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

Muscle Performance as a Predictor of Bone Health: Among Community-Dwelling Postmenopausal Japanese Women from Setagaya-Aoba Study

Osteoporosis is a significant health concern for postmenopausal women, necessitating efficient screening methods for bone health. This study explores the potential of muscle function, assessed through the 30-s chair stand test (CS-30), as an indicator for low bone stiffness in this demographic, aiming to establish a practical threshold for large-scale fitness surveillance without the need for specialized tools. We analyzed data from 1055 community-dwelling postmenopausal Japanese women, aged 41-89 years, collected between 2016 and 2019. Participants underwent CS-30 to evaluate muscle function alongside quantitative ultrasound (QUS) measurements to assess bone stiffness. The cohort was divided into two groups for the development and validation of a cutoff point for low bone stiffness, defined as a QUS speed of sound less than 1487.3 m/s. The CS-30 cutoff was determined using receiver operating characteristic (ROC) curve analysis and validated through logistic regression, accounting for age, body mass index, and smoking status. Among 577 postmenopausal women, 16.0% exhibited low bone stiffness. In the development group (n = 382), ROC analysis identified a CS-30 cutoff of 25 repetitions for detecting low bone stiffness, with an area under the curve of 0.744 (P < 0.001). In the validation group (n = 195), participants performing ≥ 25 repetitions had a higher risk of low bone stiffness compared to those performing ≤ 24 repetitions. The CS-30 test is an effective preliminary screening tool for identifying postmenopausal women at risk of low bone stiffness, with a threshold of 25 repetitions. This method could facilitate early detection of individuals at higher osteoporosis risk, promoting timely intervention.

Effects of muscle quantity, muscle quality, and phase angle on whole-body reaction time in 5164 adults aged 20-91 years

PURPOSE

Muscle quantity, defined as appendicular lean mass (ALM); muscle quality, defined as the ratio of muscle strength to ALM; and bioelectrical impedance analysis (BIA)-derived phase angle (PhA) are determinants of physical performance. We examined whether muscle quality indices were significant predictors of the whole-body reaction time (WBRT) in healthy female and male adults aged 20-91 years.

METHODS

Data from 5164 adults (2869 women and 2295 men; mean age ± standard deviation, 60.9 ± 15.6 years) were analyzed. Height and weight were measured, and body mass index was calculated. ALM was estimated using a previously validated 8-electrode multi-frequency BIA. PhA was measured at 50 kHz using a BIA device. Knee extension strength (KES), leg extension power (LEP), and flexibility were examined. The ALM to weight (ALM/weight), KES to ALM (KES/ALM), and LEP to KES (LEP/KES) ratios were calculated. In the WBRT test, participants were asked to stand on a force plate and jump upright as quickly as possible in response to a light stimulus. The WBRT was divided into the response initiation and motion execution phases.

RESULTS

ALM/weight, KES/ALM, LEP/KES, PhA, and flexibility were significant independent predictors of WBRT and the time of the motion execution phase (p < 0.001). However, PhA was not a significant predictor of the time of response initiation phase.

CONCLUSION

Muscle quantity (ALM/weight), muscle quality (KES/ALM and LEP/KES), PhA, and flexibility are determinants of WBRT test performance, particularly in the motion execution phase.

Cardiorespiratory Fitness and Bone Turnover Markers in Adults With Metabolic Syndrome: The Mediator Role of Inflammation

The relationship between inflammatory markers and bone turnover in adults is well known, and a negative association between cardiorespiratory fitness (CRF) and inflammatory markers has also been described. Hence, we tested whether the association between CRF and bone turnover markers is mediated by inflammatory markers in adults with metabolic syndrome. A total of 81 adults (58.5 ± 5.0 years, 62.7% women) were included in the analysis. CRF was measured by the 6-min walking test. Serum interleukin (IL)-1β, IL-6, IL-10, tumor necrosis factor alpha, high-sensitivity c-reactive protein (hsCRP) and vascular endothelial growth factor, collagen type I cross-linked C-telopeptide, procollagen type I N-terminal propeptide (P1NP), and total osteocalcin were assessed using a sensitive ELISA kit. Body composition was assessed by dual-energy X-ray absorptiometry. Partial correlation was used to test the relationship between CRF, inflammatory markers, and bone turnover markers, controlling for sex, lean mass, and fat mass. Boot-strapped mediation procedures were performed, and indirect effects with confidence intervals not including zero were interpreted as statistically significant. CRF was positively correlated with P1NP levels (r = .228, p = .044) and osteocalcin levels (r = .296, p = .009). Furthermore, CRF was positively correlated with IL-1β levels (r = .340, p = .002) and negatively correlated with hsCRP levels (r = -.335, p = .003), whereas IL-1β levels were positively correlated with P1NP levels (r = .245, p = .030), and hsCRP levels were negatively correlated with P1NP levels (r = -.319, p = .004). Finally, the association between CRF and P1NP levels was totally mediated by hsCRP (percentage of mediation = 39.9). Therefore, CRF benefits on bone formation could be dependent on hsCRP concentrations in this population.