Recently, I have written a couple of blogs on the muscle-to-bone ratio (MBR). The first blog explored the theory and meaning behind MBR while the next two blogs we explored MBR in National League Football (NFL) players.
Another ratio that my laboratory has started to explore is what we have termed the soft tissue-to-bone ratio (SBR). The SBR is determined by dividing the soft tissue masses (i.e., lean mass + fat mass) by bone mass. Since the SBR is similar to the MBR, which is just lean mass divided by bone mass, you may ask why bother adding fat mass into the ratio since muscle mass is still a large part of either ratio. Even though fat mass may not exert mechanical force on the bone like muscle mass does it still adds weight to the bone. In support of this, a study in children found that increased amounts of fat mass, even when normalized for lean mass, was negatively associated with bone strength (Ducher et al., 2009). It may be that increased loading of the bone as a result from lean mass and fat mass may negatively impact bone mass. Indicating that bone may be poorly adapting to increased loading and may explain why children with obesity have an increased risk of fractures.
The SBR may also provide other insight to the development of cardiovascular risk that the MBR does not. In a recent study from my own laboratory, we explored the association of MBR and SBR in children and adolescents with obesity (Czeck et al., 2023). In this study, we observed that children with obesity had a higher MBR and a higher SBR compared to their normal-weight peers. Both MBR and SBR were negatively associated with high density lipoprotein (HDL), as MBR and SBR decreased, HDL increased. This study also found that SBR was positively associated with insulin, low density lipoprotein (LDL), very low-density lipoprotein (VLDL), and triglycerides. Indicating that as SBR increases (i.e., more lean mass and fat mass relative to bone mass), so do insulin, LDL, VLDL, and triglyceride levels. Higher levels of insulin and atherogenic lipoproteins are potential cardiometabolic disease risk factors associated with obesity. Notably, the associations of cardiometabolic risk factors were with SBR and not MBR. These observations suggest that the addition of fat mass in the ratio was driving these significant associations. Thus, as the SBR increases we observe a relative decrease in functional tissue (i.e., increasing fat mass relative to lean mass and bone mass). We hypothesized that the decrease in functional tissue as assessed by the SBR may be clinically significant as it may be used as an indicator for cardiometabolic disease risk in children and adolescents.
Although MBR has been explored in a few different sports to our knowledge SBR has not been explored in athletic populations. Therefore, I thought it might be of interest to look at this variable in our National League Football (NFL) players. So, in the next couple of blogs, we will explore the SBR in NFL players and see what new information it yields in this population. In the first blog, we will compare the SBR in NFL players to a healthy aged-matched control group. In the second blog we will explore the SBR in these NFL players by position. Hopefully, you will find these next two blogs of interest.
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.
Ducher G, Bass SL, Naughton GA, Eser P, Telford RD, Daly RM. Overweight children have a greater proportion of fat mass relative to muscle mass in the upper limbs than in the lower limbs: implications for bone strength at the distal forearm. American Journal of Clinical Nutrition 2009:90(4):1104–1111.
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.