Background: While the relationship between muscle size and strength is well understood, the same cannot be said for muscle density. Muscle density from CT is thought to reflect degree of fat infiltration which may impair muscle function. As ageing is associated with both a loss of muscle mass and increasing fat infiltration, measures of muscle mass alone may not adequately represent age-related loss in function. Further, the relationship of muscle density to bone strength is not fully understood. Our goal was to determine the relationship between pQCT-derived muscle area (MA) and density (MD) and both muscle and bone strength.
Methods: Ethical approval was obtained (AHS/52/14/HREC). Participants underwent pQCT scans of the dominant thigh (33% from distal) for muscle and bone area and density. Knee extensor strength was tested with an isokinetic dynamometer (Biodex). Linear regressions were used to determine the ability of MA and MD to predict variations in parameters of muscle and bone strength.
Results: 52 participants (33.8±12.0yo) volunteered. MA was highly predictive of muscle strength in all participants, and of bone area and strength in younger participants (24.4±3.1yo). MD was not related to bone density, or to any bone parameter in the older (42.4±10.8yo) participants.
|Muscle strength||Bone area||Stress-strain index|
|Younger adults (n=26)||MD||R2=0.15||P=0.05||R2=0.28||P=0.05||R2=0.17||P=0.04|
|Older adults (n=26)||MD||R2=0.26||P=0.01||R2=0.01||P=0.98||R2=0.01||P=0.68|
|Whole group (n=52)||MD||R2=0.18||P=0.002||R2=0.06||P=0.08||R2=0.03||P=0.21|
Conclusion: As previously observed, thigh muscle size predicts the vast majority of variance in both muscle and bone strength, particularly in young adults. Thigh muscle density has a much weaker relationship with muscle strength, and is only related to indices of bone strength in younger adults.
Disclosure: The authors declared no competing interests. Tom Gerrits was supported by a Travel Award from Radboud University Nijmegen.