Purpose Ultrasound-based prediction methods for the detection of low muscle mass for sarcopenia in older adults have been explored previously; however, the muscle that most accurately predicts it is unclear. This study aimed to clarify prediction accuracy and cut-off values for ultrasound-derived thigh and lower leg muscle thickness (MT) to detect low skeletal muscle mass index (SMI) in older adults and to estimate cut-off values based on two standard deviations (SD) below younger adult means for the corresponding muscles as an early detection tool for site-specific low muscle mass. Methods This study included 204 community-dwelling older (64 males, 140 females, mean age: 75.4 years) and 59 younger (31 males, 28 females, mean age: 22.3 years) adults. The MT of the rectus femoris, vastus intermedius, gastrocnemius, and soleus muscles was measured using ultrasound; SMI was measured using bioelectrical impedance analysis. Results The prevalence of a low SMI among older adults was 20.3% (n=13) for males and 21.4% (n=30) for females. The receiver operating characteristic analysis revealed that the total MT for the four muscles measured presented the highest area under the curve (AUC) value to predict low SMI for males (0.849) and females (0.776). The AUC value was the highest for the total MT of the gastrocnemius and soleus muscles for males and the gastrocnemius for females (0.836, 0.748; cut-off value: 5.67 cm, 1.42 cm, respectively). Muscle-specific differences between the low SMI-predicting and SD-based cut-off values were observed. The SD-based value for the rectus femoris (1.85 cm) was substantially higher than the low SMI-predicting value (1.51 cm) in males. Conclusion Ultrasound measurement of lower leg muscles may be a simple, robust measure to detect low muscle mass for sarcopenia. Additionally, cut-off values for site-specific muscle mass loss may not always agree with those for whole-limb muscle mass loss.
Ultrasonic echo intensity (EI), an easy-to-use measure of intramuscular fat and fibrous tissues, is known to increase with aging. However, age-related changes in EI have not been examined in a longitudinal design. The objective of this study was to investigate 4-year longitudinal changes in the EI of the quadriceps femoris in older adults, based on difference in physical activity (PA). This study included 131 community-dwelling older adults with a mean age of 72.9 {plus minus} 5.2 years. Subcutaneous fat thickness (FT), muscle thickness (MT), and EI of the quadriceps femoris were measured by ultrasound. Isometric knee extensor strength was also measured. PA was assessed using a questionnaire at baseline, and participants were classified into the high- or low-PA groups. In 4 years, significant decrease in FT, MT, and strength was observed in both groups (P < 0.05) while significant decrease in EI was observed only in the high-PA group (P < 0.05). Multiple linear regression analyses revealed that the difference in PA was a significant predictor of 4-year changes in MT (β= 0.189, P = 0.031) and EI (β= -3.145, P = 0.045), but not in the body mass index, FT, or strength adjusted for potential confounders. The present findings suggest that greater PA has a positive effect on longitudinal changes in the MT and EI of the quadriceps femoris in older adults. In addition, greater PA may contribute to future decrease in EI, and increase in EI may not occur in 4 years even in older adults with lesser PA.
The present study aims to examine (1) the preoperative factors that can predict postoperative falls, (2) whether postoperative physical activity (PA) mediates the relationship between fall incidence and gait function, and (3) whether postoperative PA levels are associated with fall risk in total knee arthroplasty (TKA) patients. Ninety-six patients (mean age: 72.0 ± 6.1 years) who were observed postoperatively for 6 months were selected. Timed up and go (TUG) was assessed as an indicator of gait function. Fall incidence and PA were investigated for 6 months post-TKA. The body mass index, history of preoperative falls, knee pain, knee extensor strength, range of motion in knee flexion, and modified gait efficacy scale were evaluated. Additionally, postoperative PA levels were categorized into three groups—low: <3,000, moderate: 3,000 to 4,000, and high: ≥4,000 steps/day. The relative fall incidence rate was calculated according to the total number of falls normalized for every 1,000 steps/day for 6 months postoperatively. Twenty-five (26.0%) of the 96 patients had at least one fall. The TUG, knee pain, and knee extensor strength were identified preoperatively as significant variables affecting postoperative falls. The mediated effects model revealed that postoperative fall incidence was predicted by preoperative TUG and postoperative PA. Postoperative PA was significantly associated with preoperative TUG. Moreover, both the preoperative TUG and postoperative PA were selected as significant variables for predicting fall incidence. Thus, postoperative PA mediates the relationship between gait function and fall incidence after TKA. Furthermore, the relative fall incidence rate associated with a low PA level was significantly higher than that associated with moderate and high PA levels. In conclusion, preoperative assessments of TUG performance, muscle strength, and knee pain were effective in predicting fall risk. Additionally, an increase in PA could contribute to reducing fall risk in TKA patients. Therefore, our results suggest that preoperative screening for fall predictors and managing postoperative PA could reduce the fall incidence in TKA patients.
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