Recently, I wrote a blog introducing what my laboratory has the soft tissue-to-bone ratio (SBR). As I indicated in that blog we had explored the SBR and the muscle-to-bone (MBR) in children in obesity and their normal weight peers and found that there were significant associations between the SBR and a number of cardiometabolic risk factors (i.e, insulin, total cholesterol, a number of lipoproteins, triglycerides, etc.). Given that he have previously written two blogs on MBR in (National League Football) players I thought it would be of interest to explore SBR in this population.
Similar to the two blogs - Part 1 and Part 2 - that I wrote on NFL players concerning MBR there is a lot of data to look at, so I am going to look at SBR in these NFL players in two different blogs. In this first blog I will discuss total as well as regional measures of SBR in NFL players (n=346) compared to a healthy aged-matched control group (n=228). In the second blog I will examine the SBR in these NFL players by position.
Referring to the original MBR blog the NFL players had significantly (p<0.0001) more total (240.3 ± 41.2 vs. 164.9 ± 45.6 lb.), fat (43.6 ± 24.9 vs. 39.3 ± 27.0 lb.), lean (186.4 ± 19.3 vs. 121.9 ± 26.0 lb.), and bone (10.1± 1.0 vs. 6.4 ± 1.5 lb.) masses than their age-matched counterparts (Figure 1). In addition, NFL players had significantly greater bone mineral density (1.61 ± 0.11 vs. 1.26 ± 0.21 g/cm2) than controls.
Now, let us look at the SBR data from this study. Although the NFL players have significantly greater amounts of both bone, fat, and lean masses than controls, they had a lower total SBR (Figure 2). Similarly, the NFL players had a lower arm and trunk SBR than controls. Surprisingly, the NFL players had a higher leg SBR than the controls. This varies from what we reported when we examined the MBR data in NFL players compared to age-matched controls. For example, the trunk MBR was significantly lower, while arm MBR was significantly greater in NFL players compared to the control group. There was no difference in leg MBR between NFL players and controls. So, why the differences between MBR and SBR between NFL players and controls? It is important to remember that SBR includes both fat and lean muscle mass while the MBR only has lean muscle mass. For example, the NFL players have less abdominal fat, so they have a lower SBR. The same reason can be applied to the lower arm SBR in NFL players. The greater leg SBR can be explained by the greater amount of lean muscle mass in the legs (67.0 ± 8.8 vs. 41.8 ± 9.8 lbs.) between NFL players and controls.
What does it all mean?
It is important to remember the SBR, like the MBR, is a ratio. Total SBR like total MBR was lower in NFL players than healthy aged-matched controls. This suggests that NFL players have a higher amount of bone for a given amount of lean muscle and fat masses. This is obviously important considering the load the bone must support. The SBR accounts for all weight that the bone must support. Our next blog will examine positional differences in total as well as regional SBR in NFL football players.
REFERENCES
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.
Czeck MA, Dengel DR, Juckett WT, Kelly AS: Muscle-to-bone and soft tissue-to-bone ratio in children and adolescents with obesity. Journal of Clinical Densitometry 2023:26(2):101360. DOI:10.1016/jocd.2023.02.001.
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.