A few studies have examined body composition changes in NCAA football players over a season. Typically, these studies have utilized a small sample of athletes, or they measured players utilizing body composition methods that were not as accurate as dual X-ray absorptiometry (DXA). In this blog, I am going to explore the changes in body composition that occur in collegiate football players during the course of a season. To do this, I examined total body composition DXA scans in over 700 collegiate male football athletes from five different NCAA Division I Universities. Athletes were scanned at various points in time and had at least one scan or multiple scans at: Pre-Season (July-September), Post-Season (December- February), and Spring Season (March-May). In total, over 2,500 scans were analyzed in this group of collegiate football players. It is important to point out that not every athlete had a scan at every time point, but we have accounted for this in the analysis. To help you look at the data in the figures below, I have used a letter system to indicate differences. If data points share the same letter (i.e., a, b, c, d), then they are not significantly different. However, if data points do not share the same letter, then those data points are significantly different from each other.

Changes in total body mass 
We will first look at changes in total body weight. In the figure below, you will notice that the data suggest that during the In-Season period, football players are at their highest total body weight. During the In-Season and through the Post-Season period, the players lose total body weight. This loss in total body weight continues through the Spring Season. This drop in total body mass during the Spring Season may be concerning for coaches. Some coaches may actually want to see an increase in lean muscle mass during the Spring Season, which would result in an increase in total body mass.

Changes in lean muscle mass 
In looking at the total body weight, one would assume that lean muscle mass and fat mass are probably remaining relatively stable as well.  A little closer look at the data suggests that there is a decline in lean muscle mass during the season, so that by the Post-Season period players have lost lean muscle mass. I think most coaches agree that they want to see their players maintain their lean muscle mass during the season and especially as they enter playoffs at the end of a season. Our data informs us that while it is desired to maintain lean muscle mass throughout a season, it does not often happen. A number of factors could be causing this such as teams scaling back their conditioning and weight lifting programs during the season and/or players may not be replenishing their protein following practice as well as they should. The data suggest that during the Spring Season, the players bring their lean muscle mass levels back to Pre-Season levels. With a loss of lean muscle mass during the season, programs may be “starting behind” with players after the season, having to first get them back to pre-season levels before substantially adding more lean muscle mass to their frames.  

Changes in fat mass 
Fat mass reveals a similar picture of total body mass in that during the season there is a trend for an increase in fat mass. This increase in fat mass would explain how total body mass or overall weight is not changing while lean mass is decreasing. This change in fat mass and lean muscle mass without a change in total body mass would argue for the need to go beyond just weighing players, since the change in body composition would go undetected using just a normal scale. In looking at the data from the Post-Season period, fat mass decreases so that it is lower after the Spring Season. This is what you would expect as athletes start to spend more time in conditioning and weight lifting programs.

Changes in percent total body fat 
The total percent body fat follows a similar pattern to fat mass during the season. During the season, there is a trend for total percent body fat to increase. Once the season is over, the total percent body fat decreases, so that by the Spring Season total percent body fat is at its lowest levels.  

What does it all mean?
So what are the takeaway messages?  I think for football programs, the most concerning point of this data is the loss of lean muscle mass during the season. By the time the post-season bowl games start, players have lost a significant amount of lean muscle mass and have increased fat mass.  There are also implications far beyond the playoffs, especially for players that need to add lean muscle mass over the course of their careers. You can see from this data that a lot of the changes in body composition that occur during the off-season are really replacing the amount of lean muscle mass that was lost during the season. Also, it is clear that DXA data can help with questions such as: 
-    How do we prevent lean muscle mass loss during the season? 
-    Do we need to do more strength training or evaluate nutrition strategies?  
-    Do we need to measure body composition more regularly to monitor in-season shifts? 

What next?
As a follow-up to this blog, the next blog will examine the question of what are the effects of this loss in lean muscle mass during the season on changes in body composition during a collegiate career. Can coaches and performance staff expect to make changes over a football player’s body composition in regards to lean muscle mass and fat mass?  Alternatively, do the season changes show a constant battle by athletes to replace the lean muscle mass that they lose over the course of a season? 

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.

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