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Peak vertical jump power predicts radial bone strength better than hand grip strength in healthy individuals

Optimizing bone strength is key to long term bone health and potentially avoidance of Osteoporotic fracture later in life. Osteoporosis is considered a pediatric disease with geriatric consequences. However, measuring bone strength in children is complex and creates a practical problem for health professionals, teachers and parents. Muscle cross sectional area (MCSA) correlates with bone strength but muscular fitness measures may serve as a better proxy to assess bone strength. A non-invasive measure of muscle fitness that correlates to bone strength may provide a means to monitor bone strength throughout the lifespan. PURPOSE: To investigate the relationship between common muscle function tests (relative grip strength (RGS), peak vertical jump power (PP)) and bone strength in the radial diaphysis and epiphysis of a healthy population. METHODS: Healthy participants (n=147 (81 female)) performed a bilateral grip strength test using a hand dynamometer, and a maximal vertical jump test. Peak vertical jump power was calculated from maximal jump height using the Sayer’s equation. Moment of inertia (MoI), cortical area (CoA), cortical bone mineral density (cBMD), and polar strength-strain index (SSIp) were measured using peripheral Quantitative Computed Tomography (pQCT) to determine bone strength parameters at the 66% radial site (predominantly cortical bone). At the 4% site (trabecular bone site), vBMC.tb, vBMD.tb, ToA.tb and BSIc were measured. Hierarchical multiple regression analyses determined the relationship of each muscle function test for each bone envelope (cortical and trabecular). RESULTS: For the cortical bone measurements: RGS, and PP were both significantly correlated with CoA, MoI, and SSIp. However, neither of the muscle function measures were correlated with cBMD. Peak vertical jump power predicted bone strength parameters to a greater extent compared to RGS. Peak Power had the largest R2 values of all 3 measurements SSIp (R2=0.541, p<0.0001), CoA (R2=0.597, p<0.0001) and MoI (R2=0.568, p<0.0001). For the trabecular bone envelope, RGS was not a predictor of bone strength however peak power was a significant predictor of vBMC.tb (R2=0.548, p<0.0001), vBMD.tb (R2=0.267, p<0.0001) ToA..tb (R2=0.419, p<0.0001) and BSIc (R2=0.489, p<0.0001). CONCLUSION: Muscle function tests provide insight into bone strength in healthy adult populations. Both RGS and PP correlated with bone strength in the cortical envelope but RGS was not a predictor of trabecular bone strength parameters at the 4% radial site. Peak vertical jump power was a significant predictor of bone strength at both trabecular and cortical radial sites. Interestingly PP, a lower limb measurement explained the most variance in the bone strength of the upper limb. Lower limb muscle power calculated by vertical jump assessment could provide a means to monitor and assess bone health.