We recently published a paper in the International Journal of Sports Medicine (Czeck et al., 2019) on body composition measures in over 200 collegiate male baseball players. In addition to measuring total body composition, we also examined the composition of throwing vs. non-throwing arms in these collegiate players.  One interesting finding of that study was the fact that pitchers’ throwing arms demonstrated significantly greater total mass, fat mass, lean mass, and bone mineral density compared to the non-throwing arm. 

I thought it would be interesting to go back to a paper (Dengel et al., 2014) I wrote on body composition in NFL football players and see if there were asymmetries between the throwing and non-throwing arms of NFL quarterbacks. We had arm data on 21 quarterbacks (Table). All of the quarterbacks in this sample threw the football with their right arms.  Unlike our baseball pitchers, there was no significant difference in total mass, fat mass or lean mass between the throwing and non-throwing arms. However, we did find significant differences in both bone mineral content (BMC) and bone mineral density (BMD) between the throwing and non-throwing arms. The lack of total, fat, and lean masses, but the difference in BMD or BMC between the throwing and non-throwing arms is similar to what we saw in our collegiate baseball catchers and outfielders (Czeck et al., 2019). 

A number of research papers have reported differences between dominant and non-dominant arms in tennis (Calbet et al., 1998), and volleyball (Calbet et al., 1999) and athletes in terms of BMC and BMD. Similar to our baseball player data, some of these papers have also shown differences in total, lean and fat masses (Calbet et al., 1998; Calbet et al., 1999; Czeck et al., 2019).  The differences in total, lean and fat masses may be related to the sport itself as well as specific training involved.  It is interesting that all sports show differences in throwing or hitting arms compared to the non-throwing or non-contact arm in regards to BMD and BMC.

What does it all mean?
So what does it all mean? First, there is the fact that NFL quarterbacks had an increase in BMC and BMD in their throwing arms compared to their non-throwing arms.  This is not too surprising given what is seen in other sports where there is a dominant arm used in the sport-specific action.  This would demonstrate some adaptation to the load placed on that arm.  Secondly, there was no corresponding difference in muscle mass in the throwing arm compared to the non-throwing arm. This may point to strength as well as other training that involves both arms. Differences in BMD and BMC between arms should not be concerning since total, muscle and fat masses were the same in the two arms is good.  Asymmetries in these three compartments may lead to injuries, so keeping them similar is recommended.


Calbet JAL, Moysi JS, Dorado C, Rodriguez LP: Bone mineral content and density in professional tennis players. Calcified Tissue International 62:491-496, 1998.
Calbet JAL, Diaz Herrera P, Rodriguez LP: High bone mineral density in male elite volleyball players. Osteoporosis International 10:468-474, 1999.
Czeck MA, Raymond-Pope CJ, Bosch TA, Bach CW, Oliver JM, Carbuhn A, Stanforth PR, Dengel DR: Total and regional body composition of NCAA division I collegiate baseball athletes. International Journal of Sports Medicine 40(7):447-452, 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.

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