Association of Knee Extensor Muscle Strength and Cardiorespiratory Fitness With Bone Stiffness in Japanese Adults: A Cross-sectional Study.

Takahisa Ohta,Naokata Ishii,Hiroyuki Sasai,Wataru Fukuda,Junzo Nagashima

doi:10.2188/jea.je20200581

Abstract

Knee extensor muscle strength and cardiorespiratory fitness (CRF) are major components of physical fitness. Because the interactive association of knee extensor muscle strength and CRF with bone health remains unclear, we aimed to investigate such association in Japanese adults. Altogether, 8,829 Japanese adults (3,731 men and 5,098 women) aged ≥45 years completed the maximum voluntary knee extension test, submaximal exercise test, medical examination, and a questionnaire on lifestyle habits. Using an osteo-sono assessment index, low bone stiffness tendency was defined as 80% under the young-adults mean. Multivariable odds ratios (ORs) and 95% confidence intervals (CIs) were calculated after confounder adjustment. Overall, 542 men (14.5%) and 978 women (19.2%) had low bone stiffness tendency. We observed an inverse association between muscle strength and low bone stiffness tendency after adjustment for CRF in both sexes (P for linear trend <0.001). Compared with the lowest CRF, the multivariable ORs for low bone stiffness tendency in the highest CRF were 0.47 (95% CI, 0.36-0.62) for men and 1.05 (95% CI, 0.82-1.35) for post-menopausal women (P < 0.001 and P = 0.704, respectively). No interactive association between muscle strength and CRF for low bone stiffness tendency existed in both sexes and irrespective of menopausal status. Knee extensor muscle strength and CRF were associated additively, not synergistically, with bone health. Maintaining high levels of both physical fitness components may improve musculoskeletal health in the cohort. The relationship between physical fitness and bone status should be longitudinally investigated in the future.

Highlights

Osteoporosis is characterized by low bone strength and an increased risk of bone fractures,[1] which is highly associated with mortality.[2,3] as osteoporosis imposes a heavy economic burden on the gross domestic product,[4] it is widely recognized as a serious public health concern in Japan and in other aged societies
This study aimed to investigate the interactive associations of knee extensor muscle strength and cardiorespiratory fitness (CRF) with bone stiffness as a marker of bone strength in Japanese adults
Low Body mass index (BMI), low knee extensor muscle strength, and low CRF were all associated with a higher prevalence of low bone stiffness tendency

Summary

Introduction

Osteoporosis is characterized by low bone strength and an increased risk of bone fractures,[1] which is highly associated with mortality.[2,3] as osteoporosis imposes a heavy economic burden on the gross domestic product,[4] it is widely recognized as a serious public health concern in Japan and in other aged societies. Japan experiences one of the most serious situations in Asia[5] because the estimated number of patients with osteoporosis exceeds 12.8 million (men: 3 million; women: 9.8 million).[6] To minimize the detrimental effects of osteoporotic fractures on a patient’s quality of life, early detection of low bone strength and preventive interventions preferably based on risk stratification are strongly needed. Because the interactive association of knee extensor muscle strength and CRF with bone health remains unclear, we aimed to investigate such association in Japanese adults

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Conclusion