Every year I gather up the numbers from the top five or six linebackers selected in the NFL draft to see if in fact the players in the NFL are getting bigger, stronger and faster. My new metric to track this is the MAT, Mass and Time and is simple the player's mass in pounds divided by their time in seconds in the 40 yard dash. The thought with this is that a 200lb linebacker who runs a 5 second dash (MAT of 40) is anecdotally less powerful on the football field than the linebacker who weighs 250 pounds and runs a 5 second dash (MAT of 50). The above chart shows the average MAT score of the last 8 years of linebackers and it does seem like they are getting more powerful - moving more weight faster.
Here are their 40 yard dash times from 2005-2012
Here are their weights from 2005-2012