Document Type

Thesis

Date of Degree

Spring 2016

Degree Name

MS (Master of Science)

Degree In

Health and Sport Studies

First Advisor

Kathleen F. Janz

Abstract

Osteoporosis is one of the most common diseases experienced in the older adult population. This condition is not only costly to manage and treat, particularly so when osteoporotic fractures occur, but also negatively impacts functional health and health-related quality of life for many individuals. This indicates the need for more to be done to prevent osteoporosis from developing initially. While bone mineral density (BMD) testing recommendations are in place for women aged 65 and older and men aged 70 and older to diagnose osteoporosis, there currently are no BMD testing recommendations for preventive or screening purposes in the general, healthy, adult population. One potential screening tool for bone strength is a peak vertical jump test. Peak vertical jump height can be used as a proxy for lower body muscle power, which has been identified as an influential factor in determining bone mass and geometry, both of which are critical aspects of bone strength. This study ascertained 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).

A total of 303 young adults (18 to 22 years, n=136 males, n=167 females) participated in these cross-sectional analyses. DXA was used to assess aBMD for total hip and femoral neck, and DXA images were used to calculate femoral neck section modulus (FN Z) values. Peripheral quantitative computed tomography (pQCT) was used to assess indices of bone strength at the tibia. Cortical bone area (CoA) and density-weighted polar section modulus strength-strain index (SSIp) were assessed at the 38% midshaft site, and bone strength index (BSI) was assessed at the 4% midshaft site. Lower body muscle power was predicted using peak vertical jump height and the Sayers et al. (1999) equation. Data were analyzed using Pearson bivariate and partial correlations to examine associations among bone strength outcomes and muscle power. Logistic regression was used to examine the probability of below-average bone strength based on muscle power. Receiver Operating Characteristic (ROC) curve analysis was used to show the tradeoff between sensitivity and specificity and to display the accuracy of a peak vertical jump test as an assessment tool for aBMD. Logistic regression indicated the odds ratio of below-average height-adjusted femoral neck aBMD decreased 5.4% for females and 3.6% for males per 50 Watts of power. ROC curve analysis showed the best sensitivity-specificity trade-off for identifying individuals with and without below-average aBMD was 5,038 Watts in males (sensitivity = 73.7%; specificity = 62.4%; AUC = 0.709, 95%CI = 0.572 - 0.847) and 3,261 Watts in females (sensitivity = 71.4%; specificity = 58.9%; AUC = 0.708, 95%CI = 0.586 - 0.829). These cut off values correspond to a vertical jump height of 54.39 cm and 36.16 cm for males and females, respectively. Taken together, the results of these analyses suggest acceptable sensitivity and specificity and moderate discriminate ability for using a measure of muscle power, assessed with a peak vertical jump test, to identify young adults with below-average aBMD.

Public Abstract

Osteoporosis is a condition when bones decrease in strength, become fragile, and break easily. Osteoporosis can impact an individual’s quality of life and their ability to carry out everyday activities. It is recommended that men and women aged 70+ and 65+ undergo (expensive) clinical testing for osteoporosis. Once osteoporosis is diagnosed, it cannot be reversed/cured. Screening for those at-risk for osteoporosis (i.e., those with below-average bone strength) earlier in adulthood would be beneficial, as it would provide the opportunity for individuals to actively take steps to optimize peak bone strength and prevent the decline of bone strength to osteoporotic levels, rather than simply identifying osteoporosis after it is too late. It has been demonstrated that strong muscles and strong bones go hand-in-hand. Having strong, powerful muscles means that bones must be strong in order to withstand the pull that muscles exert. Testing muscle power could be a method for assessing bone strength.

Three hundred and three individuals (18-22yrs; 136 males; 167 females) underwent clinical tests for bone strength and structure, and did a peak vertical jump test to assess muscle power. Relationships between muscle power and bone strength were examined, and probabilities were calculated to see if low muscle power predicted below-average bone strength. Results indicated the odds of having below-average bone strength decreased 5.4% for females and 3.6% for males per 50 Watts of power. These results suggest muscle power (from vertical jump height) to be a reasonably accurate method of identifying young adults with below-average bone strength.

Keywords

publicabstract, BMD, bone strength, jump power, osteoporosis prevention, screening tool, vertical jump

Pages

viii, 84

Bibliography

79-84

Copyright

Copyright 2016 Maggie Marie King

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