How NFL rule changes made linemen gigantic

NFL players have become absolutely enormous over the past few decades.

But the growth hasn’t been equal across every player position — linemen have grown at much faster rates than non-linemen. You can see just how exponential that growth was in this graph by Alex Bresler:

In 1970, only one NFL player weighed over 300 pounds. That number grew each decade — from three in 1980, to 94 in 1990, to 301 in 2000, and finally to 532 in training camps in 2010.

So what changed?

Before 1950, the NFL limited substitutions. That meant that players often had to play multiple positions, and weren’t able to specialize. On top of that, restrictions on blocking below the waist during the 1970s allowed for linemen to become more top-heavy without having to worry about blocking moves that could knock out their knees. Paired with more advanced nutritional and training practices, the past three decades have enabled unprecedented growth in linemen’s body size.

But the rapid physical changes comes with serious health consequences. A 1994 government study found that NFL linemen die of heart disease at rates 52% higher than that of the general population, and three times the rates of NFL non-linemen. Further research in 2008 found that linemen suffer disproportionately from metabolic syndrome, which includes risk factors like obesity and high blood pressure.

Watch the video above to learn more about how this striking change happened — and what it means for players’ health.