Voluntary activation of human knee extensors during isotonic shortening contractions

PURPOSE

The interpolated twitch technique (ITT) is often used to assess voluntary activation during isometric contractions; however, this may have limited relevance to dynamic contractions. Although the ITT has been applied to relatively slow isokinetic contractions (< 150°/s), it has received limited consideration during unconstrained velocity (i.e., isotonic) contractions, despite their relevance to natural movements. Here, we explored the ITT during isotonic knee extension contractions using a modified dynamometer.

METHODS

Young males (n = 6) and females (n = 4) performed isometric and isotonic knee extension contractions of sub-maximal and maximal intensities with doublet (150 Hz) muscle belly stimulations to assess voluntary activation. Following each voluntary isotonic contraction (velocity range ~ 35°/s to ~ 275°/s), resting potentiated doublets were evaluated during passive joint rotation at the same angular velocity achieved during voluntary efforts, to account for force-velocity characteristics. Correlations between voluntary activation and the proportion of maximal torque or power were evaluated for isometric and isotonic contractions, respectively.

RESULTS

Isometric voluntary activation was strongly correlated with increasing torque output (r = 0.96, p < 0.001). Doublet torque during passive joint rotation displayed a hyperbolic relationship with increasing angular velocity (r = 0.98, p < 0.001). Isotonic voluntary activation was strongly correlated with increasing power output (r = 0.89, p < 0.001). During maximal effort contractions, no differences were observed in voluntary activation between isometric and isotonic conditions (89.4% vs. 89.2%, p = 0.904).

CONCLUSIONS

The ITT is a valid approach to evaluate voluntary activation during an isotonic contraction using a modified dynamometer. Participants were able to achieve a similar high level of voluntary activation during isometric and isotonic contractions.

Electrically Evoked Isotonic Plantar Flexion Contractions Are Impaired Less than Voluntary After a Dynamic Fatiguing Task

PURPOSE

Evaluating central and peripheral processes responsible for reduced power after dynamic fatiguing tasks are often limited to isometric torque, which may not accurately reflect dynamic contractile performance. Here, we compare voluntary and electrically evoked peak power (and its determinants: dynamic torque and velocity) and rate of velocity development (RVD) before and after a dynamic fatiguing task using concentric Plantar flexion contractions.

METHODS

Young (18-32 yr) males ( n = 11) and females ( n = 2) performed maximal-effort isotonic Plantar flexion contractions using a load of 20% isometric torque until an approximately 75% reduction in peak power. Voluntary and electrically evoked (300 Hz tibial nerve stimulation) contractions loaded to 20% and 40% isometric torque through 25° ankle joint range of motion were compared before and 0, 2.5, 5, and 10 min after task termination.

RESULTS

At task termination, peak power and RVD of voluntary contractions at both loads were reduced more (~40% to 50% reduction) than electrically evoked (~25% to 35% reduction) contractions ( P < 0.001 and P = 0.003). Throughout the recovery period, electrically evoked peak power and RVD returned to baseline sooner (<5 min) than voluntary contractions, which were still depressed at 10 min. Reductions in peak power for the 20% load were equally due to impaired dynamic torque and velocity, whereas velocity was impaired more than dynamic torque ( P < 0.001) for the 40% load.

CONCLUSIONS

The relative preservation of electrically evoked power and RVD compared with voluntary contractions at task termination and quicker recovery to baseline indicates that the reductions in dynamic contractile performance after task termination are due to both central and peripheral processes; however, the relative contribution of dynamic torque and velocity is load dependent.

Calcaneal tendon stiffness is not associated with dynamic time-dependent contractile output

The ability to rapidly generate muscular torque and velocity is important in specialized activities and daily tasks of living. Tendon stiffness is one factor in the neuromuscular system that influences musculoskeletal torque transmission. Previous studies have reported weak-to-moderate correlations between tendon stiffness and rate of torque development (RTD). However, these correlations have been reported only for isometric contractions, which may not be relevant to contractions involving joint rotation (i.e., dynamic). The purpose was to investigate the effect of calcaneal tendon stiffness on the dynamic RTD and rate of velocity development (RVD) in plantar flexor muscles. Young adult males (n = 13) and females (n = 2) performed prone isometric- and isotonic-mode maximal voluntary plantar flexion contractions (MVC). Ultrasound imaging was used to quantify tendon morphological characteristics to estimate Young's elastic modulus (YM). Maximal voluntary and electrically evoked (300 Hz) isometric- and isotonic-mode (at 10% and 40% MVC loads) contractions were evaluated for RTD and RVD through a 25° ankle joint range of motion. YM was correlated with isometric RTD, but only for evoked contractions (RTD_0-50 ms: r = 0.54, p = 0.02, RTD_0-200 ms: r = 0.62, p = 0.01). Conversely, YM was not correlated with dynamic RTD (voluntary: r = -0.07-0.41, p = 0.06-0.40, evoked: r = -0.2-0.3, p = 0.14-0.24) nor RVD (voluntary: r = -0.08-0.24, p = 0.27-0.40, evoked: r = 0.12-0.3, p = 0.14-0.34). These correlations would indicate that calcaneal tendon stiffness is an important factor for rapid isometric torque development, but less so for isotonic contractions. The determinants of dynamic contractile rates are more complex and warrant further study.

Methodological and Clinimetric Evaluation of Inspiratory Respiratory Muscle Ultrasound in the Critical Care Setting: A Systematic Review and Meta-Analysis

OBJECTIVE

Significant variations exist in the use of respiratory muscle ultrasound in intensive care with no society-level consensus on the optimal methodology. This systematic review aims to evaluate, synthesize, and compare the clinimetric properties of different image acquisition and analysis methodologies.

DATA SOURCES

Systematic search of five databases up to November 24, 2021.

STUDY SELECTION

Studies were included if they enrolled at least 50 adult ICU patients, reported respiratory muscle (diaphragm or intercostal) ultrasound measuring either echotexture, muscle thickness, thickening fraction, or excursion, and evaluated at least one clinimetric property. Two independent reviewers assessed titles, abstracts, and full text against eligibility.

DATA EXTRACTION

Study demographics, ultrasound methodologies, and clinimetric data.

DATA SYNTHESIS

Sixty studies, including 5,025 patients, were included with 39 studies contributing to meta-analyses. Most commonly measured was diaphragm thickness (DT) or diaphragm thickening fraction (DTF) using a linear transducer in B-mode, or diaphragm excursion (DE) using a curvilinear transducer in M-mode. There are significant variations in imaging methodology and acquisition across all studies. Inter- and intrarater measurement reliabilities were generally excellent, with the highest reliability reported for DT (ICC, 0.98; 95% CI, 0.94-0.99). Pooled data demonstrated acceptable to excellent accuracy for DT, DTF, and DE to predicting weaning outcome after 48 to 72 hours postextubation (DTF AUC, 0.79; 95% CI, 0.73-0.85). DT imaging was responsive to change over time. Only three eligible studies were available for intercostal muscles. Intercostal thickening fraction was shown to have excellent accuracy of predicting weaning outcome after 48-hour postextubation (AUC, 0.84; 95% CI, 0.78-0.91).

CONCLUSIONS

Diaphragm muscle ultrasound is reliable, valid, and responsive in ICU patients, but significant variation exists in the imaging acquisition and analysis methodologies. Future work should focus on developing standardized protocols for ultrasound imaging and consider further research into the role of intercostal muscle imaging.

Test-retest repeatability of electrically evoked isotonic power and isometric torque in the plantar flexors

Electrically evoked isometric torque has good to excellent repeatability, but the degree of repeatability for electrically evoked isotonic power is unknown. We evaluated the test-retest repeatability of plantar flexion isometric torque and isotonic power evoked using brief tetanic trains at 10 and 50 Hz. Both torque and power had excellent (intraclass correlation coefficient >0.9) repeatability at low and high frequencies. Similar to isometric torque, electrically evoked isotonic power is a stable measure for studying dynamic muscle function.

Associations between Pretreatment Body Composition Features and Clinical Outcomes among Patients with Metastatic Clear Cell Renal Cell Carcinoma Treated with Immune Checkpoint Blockade

PURPOSE

High body mass index (BMI) may lead to improved immune-checkpoint blockade (ICB) outcomes in metastatic clear cell renal cell carcinoma (mccRCC). However, BMI is a crude body size measure. We investigated BMI and radiographically assessed body composition (BC) parameters association with mccRCC ICB outcomes.

EXPERIMENTAL DESIGN

Retrospective study of ICB-treated patients with mccRCC. BMI and BC variables [skeletal muscle index (SMI) and multiple adiposity indexes] were determined using pretreatment CT scans. We examined the associations between BMI and BC variables with ICB outcomes. Therapeutic responses per RECIST v1.1 were determined. We compared whole-transcriptomic patterns with BC variables in a separate cohort of 62 primary tumor samples.

RESULTS

205 patients with mccRCC were included in the cohort (74% were male, 71% were overweight/obese, and 53% were classified as low SMI). High-BMI patients experienced longer overall survival (OS) than normal-weight patients [unadjusted HR, 0.66; 95% confidence interval (CI), 0.45-0.97; P = 0.035]. The only BC variable associated with OS was SMI [unadjusted HR comparing low vs. high SMI 1.65 (95% CI: 1.13-2.43); P = 0.009]. However, this OS association became nonsignificant after adjusting for International Metastatic Renal Cell Carcinoma Database Consortium score and line of therapy. No OS association was seen for adiposity and no BC variable was associated with progression-free survival or radiological responses. Tumors from patients with low SMI displayed increased angiogenic, inflammatory, and myeloid signals.

CONCLUSIONS

Our findings highlight the relevance of skeletal muscle in the BMI paradox. Future studies should investigate if addressing low skeletal muscle in metastatic patients treated with ICB can improve survival.

Influence of Subcutaneous Adipose Tissue and Skeletal Muscle Thickness on Rectus Femoris Echo Intensity in Younger and Older Males and Females

OBJECTIVES

Ultrasound measurements of muscle echo intensity are commonly used surrogates of muscle composition (eg, intramuscular adipose tissue). However, given that soundwaves are increasingly attenuated with tissue depth, the interpretation of echo intensity may be confounded by adipose and skeletal muscle thickness. Our objectives are to compare the associations between adipose or muscle tissue thickness and rectus femoris echo intensity in younger and older males and females.

METHODS

Participants included in this analysis were derived from 3 previously published cohorts of younger (<45 years) and older (≥60 years) males and females. Ultrasound images of the rectus femoris were evaluated for muscle thickness, echo intensity, and subcutaneous adipose tissue thickness.

RESULTS

Older adults (n: 49 males, 19 females) had a higher body mass index (P = .001) compared with younger adults (n: 37 males, 49 females). Muscle thickness was negatively associated with echo intensity in older males (r = -0.59) and females (r = -0.53), whereas no associations were observed in younger males (r = 0.00) or females (r = -0.11). Subcutaneous adipose tissue thickness displayed no associations with echo intensity in any group.

CONCLUSIONS

Despite the known influence of subcutaneous adipose tissue thickness on beam attenuation, we observed no association with muscle echo intensity, indicating that adipose tissue correction may be required to better understand muscle echo intensity across differences in adiposity. The negative associations between muscle thickness and echo intensity in older, but not younger adults, suggests these associations may be related to the co-occurrence of skeletal muscle atrophy and intramuscular adipose tissue infiltration with advancing age.

Age-related performance fatigability: a comprehensive review of dynamic tasks

Adult ageing is associated with a myriad of changes within the neuromuscular system, leading to reductions in contractile function of old adults. One of the consequences of these age-related neuromuscular adaptations is altered performance fatigability, which can limit the ability of old adults to perform activities of daily living. Whereas age-related fatigability of isometric tasks has been well characterized, considerably less is known about fatigability of old adults during dynamic tasks involving movement about a joint, which provides a more functionally relevant task compared to static contractions. This review provides a comprehensive summary of age-related fatigability in dynamic contractions, where the importance of task specificity is highlighted with a brief discussion of the potential mechanisms responsible for differences in fatigability between young and old adults. The angular velocity of the task is critical for evaluating age-related fatigability, as tasks which constrain angular velocity (i.e., isokinetic) produce equivocal age-related differences in fatigability, whereas tasks involving unconstrained velocity (i.e., isotonic-like) consistently induce greater fatigability of old compared to young adults. These unconstrained velocity tasks, that are more closely associated with natural movements, offer an excellent model to uncover the underlying age-related mechanisms of increased fatigability. Future work evaluating the mechanisms of increased age-related fatigability of dynamic tasks should be evaluated using task-specific contractions (i.e., dynamic), particularly for assessment of spinal and supra-spinal components. Advancing our understanding of age-related fatigability is likely to yield novel insights and approaches for improving mobility limitations in old adults.

Frequency dependent coexistence of muscle fatigue and potentiation assessed by concentric isotonic contractions in human plantar flexors

The purpose was to investigate whether post-activation potentiation (PAP) mitigates power (i.e., torque x angular velocity) loss during dynamic fatiguing contractions and subsequent recovery by enhancing either muscle torque or angular velocity in human plantar flexors. In 12 participants, electrically stimulated (1, 10 and 50 Hz) dynamic contractions were done during a voluntary isotonic fatiguing protocol (20 and 50% voluntary decreases) until a 75% loss in voluntary peak power, and throughout 30 minutes of recovery. At the initial portion of fatigue (20% decrease), power responses of evoked low frequencies (1 and 10 Hz) were enhanced due to PAP (156 and 137%, respectively, P<0.001), while voluntary maximal efforts were depressed due to fatiguing mechanisms. Following the fatiguing task, prolonged low-frequency force depression (PLFFD) was evident by reduced 10:50 Hz peak power ratios (21 - 24%) from 3-min onwards during the 30-min recovery (P<0.005). Inducing PAP with maximal voluntary contractions during PLFFD enhanced the peak power responses of low frequencies (1 and 10 Hz) by 128 - 160 %, P<0.01. This PAP response mitigated the effects of PLFFD as the 1:50 (P<0.05) and 10:50 (P>0.4) Hz peak power ratios were greater or not different from the pre-fatigue values. Additionally, PAP enhanced peak torque more than peak angular velocity during both baseline and fatigue measurements (P<0.03). These results indicate that PAP can ameliorate PLFFD acutely when evaluated during concentric isotonic contractions and that peak torque is enhanced to a greater degree compared to peak angular velocity at baseline and in a fatigued state.

Association of strength, power, and function with muscle thickness, echo intensity, and lean tissue in older males

Dual-energy X-ray absorptiometry (DXA) appendicular lean tissue is used to screen older adults for sarcopenia. However, emerging data indicates that ageing-related muscle atrophy largely occurs within specific muscles, which may be masked using appendicular lean tissue. Comparisons between appendicular lean tissue and site-specific measures of muscle in relation to strength and physical function are needed to advance our understanding of these features in the context of poor muscle function in aged adults. Our primary objective was to compare correlations between lean tissue and site-specific muscle characteristics in relation to strength and physical function in older males. Older males (≥65 years) were evaluated for muscle strength, physical function (6-minute walk and 30-second sit-to-stand), and muscle size (appendicular and site-specific) and composition (echo intensity) using DXA and ultrasound. Of the 32 older males (75.4 ± 7.9 years), 12 had low appendicular lean tissue. All DXA and ultrasound muscle characteristics were associated (r = 0.39 to 0.83, p < 0.05) with torque or power producing capabilities. Except for the knee flexors, no differences in correlation coefficients were observed between muscle thickness or regional lean tissue in relation to muscle strength. Neither DXA nor ultrasound muscle characteristics were associated with physical function. In older males, ultrasound-based muscle thickness and DXA lean tissue provided similar associations with strength. Novelty: Lean tissue and muscle thickness provide similar associations with strength. Muscle thickness can distinguish low and normal appendicular lean tissue in older adults.

Altered features of body composition in older adults with type 2 diabetes and prediabetes compared with matched controls

BACKGROUND

Ageing is accompanied by muscle loss and fat gain, which may elevate the risk of type 2 diabetes (T2D). However, there is a paucity of data on the distribution of regional lean and fat tissue in older adults with T2D or prediabetes compared with healthy controls. The objective of this study was to compare regional body composition [by dual-energy x-ray absorptiometry (DXA)], muscle and subcutaneous adipose tissue (SAT) thicknesses (by ultrasound), and ultrasound-based muscle texture features in older adults with T2D or prediabetes compared with normoglycaemic controls.

METHODS

Eighteen adults > 60 years with T2D or prediabetes (T2D group) were individually matched to normoglycaemic participants [healthy matched (HM) group] for age (±5 years), sex, and body fat (±2.5%). In a single study visit, all participants received a whole-body DXA scan and ultrasound assessment of the abdomen and anterior thigh. At these two landmarks, we used ultrasound to measure muscle and SAT thickness, as well as texture features of the rectus femoris and rectus abdominis. We also conducted an exploratory subanalysis on a subset of participants (n = 14/18 in the T2D group and n = 10/18 in the HM group) who underwent additional assessments including strength testing of the knee extensors (using a Biodex dynamometer), and a fasting blood sample for the measurement of circulating markers of glucose metabolism [glucose, insulin, c-peptide, and the homoeostatic model assessment of insulin resistance (HOMA-IR)].

RESULTS

The T2D group was 72 ± 8 years old (mean ± SD), predominantly male (n = 15/18; 83%), and overweight (BMI: 27.8 ± 4.2 kg/m² , 33.2 ± 5.3% body fat). DXA-derived upper arm lean mass was 0.4 kg greater (P = 0.034), and leg fat mass was 1.4 kg lower (P = 0.048), in the T2D vs. HM group. Ultrasound-based texture features were distinct between the groups [rectus abdominis blob size: 0.07 ± 0.06 vs. 0.30 ± 0.43 cm² , P = 0.045; rectus femoris local binary pattern (LBP) entropy: 4.65 ± 0.05 vs. 4.59 ± 0.08 A.U., P = 0.007]. When all participants who underwent additional assessments were pooled (n = 24), we observed that certain ultrasound-based muscle texture features correlated significantly with muscle strength (rectus abdominis histogram skew vs. power during an isokinetic contraction at 60°/s: r = 0.601, P = 0.003) and insulin resistance (rectus femoris LBP entropy vs. HOMA-IR: r = 0.419, P = 0.042).

CONCLUSIONS

Our findings suggest a novel body composition phenotype specific to older adults with T2D or prediabetes. We are also the first to report that ultrasound-based texture features correspond with functional outcomes. Future larger scale studies are needed to uncover the mechanisms underpinning these regional body composition differences.

Rectus Abdominis Muscle Thickness is a Valid Measure of Cross-Sectional Area: Implications for Ultrasound

RATIONALE AND OBJECTIVES

The rectus abdominis muscle exhibits early and significant muscle atrophy, which has largely been characterized using ultrasound measured muscle thickness. However, the validity of rectus abdominis muscle thickness as a metric of muscle size has not been established, limiting precise interpretation of age-related changes. In a heterogeneous cohort of women and men, our objectives were to: (1) evaluate the association between rectus abdominis muscle thickness and cross-sectional area (CSA), and (2) examine if the visceral adipose tissue (VAT) compartment confounds the validity of rectus abdominis muscle thickness.

MATERIALS AND METHODS

Abdominal computed tomography scans of the third lumbar vertebrae from clinical and healthy populations were used to evaluate rectus abdominis thickness and CSA, and VAT CSA. Computed tomography scans were utilized due to the limited field of view of ultrasound imaging to capture the rectus abdominis CSA.

RESULTS

A total of 348 individuals (31% women) were included in this analysis, with a mean ± standard deviation age and body mass index of 51.2 ± 15.4 years and 28.0 ± 5.1 kg/m², respectively. Significant correlations were observed between rectus abdominis thickness and CSA for women (r = 0.758; p < 0.001) and men (r = 0.688; p < 0.001). Independent of age, VAT CSA was negatively associated with rectus abdominis thickness in men (p = 0.011), but not women (p = 0.446).

CONCLUSION

These data support the use of rectus abdominis muscle thickness as a measurement of muscle size in both women and men; however, the VAT compartment may confound its validity to a minor extent in men.

Associations between skeletal muscle echo intensity and thickness in relation to glucose homeostasis in healthy and glucose impaired older males

BACKGROUND

Aging-related changes in muscle composition and mass may predispose older adults to developing insulin resistance. Ultrasound echo intensity and thickness are surrogates of muscle composition and mass, however, their associations with glucose homeostasis are not well established. We examined how muscle echo intensity and thickness correlate with markers of glucose homeostasis in older (≥65 years) males with normal (n = 22) or impaired (n = 10) glucose control.

METHODS

Echo intensity was measured for the biceps brachii, rectus abdominis, and rectus femoris. Muscle thickness was evaluated for the biceps brachii + brachioradialis, rectus abdominis, and rectus femoris + vastus intermedius. Glucose homeostasis was evaluated using a 2-h oral glucose tolerance test.

RESULTS

In older males with normal glucose homeostasis, higher echo intensity of the rectus abdominis and rectus femoris was moderately (r = 0.36 to 0.59) associated with 2-h glucose. On the contrary, higher muscle echo intensity of the rectus abdominis, biceps brachii, and rectus femoris was moderately-to-strongly (r = -0.36 to -0.79) associated with indices of better glucose homeostasis in the impaired group. Rectus abdominis muscle thickness was moderately associated (r = 0.36) with better glucose tolerance in the normal glucose homeostasis; however, in the glucose impaired group, muscle thickness was associated with (r = 0.37 to 0.73) with poorer glucose homeostasis.

CONCLUSIONS

Muscle echo intensity displays divergent associations with glucose homeostasis in older males with normal compared to impaired glucose control. Larger muscle thickness was associated with poorer glucose homeostasis in the glucose impaired group, but rectus abdominis muscle thickness was correlated with better homeostasis in healthy older males.

Older males exhibit reduced anterior upper leg and anterior abdominal muscle thickness compared to younger males when matched for relative appendicular lean tissue

Background Ageing-related muscle atrophy does not occur uniformly across the body; rather, atrophy occurs to a greater extent in specific muscle groups compared to others. However, site-specific comparisons of muscle mass between older and younger adults typically do not account for relative muscle mass (i.e., matched for age- and sex-specific percentiles), which may confound site-specific differences. Furthermore, the uniformity of ageing-related differences in muscle composition (e.g., intramuscular adipose tissue) across the body are not well characterized. Purpose To examine site-specific muscle mass and composition differences between younger and older males matched for relative muscle mass. Methods Younger (18-44 years old, n = 19) and older (≥65 years old, n = 19) males were matched for relative appendicular lean tissue index (NHANES age- and sex-specific Z-scores) measured using dual-energy x-ray absorptiometry. Site-specific differences in skeletal muscle size (thickness) and composition (echo-intensity) were evaluated using ultrasound for 8 distinct landmarks across the body. Results Relative appendicular lean tissue mass was well matched between younger and older males (Z-score difference: -0.02, p = 0.927). Compared with younger males, older males had smaller muscle thickness for the anterior upper leg (difference: -1.08 cm, p < 0.001) and anterior abdomen (difference: -0.53 cm, p < 0.001). However, older adults displayed higher echo intensity across all muscles (p < 0.05), except for the posterior upper arm (p = 0.377), in comparison to the younger males. Conclusions When matched for relative appendicular lean tissue, muscle thickness differences between younger and older males are not-uniform across the body, whereas echo intensity was more uniformly higher in the older males.

Muscle Composition Analysis of Ultrasound Images: A Narrative Review of Texture Analysis

Skeletal muscle composition, often characterized by the degree of intramuscular adipose tissue, deteriorates with aging and disease and contributes to impairments in function and metabolism. Ultrasound can provide surrogate measures of muscle composition through measurement of echo intensity; however, there are several limitations associated with its analysis. More complex image processing features, broadly known as texture analysis, can also provide surrogates of muscle composition and may circumvent some of the limitations associated with muscle echo intensity. Here, texture features from the intensity histogram, gray-level co-occurrence matrix, run-length matrix, local binary pattern, blob analysis, texture anisotropy index and wavelet analysis are discussed. The purpose of this review was to provide a conceptual understanding of texture analysis as it pertains to muscle composition of ultrasound images.

Site-specific skeletal muscle echo intensity and thickness differences in subcutaneous adipose tissue matched older and younger adults

BACKGROUND

Age-related deterioration of muscle mass does not occur uniformly across the body. However, there is limited knowledge on the uniformity of age-related muscle composition changes across the body.

OBJECTIVE

Our primary objective was to evaluate muscle composition differences between younger and older adults across multiple muscle groups.

METHODS

We re-analysed data from a previously published cohort to evaluate differences in ultrasound muscle composition (echo intensity) between younger (<45 years) and older (>60 years) adults, when matched for adipose tissue mass at the anterior upper arm, anterior upper leg and abdominal muscles. Analysis of echo intensity is confounded by subcutaneous adipose tissue (SAT) thickness overlaying the muscle; we accounted for these effects by matching older and younger adults (1:1), stratified by sex, for absolute SAT thickness at each landmark.

RESULTS

From 96 adults (n = females), 58 (n = 34) were SAT matched at the anterior upper arm, 52 (n = 30) at the anterior upper leg and 60 (n = 30) at the abdominal region; thus, there were no age group differences in SAT thickness at each landmark. In comparison with younger adults, older adults presented with greater echo intensity at the anterior upper leg (females:40.3 ± 6.8 vs. 52.4 ± 7.6; males:35.7 ± 8.0 vs. 54.3 ± 9.8, p < .01) and abdominal (females:38.7 ± 27.6 vs. 73.4 ± 31.0; males:18.7 ± 15.2 vs. 60.9 ± 23.4, p < .01) muscles, but not anterior upper arm muscles (females:47.0 ± 6.5 vs. 53.2 ± 13.1; males:43.4 ± 8.9 vs. 48.9 ± 10.1, p = .18).

CONCLUSIONS

Distinct age-related differences in trunk and lower limb muscle composition were evident compared to upper limb muscles; highlighting the importance of quantifying specific muscle groups when evaluating age-associated muscle characteristics.

Myokines and adipokines in sarcopenia: understanding cross-talk between skeletal muscle and adipose tissue and the role of exercise

Detrimental age-associated changes in skeletal muscle and adipose tissue increase the risk of sarcopenia. Age-related changes in myokines, such as myostatin and irisin, as well as adipokines, such as leptin and adiponectin, contribute to cross-talk between muscle and adipose tissue. These age-related changes in myokines and adipokines have important implications for sarcopenia, however, recent literature highlights discrepancies in these relationships. Exercise may alter serum profiles and muscle receptor expression of these factors, but future work is needed to determine whether these changes in myokines and adipokines relate to improvements in muscle mass and function. Here, we describe myokine-mediated and adipokine-mediated interactions between muscle and adipose tissue, and discuss the fundamental importance of these cytokines to understanding the development of sarcopenia.

Automated body composition analysis of clinically acquired computed tomography scans using neural networks

BACKGROUND & AIMS

The quantity and quality of skeletal muscle and adipose tissue is an important prognostic factor for clinical outcomes across several illnesses. Clinically acquired computed tomography (CT) scans are commonly used for quantification of body composition, but manual analysis is laborious and costly. The primary aim of this study was to develop an automated body composition analysis framework using CT scans.

METHODS

CT scans of the 3rd lumbar vertebrae from critically ill, liver cirrhosis, pancreatic cancer, and clear cell renal cell carcinoma patients, as well as renal and liver donors, were manually analyzed for body composition. Ninety percent of scans were used for developing and validating a neural network for the automated segmentation of skeletal muscle and adipose tissues. Network accuracy was evaluated with the remaining 10 percent of scans using the Dice similarity coefficient (DSC), which quantifies the overlap (0 = no overlap, 1 = perfect overlap) between human and automated segmentations.

RESULTS

Of the 893 patients, 44% were female, with a mean (±SD) age and body mass index of 52.7 (±15.8) years old and 28.0 (±6.1) kg/m², respectively. In the testing cohort (n = 89), DSC scores indicated excellent agreement between human and network-predicted segmentations for skeletal muscle (0.983 ± 0.013), and intermuscular (0.900 ± 0.034), visceral (0.979 ± 0.019), and subcutaneous (0.986 ± 0.016) adipose tissue. Network segmentation took ~350 milliseconds/scan using modern computing hardware.

CONCLUSIONS

Our network displayed excellent ability to analyze diverse body composition phenotypes and clinical cohorts, which will create feasible opportunities to advance our capacity to predict health outcomes in clinical populations.

Body Composition Analysis of Computed Tomography Scans in Clinical Populations: The Role of Deep Learning

BACKGROUND

Body composition is increasingly being recognized as an important prognostic factor for health outcomes across cancer, liver cirrhosis, and critically ill patients. Computed tomography (CT) scans, when taken as part of routine care, provide an excellent opportunity to precisely measure the quantity and quality of skeletal muscle and adipose tissue. However, manual analysis of CT scans is costly and time-intensive, limiting the widespread adoption of CT-based measurements of body composition.

SUMMARY

Advances in deep learning have demonstrated excellent success in biomedical image analysis. Several recent publications have demonstrated excellent accuracy in comparison to human raters for the measurement of skeletal muscle, visceral adipose, and subcutaneous adipose tissue from the lumbar vertebrae region, indicating that analysis of body composition may be successfully automated using deep neural networks. Key Messages: The high accuracy and drastically improved speed of CT body composition analysis (<1 s/scan for neural networks vs. 15 min/scan for human analysis) suggest that neural networks may aid researchers and clinicians in better understanding the role of body composition in clinical populations by enabling cost-effective, large-scale research studies. As the role of body composition in clinical settings and the field of automated analysis advance, it will be critical to examine how clinicians interact with these systems and to evaluate whether these technologies are beneficial in improving treatment and health outcomes for patients.

Influence of Contrast Administration on Computed Tomography-Based Analysis of Visceral Adipose and Skeletal Muscle Tissue in Clear Cell Renal Cell Carcinoma

BACKGROUND

Computed tomography (CT) scans are being utilized to examine the influence of skeletal muscle and visceral adipose quantity and quality on health-related outcomes in clinical populations. However, little is known about the influence of contrast administration on these parameters.

METHODS

Precontrast, arterial, and 3-minute postcontrast CT images of 45 patients with clear cell renal cell carcinoma were downloaded from The Cancer Imaging Archive and retrospectively analyzed for visceral adipose cross-sectional area (CSA) and density, and muscle CSA and density at the third lumbar vertebrae. Low muscle CSA index was defined as ≤38.9 cm² /m² for women and ≤55.4 cm² /m² for men. Low muscle density was defined as <41 Hounsfield units (HU) for body mass index (BMI) <24.9 kg/m² and <33 HU for BMI ≥25.0 kg/m² .

RESULTS

In both the arterial and 3-minute phases, contrast administration decreased visceral adipose CSA (-20.9 and -20.9 cm² ; P < .001) and increased visceral adipose density (4.8 and 5.8 HU; P < .001), relative to precontrast images. Muscle CSA index marginally increased in the arterial (0.6 cm² /m² ; P = .007) and 3-minute phases (0.8 cm² /m² ; P < .001). This likely represents clinically insignificant changes because it does not alter the identification of low muscle CSA (44.4% vs 42.2%; P = 1.00). Skeletal muscle density increased in the arterial (6.4 HU; P < .001) and 3-minute phases (8.7 HU; P < .001), which altered the identification of low muscle density (6.7% vs 31.1%; P < .001).

CONCLUSIONS

Future analyses should consider the phase of contrast during CT imaging because it may alter the interpretations of several parameters.

Development of a bedside viable ultrasound protocol to quantify appendicular lean tissue mass

BACKGROUND

Ultrasound is a non-invasive and readily available tool that can be prospectively applied at the bedside to assess muscle mass in clinical settings. The four-site protocol, which images two anatomical sites on each quadriceps, may be a viable bedside method, but its ability to predict musculature has not been compared against whole-body reference methods. Our primary objectives were to (i) compare the four-site protocol's ability to predict appendicular lean tissue mass from dual-energy X-ray absorptiometry; (ii) optimize the predictability of the four-site protocol with additional anatomical muscle thicknesses and easily obtained covariates; and (iii) assess the ability of the optimized protocol to identify individuals with low lean tissue mass.

METHODS

This observational cross-sectional study recruited 96 university and community dwelling adults. Participants underwent ultrasound scans for assessment of muscle thickness and whole-body dual-energy X-ray absorptiometry scans for assessment of appendicular lean tissue. Ultrasound protocols included (i) the nine-site protocol, which images nine anterior and posterior muscle groups in supine and prone positions, and (ii) the four-site protocol, which images two anterior sites on each quadriceps muscle group in a supine position.

RESULTS

The four-site protocol was strongly associated (R2  = 0.72) with appendicular lean tissue mass, but Bland-Altman analysis displayed wide limits of agreement (-5.67, 5.67 kg). Incorporating the anterior upper arm muscle thickness, and covariates age and sex, alongside the four-site protocol, improved the association (R2  = 0.91) with appendicular lean tissue and displayed narrower limits of agreement (-3.18, 3.18 kg). The optimized protocol demonstrated a strong ability to identify low lean tissue mass (area under the curve = 0.89).

CONCLUSIONS

The four-site protocol can be improved with the addition of the anterior upper arm muscle thickness, sex, and age when predicting appendicular lean tissue mass. This optimized protocol can accurately identify low lean tissue mass, while still being easily applied at the bedside.

Validation of Bedside Ultrasound of Muscle Layer Thickness of the Quadriceps in the Critically Ill Patient (VALIDUM Study)

BACKGROUND

In critically ill patients, muscle atrophy is associated with long-term disability and mortality. Bedside ultrasound may quantify muscle mass, but it has not been validated in the intensive care unit (ICU). Here, we compared ultrasound-based quadriceps muscle layer thickness (QMLT) with precise quantifications of computed tomography (CT)-based muscle cross-sectional area (CSA).

METHODS

Patients ≥18 years old with abdominal CT scans performed for clinical reasons were recruited from 9 ICUs for an ultrasound assessment of the quadriceps. CT scans of the third lumbar vertebra, performed <24 hours before or <72 hours after ICU admission, were analyzed for CSA. Low muscularity was defined as 170 cm² for men and 110 cm² for women. The ultrasound probe was maximally compressed against the skin and QMLT was measured on 2 sites of each quadriceps <72 hours of the CT scan.

RESULTS

Mean CT-derived muscle CSA was 109 ± 25 cm² for women and 168 ± 37 cm² for men, where 58% of patients exhibited low muscularity; only 2.7% patients were underweight according to body mass index. QMLT was positively correlated with CT CSA ( r = 0.45, P < .001). Based on logistic regression to predict low muscularity, QMLT independently generated a concordance index ( c) of 0.67 ( P < .002), which increased to 0.77 ( P < .001) when age, sex, body mass index, Charlson Comorbidity Index, and admission type (surgical vs medical) were added.

CONCLUSIONS

Our results suggest that QMLT alone with our current protocol may not accurately identify patients with low muscle mass.