s not surprising that power is rewarded.

How does power relate to weight? One must be able to move something slowly before one can move it quickly. Moving heavy things slowly is Strength. Moving heavy things quickly is Power. Muscle size and muscle fiber type are directly related to Strength and ultimately Power.

There is a point of diminishing returns. It looks like MLB clubs are still looking for that point.

To put things into perspective, the average weight of Tennis players (another sprint sport) also seems to be rising. The top tennis players in the world right now weigh between 185 and well over 200lbs.

Whatever the reason for the gains are, the fact remains that it’s happening and has been for a very long time.

UPDATE (6 JAN 2017):

For those watching this story, the data set has been updated with 2016 season data: https://public.tableau.com/profile/carleton#!/vizhome/MLBWeightvsSeason/Story

The average weight is down 1 pound from 2015 to 2016: