Muscle Power Predicts Adolescent Bone Strength

Abstract

Purpose To assess association between lower body muscle power and bone strength, as well as the mediating effect of muscle cross-sectional area (MCSA) on that association. Methods Participants (N=141 males; 162 females) were approximately 17 years. Muscle power was predicted using vertical jump and the Sayers equation. Using peripheral quantitative computed tomography (pQCT), bone strength indices were obtained at two locations of the tibia, corresponding to primary stressors acting upon each site: bone strength index for compression (BSI) at the distal 4% site; density-weighted polar section modulus strength-strain index [SSIp] and cortical bone area (CoA) at the 66% mid-shaft site for torsion. Muscle cross-sectional area (MCSA) was measured at the 66% site. Pearson bivariate and partial correlation coefficients were estimated to quantify the strength of the associations among variables. Direct and indirect mediation model effects were estimated and 95% bootstrap confidence intervals were constructed to test the causal hypothesis. Height and maturity were examined as covariates. Results Pearson correlation coefficients among muscle power, MCSA, and bone strength were statistically significant (p<0.01) and ranged from r=0.54 to 0.78. After adjustment for covariates, associations were reduced (r=0.37 to 0.69) (p<0.01). Mediation models for males for BSI, SSIp, and CoA accounted for 38%, 66%, and 54% of the variance in bone strength, respectively. Models for females for BSI, SSIp, and CoA accounted for 46%, 77%, and 66% of the variance, respectively. Conclusions We found strong and consistent associations, as well as direct and indirect pathways, among muscle power, MCSA, and tibia strength. These results support the use of muscle power as a component of health-related fitness in bone health interventions for older adolescents.

Vertical Jump Test as a Health-Promotion Screening Tool for Predicting Bone Strength in Young Adults

“…These unfavorable lever arms require muscles to transmit greater forces to bones per kilogram of body weight than is being moved . While measures of muscle size have been consistently reported as strong predictors of bone strength Sumnik et al, 2006), size does not necessarily determine how powerfully/forcefully a muscle can contract and therefore does not fully reflect muscle function, which is primarily influenced by physical activity (Janz et al, 2015).…”

“…Due to the cross-sectional nature of this study, the direction of causality between bone strength and muscle function could not be determined, however, previous research looking at the relationship between bone and muscle changes over time suggests that changes (gains or losses) in muscle strength affect bone, rather than the opposite. Janz, Letuchy, Burns, Francis, and Levy (2015) studied the use of a simple field measure of muscle power, the vertical jump, in predicting bone strength in a crosssectional study of 141 male and 162 female adolescents approximately 17 years of age from the Iowa Bone Development Study. The purpose of the study was to assess the association between lower body muscle power and bone strength, and to see if muscle cross-sectional area served as a mediator for this association.…”

“…Further, lower body muscle power has been identified as an influential factor in determining bone mass and geometry (Ashe et al, 2008;Baechle & Earle, 2000;Hardcastle et al, 2014;Janz et al, 2015;Schoenau & Frost, 2002). A peak vertical jump test, often used by physical fitness and human performance specialists, is a popular surrogate method for assessing muscle power (Amonette et al, 2012;Hardcastle et al, 2014;Janz et al, 2015;Johnson & Bahamonde, 1996;Munukka et al, 2014;Rantalainen et al, 2009;Rantalainen et al, 2010) and could be an easy, non-invasive, and inexpensive avenue to assess bone strength. This study aimed to ascertain the relationship between muscle power and bone strength, as well as the capacity of a peak vertical jump test to identify young adults with below-average areal BMD (aBMD), defined as a femoral neck aBMD Z-score of ≤ -1.0 standard deviation (SD), adjusted for height using the Zemel et al (2011) population-based approach.…”

“…The Iowa Bone Development Study (IBDS) is an ongoing, longitudinal study of bone health throughout childhood, adolescence, and young adulthood (Janz et al, 2014;Janz et al, 2015). Participants for the IBDS were recruited from 1998 to 2001, when subjects were approximately 5 years of age, from a larger group of Midwestern children (n = 890) that had been recruited and were already participating in the Iowa Fluoride Study (Janz et al, 2014;Janz et al, 2015).…”

“…Participants for the IBDS were recruited from 1998 to 2001, when subjects were approximately 5 years of age, from a larger group of Midwestern children (n = 890) that had been recruited and were already participating in the Iowa Fluoride Study (Janz et al, 2014;Janz et al, 2015). Original recruitment for the Iowa Fluoride Study occurred in eight Iowa hospitals from 1992 to 1995 immediately following birth.…”