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. Author manuscript; available in PMC: 2016 Oct 1.
Published in final edited form as: Med Sci Sports Exerc. 2015 Oct;47(10):2201–2206. doi: 10.1249/MSS.0000000000000648

Table 3.

Mediating effect of muscle cross-sectional area on association of bone strength measures with muscle power

Males Females
β SE βSTD β SE βSTD
Model for BSI 4% tibia sitea
Effect of muscle power on MCSA 0.84** 0.10 0.54 0.86** 0.08 0.65
Effect of MCSA on BSI 0.05* 0.02 0.25 0.12** 0.02 0.53
Total effect of muscle power on BSI 0.16** 0.03 0.48 0.12** 0.02 0.43
Direct effect of muscle power on BSI 0.12** 0.03 0.35 0.02 0.02 0.08
Indirect effect through MCSA 0.04 0.02 0.14 0.10 0.02 0.35
 Bias-corrected 95% CI from bootstrapping (0.01, 0.08) (0.07, 0.14)
Model R2 0.38 0.46
Model for SSIp 66% tibia siteb
Effect of muscle power on MCSA 0.96** 0.11 0.61 0.93** 0.09 0.71
Effect of MCSA on SSIp (66%) 1.72** 0.37 0.33 1.25** 0.27 0.26
Total effect of muscle power on SSIp (66%) 3.73** 0.49 0.53 3.23** 0.32 0.51
Direct effect of muscle power on SSIp (66%) 2.08** 0.58 0.33 2.06** 0.39 0.33
Indirect effect though MCSA 1.66 0.43 0.20 1.16 0.27 0.18
 Bias-corrected 95% CI from bootstrapping (0.83, 2.54) (0.67, 1.69)
Model R2 0.66 0.77
Model for CoA 66% tibia siteb
Effect of muscle power on MCSA 0.96** 0.11 0.61 0.93** 0.09 0.71
Effect of MCSA on CoA (66%) 0.12* 0.03 0.29 0.15** 0.03 0.39
Total effect of muscle power on CoA (66%) 0.31** 0.04 0.55 0.22** 0.03 0.43
Direct effect of muscle power on CoA (66%) 0.21** 0.05 0.38 0.08* 0.04 0.15
Indirect effect though MCSA 0.10 0.03 0.18 0.14 0.03 0.28
 Bias-corrected 95% CI from bootstrapping (0.04, 0.17) (0.09, 0.21)
Model R2 0.54 0.66

β, regression parameter estimate; SE, standard error; βSTD, standardized regression parameter estimate by sex to Z-scores (with mean = 0 and SD = 1); BSI, bone strength index; MCSA, muscle cross-sectional area; SSIp, density-weighted polar section modulus (strength-strain index); CoA, cortical bone area

Model parameters β are reported per increase in MCSA = 10 mm2 and increase in muscle power = 10 Watts

*

p-value < 0.05,

**

p-value < 0.001

a

Covariate included in analysis: maturity (years from PHV age)

b

Covariates included in analysis: maturity (years from PHV age) and height (cm)