Background: Jumping mechanography has been developed to accurately estimate maximal muscle forces and might therefore be useful when investigating functional muscle-bone relationships. The objective was to determine whether mechanography derived peak jump power or force have greater explanatory capacity concerning bone parameters than other estimates of skeletal muscle derived mechanical loading.
Methods: Data from 181 healthy men (25-45 years) participating in a cross-sectional, population-based sibling study were used. Estimates of mechanical loading included isokinetic peak torque of the quadriceps muscle, DXA-derived leg lean mass (LLM), mechanography derived peak jump power and force and pQCT-derived muscle cross-sectional area (CSMA). Mid-tibial cortical bone parameters were assessed by pQCT. Analyses were adjusted for age, height and weight. Endosteal circumference was additionally adjusted for periosteal circumference (PC) to provide an estimate of endosteal expansion (ECPC).
Results: Jump power and force correlated positively with cortical thickness (ß=0.25,p=0.007 and ß=0.34,p<0.001, respectively) and strength strain index (SSI) (ß=0.30,p=0.003 and ß=0.23,p=0.001), and inversely with ECPC (ß=-0.13,p=0.003 and ß=-0.16,p<0.001). Force but not power was associated with cortical over total bone area ratio (CrtA/TotA) (ß=0.25,p=0.002). CSMA correlated positively with PC (ß=0.21,p=0.001) and SSI (ß=0.26,p<0.001) and inversely with ECPC (ß=-0.09,p=0.016). LLM correlated with all cortical parameters except CrtA/TotA (ß=0.56,p<0.001 for PC; ß=-0.25,p<0.001 for ECPC; ß=0.37,p=0.003 for cortical thickness; ß=0.61,p<0.001 for SSI). Quadriceps torque only correlated with PC (ß=0.21,p=0.023). Based on R2 statistics, LLM was superior in explaining variation in PC (R2=0.547) and SSI (R2=0.562) whereas jump force was superior in explaining variation in ECPC (R2=0.262), cortical thickness (R2=0.236) and CrtA/TotA (R2=0.215), compared with other estimates of mechanical loading.
Conclusion: While LLM was the strongest predictor of overall bone size and strength, jump force was the main determinant of cortical bone size, apparently by limiting endosteal expansion. These data indicate that jumping mechanography provides important additional information in the evaluation of muscle-bone relationships.
Disclosure: The authors declared no competing interests.