Intramuscular fat infiltration influences mechanical properties during muscle contraction in older women.

Although evidence suggests that intramuscular fat infiltration may influence muscle strength, the precise mechanisms remain unclear. This study aimed to determine whether intramuscular fat infiltration affects muscle mechanical properties during contraction, and whether these mechanical properties mediate the relationship between intramuscular fat infiltration and muscle strength. Seventy-nine healthy older women aged 75.1±6.8 years were included in this study. The echo intensity (EI) of the vastus lateralis (VL) was measured as an intramuscular fat infiltration index using B-mode ultrasonography. Maximum voluntary isometric contraction strength (MVIC) was assessed using a dynamometer. The VL shear elastic modulus (G), a mechanical property index, was measured using ultrasound shear wave elastography under various muscle contraction conditions, at rest and at 15, 30, and 45% MVIC (G0, G15, G30, and G45). To evaluate the degree of increase in the shear elastic modulus with increasing muscle contraction intensity, the slope of the regression line (Gslope) between muscle contraction and shear elastic modulus was calculated for each participant. The results showed that EI was significantly associated with G30 and G45 but not with G0 or G15. The EI can significantly explain the inter-individual differences in Gslope. Mediation analysis revealed that the effect of EI on MVIC through Gslope was significant (indirect effect = -0.31, 95% confidence interval [-0.57, -0.12]). These findings suggest that a greater EI is associated with a lower G during muscle contraction. Furthermore, our results show that the relationship between EI and MVIC is mediated by Gslope.

Age-related change in gait efficacy and predictors of its decline: A 3-year longitudinal study.

AIM: This study aimed to calculate the minimal clinically important difference (MCID) for a modified Gait Efficacy Scale (mGES) over 3 years and to clarify the predictors of mGES decline. METHODS: In total, 87 community-dwelling older adults were enrolled in this 3-year longitudinal study. The mGES, fall history and physical function (chair stand frequency, open-eyes one-leg stand, open-close stepping test, walking speed, walking endurance [shuttle stamina walk test] and physical activity) were assessed at baseline. After a 3-year follow-up period, the mGES and Global Rating of Change Scale were assessed. The MCID was calculated using anchor-based methods, with the Global Rating of Change Scale as an anchor. The participants were classified into the decline and keep groups based on whether the changes in the mGES were greater than the MCID. A logistic regression analysis was conducted using the mGES as the dependent variable and physical characteristics, fall history, and physical function as independent variables. RESULTS: The MCID for the mGES over 3 years was -7.38 points. A logistic regression analysis identified low open-close stepping (odds ratio, 0.87; 95% confidence interval, 0.782-0.985; P = 0.027) and the shuttle stamina walk test (odds ratio, 0.974; 95% confidence interval, 0.949-1.000; P = 0.049) as predictors of the mGES decline. CONCLUSION: These findings suggest that a change of 7.38 points in the mGES was clinically significant and that poor agility and walking endurance can predict future decline in the mGES. Geriatr Gerontol Int 2024; 24: 90-94.