This is the second blog on body composition in college and professional football players.  As I stated in the first blog, we recently published a paper in the Journal of Strength and Conditioning Research (Bosch et al., 2019) on body composition measures in over 467 NCAA Division 1 collegiate football players. This recently published paper is a companion to the scientific papers we published on body composition in National Football League (NFL) players (Bosch et al., 2014; Dengel et al., 2014). Those two papers on professional football players reported body composition measures on 342 NFL players. I thought it would be fun to compare the collegiate football players to our NFL football players. All three of these studies used the same model of dual X-ray absorptiometer (DXA) so it allows us to make comparisons between these two groups of football players without having to worry about differences in DXA scanners. In the first blog, we looked at both collegiate and professional offensive players. (i.e., offensive lineman, tight ends, running backs, quarterbacks and wide receivers). In this blog, we will look at defensive players (i.e., defensive lineman, linebackers and defensive backs).  

Physical characteristics of collegiate and NFL football players.
In the table below, you will find the physical characteristics for our defensive football players.  The table has the mean values plus the standard deviation for each variable.  The ranges for each variable can be found in parentheses next to the mean value. The defensive players are grouped into one of three defensive positions (i.e., defensive lineman [DL], linebackers [LB], and defensive backs [DB]).  What is interesting about the table below is that besides age the mean values for height, weight, and body mass index (BMI) are very similar between college and professional defensive football players. We also found this to be true in our comparison of collegiate and professional offensive football players. In addition, the ranges for height and weight in both college and professional defensive football players are quite large; indicating that even within defensive positions, there is a range of sizes for players.  One explanation for these large differences in ranges may be the varied defensive alignments that are seen in both college and professional football teams.  In addition, we are starting to see more and more hybrid players being employed in various football defensive schemes.  For example, some defensive schemes use a larger than normal strong safety or a smaller, quicker lineman. Another interesting aspect of the table are the mean values for BMI for both college and professional football players.  BMI is a measure of body composition based on height and weight. Using this measure of body composition, all of the defensive positions would be overweight (BMI 25-29.9 kg/m2) while defensive linemen and linebackers would be classified as obese (BMI of 30 kg/m2 or greater).  This is very similar to what we saw in both the collegiate and professional offensive football players.  This indicates the problem of using height, weight, and BMI to assess the body composition of both collegiate and professional football players. 

Percent total body fat
Now let us look at percent fat for our collegiate and professional defensive football players.  In the figure below I have graphed total percent body fat for both NFL (blue bars) and collegiate defensive football players (red bars).  Again, the means for the different defensive positions are very similar.  Like height and weight, the ranges for percent total body (located above the bars) are similar in their magnitude.  In addition, professional as well as collegiate defensive backs had the lowest percent total body fat of the three defensive positions.  Defensive backs mirror the wide receivers on offense in that they have the lowest percent fat of their group.

What does it all mean?
So what does it all mean? First, the data in these two blogs provide trainers and coaches who use DXA to examine body composition in their players a place to look at normative data by offensive and defensive positions for both professional and collegiate football players.  Secondly, it is clear that using simple measures such as height, weight, and BMI will incorrectly classify football players.  Finally, the data presented here demonstrate why more accurate methods such as DXA are needed to assess body composition in this group of athletes.  In upcoming blogs, we will dig deeper into body composition determined by DXA in collegiate and professional football players. For those that want more detailed information found in this paper and other papers we have written on this topic, please look at the references cited below.

Bosch TA, Burruss TP, Weir NL, Fielding KA, Engel BE, Weston TD, Dengel DR: Abdominal body composition difference in NFL football players. Journal of Strength and Conditioning Research 28(12):3313-3319, 2014.

Bosch TA, Carbuhn A, Stanforth PR, Oliver JM, Keller KA, Dengel DR: Body composition and bone mineral density of division 1 collegiate football players: a consortium of college athlete research study. Journal of Strength and Conditioning Research 33(5):1339-1346, 2019. 

Dengel DR, Bosch TA, Burruss TP, Fielding KA, Engel BE, Weir NL, Weston TD: Body composition of National Football League players. Journal of Strength and Conditioning Research 28(1):1-6, 2014.

About the Author
Donald Dengel, Ph.D., is a Professor in the School of Kinesiology at the University of Minnesota and is a co-founder of Dexalytics. He serves as the Director of the Laboratory of Integrative Human Physiology, which provides clinical vascular, metabolic, exercise and body composition testing for researchers across the University of Minnesota.

Read Part 1 - Offense
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