Initially, I wrote a blog on a recent body composition metric (i.e., muscle-to-bone ratio) that is gaining traction in the world of athletics and performance. As a follow-up to that blog, I wrote another blog that discussed a recent scientific paper [Dengel et al., 2023] that came out of my laboratory on the muscle-to-bone ratio (MBR) in National League Football (NFL) players. In that blog, we compared NFL players (n=346) to a healthy aged-matched male (n=228) control group. Both groups had their muscle and bone masses determined using dual X-ray absorptiometry (DXA) and these values were then used to calculate total as well as regional MBR. The blog discussed the difference in total as well as regional MBR values between age-matched healthy controls and NFL players. In that scientific paper [Dengel et al., 2023] we also examined total as well as regional MBR by position in the NFL players. The NFL players were categorized by position into one of nine position categories: defensive backs (DB, n=64), defensive lineman (DL, n=47), linebackers (LB, n=48), offensive lineman (OL, n=38), quarterbacks (QB, n=21), running backs (RB, n=29), tight ends (TE, n=27) and wide receivers (WR, n=55). Punters and place kickers were combined into one category named punters/kickers (PK, n=17). Total MBR as well as regional (i.e., arm, leg, and trunk) MBRs were calculated from DXA measures of muscle and bone masses. In this blog we will look total as well as regional MBR by position in this group of NFL players.

So, let’s look at the positional total and regional MBR data. If you look at the figure below, you will notice that above each player position there is an image that sort of looks like a violin. These “violins” depict distributions of the data for each group using what are called density curves. The width of each curve corresponds with the approximate frequency (i.e., number) of data points or players in each region. Above each violin image there is a letter or series of letters. Violin images (i.e., positions) that share a letter with another violin image are not significantly different from each other. On the other hand, violin images that do not share the same letter are significantly different from each other. If you look at the total MBR panel at the bottom right corner of the figure you will notice that all the violin images have the same letter indicating that there were no positional differences in total MBR between the different positions. However, if you look at the arms, legs, and trunk panels of the figure below you will notice that not all positions share the same letter. For example, in the arm MBR panel (upper left corner panel), QB and DL violin images do not share the same letter. Indicating that the arm MBR is significantly lower in QB than DL. This indicates that DL had a greater amount of muscle mass per unit of bone mass than in the QB. There were no other differences in arm MBR between any of the other positions. The trunk MBR (lower left corner panel) shows PK having a significantly greater trunk MBR than OL. This would suggest that the PK have a greater amount of lean mass for the same amount of bone mass. There were several differences in leg MBR (upper right corner panel) between the different positions. QB and PK had the lowest leg MBR values, while OL and DL had the highest leg MBR values. This was evident in positions that mirror each other such as WR and DB as well as OL and DL. The fact that leg MBR values were similar in offensive and defensive positions that mirror each other is not too surprising. We have previously reported [Dengel et al., 2014; Bosch et al., 2019] that offensive and defensive positions that mirror each other have similar total as well as regional measures of fat, lean, and bone masses. In the present study, we also observed similar overall patterns of body compositions in individuals who played offensive or defensive that mirrored each other. Although OL had a higher percent body fat and total fat mass than DL, the two positions were similar in overall bone and lean masses.

What does it all mean?
As we pointed out in our first blog examining data from this published paper the DXA allows coaches and athletic trainers with a method to determine MBR that does not require specialized anthropometric devices. In addition, the DXA can provide both total as well as regional measures of MBR and is much faster and more accurate than anthropometric methods to calculate MBR. 

The data found in this manuscript [Dengel et al., 2023] also creates templates for comparison of total as well as regional MBR values for NFL players at different positions. Future studies are needed to investigate the relationship between MBR and performance metrics (e.g., power, strength, and game performance), as well determine if changes in MBR are related to changes in physiological and mechanical loading.

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.

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, Evanoff NG. Positional Differences in Muscle-to-bone ratio in National Football League Players. International Journal of Sports Medicine 44:720-727, 2023.

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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