Total body skeletal muscle mass: estimation by creatine (methyl-d3) dilution in humans

A protocol for remote collection of skeletal muscle mass via D3-creatine dilution in community-dwelling postmenopausal women from the Women's Health Initiative

BACKGROUND

There is emerging evidence that cancer and its treatments may accelerate the normal aging process, increasing the magnitude and rate of decline in functional capacity. This accelerated aging process is hypothesized to hasten the occurrence of common adverse age-related outcomes in cancer survivors, including loss of muscle mass and decrease in physical function. However, there is no data describing age-related loss of muscle mass and its relation to physical function in the long-term in cancer survivors.

METHODS

This study protocol describes the use of a novel method of muscle mass measurement, D3-creatine dilution method (D3Cr), in a large sample (n~6000) of community dwelling postmenopausal women from the Women's Health Initiative (WHI). D3Cr will be used to obtain a direct measure of muscle mass remotely. Participants will be drawn from two sub-cohorts embedded within the WHI that have recently completed an in-home visit. Cancer survivors will be drawn from the Life and Longevity After Cancer (LILAC) cohort, and cancer-free controls will be drawn from the WHI Long Life Study 2. The overall objective of this study is to examine the antecedents and consequences of low muscle mass in cancer survivors. The study aims are to: 1) create age-standardized muscle mass percentile curves and z-scores to characterize the distribution of D3- muscle mass in cancer survivors and non-cancer controls, 2) compare muscle mass, physical function, and functional decline in cancer survivors and non- cancer controls, and 3) use machine learning approaches to generate multivariate risk-prediction algorithms to detect low muscle mass.

DISCUSSION

The D3Cr method will transform our ability to measure muscle mass in large-scale epidemiologic research. This study is an opportunity to advance our understanding of a key source of morbidity among older and long-term female cancer survivors. This project will fill knowledge gaps, including the antecedents and consequences of low muscle mass, and use innovative methods to overcome common sources of bias in cancer research. The results of this study will be used to develop interventions to mitigate the harmful effects of low muscle mass in older adults and promote healthy survivorship in cancer survivors in the old (>65) and oldest-old (>85) age groups.

Estimating Muscle Mass Using D3-Creatine Dilution: A Narrative Review of Clinical Implications and Comparison With Other Methods

BACKGROUND

The D3-creatine (D3-Cr) dilution method is of emerging interest for estimating total-body skeletal muscle mass. This review explores the association of muscle mass estimated via D3-Cr with various clinical outcomes and provides a summary of the literature comparing D3-Cr with other body composition techniques.

METHODS

A literature search was conducted on PubMed/MEDLINE and Web of Science for studies using D3-Cr to measure muscle in adult populations (ie, ≥18 years old) from inception until September 2023.

RESULTS

Out of the 23 included studies, 15 investigated the correlation between D3-Cr and clinical outcomes. More consistent associations were reported for mortality (100%, n = 2), mobility disability (100%; n = 5), falls and fractures (100%; n = 3), physical performance (63.3%; n = 11), muscle strength (44.4%; n = 9), and muscle composition (33.3%; n = 3). However, conflicting findings were also reported for such correlations. Among the 23 studies, 14 compared D3-Cr-estimated muscle with other body composition techniques, including magnetic resonance imaging (MRI) as a reference method. Strong and positive correlations were found between D3-Cr and MRI. Nonetheless, variations in muscle measurements were noted, with differences in D3-Cr values ranging from 0.62 kg lower to 13.47 kg higher compared to MRI.

CONCLUSIONS

D3-Cr-estimated muscle mass may be a valuable predictor of clinical outcomes showing consistent associations with falls and fractures, mobility disability, and mortality. However, less consistent associations were found with muscle strength and composition, and physical performance. Although a strong correlation exists between D3-Cr-estimated muscle mass and MRI measurements, under- or overestimation may occur.

Energetics and clinical factors for the time required to walk 400 m: The Study of Muscle, Mobility and Aging (SOMMA)

BACKGROUND

Walking slows with aging often leading to mobility disability. Mitochondrial energetics has been found to be associated with gait speed over short distances. Additionally, walking is a complex activity but few clinical factors that may be associated with walk time have been studied.

METHODS

We examined 879 participants ≥70 years and measured the time to walk 400 m. We tested the hypothesis that decreased mitochondrial energetics by respirometry in muscle biopsies and magnetic resonance spectroscopy in the thigh and is associated with longer time to walk 400 m. We also used cardiopulmonary exercise testing to assess the energetic costs of walking: maximum oxygen consumption (VO2peak) and energy cost-capacity (the ratio of VO2, at a slow speed to VO2peak). In addition, we tested the hypothesis that selected clinical factors would also be associated with 400-m walk time.

RESULTS

Lower Max OXPHOS was associated with longer walk time, and the association was explained by the energetic costs of walking, leg power, and weight. Additionally, a multivariate model revealed that longer walk time was also significantly associated with lower VO2peak, greater cost-capacity ratio, weaker leg power, heavier weight, hip and knee stiffness, peripheral neuropathy, greater perceived exertion while walking slowly, greater physical fatigability, less moderate-to-vigorous exercise, less sedentary time, and anemia. Significant associations between age, sex, muscle mass, and peripheral artery disease with 400-m walk time were explained by other clinical and physiologic factors.

CONCLUSIONS

Lower mitochondrial energetics is associated with needing more time to walk 400 m. This supports the value of developing interventions to improve mitochondrial energetics. Additionally, doing more moderate-to-vigorous exercise, increasing leg power, reducing weight, treating hip and knee stiffness, and screening for and treating anemia may reduce the time required to walk 400 m and reduce the risk of mobility disability.

Stimulation of muscle protein synthesis with low-dose amino acid composition in older individuals

Essential amino acid (EAA)-based compositions have been shown to be effective stimulators of muscle protein synthesis, but the lower limit of effective dosage is not clear. We have used stable isotope tracer methodology to quantify the response of muscle protein fractional synthetic rate (FSR) to a dose of 3.6 g of a high-leucine composition of EAAs plus arginine in older subjects. Muscle protein FSR increased 0.058%/hour over 3 h following consumption. When account was taken of the total muscle mass, this increase in muscle protein FSR represented approximately 80% of ingested EAAs. We conclude that a low dose of an EAA-based composition can effectively stimulate muscle protein synthesis.

D3Creatine Dilution as a Direct, Non-invasive and Accurate Measurement of Muscle Mass for Aging Research

Initial definitions of sarcopenia included the age-associated loss of skeletal muscle mass that was presumed to be associated with late-life reduced functional capacity, disability and loss of independence. Because no method for determination of muscle mass was available for large cohort studies of aging men and women, lean body mass determined by dual X-ray absorptiometry or bioelectrical impedance was used as a surrogate measure of muscle mass. The data from these studies showed either no or a poor relationship between LBM and functional capacity and health related outcomes, leading to the conclusion of many that the amount of muscle may not be associated with these age-associated outcomes. It was assumed that some undefined index of muscle quality is the critical contributor. These studies also consistently showed that muscle strength is lost more quickly than lean mass. Total body muscle mass can now be measured directly, accurately and non-invasively using the D3creatine (D3Cr) dilution method. D3Cr muscle mass, but not DXA derived LBM, is strongly associated with functional capacity, falls and insulin resistance in older men and women. In addition, D3Cr muscle mass is associated with risk of disability, hip fracture and mortality. New and emerging data demonstrate that low muscle mass may serve as a diagnostic criterion for sarcopenia.

Proportion of caloric restriction-induced weight loss as skeletal muscle

OBJECTIVE

This study's objective was to develop models predicting the relative reduction in skeletal muscle (SM) mass during periods of voluntary calorie restriction (CR) and to validate model predictions in longitudinally monitored samples.

METHODS

The model development group included healthy nonexercising adults (n = 897) who had whole-body SM mass measured with magnetic resonance imaging. Model predictions of relative SM changes with CR were evaluated in two longitudinal studies, one 12 to 14 weeks in duration (n = 74) and the other 12 months in duration (n = 26).

RESULTS

A series of SM prediction models were developed in a sample of 415 males and 482 females. Model-predicted changes in SM mass relative to changes in body weight (i.e., ΔSM/Δbody weight) with a representative model were (mean ± SE) 0.26 ± 0.013 in males and 0.14 ± 0.007 in females (sex difference, p < 0.001). The actual mean proportions of weight loss as SM in the longitudinal studies were 0.23 ± 0.02/0.20 ± 0.06 in males and 0.10 ± 0.02/0.17 ± 0.03 in females, similar to model-predicted values.

CONCLUSIONS

Nonelderly males and females with overweight and obesity experience respective reductions in SM mass with voluntary CR in the absence of a structured exercise program of about 2 to 2.5 kg and 1 to 1.5 kg per 10-kg weight loss, respectively. These estimates are predicted to be influenced by interactions between age and body mass index in males, a hypothesis that needs future testing.

The association between chrononutrition behaviors and muscle health among older adults: The study of muscle, mobility and aging

Emerging studies highlight chrononutrition's impact on body composition through circadian clock entrainment, but its effect on older adults' muscle health remains largely overlooked. To determine the associations between chrononutrition behaviors and muscle health in older adults. Dietary data from 828 older adults (76 ± 5 years) recorded food/beverage amounts and their clock time over the past 24 h. Studied chrononutrition behaviors included: (1) The clock time of the first and last food/beverage intake; (2) Eating window (the time elapsed between the first and last intake); and (3) Eating frequency (Number of self-identified eating events logged with changed meal occasion and clock time). Muscle mass (D3 -creatine), leg muscle volume (MRI), grip strength (hand-held dynamometer), and leg power (Keiser) were used as outcomes. We used linear regression to assess the relationships between chrononutrition and muscle health, adjusting for age, sex, race, marital status, education, study site, self-reported health, energy, protein, fiber intake, weight, height, and moderate-to-vigorous physical activity. Average eating window was 11 ± 2 h/day; first and last intake times were at 8:22 and 19:22, respectively. After multivariable adjustment, a longer eating window and a later last intake time were associated with greater muscle mass (β ± SE: 0.18 ± 0.09; 0.27 ± 0.11, respectively, p < 0.05). The longer eating window was also marginally associated with higher leg power (p = 0.058). An earlier intake time was associated with higher grip strength (-0.38 ± 0.15; p = 0.012). Chrononutrition behaviors, including longer eating window, later last intake time, and earlier first intake time were associated with better muscle mass and function in older adults.

D3-creatine dilution, computed tomography and dual-energy X-ray absorptiometry for assessing myopenia and physical function in colon cancer: A cross-sectional study

BACKGROUND

Low skeletal muscle mass (myopenia) is common in cancer populations and is associated with functional decline and mortality, but prior oncology studies did not assess total body skeletal muscle mass. Instead, they measured surrogates such as cross-sectional area (CSA) of skeletal muscle at L3 from computed tomography (CT) or appendicular lean mass (ALM) from dual-energy X-ray absorptiometry (DXA). D3-creatine (D3Cr) dilution is a non-invasive method to assess total body skeletal muscle mass, which has been examined in a variety of populations but not in cancer. To compare the associations of D3Cr muscle mass, CT CSA, and DXA ALM with myopenia and physical function, we conducted a cross-sectional study among 119 patients with colon cancer (2018-2022).

METHODS

For each technique (D3Cr, CT and DXA), myopenia was defined as the lowest sex-specific quartile of its measurement. Physical function was measured by the short physical performance battery and grip strength. We calculated Pearson correlations (r) among three techniques, computed Cohen's kappa coefficients (κ) to assess the agreement of myopenia, and estimated Pearson correlations (r) of three techniques with physical function. All analyses were sex-specific.

RESULTS

Sixty-one (51.3%) participants were male, the mean (standard deviation) age was 56.6 (12.9) years, and most (68.9%) had high physical function (short physical performance battery: ≥11 points). Correlations and myopenia agreement among three techniques were greater in men than women; for example, regarding D3Cr muscle mass versus CT CSA, r was 0.73 (P < 0.001) for men versus 0.45 (P < 0.001) for women, and κ was 0.82 (95% CI: 0.65, 0.99) for men versus 0.24 (95% CI: -0.08, 0.52) for women. Among men, higher D3Cr muscle mass was significantly correlated with faster gait speed (r = 0.43, P < 0.01) and stronger grip strength (r = 0.32, P < 0.05); similar correlations were observed for CT CSA and DXA ALM. However, among women, no measure of muscle or lean mass was significantly associated with physical function.

CONCLUSIONS

This is the first study using D3-creatine dilution method to assess muscle mass in a cancer population. Regardless of the techniques used for muscle or lean mass assessment, we observed stronger correlations, greater myopenia agreement, and more significant associations with physical function in men with colon cancer than women. D3Cr, CT and DXA are not interchangeable methods for assessing myopenia and physical function, especially in women with colon cancer. Future studies should consider relative advantages of these techniques and examine the D3-creatine dilution method in other cancer types.

The association between chrononutrition behaviors and muscle health among older adults: The Study of Muscle, Mobility and Aging (SOMMA)

Background

Emerging studies highlight chrononutrition's impact on body composition through circadian clock entrainment, but its effect on older adults' muscle health remains largely overlooked.

Objective

To determine the associations between chrononutrition behaviors and muscle health in older adults.

Methods

Dietary data from 828 older adults (76±5y) recorded food/beverage amounts and their clock time over the past 24 hours. Studied chrononutrition behaviors included: 1) The clock time of the first and last food/beverage intake; 2) Eating window (the time elapsed between the first and last intake); and 3) Eating frequency (Number of self-identified eating events logged with changed meal occasion and clock time). Muscle mass (D 3 -creatine), leg muscle volume (MRI), grip strength (hand-held dynamometer), and leg power (Keiser) were used as outcomes. We used linear regression to assess the relationships between chrononutrition and muscle health, adjusting for age, sex, race, marital status, education, study site, self-reported health, energy, protein, fiber intake, weight, height, and moderate-to-vigorous physical activity.

Results

Average eating window was 11±2 h/d; first and last intake times were at 8:22 and 19:22, respectively. After multivariable adjustment, a longer eating window and a later last intake time were associated with greater muscle mass (β±SE: 0.18±0.09; 0.27±0.11, respectively, P <0.05). The longer eating window was also marginally associated with higher leg power ( P =0.058). An earlier intake time was associated with higher grip strength (-0.38±0.15; P =0.012).

Conclusions

Chrononutrition behaviors, including longer eating window, later last intake time, and earlier first intake time were associated with better muscle mass and function in older adults.

GRAPHICAL ABSTRACT

Key findings

Chrononutrition behaviors, including longer eating window, later last intake time, and earlier first intake time were associated with better muscle mass and function in older adults.

Associations between D3Cr muscle mass and MR thigh muscle volume with strength, power, physical performance, fitness, and limitations in older adults in the SOMMA study

Background

Different measures to assess muscle size - magnetic resonance (MR) derived thigh muscle volume and d3-creatine dilution derived muscle mass (D3Cr muscle mass) - may have similar associations with strength, power, physical performance, fitness, and functional limitations in older adults.

Methods

Men (N=345) and women (N=482) aged ≥70 years from the Study of Muscle, Mobility and Aging completed exams including leg extension strength (1-repetition max) and cardiopulmonary exercise testing to assess fitness (VO2peak). Correlations and adjusted regression models stratified by sex were used to assess the association between muscle size measures and study outcomes; we tested for sex interactions.

Results

D3Cr muscle mass and MR thigh muscle volume were correlated (men: r=0.62, women: r=0.51, p<.001). Lower D3Cr muscle mass and lower MR thigh muscle volume were associated with lower strength and lower VO2peak in both men and women; D3Cr muscle mass was more strongly associated with strength in men than in women (p-int<0.05). There were correlations, though less consistent, between muscle size or mass with physical performance and function. Associations between the muscle size measures and the study outcomes occasionally varied by sex, and associations of MR thigh muscle volume were, at times, slightly more strongly associated with the study outcomes than was D3Cr muscle mass.

Conclusions

Less muscle -measured by either D3Cr muscle mass or MR thigh muscle volume - was associated with lower strength and worse performance. Varied associations by sex and assessment method suggest consideration be given to which measurement to use in future studies.

Energetics and Clinical Factors for the Time Required to Walk 400 Meters The Study of Muscle, Mobility and Aging (SOMMA)

Background

Walking slows with aging often leading to mobility disability. Mitochondrial energetics has been found to influence gait speed over short distances. Additionally, walking is a complex activity but few clinical factors that may influence walk time have been studied.

Methods

We examined 879 participants ≥70 years and measured the time to walk 400m. We tested the hypothesis that decreased mitochondrial energetics by respirometry in muscle biopsies and magnetic resonance spectroscopy in the thigh, is associated with longer time to walk 400m. We also used cardiopulmonary exercise testing to assess the energetic costs of walking: maximum oxygen consumption (VO 2 peak) and energy cost-capacity (the ratio of VO2, at a slow speed to VO 2 peak). In addition, we tested the hypothesis that selected clinical factors would also be associated with 400m walk time.

Results

Lower Max OXPHOS was associated with longer walk time and the association was explained by the energetics costs of walking, leg power and weight. Additionally, a multivariate model revealed that longer walk time was also significantly associated with lower VO 2 peak, greater cost-capacity ratio, weaker leg power, heavier weight, hip and knee stiffness, peripheral neuropathy, greater perceived exertion while walking slowly, greater physical fatigability, less moderate-to-vigorous exercise, less sedentary time and anemia. Significant associations between age, sex, muscle mass, and peripheral artery disease with 400m walk time were explained by other clinical and physiologic factors.

Conclusions

Lower mitochondrial energetics is associated with needing more time to walk 400m. This supports the value of developing interventions to improve mitochondrial energetics. Additionally, doing more moderate-to-vigorous exercise, increasing leg power, reducing weight, treating hip and knee stiffness, and screening for and treating anemia may reduce the time required to walk 400m and reduce the risk of mobility disability.

A simplified D3 -creatine dilution method for skeletal muscle mass determination with dynamic correction of creatinine and D3 -creatinine using ultra-performance liquid chromatography-tandem mass spectrometry

This study developed a simple method for muscle mass determination based on D3 -creatine dilution by removing the matrix effects of ultra-performance liquid chromatography-tandem mass spectrometry analysis through mutual correction of creatinine and D3 -creatinine. Rats were administered an oral tracer dose of D3 -creatine at age 6 weeks. Creatinine and D3 -creatinine in urine were detected using ultra-performance liquid chromatography-tandem mass spectrometry after diluting 20 times to obtain D3 -creatinine enrichment factor (mole percent excess). The mole percent excess obtained from peak area could be used to calculate muscle mass using the improved formula. The limit of detection was 0.500 ng/mL for D3 -creatinine. Creatinine and D3 -creatinine could be mutually corrected because of the same matrix effect, and D3 -creatine spillage was negligible within 0.22%. Isotopic steady time was consistent with that obtained using conventional methods. Bland-Altman plots demonstrated the satisfying consistency between the proposed method and magnetic resonance imaging. This is a simple and rapid measuring method of muscle mass based on D3 -creatine dilution that requires no accurate quantification of creatinine and D3 -creatinine concentrations and no urine sample collection to obtain D3 -creatine spillage.

The Study of Muscle, Mobility and Aging (SOMMA): A Unique Cohort Study About the Cellular Biology of Aging and Age-related Loss of Mobility

BACKGROUND

The Study of Muscle, Mobility and Aging (SOMMA) aims to understand the biological basis of many facets of human aging, with a focus on mobility decline, by creating a unique platform of data, tissues, and images.

METHODS

The multidisciplinary SOMMA team includes 2 clinical centers (University of Pittsburgh and Wake Forest University), a biorepository (Translational Research Institute at Advent Health), and the San Francisco Coordinating Center (California Pacific Medical Center Research Institute). Enrollees were age ≥70 years, able to walk ≥0.6 m/s (4 m); able to complete 400 m walk, free of life-threatening disease, and had no contraindications to magnetic resonance or tissue collection. Participants are followed with 6-month phone contacts and annual in-person exams. At baseline, SOMMA collected biospecimens (muscle and adipose tissue, blood, urine, fecal samples); a variety of questionnaires; physical and cognitive assessments; whole-body imaging (magnetic resonance and computed tomography); accelerometry; and cardiopulmonary exercise testing. Primary outcomes include change in walking speed, change in fitness, and objective mobility disability (able to walk 400 m in 15 minutes and change in 400 m speed). Incident events, including hospitalizations, cancer diagnoses, fractures, and mortality are collected and centrally adjudicated by study physicians.

RESULTS

SOMMA exceeded its goals by enrolling 879 participants, despite being slowed by the COVID-19 pandemic: 59.2% women; mean age 76.3 ± 5.0 years (range 70-94); mean walking speed 1.04 ± 0.20 m/s; 15.8% identify as other than Non-Hispanic White. Over 97% had data for key measurements.

CONCLUSIONS

SOMMA will provide the foundation for discoveries in the biology of human aging and mobility.

Body Composition, Relative Dose Intensity, and Adverse Events among Patients with Colon Cancer

BACKGROUND

Despite evidence that low muscle increases the risk of chemotoxicity, most chemotherapies are dosed on body surface area without considering body composition. Among 178 patients with colon cancer, we assessed muscle and adipose tissue with multiple techniques and examined their associations with relative dose intensity (RDI) and adverse events.

METHODS

We estimated (i) cross-sectional skeletal muscle area (SMA) and total adipose tissue (TAT) area at L3 from computed tomography (CT); (ii) appendicular lean mass (ALM) and total body fat (TBF) mass from dual-energy X-ray absorptiometry (DXA); and (iii) total body skeletal muscle mass using D3-creatine (D3Cr) dilution. We standardized each measurement by its sex-specific standard deviation (SD). The primary outcome was reduced RDI (RDI <85%). The secondary outcome was the number of moderate and severe adverse events during each cycle of chemotherapy. We estimated the associations of muscle and adipose tissue measurements (per SD increase) with reduced RDI using logistic regression and adverse events using generalized estimating equations for repeated measures.

RESULTS

Higher CT SMA and DXA ALM were significantly associated with a lower risk of reduced RDI [odds ratios: 0.56 (0.38-0.81) for CT SMA; 0.56 (0.37-0.84) for DXA ALM]. No measurements of muscle or adipose tissue were associated with adverse events.

CONCLUSIONS

More muscle was associated with improved chemotherapy completion among patients with colon cancer, whereas muscle and adipose tissue were not associated with adverse events.

IMPACT

Considering body composition may help personalize dosing for colon cancer chemotherapy by identifying patients at risk for poor chemotherapy outcomes.

Infant body composition: A comprehensive overview of assessment techniques, nutrition factors, and health outcomes

Body composition assessment is a valuable tool for clinical assessment and research that has implications for long-term health. Unlike traditional measurements such as anthropometrics or body mass index, body composition assessments provide more accurate measures of body fatness and lean mass. Moreover, depending on the technique, they can offer insight into regional body composition, bone mineral density, and brown adipose tissue. Various methods of body composition assessment exist, including air displacement plethysmography, dual-energy x-ray absorptiometry, bioelectrical impedance, magnetic resonance imaging, D3 creatine, ultrasound, and skinfold thickness, each with its own strengths and limitations. In infants, several feeding practices and nutrition factors are associated with body composition outcomes, such as breast milk vs formula feeding, protein intake, breast milk composition, and postdischarge formulas for preterm infants. Longitudinal studies suggest that body composition in infancy predicts later body composition, obesity, and other cardiometabolic outcomes in childhood, making it a useful early marker of cardiometabolic health in both term and preterm infants. Emerging evidence also suggests that body composition during infancy predicts neurodevelopmental outcomes, particularly in preterm infants at high risk of neurodevelopmental impairment. The purpose of this narrative review is to provide clinicians and researchers with a comprehensive overview of body composition assessment techniques, summarize the links between specific nutrition practices and body composition in infancy, and describe the neurodevelopmental and cardiometabolic outcomes associated with body composition patterns in term and preterm infants.

Estimation of skeletal muscle mass in 4-year-old children using the D3-creatine dilution method

BACKGROUND

Given limited experience in applying the creatine-(methyl-D3) (D3Cr) dilution method to measure skeletal muscle mass (SMM) in young children, the feasibility of deployment in a fielding setting and performance of the method was assessed in a cohort of 4-year-old children in Dhaka, Bangladesh.

METHODS

Following D3Cr oral dose (10 mg) administration, single fasting urine samples were collected at 2-4 days (n = 100). Twenty-four-hour post-dose collections and serial spot urine samples on days 2, 3 and 4 were obtained in a subset of participants (n = 10). Urinary creatine, creatinine, D3Cr and D3-creatinine enrichment were analyzed by liquid chromatography-tandem mass spectrometry. Appendicular lean mass (ALM) was measured by dual-energy x-ray absorptiometry and grip strength was measured by a hand-held dynamometer.

RESULTS

SMM was measured successfully in 91% of participants, and there were no adverse events. Mean ± SD SMM was greater than ALM (4.5 ± 0.4 and 3.2 ± 0.6 kg, respectively). Precision of SMM was low (intraclass correlation = 0.20; 95% CI: 0.02, 0.75; n = 10). Grip strength was not associated with SMM in multivariable analysis (0.004 kg per 100 g of SMM; 95% CI: -0.031, 0.038; n = 91).

CONCLUSIONS

The D3Cr dilution method was feasible in a community setting. However, high within-child variability in SMM estimates suggests the need for further optimization of this approach.

IMPACT

The D3-creatine (D3Cr) stable isotope dilution method was considered a feasible method for the estimation of skeletal muscle mass (SMM) in young children in a community setting and was well accepted among participants. SMM was weakly associated with both dual-energy x-ray absorptiometry-derived values of appendicular lean mass and grip strength. High within-child variability in estimated values of SMM suggests that further optimization of the D3Cr stable isotope dilution method is required prior to implementation in community research settings.

Comparing D3-Creatine Dilution and Dual-Energy X-ray Absorptiometry Muscle Mass Responses to Strength Training in Low-Functioning Older Adults

BACKGROUND

In contrast to dual-energy x-ray absorptiometry (DXA), the D3-creatine (D3Cr) dilution method provides a direct measure of skeletal muscle mass and in a cohort of older men has been strongly associated with health-related outcomes. However, sensitivity to detect changes in D3Cr-derived muscle mass due to an intervention is limited.

METHODS

Twenty-one older adults (≥70 years) with low-to-moderate physical function were randomized to a 15-week high-intensity strength training (ST) or a health education (HE) group. Full-body progressive intensity ST was performed 3 days per week.

RESULTS

The mean age was 82.1 years, with 64% females. After 15 weeks, both D3Cr muscle mass (MM; 2.29 kg; 95% CI: 0.22, 4.36) and DXA appendicular lean mass (ALM; 1.04 kg; 95% CI: 0.31, 1.77) were greater in ST group compared to HE. Baseline correlations between D3Cr MM and DXA ALM (r = 0.79; 95% CI: 0.53, 0.92) or total lean body mass (LBM; r = 0.79; 95% CI: 0.52, 0.91) were high. However, longitudinal changes in D3Cr MM were weakly correlated with changes in DXA ALM (r = 0.19; 95% CI: -0.35, 0.64) and LBM (r = 0.40; 95% CI: -0.13, 0.76). More participants showed positive response rates, defined as a >5% increase from baseline, with D3Cr MM (80%) than DXA measures (14%-43%).

CONCLUSIONS

A progressive ST intervention in low-functioning older adults increased D3Cr MM and DXA ALM. These data suggest that the D3Cr dilution is potentially sensitive to detect changes in muscle mass in response to resistance exercise training. These results are preliminary and could be used for planning larger trials to replicate these results.

The D3 -creatine dilution method non-invasively measures muscle mass in mice

Developing accurate methods to quantify age-related muscle loss (sarcopenia) could greatly accelerate development of therapies to treat muscle loss in the elderly, as current methods are inaccurate or expensive. The current gold standard method for quantifying sarcopenia is dual-energy X-ray absorptiometry (DXA) but does not measure muscle directly-it is a composite measure quantifying "lean mass" (muscle) excluding fat and bone. In humans, DXA overestimates muscle mass, which has led to erroneous conclusions about the importance of skeletal muscle in human health and disease. In animal models, DXA is a popular method for measuring lean mass. However, instrumentation is expensive and is potentially limited by anesthesia concerns. Recently, the D3 -creatine (D3 Cr) dilution method for quantifying muscle mass was developed in humans and rats. This method is faster, cheaper, and more accurate than DXA. Here, we demonstrate that the D3 Cr method is a specific assay for muscle mass in mice, and we test associations with DXA and body weight. We evaluated the D3 Cr method compared to DXA-determined lean body mass (LBM) in aged mice and reported that DXA consistently overestimates muscle mass with age. Overall, we provide evidence that the D3 Cr dilution method directly measures muscle mass in mice. Combined with its ease of use, accessibility, and non-invasive nature, the method may prove to more quickly advance development of preclinical therapies targeting sarcopenia.

Optimizing the Design of Clinical Trials to Evaluate the Efficacy of Function-Promoting Therapies

BACKGROUND

Several candidate molecules that may have application in treating physical limitations associated with aging and chronic diseases are in development. Challenges in the framing of indications, eligibility criteria, and endpoints and the lack of regulatory guidance have hindered the development of function-promoting therapies.

METHODS

Experts from academia, pharmaceutical industry, National Institutes of Health (NIH), and Food and Drug Administration (FDA) discussed optimization of trial design including the framing of indications, eligibility criteria, and endpoints.

RESULTS

Mobility disability associated with aging and chronic diseases is an attractive indication because it is recognized by geriatricians as a common condition associated with adverse outcomes, and it can be ascertained reliably. Other conditions associated with functional limitation in older adults include hospitalization for acute illnesses, cancer cachexia, and fall injuries. Efforts are underway to harmonize definitions of sarcopenia and frailty. Eligibility criteria should reconcile the goals of selecting participants with the condition and ensuring generalizability and ease of recruitment. An accurate measure of muscle mass (eg, D3 creatine dilution) could be a good biomarker in early-phase trials. Performance-based and patient-reported measures of physical function are needed to demonstrate whether treatment improves how a person lives, functions, or feels. Multicomponent functional training that integrates training in balance, stability, strength, and functional tasks with cognitive and behavioral strategies may be needed to translate drug-induced muscle mass gains into functional improvements.

CONCLUSIONS

Collaborations among academic investigators, NIH, FDA, pharmaceutical industry, patients, and professional societies are needed to conduct well-designed trials of function-promoting pharmacological agents with and without multicomponent functional training.

Defining and diagnosing sarcopenia: Is the glass now half full?

Low muscle mass and function exert a substantial negative impact on quality of life, health and ultimately survival, but their definition, identification and combination to define sarcopenia have suffered from lack of universal consensus. Methodological issues have also contributed to incomplete agreement, as different approaches, techniques and potential surrogate measures inevitably lead to partly different conclusions. As a consequence: 1) awareness of sarcopenia and implementation of diagnostic procedures in clinical practice have been limited; 2) patient identification and evaluation of therapeutic strategies is largely incomplete. Significant progress has however recently occurred after major diagnostic algorithms have been developed, with common features and promising perspectives for growing consensus. At the same time, the need for further refinement of the sarcopenia concept has emerged, to address its increasingly recognized clinical heterogeneity. This includes potential differential underlying mechanisms and clinical features for age- and disease-driven sarcopenia, and the emerging challenge of sarcopenia in persons with obesity. Here, we will review existing algorithms to diagnose sarcopenia, and major open methodological issues to assess skeletal muscle mass and function under different clinical conditions, in order to highlight similarities and differences. Potential for consensus on sarcopenia diagnosis as well as emerging new challenges will be discussed.

Sarcopenia and Cardiovascular Diseases

Sarcopenia is the loss of muscle strength, mass, and function, which is often exacerbated by chronic comorbidities including cardiovascular diseases, chronic kidney disease, and cancer. Sarcopenia is associated with faster progression of cardiovascular diseases and higher risk of mortality, falls, and reduced quality of life, particularly among older adults. Although the pathophysiologic mechanisms are complex, the broad underlying cause of sarcopenia includes an imbalance between anabolic and catabolic muscle homeostasis with or without neuronal degeneration. The intrinsic molecular mechanisms of aging, chronic illness, malnutrition, and immobility are associated with the development of sarcopenia. Screening and testing for sarcopenia may be particularly important among those with chronic disease states. Early recognition of sarcopenia is important because it can provide an opportunity for interventions to reverse or delay the progression of muscle disorder, which may ultimately impact cardiovascular outcomes. Relying on body mass index is not useful for screening because many patients will have sarcopenic obesity, a particularly important phenotype among older cardiac patients. In this review, we aimed to: (1) provide a definition of sarcopenia within the context of muscle wasting disorders; (2) summarize the associations between sarcopenia and different cardiovascular diseases; (3) highlight an approach for a diagnostic evaluation; (4) discuss management strategies for sarcopenia; and (5) outline key gaps in knowledge with implications for the future of the field.

Multisystem physiological perspective of human frailty and its modulation by physical activity

"Frailty" is a term used to refer to a state characterized by enhanced vulnerability to, and impaired recovery from, stressors compared with a nonfrail state, which is increasingly viewed as a loss of resilience. With increasing life expectancy and the associated rise in years spent with physical frailty, there is a need to understand the clinical and physiological features of frailty and the factors driving it. We describe the clinical definitions of age-related frailty and their limitations in allowing us to understand the pathogenesis of this prevalent condition. Given that age-related frailty manifests in the form of functional declines such as poor balance, falls, and immobility, as an alternative we view frailty from a physiological viewpoint and describe what is known of the organ-based components of frailty, including adiposity, the brain, and neuromuscular, skeletal muscle, immune, and cardiovascular systems, as individual systems and as components in multisystem dysregulation. By doing so we aim to highlight current understanding of the physiological phenotype of frailty and reveal key knowledge gaps and potential mechanistic drivers of the trajectory to frailty. We also review the studies in humans that have intervened with exercise to reduce frailty. We conclude that more longitudinal and interventional clinical studies are required in older adults. Such observational studies should interrogate the progression from a nonfrail to a frail state, assessing individual elements of frailty to produce a deep physiological phenotype of the syndrome. The findings will identify mechanistic drivers of frailty and allow targeted interventions to diminish frailty progression.

An elusive consensus definition of sarcopenia impedes research and clinical treatment: A narrative review

The definition of sarcopenia, the age-related loss of muscle mass, has evolved since the term's inception and yet there is no consensus. Many of the identified definitions of sarcopenia centre their criteria around the loss of muscle mass, loss of function, and weakness. Common variables to various definitions of sarcopenia are appendicular lean soft tissue mass (often called muscle mass), grip strength, and gait speed. However, a lack of consensus remains among operational definitions and diagnostics for this newly recognized disease and may be attributed to the absence of appropriate tools that accurately measure the outcomes of interest, such as skeletal muscle instead of lean mass. In this narrative review, we describe the evolution of the consensus groups' definition of sarcopenia, address the need for more accurate measures of muscle mass and function, and effective, low-cost treatments (i.e., resistance training and diet) for this disease. Consensus on what constitutes sarcopenia is critical to propel research in the field and, importantly, provide what prognostic value a sarcopenia diagnosis provides and how such a patient would be treated.

Skeletal muscle mass can be estimated by creatine (methyl-d3) dilution and is correlated with fat-free mass in active young males

BACKGROUND

Assessing whole-body skeletal muscle mass (SMM) and fat-free mass (FFM) is essential for the adequate nutritional management and training evaluation of athletes and trained individuals. This study aimed to determine the relationship between SMM assessed using the creatine (methyl-d₃) dilution (D₃-creatine) method and SMM estimated by whole-body magnetic resonance imaging (MRI) in healthy young men undergoing exercise training. Additionally, we examined the association between FFM measured using the four-component (4C) method (FFM_4C) and the total body protein value estimated using 4C (TBpro_4C).

METHODS AND RESULTS

We analyzed the data of 29 males (mean age, 19.9 ± 1.8 years) who exercised regularly. SMM measurements were obtained using the D₃-creatine method (SMM_D3-creatine) and MRI (SMM_MRI). The SMM_D3-creatine adjusted to 4.3 g/SMM kg was significantly higher than SMM_MRI (p < 0.01). The fit of the creatine pool size compared with SMM_MRI was 5.0 g/SMM_MRI kg. SMM_MRI was significantly correlated with both SMM_D3-creatine adjusted to 4.3 g/kg and 5.1 g/kg. TBpro_4C was significantly lower than SMM_MRI (p < 0.01). Contrastingly, FFM_4C was significantly higher than SMM_MRI (p < 0.01).

CONCLUSIONS

SMM_D3-creatine adjusted to 4.3 g/SMM kg-a previously reported value-may differ for athletes and active young males. We believe that a value of 5.0-5.1 g/SMM kg better estimates the total muscle mass in this population. Traditional FFM estimation highly correlates with SMM_MRI in well-trained young males, and the relationships appear strong enough for total body protein or SMM to be estimated through the FFM value.

Limited physician knowledge of sarcopenia: A survey

BACKGROUND

Sarcopenia, a reduction in skeletal muscle mass and function, is a condition that contributes to functional decline and disability in older adults. Although research on this geriatric condition has developed rapidly in recent years, little work has been done to document whether practicing physicians are incorporating sarcopenia into their clinical practice.

METHODS

An online survey of 253 practicing U.S. physicians assessed knowledge of sarcopenia, use of the term in practice, motivation for screening patients, and diagnostic and treatment approaches. They were board certified in four practice areas: internal medicine (n = 69), family medicine (n = 69), geriatrics (n = 40), or physical medicine and rehabilitation (PM&R) (n = 75).

RESULTS

Less than 20% of internists and family medicine physicians reported being very familiar with the term sarcopenia, with substantially higher familiarity at this level reported among geriatricians (70%) and among PM&R specialists (41%). Two additional findings pointed to deficiencies in sarcopenia knowledge and practice: participants substantially overestimated the prevalence of sarcopenia in older adults (44% of participants reported an expected prevalence of >25%) compared to findings from published studies (indicating 10% of older adults experience sarcopenia); over 75% reported not typically using specific diagnostic criteria or being unsure if their approach utilized any specific criteria. When asked what terminology they use in a medical chart for a patient presenting with significant loss of muscle mass and strength, only 8% said sarcopenia.

CONCLUSIONS

Sarcopenia, a condition that can have a major impact on older adults as they age, has not been fully incorporated into the knowledge base and practices of active physicians. The survey data suggest that improving physician familiarity with sarcopenia and having universal agreement on criteria for diagnosis may increase the screening for and treatment of sarcopenia.

Association of muscle mass measured by D3-Creatine (D3Cr), sarcopenic obesity, and insulin-glucose homeostasis in postmenopausal women

The D3-Creatine (D3Cr) dilution method is a direct and accurate measure of skeletal muscle mass. In this study, we examined the association of D3Cr muscle mass with measures of insulin-glucose homeostasis in community dwelling postmenopausal women. Additionally, we examined association of sarcopenic obesity, defined as low D3Cr muscle mass and high percent body fat, with fasting plasma glucose, insulin, hemoglobin A1c and insulin resistance. Insulin resistance was measured by the homeostatic measure of insulin resistance (HOMA-IR). This pilot study included 74 participants (mean age = 82.3 years) from the Women's Health Initiative-Buffalo site. The D3Cr method was initiated at a clinic visit and used to measure muscle mass via remote urine sample collection. Descriptive and graphical approaches and age-adjusted linear regression models were used to analyze study data. We examined muscle mass as an absolute value (kg) and scaled to body weight (D3Cr muscle mass/kg). There was an inverse relationship between skeletal muscle mass, and impaired insulin-glucose homeostasis. Women with low muscle mass had higher levels of insulin (uIU/mL; β = -0.40; 95% CI: -0.79, -0.01), fasting plasma glucose (mg/dL; β = -0.1; 95% CI: -0.2, 0.03), HbA1c (%; β = -2.30; 95% CI: -5.7, 1.1), and calculated homeostatic model of insulin resistance, HOMA-IR, (β = -1.49; 95% CI: -2.9, -0.1). Sarcopenic obesity was common in this population of women; 41% of participants were categorized as having low muscle mass and high percent body fat. Results demonstrate that D3Cr muscle mass is independently associated with measures of insulin-glucose homeostasis, but obesity is a stronger predictor of insulin resistance than muscle mass.

D3 -creatine dilution for skeletal muscle mass measurement: historical development and current status

The French chemist Michel Eugène Chevreul discovered creatine in meat two centuries ago. Extensive biochemical and physiological studies of this organic molecule followed with confirmation that creatine is found within the cytoplasm and mitochondria of human skeletal muscles. Two groups of investigators exploited these relationships five decades ago by first estimating the creatine pool size in vivo with ¹⁴ C and ¹⁵ N labelled isotopes. Skeletal muscle mass (kg) was then calculated by dividing the creatine pool size (g) by muscle creatine concentration (g/kg) measured on a single muscle biopsy or estimated from the literature. This approach for quantifying skeletal muscle mass is generating renewed interest with the recent introduction of a practical stable isotope (creatine-(methyl-d₃ )) dilution method for estimating the creatine pool size across the full human lifespan. The need for a muscle biopsy has been eliminated by assuming a constant value for whole-body skeletal muscle creatine concentration of 4.3 g/kg wet weight. The current single compartment model of estimating creatine pool size and skeletal muscle mass rests on four main assumptions: tracer absorption is complete; tracer is all retained; tracer is distributed solely in skeletal muscle; and skeletal muscle creatine concentration is known and constant. Three of these assumptions are false to varying degrees. Not all tracer is retained with urinary isotope losses ranging from 0% to 9%; an empirical equation requiring further validation is used to correct for spillage. Not all tracer is distributed in skeletal muscle with non-muscle creatine sources ranging from 2% to 10% with a definitive value lacking. Lastly, skeletal muscle creatine concentration is not constant and varies between muscles (e.g. 3.89-4.62 g/kg), with diets (e.g. vegetarian and omnivore), across age groups (e.g. middle-age, ~4.5 g/kg; old-age, 4.0 g/kg), activity levels (e.g. athletes, ~5 g/kg) and in disease states (e.g. muscular dystrophies, <3 g/kg). Some of the variability in skeletal muscle creatine concentrations can be attributed to heterogeneity in the proportions of wet skeletal muscle as myofibres, connective tissues, and fat. These observations raise serious concerns regarding the accuracy of the deuterated-creatine dilution method for estimating total body skeletal muscle mass as now defined by cadaver analyses of whole wet tissues and in vivo approaches such as magnetic resonance imaging. A new framework is needed in thinking about how this potentially valuable method for measuring the creatine pool size in vivo can be used in the future to study skeletal muscle biology in health and disease.

Tracing metabolic flux in vivo: basic model structures of tracer methodology

Molecules in living organisms are in a constant state of turnover at varying rates, i.e., synthesis, breakdown, oxidation, and/or conversion to different compounds. Despite the dynamic nature of biomolecules, metabolic research has focused heavily on static, snapshot information such as the abundances of mRNA, protein, and metabolites and/or (in)activation of molecular signaling, often leading to erroneous conclusions regarding metabolic status. Over the past century, stable, non-radioactive isotope tracers have been widely used to provide critical information on the dynamics of specific biomolecules (metabolites and polymers including lipids, proteins, and DNA), in studies in vitro in cells as well as in vivo in both animals and humans. In this review, we discuss (1) the historical background of the use of stable isotope tracer methodology in metabolic research; (2) the importance of obtaining kinetic information for a better understanding of metabolism; and (3) the basic principles and model structures of stable isotope tracer methodology using ¹³C-, ¹⁵N-, or ²H-labeled tracers.

Tagging biomolecules with stable isotopes of specific atoms can reveal details of the molecular inter-conversions of metabolism. The masses of the tracer isotopes used are greater than those of the more common atomic forms. This allows their movement through different metabolic pathways to be detected using mass spectrometry and modeling. Il-Young Kim at Gachon University School of Medicine in South Korea and colleagues focus their review on the use of stable, non-radioactive isotope tracers, especially, of carbon, nitrogen, and hydrogen, to study metabolism in live humans and other animals. They cover the basic model structures of tracer methodology that serve as the fundamental basis for various tracer methods available and the most recent applications. Their procedure is especially useful for monitoring the rates of metabolic inter-conversions, which can reveal aspects of health and disease.

Guidance for assessment of the muscle mass phenotypic criterion for the Global Leadership Initiative on Malnutrition diagnosis of malnutrition

The Global Leadership Initiative on Malnutrition (GLIM) provides consensus criteria for the diagnosis of malnutrition that can be widely applied. The GLIM approach is based on the assessment of three phenotypic (weight loss, low body mass index, and low skeletal muscle mass) and two etiologic (low food intake and presence of disease with systemic inflammation) criteria, with diagnosis confirmed by any combination of one phenotypic and one etiologic criterion fulfilled. Assessment of muscle mass is less commonly performed than other phenotypic malnutrition criteria, and its interpretation may be less straightforward, particularly in settings that lack access to skilled clinical nutrition practitioners and/or to body composition methodologies. In order to promote the widespread assessment of skeletal muscle mass as an integral part of the GLIM diagnosis of malnutrition, the GLIM consortium appointed a working group to provide consensus-based guidance on assessment of skeletal muscle mass. When such methods and skills are available, quantitative assessment of muscle mass should be measured or estimated using dual-energy x-ray absorptiometry, computerized tomography, or bioelectrical impedance analysis. For settings where these resources are not available, then the use of anthropometric measures and physical examination are also endorsed. Validated ethnic- and sex-specific cutoff values for each measurement and tool are recommended when available. Measurement of skeletal muscle function is not advised as surrogate measurement of muscle mass. However, once malnutrition is diagnosed, skeletal muscle function should be investigated as a relevant component of sarcopenia and for complete nutrition assessment of persons with malnutrition.

Effects of Testosterone on Mixed-Muscle Protein Synthesis and Proteome Dynamics During Energy Deficit

CONTEXT

Effects of testosterone on integrated muscle protein metabolism and muscle mass during energy deficit are undetermined.

OBJECTIVE

The objective was to determine the effects of testosterone on mixed-muscle protein synthesis (MPS), proteome-wide fractional synthesis rates (FSR), and skeletal muscle mass during energy deficit.

DESIGN

This was a randomized, double-blind, placebo-controlled trial.

SETTING

The study was conducted at Pennington Biomedical Research Center.

PARTICIPANTS

Fifty healthy men.

INTERVENTION

The study consisted of 14 days of weight maintenance, followed by a 28-day 55% energy deficit with 200 mg testosterone enanthate (TEST, n = 24) or placebo (PLA, n = 26) weekly, and up to 42 days of ad libitum recovery feeding.

MAIN OUTCOME MEASURES

Mixed-MPS and proteome-wide FSR before (Pre), during (Mid), and after (Post) the energy deficit were determined using heavy water (days 1-42) and muscle biopsies. Muscle mass was determined using the D3-creatine dilution method.

RESULTS

Mixed-MPS was lower than Pre at Mid and Post (P < 0.0005), with no difference between TEST and PLA. The proportion of individual proteins with numerically higher FSR in TEST than PLA was significant by 2-tailed binomial test at Post (52/67; P < 0.05), but not Mid (32/67; P > 0.05). Muscle mass was unchanged during energy deficit but was greater in TEST than PLA during recovery (P < 0.05).

CONCLUSIONS

The high proportion of individual proteins with greater FSR in TEST than PLA at Post suggests exogenous testosterone exerted a delayed but broad stimulatory effect on synthesis rates across the muscle proteome during energy deficit, resulting in muscle mass accretion during subsequent recovery.

Association Between Muscle Mass Determined by D3 -Creatine Dilution and Incident Fractures in a Prospective Cohort Study of Older Men

The relation between a novel measure of total skeletal muscle mass (assessed by D₃ -creatine dilution [D₃ Cr]) and incident fracture is unknown. In 1363 men (mean age 84.2 years), we determined D₃ Cr muscle mass; Fracture Risk Assessment Tool (FRAX) 10-year probability of hip and major osteoporotic (hip, humerus, vertebral, forearm) fracture; and femoral neck bone mineral density (BMD) (by dual-energy X-ray absorptiometry [DXA]). Incident fractures were centrally adjudicated by review of radiology reports over 4.6 years. Correlations adjusted for weight and height were calculated between femoral neck BMD and D₃ Cr muscle mass. Across quartiles of D₃ Cr muscle mass/weight, proportional hazards models calculated hazard ratios (HRs) for any (n = 180); nonspine (n = 153); major osteoporotic fracture (n = 85); and hip fracture (n = 40) after adjustment for age, femoral neck BMD, recurrent fall history, and FRAX probability. Models were then adjusted to evaluate the mediating influence of physical performance (walking speed, chair stands, and grip strength). D₃ Cr muscle mass was weakly correlated with femoral BMD (r = 0.10, p < 0.001). Compared to men in the highest quartile, those in the lowest quartile of D₃ Cr muscle mass/weight had an increased risk of any clinical fracture (HR 1.8; 95% confidence interval [CI], 1.1-2.8); nonspine fracture (HR 1.8; 95% CI, 1.1-3.0), major osteoporotic fracture (HR 2.3; 95% CI, 1.2-4.6), and hip fracture (HR 5.9; 95% CI, 1.6-21.1). Results were attenuated after adjustment for physical performance, but associations remained borderline significant for hip and major osteoporotic fractures (p ≥ 0.05 to 0.10). Low D₃ Cr muscle mass/weight is associated with a markedly high risk of hip and potentially other fractures in older men; this association is partially mediated by physical performance. © 2022 American Society for Bone and Mineral Research (ASBMR).

Investigating the Efficacy of an 18-Week Postpartum Rehabilitation and Physical Development Intervention on Occupational Physical Performance and Musculoskeletal Health in UK Servicewomen: Protocol for an Independent Group Study Design

Background

Postpartum women are at an increased risk of pelvic floor dysfunction, musculoskeletal injury, and poor psychological health and have reduced physical fitness compared to before pregnancy. There is no formal, evidence-based rehabilitation and physical development program for returning UK servicewomen to work following childbirth.

Objective

This study aims to examine the efficacy of a rehabilitation and physical development intervention for returning postpartum UK servicewomen to occupational fitness.

Methods

Eligible servicewomen will be assigned to a training or control group in a nonrandomized controlled trial 6 weeks after childbirth. Group allocation will be based on the location of standard pregnancy and postpartum care. The control group will receive standard care, with no prescribed intervention. The training group will start an 18-week core and pelvic health rehabilitation program 6 weeks post partum and a 12-week resistance and high-intensity interval training program 12 weeks post partum. All participants will attend 4 testing sessions at 6, 12, 18, and 24 weeks post partum for the assessment of occupational physical performance, pelvic health, psychological well-being, quality of life, and musculoskeletal health outcomes. Occupational physical performance tests will include vertical jump, mid-thigh pull, seated medicine ball throw, and a timed 2-km run. Pelvic health tests will include the Pelvic Organ Prolapse Quantification system, the PERFECT (power, endurance, repetitions, fast, every contraction timed) scheme for pelvic floor strength, musculoskeletal physiotherapy assessment, the Pelvic Floor Distress Inventory–20 questionnaire, and the International Consultation on Incontinence Questionnaire–Vaginal Symptoms. Psychological well-being and quality of life tests will include the World Health Organization Quality of Life questionnaire and the Edinburgh Postnatal Depression Scale. Musculoskeletal health outcomes will include body composition; whole-body areal bone mineral density; tibial volumetric bone mineral density, geometry, and microarchitecture; patella tendon properties; muscle architecture; muscle protein and collagen turnover; and muscle mass and muscle breakdown. Data will be analyzed using linear mixed-effects models, with participants included as random effects, and group and time as fixed effects to assess within- and between-group differences over time.

Results

This study received ethical approval in April 2019 and recruitment started in July 2019. The study was paused in March 2020 owing to the COVID-19 pandemic. Recruitment restarted in May 2021. The results are expected in September 2022.

Conclusions

This study will inform the best practice for the safe and optimal return of postpartum servicewomen to physically and mentally demanding jobs.

Trial Registration

ClinicalTrials.gov NCT04332757; https://clinicaltrials.gov/ct2/show/NCT04332757

International Registered Report Identifier (IRRID)

DERR1-10.2196/32315

Factor analysis to determine relative contributions of strength, physical performance, body composition and muscle mass to disability and mobility disability outcomes in older men

BACKGROUND

It is not known how measures of body composition, strength and physical performance are interrelated or how empirical groupings of these measures relate to disability and mobility disability.

METHODS

Muscle mass was assessed by D3-creatine dilution (D3Cr muscle mass) in 1345 men (84.1 ± 4.1 years) enrolled in the Osteoporotic Fractures in Men (MrOS) study. Participants completed anthropomorphic measures, walk speed, grip strength, chair stands, and dual x-ray absorptiometry (DXA) estimated appendicular lean mass (ALM) and body fat percentage. Men reported limitations in mobility, activities of daily living (ADLs) and instrumental ADLs at initial and over 2.2 ± 0.3 years. Factor analysis reduced variables into related groups and negative binomial models calculated relative risk (RR) of factors with mobility and disability outcomes.

RESULTS

Factor analysis reduced 10 variables into four factors: Factor 1, body composition, including ALM, body fat percentage, weight and muscle mass; Factor 2, body size and lean mass, including height, weight and ALM; Factor 3, muscle mass, strength and performance, including walk speed, chair stands, grip strength, and muscle mass; and Factor 4, lean mass and weight, including ALM and weight. Only Factor 3 was significantly associated (p-value < .001) with prevalent disability (RR per standard deviation increment in factor score (reflecting higher muscle mass, strength and physical performance) 0.44, 0.35-0.56) and mobility disability (RR 0.22, 0.17 0.28), and incident mobility disability (RR 0.37, 0.27-0.50).

CONCLUSION

D3Cr muscle mass was the only body composition variable that co-segregated with strength and physical performance measures, and contributed to a factor that was associated with disability outcomes in older men.

Adapting MultiPLe behavior Interventions that eFfectively Improve (AMPLIFI) cancer survivor health: program project protocols for remote lifestyle intervention and assessment in 3 inter-related randomized controlled trials among survivors of obesity-related cancers

BACKGROUND

Scalable, multiple behavior change interventions are needed to address poor diet, inactivity, and excess adiposity among the rising number of cancer survivors. Efficacy-tested diet (RENEW) and exercise (BEAT Cancer) programs were adapted for web delivery among middle-aged and older cancer survivors for the AMPLIFI study, a National Cancer Institute-funded, multi-site, program project.

METHODS

Throughout the continental U.S., survivors of several obesity-related cancers are being recruited for three interconnected randomized controlled trials (RCTs). Projects 1 and 2 test 6-month diet or exercise interventions versus a wait-list control condition. Upon completion of the 6-month study period, the intervention participants receive the next behavior change sequence (i.e., diet receives exercise, exercise receives diet) and the wait-list control arm initiates a 12-month combined diet and exercise intervention. Project 3 tests the efficacy of the sequential versus simultaneous interventions. Assessments occur at baseline and semi-annually for up to 2-years and include: body mass index, health behaviors (diet quality, accelerometry-assessed physical activity/sleep), waist circumference, D3 creatine-assessed muscle mass, physical performance, potential mediators/moderators of treatment efficacy, biomarkers of inflammation and metabolic regulation, health care utilization, cost, and overall health. Four shared resources support AMPLIFI RCTs: 1) Administrative; 2) Adaptation, Dissemination and Implementation; 3) Recruitment and Retention; and 4) Assessment and Analysis.

DISCUSSION

Representing a new generation of RCTs, AMPLIFI will exclusively use remote technologies to recruit, intervene and assess the efficacy of the newly-adapted, web-based diet and exercise interventions and determine whether sequential or combined delivery works best for at-risk (older, rural, racial minority) cancer survivors.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT04000880 . Registered 27 June 2019.

Commentary on Guidance for assessment of the muscle mass phenotypic criterion for the Global Leadership Initiative on Malnutrition (GLIM) diagnosis of malnutrition

The assessment of body composition and its relation to health outcomes has been an integral component of medical research. While body mass index is used as an index of overweight and obesity, the effects of the major individual components of body mass, including fat and skeletal muscle, on outcomes depends upon the accuracy of the method being used. Body composition may be measured using several different methods, each of which rely on assumptions that may not be true in all populations, ages, or clinical conditions. This article is protected by copyright. All rights reserved.

Guidance for assessment of the muscle mass phenotypic criterion for the Global Leadership Initiative on Malnutrition (GLIM) diagnosis of malnutrition

The Global Leadership Initiative on Malnutrition (GLIM) provides consensus criteria for the diagnosis of malnutrition that can be widely applied. The GLIM approach is based on the assessment of three phenotypic (weight loss, low body mass index, and low skeletal muscle mass) and two etiologic (low food intake and presence of disease with systemic inflammation) criteria, with diagnosis confirmed by any combination of one phenotypic and one etiologic criterion fulfilled. Assessment of muscle mass is less commonly performed than other phenotypic malnutrition criteria, and its interpretation may be less straightforward, particularly in settings that lack access to skilled clinical nutrition practitioners and/or to body composition methodologies. In order to promote the widespread assessment of skeletal muscle mass as an integral part of the GLIM diagnosis of malnutrition, the GLIM consortium appointed a working group to provide consensus-based guidance on assessment of skeletal muscle mass. When such methods and skills are available, quantitative assessment of muscle mass should be measured or estimated using dual-energy x-ray absorptiometry, computerized tomography, or bioelectrical impedance analysis. For settings where these resources are not available, then the use of anthropometric measures and physical examination are also endorsed. Validated ethnic- and sex-specific cutoff values for each measurement and tool are recommended when available. Measurement of skeletal muscle function is not advised as surrogate measurement of muscle mass. However, once malnutrition is diagnosed, skeletal muscle function should be investigated as a relevant component of sarcopenia and for complete nutrition assessment of persons with malnutrition.

Serum irisin level is independent of sarcopenia and related muscle parameters in older adults

BACKGROUND

Accumulating evidence indicates that irisin, a myokine consisting of 112 amino acids, protects against muscle wasting in an autocrine manner; however, its impact on human muscle metabolism is still inconclusive. In this cross-sectional study, we aimed to investigate whether circulating irisin could be a potential biomarker reflecting muscle health in older adults.

METHODS

Comprehensive assessment of muscle mass; muscle function, including grip strength, gait speed, chair stand test, and short physical performance battery (SPPB); and muscle quality was performed in 143 older adults who visited outpatient geriatrics and endocrinology clinics. Sarcopenia was defined using the Asian-specific cutoff value. Blood samples were also collected to determine serum irisin concentration which was measured using enzyme immunoassay.

RESULTS

The serum irisin level was not significantly different according to the status of sarcopenia, low muscle mass, weak muscle strength, poor physical performance, and poor muscle quality, before or after adjustment for age, sex, appendicular skeletal muscle (ASM), and body mass index. Consistently, the association of circulating irisin level with sarcopenia-related parameters (skeletal muscle index, grip strength, gait speed, chair stand test, SPPB, and grip strength/body weight or ASM) was not evident in any adjustment models.

CONCLUSIONS

Despite the clear implication of irisin's involvement in muscle metabolism based on experimental research, we did not observe a definite association between its serum level and clinical muscle parameters in humans. These results suggest that the blood irisin level may not accurately predict the risk of sarcopenia in older adults.

Quality Matters as Much as Quantity of Skeletal Muscle: Clinical Implications of Myosteatosis in Cardiometabolic Health

Although age-related changes in skeletal muscles are closely associated with decreases in muscle strength and functional decline, their associations with cardiometabolic diseases in the literature are inconsistent. Such inconsistency could be explained by the fact that muscle quality-which is closely associated with fatty infiltration of the muscle (i.e., myosteatosis)-is as important as muscle quantity in cardiometabolic health. However, muscle quality has been less explored compared with muscle mass. Moreover, the standard definition of myosteatosis and its assessment methods have not been established yet. Recently, some techniques using single axial computed tomography (CT) images have been introduced and utilized in many studies, as the mass and quality of abdominal muscles could be measured opportunistically on abdominal CT scans obtained during routine clinical care. Yet, the mechanisms by which myosteatosis affect metabolic and cardiovascular health remain largely unknown. In this review, we explore the recent advances in the assessment of myosteatosis and its changes associated with aging. We also review the recent literature on the clinical implication of myosteatosis by focusing on metabolic and cardiovascular diseases. Finally, we discuss the challenges and unanswered questions that need addressing to set myosteatosis as a therapeutic target for the prevention or treatment of cardiometabolic diseases.

Combined in vivo muscle mass, muscle protein synthesis and muscle protein breakdown measurement: a 'Combined Oral Stable Isotope Assessment of Muscle (COSIAM)' approach

Optimising approaches for measuring skeletal muscle mass and turnover that are widely applicable, minimally invasive and cost effective is crucial in furthering research into sarcopenia and cachexia. Traditional approaches for measurement of muscle protein turnover require infusion of expensive, sterile, isotopically labelled tracers which limits the applicability of these approaches in certain populations (e.g. clinical, frail elderly). To concurrently quantify skeletal muscle mass and muscle protein turnover i.e. muscle protein synthesis (MPS) and muscle protein breakdown (MPB), in elderly human volunteers using stable-isotope labelled tracers i.e. Methyl-[D₃]-creatine (D₃-Cr), deuterium oxide (D₂O), and Methyl-[D₃]-3-methylhistidine (D₃-3MH), to measure muscle mass, MPS and MPB, respectively. We recruited 10 older males (71 ± 4 y, BMI: 25 ± 4 kg^.m², mean ± SD) into a 4-day study, with DXA and consumption of D₂O and D₃-Cr tracers on day 1. D₃-3MH was consumed on day 3, 24 h prior to returning to the lab. From urine, saliva and blood samples, and a single muscle biopsy (vastus lateralis), we determined muscle mass, MPS and MPB. D₃-Cr derived muscle mass was positively correlated to appendicular fat-free mass (AFFM) estimated by DXA (r = 0.69, P = 0.027). Rates of cumulative myofibrillar MPS over 3 days were 0.072%/h (95% CI, 0.064 to 0.081%/h). Whole-body MPB over 6 h was 0.052 (95% CI, 0.038 to 0.067). These rates were similar to previous literature. We demonstrate the potential for D₃-Cr to be used alongside D₂O and D₃-3MH for concurrent measurement of muscle mass, MPS, and MPB using a minimally invasive design, applicable for clinical and frail populations.

Science-based policy: targeted nutrition for all ages and the role of bioactives

Globally, there has been a marked increase in longevity, but it is also apparent that significant inequalities remain, especially the inequality related to insufficient 'health' to enjoy or at least survive those later years. The major causes include lack of access to proper nutrition and healthcare services, and often the basic information to make the personal decisions related to diet and healthcare options and opportunities. Proper nutrition can be the best predictor of a long healthy life expectancy and, conversely, when inadequate and/or improper a prognosticator of a sharply curtailed expectancy. There is a dichotomy in both developed and developing countries as their populations are experiencing the phenomenon of being 'over fed and under nourished', i.e., caloric/energy excess and lack of essential nutrients, leading to health deficiencies, skyrocketing global obesity rates, excess chronic diseases, and premature mortality. There is need for new and/or innovative approaches to promoting health as individuals' age, and for public health programs to be a proactive blessing and not an archaic status quo 'eat your vegetables' mandate. A framework for progress has been proposed and published by the World Health Organization in their Global Strategy and Action Plan on Ageing and Health (WHO (2017) Advancing the right to health: the vital role of law. https://apps.who.int/iris/bitstream/handle/10665/252815/9789241511384-eng.pdf?sequence=1&isAllowed=y . Accessed 07 Jun 2021; WHO (2020a) What is Health Promotion. www.who.int/healthpromotion/fact-sheet/en/ . Accessed 07 Jun 2021; WHO (2020b) NCD mortality and morbidity. www.who.int/gho/ncd/mortality_morbidity/en/ . Accessed 07 Jun 2021). Couple this WHO mandate with current academic research into the processes of ageing, and the ingredients or regimens that have shown benefit and/or promise of such benefits. Now is the time for public health policy to 'not let the perfect be the enemy of the good,' but to progressively make health-promoting nutrition recommendations.

Profoundly lower muscle mass and rate of contractile protein synthesis in boys with Duchenne muscular dystrophy

Boys with Duchenne muscular dystrophy (DMD) experience a progressive loss of functional muscle mass, with fibrosis and lipid accumulation. Accurate evaluation of whole-body functional muscle mass (MM) in DMD patients has not previously been possible and the rate of synthesis of muscle proteins remains unexplored. We used non-invasive, stable isotope-based methods from plasma and urine to measure the fractional rate of muscle protein synthesis (FSR) functional muscle mass (MM), and fat free mass (FFM) in 10 DMD (6-17 years) and 9 age-matched healthy subjects. An oral dose of D₃ creatine in 70% ² H₂ O was administered to determine MM and FFM followed by daily 70% ² H₂ O to measure protein FSR. Functional MM was profoundly reduced in DMD subjects compared to controls (17% vs. 41% of body weight, P < 0.0001), particularly in older, non-ambulant patients in whom functional MM was extraordinarily low (<13% body weight). We explored the urine proteome to measure FSR of skeletal muscle-derived proteins. Titin, myosin light chain and gelsolin FSRs were substantially lower in DMD subjects compared to controls (27%, 11% and 40% of control, respectively, P < 0.0001) and were strongly correlated. There were no differences in muscle-derived sarcoplasmic proteins FSRs (creatine kinase M-type and carbonic anhydrase-3) measured in plasma. These data demonstrate that both functional MM, body composition and muscle protein synthesis rates can be quantified non-invasively and are markedly different between DMD and control subjects and suggest that the rate of contractile but not sarcoplasmic protein synthesis is affected by a lack of dystrophin. KEY POINTS: Duchenne muscular dystrophy (DMD) results in a progressive loss of functional skeletal muscle but total body functional muscle mass or rates of muscle protein synthesis have not previously been assessed in these patients. D₃ -creatine dilution was used to measure total functional muscle mass and oral ² H₂ O was used to examine the rates of muscle protein synthesis non-invasively in boys with DMD and healthy controls using urine samples. Muscle mass was profoundly lower in DMD compared to control subjects, particularly in older, non-ambulant patients. The rates of contractile protein synthesis but not sarcoplasmic proteins were substantially lower in DMD. These results may provide non-invasive biomarkers for disease progression and therapeutic efficacy in DMD and other neuromuscular diseases.

Imaging modalities for diagnosis and monitoring of cancer cachexia

Cachexia, a multifactorial wasting syndrome, is highly prevalent among advanced-stage cancer patients. Unlike weight loss in healthy humans, the progressive loss of body weight in cancer cachexia primarily implicates lean body mass, caused by an aberrant metabolism and systemic inflammation. This may lead to disease aggravation, poorer quality of life, and increased mortality. Timely detection is, therefore, crucial, as is the careful monitoring of cancer progression, in an effort to improve management, facilitate individual treatment and minimize disease complications. A detailed analysis of body composition and tissue changes using imaging modalities—that is, computed tomography, magnetic resonance imaging, (¹⁸F) fluoro-2-deoxy-d-glucose (¹⁸FDG) PET and dual-energy X-ray absorptiometry—shows great premise for charting the course of cachexia. Quantitative and qualitative changes to adipose tissue, organs, and muscle compartments, particularly of the trunk and extremities, could present important biomarkers for phenotyping cachexia and determining its onset in patients. In this review, we present and compare the imaging techniques that have been used in the setting of cancer cachexia. Their individual limitations, drawbacks in the face of clinical routine care, and relevance in oncology are also discussed.

CT muscle density, D3Cr muscle mass and body fat associations with physical performance, mobility outcomes and mortality risk in older men

BACKGROUND

Muscle mass declines with age, while body adiposity increases. Sarcopenic obesity has been proposed to be particularly deleterious. However, previous methods for estimating muscle mass have been inadequate, and the relative contributions of total body fat vs. muscle fat to adverse outcomes have been unclear.

METHODS

In a large cohort of older men (N= 1017), we measured muscle mass (D3 creatine dilution), muscle density (high resolution peripheral computed tomography in the diaphyseal tibia) as a proxy of muscle fat, and total body fat (dual energy x-ray absorptiometry). We examined their associations with physical performance (walking speed, grip strength, chair stand time), the risk of mobility outcomes (mobility limitations, mobility disability), and the risk of death over ~5 years.

RESULTS

In combined models, lower muscle mass and muscle density were independently associated with worse physical performance and the risk of adverse outcomes, while total body fat was minimally related to physical performance and not related to mobility outcomes or mortality. For example, the relative risks for mortality per 1 standardized unit increase in muscle density, muscle mass, and total body fat were 0.84 (95% CI: 0.74, 0.70), 0.70 (0.57, 0.86), and 0.90 (0.64, 1.25), respectively.

CONCLUSIONS

Muscle mass and muscle density were associated with physical performance and adverse outcomes, and had independent, additive effects. There was little additional contribution of total body fat.

MRI-Determined Psoas Muscle Fat Infiltration Correlates with Severity of Weight Loss during Cancer Cachexia

PURPOSE

To evaluate the suitability of psoas and erector spinae muscle proton density fat fraction (PDFF) and fat volume as biomarkers for monitoring cachexia severity in an oncological cohort, and to evaluate regional variances in muscle parameters over time.

METHODS

In this prospective study, 58 oncological patients were examined by a 3 T MRI receiving between one and five scans. Muscle volume and PDFF were measured, segmentation masks were divided into proximal, middle and distal muscle section.

RESULTS

A regional variation of fat distribution in erector spinae muscle at baseline was found (p < 0.01). During follow-ups significant relative change of muscle parameters was observed. Relative maximum change of erector spinae muscle showed a significant regional variation. Correlation testing with age as a covariate revealed significant correlations for baseline psoas fat volume (r = -0.55, p < 0.01) and baseline psoas PDFF (r = -0.52, p = 0.02) with maximum BMI change during the course of the disease.

CONCLUSION

In erector spinae muscles, a regional variation of fat distribution at baseline and relative maximum change of muscle parameters was observed. Our results indicate that psoas muscle PDFF and fat volume could serve as MRI-determined biomarkers for early risk stratification and disease monitoring regarding progression and severity of weight loss in cancer cachexia.

Sarcopenia measurement in research and clinical practice

Sarcopenia is a disease related to accelerated loss of skeletal muscle and subsequent decline in functional capacity. It affects approximately 13% of the world's population aged over 60 years. Sarcopenia is primarily managed and prevented through a combination of exercise prescription combined with appropriate nutritional strategies. This review outlines diagnostic and case finding/screening tools for age-related (primary) sarcopenia used in research and clinical practice. Diagnostic tools critically reviewed include those of the: European Workgroup for Sarcopenia (EWGSOP) versions 1 and 2; Asian Working Group for Sarcopenia (AWGS) versions 1 and 2; Foundation for the National Institutes of Health (FNIH); and the Sarcopenia Definition and Outcomes Consortium (SDOC). Criteria used by diagnostic tools (muscle mass, muscle strength and physical functioning/performance) are also detailed. Case-finding tools include the SARC-F questionnaire, Ishii's formula and Goodman's screening grid. Additionally, this review discusses the strengths and weaknesses of each diagnostic and case-finding tool, and examines their ability to reliably predict adverse clinical outcomes and patient responses to potential therapies.

Muscle Mass Assessed by the D3-Creatine Dilution Method and Incident Self-reported Disability and Mortality in a Prospective Observational Study of Community-Dwelling Older Men

BACKGROUND

Whether low muscle mass is a risk factor for disability and mortality is unclear. Associations between approximations of muscle mass (including lean mass from dual-energy x-ray absorptiometry [DXA]), and these outcomes are inconsistent.

METHODS

Muscle mass measured by deuterated creatine (D3Cr) dilution and appendicular lean mass (ALM, by DXA) were assessed at the Year 14 Visit (2014-2016) of the prospective Osteoporotic Fractures in Men study (N = 1,425, age 77-101 years). Disability in activities of daily living (ADLs), instrumental ADLs, and mobility tasks was self-reported at the Year 14 visit and 2.2 years later; deaths were centrally adjudicated over 3.3 years. Relative risks and 95% confidence intervals (CI) were estimated per standard deviation decrement with negative binomial, logistic regression, or proportional hazards models.

RESULTS

In age- and clinical center-adjusted models, the relative risks per decrement in D3Cr muscle mass/wgt was 1.9 (95% CI: 1.2, 3.1) for incident self-reported ADL disability; 1.5 (95% CI: 1.3, 1.9) for instrumental ADL disability; and 1.8 (95% CI: 1.5, 2.2) for mobility disability. In age-, clinical center-, and weight-adjusted models, the relative risks per decrement in D3Cr muscle mass was 1.8 (95% CI: 1.5, 2.2) for all-cause mortality. In contrast, lower DXA ALM was not associated with any outcome. Associations of D3Cr muscle mass with these outcomes were slightly attenuated after adjustment for confounding factors and the potentially mediating effects of strength and physical performance.

CONCLUSIONS

Low muscle mass as measured by D3Cr dilution is a novel risk factor for clinically meaningful outcomes in older men.