PURPOSE: To examine the independent associations of muscular strength (MS) and cardiorespiratory fitness (CRF) with the prevalence of osteopenia in older adults.
METHODS: This cross-sectional study consisted of 127 men and 177 women aged ≥65 years old (mean age 74) from the Physical Activity and Aging Study (PAAS). MS was assessed by 1-repetition maximum (1-RM) leg press (lbs) and CRF was assessed by time (minutes) to complete a 400-meter walk test. Both MS and CRF were categorized into four groups based on the sex-specific quartiles of each MS and CRF. Bone mineral density was assessed by dual-energy X-ray absorptiometry (DXA), and osteopenia (pre- osteoporosis stage) was defined as t-score below -1.0 following the World Health Organization guidelines. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using logistic regression to determine the independent associations of MS and CRF with the prevalence of osteopenia.
RESULTS: The prevalence of osteopenia was 45.4% in this study. Compared to the lower MS quartile 1 (lowest 25%), ORs (95% CIs) of osteopenia in MS quartiles 2, 3, and 4 were 0.75 (0.36-1.58), 0.33 (0.15-0.73), and 0.25 (0.11-0.59), respectively, after adjusting for age, sex, heavy alcohol consumption (>14 drinks per week for male, >7 for female), smoking status, physical activity, and CRF. However, we found that CRF was not significantly associated with the prevalence of osteopenia after adjusting for the confounders including MS in this study (trend P=0.19). In the stratified analysis by CRF, we found that higher MS was significantly associated with lower prevalence of osteopenia in both low CRF (lower 50%) (trend P=0.02) and high CRF (higher 50%) (trend P=0.03) after adjusting for age, sex, heavy alcohol consumption, smoking status, and leisure-time physical activity.
CONCLUSION: Higher MS, independent of CRF, was associated with a lower prevalence of osteopenia in older adults. However, prospective studies are required to make causal inferences between MS, independent of and combined with CRF, and the development of osteopenia and osteoporosis in older adults.