Comparing current eras of football with those in past is an enterprise beset by a legion of difficulties. The most obvious challenges involve changes in the rules, evolution of strategy and the improvement in equipment.

One measure that is intuitively obvious but lacking in statistical evidence involves the changes in the physiology of the players. Are the men playing football at the college and professional levels bigger, faster and stronger than they were in preceding decades?

As an example, Alabama's starting center Ryan Kelly is listed at 6-5, 290 pounds. In 1947, Alabama's All-American center Vaughn Mancha (pictured) was 6-1 and weighed 238 pounds.

A study published in the Journal of Strength and Conditioning Research earlier this year found that this was, in fact, the case. The group of researchers with Grand Valley State University and the University of Connecticut examined 55 studies conducted since 1971 examining player size as far back as 1942.

It should be noted that, according to the authors, the study wasn't undertaken to prove players are bigger than they used to be, but rather to systematically examine the changes so they can be better evaluated.

Players were split into skill level (college and professional) then grouped in three categories: mixed linemen (offensive and defensive linemen, tight ends, and linebackers), mixed offensive backs (quarterback and running backs), and mixed skilled positions (defensive backs and wide receivers).

Over the past seventy years college players in all three groups showed dramatic increase in weight: mixed linemen increased 0.338-0.900 kilograms per year, mixed offensive backs increased 0.089-0.298 kilograms per year and mixed skilled players increased 0.078-0.334 kilograms per year.

The results also show that there was a significant increase in body composition of college football players. College level mixed linemen gained 0.046-0.275% fat per year, according to the study.

Also notable is what the researchers didn't find. There was no significant change in body height for college level players and professional level players showed no significant change in both body height and body composition.

The study outlined some theories as for what may have caused these changes. They cited the implementation of year-round strength and conditioning programs, better training, improvements in nutrition as well as "possibly even the use of performance enhancing drugs."