Muscle Size Research Articles

Reliability of Ultrasonographically Acquired Muscle Morphology Based on a Cohort of Men and Women

Objective: The objective was to evaluate intrarater and inter-rater reliability of ultrasonography muscle morphology measurements in men and women, considering morphological differences between the genders. Materials and Methods: Thirty-two healthy subjects (16 male; 16 female; 26.6 ± 4.9 years) participated in two evaluation days. On day 1, subjects were evaluated by a single experienced rater, who repeated the evaluation on the next testing day along with two other raters. Muscle morphology of quadriceps femoris (QMT), rectus femoris (RFMT), vastus intermedius (VIMT), vastus medialis (VMMT), and vastus lateralis (VLMT) muscle thickness, rectus femoris muscle cross-sectional area (RFCSA), vastus lateralis muscle fascicle length (VLFL), and pennation angle (VLPA) were obtained. Reliability was evaluated by intraclass correlation coefficients (ICCs). Results: All intrarater comparisons demonstrated good reliability (ICC >0.90), even after participants’ gender stratification (ICC >0.81). Inter-rater comparisons for RFCSA, and muscle thickness showed good reliability (ICC >0.76). Male’s VLFL and VLPA reliability was considered insufficient (ICC = 0.58 and 0.60, respectively), while female’s was slightly higher (ICC = 0.79 and 0.75, respectively). Conclusion: Ultrasonography has potential to be used to observe changes in muscle size, but pennation angle and fascicle length should be evaluated by the same rater.

Effect of different load during eccentric training with blood flow restriction on muscle size, strength, and performance: A randomized controlled trial✰

Background/Objectivestudies on eccentric training with blood flow restriction (BFR) still has gaps, especially in strength and muscle hypertrophy. Therefore, this study aimed to analyze and compare the effects of six weeks of eccentric training of knee extensors at different load associated or not with BFR on strength, hypertrophy, and performance of knee extensors. Methods61 men, healthy and untrained, performed six weeks of quadriceps muscle eccentric training in isokinetic dynamometer were randomized into four groups: high-load eccentric training with BFR (HLET-BFR), low-load eccentric training with BFR (LLET-BFR), high-load eccentric training (HLET) and low-load eccentric training (LLET). The strength, muscle structure and performance outcomes were evaluated at baseline, after 3 and 6 weeks of training. Resultsfor eccentric peak torque in the first three weeks, HLET was superior to LLET, but similar to LLET-BFR. In the final three weeks, superiority was observed in relation to LLET-BFR; however, there was no difference in relation to HIET-BFR. For the outcomes isometric and concentric peak torque, muscle structure and performance, there were no differences between groups. Conclusioneccentric training led to strengthening of knee extensors and improved performance, but without altering the muscle structure. LLET-BFR promoted gains similar to HLET in the first three weeks of training.

Training Effects of Traditional versus Cluster Set Configuration with and without Blood Flow Restriction.

Purpose: This study compared the effects of four different resistance training (RT) programs that differed in the set configuration (cluster vs. traditional) and the blood flow condition [free-flow (FF) vs. blood flow restriction (BFR)] on strength, neuromuscular and hypertrophic adaptations.Methods: Forty-two resistance-trained males were randomly assigned into four protocols that differed in the set configuration (TRA: without rest between repetitions vs. CLU: 30 s rest every 2 repetitions) and in the blood flow condition [FF vs. BFR (50% of arterial occlusion pressure)]. Subjects followed an 8-week RT program, twice per week, with similar intensity (55%-65% 1RM), sets (3), repetitions per set (10-6), and resting time (2 minutes) in the full-squat (SQ) exercise. Before and after the RT program, they were evaluated for: 1) muscle size of the vastus lateralis; 2) vertical jump; 3) maximal isometric contraction; 4) progressive loading test; and 5) fatigue test.Results: BFR-TRA and FF-CLU induced greater increases in 1RM, and velocity against submaximal loads than FF-TRA and BFR-CLU (BFR × time and CLU × time interactions, p = 0.02). The TRA protocols showed greater increases in maximal isometric force than CLU (CLU × time interaction, p = 0.03). BFR did not enhance jump performance unlike the FF protocols (p < 0.01). The TRA protocols induced greater hypertrophy in the distal region of the vastus lateralis than CLU protocols (CLU × time interaction, p = 0.04), with BFR-TRA producing the greatest gains in all vastus lateralis sections.Conclusions: The different combinations of set configurations and blood flow conditions resulted in highly specific adaptations that illustrate the potential of adaptation for each protocol. The divergent underlying mechanisms of CLU and BFR methodologies may offset each other when combined.

Motor unit adaptation to disuse: crossing the threshold from firing rate suppression to neuromuscular junction transmission.

Neural conditioning to scenarios of muscle disuse is undoubtedly a cause of functional decrements that typically exceed losses of muscle size. Yet establishing the relative contribution of neural adaptation and the specific location in the motor pathway remains technically challenging. Several studies of healthy humans have targeted this system and have established that motor unit firing rate is suppressed following disuse, with a number of critical caveats. It is suppressed in the immobilized limb only, at relative and absolute force levels, and preferentially targets lower-threshold motor units. Concomitantly, electrophysiological investigation of neuromuscular junction transmission (NMJ) stability of lower-threshold motor units reveals minimal change following disuse. These findings contrast with numerous other methods, which show clear involvement of the NMJ but are unable to characterize the motor unit to which they belong. It is physiologically plausible that decrements observed following disuse are a result of suppressed firing rate of lower-threshold motor units and impairment of transmission of the NMJ of higher-threshold motor units. As such, motor units within the pool should be viewed in light of their varying susceptibility to disuse.

Adaptation and innovation in darter fish cranial musculature (Etheostomatinae: Percidae): insights from diceCT

Abstract Fish skulls are often highly kinetic, with multiple linkage and lever systems powered by a diverse suite of muscles. Comparative analysis of the evolution of soft-tissue structures in the fish skull is often limited under traditional approaches, while new imaging techniques like diceCT (diffusible iodine-based contrast-enhanced computed tomography) allow for high-resolution imaging of muscles in situ. Darters (Percidae: Etheostomatinae) are a diminutive and species-rich clade of lotic freshwater fishes, which show diverse head shapes believed to be associated with different foraging strategies. We used diceCT to sample all major cranial adductors and abductors responsible for movement of the jaw, hyoid, operculum, and suspensorium from 29 species. We applied comparative phylogenetic approaches to analyse the evolutionary trends in muscle size across the clade. We found two major patterns: (i) darter cranial muscles show fundamental trade-offs relating to investment in musculature, as well as buccal expansion vs. biting attributes; early divergence in muscle size appears to be associated with shifts in habitat use and foraging; (ii) darter adductor mandibulae show high variation in architecture (fibre orientation, divisions). This study highlights how new imaging techniques can provide novel insights into the anatomy of even well-sampled/represented clades.

Intra-Rater Reliability of Panoramic Ultrasound Imaging for Determining Quadriceps Muscle Cross-Sectional Area inMiddle-Aged and Elderly Adults.

Panoramic ultrasound (US) is an extended field-of-view (EFOV) imaging technique that enables visualization of large-scale skeletal muscles. This technique has previously been found to produce valid and reliable quantifications of muscle morphology in primarily young male subjects. The purpose was to investigate the intra-rater between-session test-retest reliability of panoramic US imaging for determining vastus lateralis (VL) and rectus femoris (RF) cross-sectional area (mCSA) in healthy middle-aged to elderly adults. In this cross-sectional study, axial panoramic US images of the RF and VL muscles were captured in 23 healthy females and males aged 47 to 78. Assessed across two sessions 3-7 days apart, intra-rater reliability was evaluated by intraclass correlation coefficients (ICC3,2), within-subject coefficient of variation , standard error of measurement (SEM), and minimal detectable change (MDC). Mean mCSA for RF was mean ± SD, 7.5 ± 2.7 cm2 on both test days, with a numeric difference of 0.8%. Mean VL mCSA was 20.6 ± 6.6 cm2 and 20.5 ± 6.5 cm2 on test days 1 and 2, respectively. Test-retest ICC were: 0.997 (95% CI: 0.994-0.999) for RF and 0.995 (95% CI: 0.989-0.998) for VL. was 2.6% for RF and 2.4% for VL. SEM was 0.2 cm2 for RF and 0.5 cm2 for VL. MDC was 0.4 cm2 for RF and 1.3 cm2 for VL. In conclusion, panoramic EFOV US is a highly reliable imaging technique for assessing RF and VL mCSA in middle-aged and elderly adults. These findings endorse the clinical and research utility of EFOV US and its sensitivity for detecting even minor changes in skeletal muscle size.

Contractile regulation of the glucocorticoid-sensitive transcriptome in young and aged skeletal muscle.

Elevated glucocorticoids alter the skeletal muscle transcriptome to induce a myopathy characterized by muscle atrophy, muscle weakness, and decreased metabolic function. These effects are more likely to occur and be more severe in aged muscles. Resistance exercise can blunt the development of glucocorticoid myopathy in young muscle, but the potential to oppose the signals initiating myopathy in aged muscle is unknown. To answer this, young (4-mo-old) and aged (24-to 25-mo-old) male C57BL/6 mice were randomized to receive either an intraperitoneal (IP) injection of dexamethasone (DEX; 2 mg/kg) or saline as a control. Two hours postinjections, the tibialis anterior (TA) muscles of mice were subjected to unilateral high-force contractions. Muscles were harvested 4 h later. The glucocorticoid- and contraction-sensitive genes were determined by RNA sequencing. The number of glucocorticoid-sensitive genes was similar between young and aged muscle. Contractions opposed changes to more glucocorticoid-sensitive genes in aged muscle, with this outcome primarily occurring when hormone levels were elevated. Glucocorticoid-sensitive gene programs opposed by contractions were primarily related to metabolism in young mice and muscle size regulation and inflammation in aged mice. In silico analysis implied peroxisome proliferator-activated receptor gamma-1 (PPARG) contributed to the contraction-induced opposition of glucocorticoid-sensitive genes in aged muscle. Increasing PPARG expression in the TA of aged mice using adeno-associated virus serotype 9 partially counteracted the glucocorticoid-induced reduction in runt-related transcription factor 1 (Runx1) mRNA content, recapitulating the effects observed by contractions. Overall, these data contribute to our understanding of the contractile regulation of the glucocorticoid transcriptome in aged skeletal muscle.NEW & NOTEWORTHY We establish the extent to which muscle contractions oppose changes to the glucocorticoid-sensitive transcriptome in both young and aged muscle. We also identify peroxisome proliferator-activated receptor gamma (PPARG) as a transcription factor likely contributing to contraction-induced opposition to the glucocorticoid transcriptome in aged muscle. Overall, these data contribute to our understanding of the contractile regulation of the glucocorticoid transcriptome.

Postsynaptic BMP signaling regulates myonuclear properties in Drosophila larval muscles.

The syncytial mammalian muscle fiber contains a heterogeneous population of (myo)nuclei. At the neuromuscular junction (NMJ), myonuclei have specialized positioning and gene expression. However, it remains unclear how myonuclei are recruited and what regulates myonuclear output at the NMJ. Here, we identify specific properties of myonuclei located near the Drosophila larval NMJ. These synaptic myonuclei have increased size in relation to their surrounding cytoplasmic domain (size scaling), increased DNA content (ploidy), and increased levels of transcription factor pMad, a readout for BMP signaling activity. Our genetic manipulations show that local BMP signaling affects muscle size, nuclear size, ploidy, and NMJ size and function. In support, RNA sequencing analysis reveals that pMad regulates genes involved in muscle growth, ploidy (i.e., E2f1), and neurotransmission. Our data suggest that muscle BMP signaling instructs synaptic myonuclear output that positively shapes the NMJ synapse. This study deepens our understanding of how myonuclear heterogeneity supports local signaling demands to fine tune cellular function and NMJ activity.

Morphological Changes in the Lumbar and Abdominal Muscles in Individuals with Sacralization

Although sacralization is one of the most common congenital anomalies of the spine, its effect on surrounding muscles is still not well known. This study was conducted to determine the size of the lumbar and abdominal muscles of the individuals with sacralization and to compare with the control group. Eighty-five participants with sacralization phenomena and fifty-six asymptomatic participants were included in this study. Sacralization was classified according to the Castellvi classification. The cross-sectional area of the multifidus lumborum, erector spinae and rectus abdominis muscles, and the section thicknesses of external abdominal oblique, internal abdominal oblique and transversus abdominis muscles were measured bilaterally on axial computed tomography images at the L1-2 and L4-5 levels. ANCOVA revealed that there is no any significant group*side interaction effect regarding muscles sizes in terms of two groups in L1-L2 and L4-L5. In addition, ANCOVA revealed a both side effect [(p=.020; η2p=.038)] and group*side interaction effect [(p=.010; η2p=.049)] regarding length of the L5 transverse process (p˃.05). Regardless of low back pain, muscle sizes are not associated with the sacralization phenomenon.

Prognostic Value of Sarcopenia in Elderly Patients with Metastatic Non-Small-Cell Lung Cancer Undergoing Radiotherapy

Background: Sarcopenia, a syndrome characterized by age-related loss of muscle mass and function, lacks universally accepted diagnostic criteria, particularly for its role as a prognostic factor in elderly patients with non-small-cell lung cancer (NSCLC). This study aimed to evaluate the prognostic significance of sarcopenia, assessed by psoas muscle size on baseline CT scans, in patients over 70 years of age with metastatic NSCLC. Methods: We retrospectively analyzed 85 elderly patients undergoing palliative radiation therapy between August 2022 and July 2024. Using morphometric analysis of psoas size, we investigated its correlation with overall survival (OS) and progression-free survival (PFS). Results: Our results showed that decreased psoas size was significantly associated with shorter OS and PFS, with median OS of 10 months and PFS of 4 months in sarcopenic patients compared to longer survival times in non-sarcopenic patients. Median survival of non-sarcopenic vs. sarcopenic patients was 21 ± 7 months (muscle area &gt; median) versus 5 ± 2.3 months (muscle area &lt; median). Multivariate analysis confirmed that psoas size, along with ECOG performance status and treatment of primary NSCLC, was a significant predictor of survival. Discussion: These findings suggest that psoas muscle size is a valuable prognostic marker for elderly NSCLC patients, potentially guiding treatment decisions and patient management. Further research is needed to validate these results and refine prognostic models for this population.

Skeletal muscle size and quality in healthy kidney donors, normal range and clinical associations

The gold standard to estimate muscle mass and quality is computed tomography (CT) scan. Lower mass and density (intramuscular fat infiltration) of skeletal muscles are markers of sarcopenia, associated with increased mortality risk, impaired physical function, and poorer prognosis across various populations and medical conditions. We aimed to describe standard reference values in healthy population, prospective kidney donors, and correlate clinical parameters to muscle mass and density. Included in the cohort 384 consecutive kidney donors. Mean age was 44.6 ± 11.5 (range 18.4–74.2), 46% were female and mean BMI was 25.6 ± 3.8 kg/m2. Our quantified reference values for psoas cross -sectional area (CSA) index at L3 level (males/females respectively) were 6.3 ± 1.8 and 4.8 ± 1.9 cm2 /m2, and density was 46.1 ± 5 and 41 ± 5 HU at that level. Older age (standardized beta coefficient − 0.12, p = 0.04), sex (− 0.32, p < 0.001) and BMI (0.17, p = 0.002) were significantly associated with CSA index of psoas at L3. Density, however, was associated with triglycerides level (− 0.21, p < 0.001), in addition to age (− 0.22, p < 0.0001), sex (− 0.27, p < 0.001) and BMI (− 0.1, p = 0.05). Our study validates the normative values of psoas muscle mass and density in healthy individuals and suggests correlations with clinical parameters. We demonstrate the significance of measuring not only the mass of the muscle, but also its density, as it has a valid association with metabolic parameters, including BMI and lipid level, even in healthy individuals and in the normal range of the tests.

Arrangements of intramembranous muscles of wings are influenced by body mass across the radiation of phyllostomid bats.

Extensive research into bat flight mechanisms has highlighted the complex functional and evolutionary dynamics of their wing structures, yet the anatomical details of certain wing muscles remain elusive. In particular, the intramembranous plagiopatagiales proprii muscles, located within the plagiopatagium-an area of the wing lacking direct joint connections-exhibit remarkable variation across bat families. These muscles, which extend anteroposteriorly in macroscopic bundles, play a crucial role in wing stiffening, modulating membrane tension, and reducing wing curvature during flight. Since larger bats tend to have higher wing loading (WL; the ratio of body mass [BMa] to wing area) and may therefore experience increased patagial curvature and resultant drag, we hypothesized that body size significantly influences the evolutionary development of the plagiopatagiales proprii muscles. This study investigates the relationship between BMa and the morphology of the plagiopatagiales proprii in New World leaf-nosed bats (Phyllostomidae), employing bivariate allometry, multivariate analysis, and comparative phylogenetic methods across 24 species from eight phyllostomid subfamilies. Our findings reveal a significant phylogenetic signal in muscle architecture, along with positive evolutionary allometry in muscle area. This suggests an adaptive increase in muscle size in larger species, likely to counterbalance the increased WL, reduce wing curvature, and minimize drag. This research enhances our understanding of the functional and adaptive morphological evolution of intramembranous wing muscles in phyllostomid bats, underscoring their evolutionary significance.

Ultrasound visualization of Botulinum toxin injection: Identifying clinical correlates to optimize outcomes in spasticity management.

Botulinum toxin injections are well established and commonly used for spasticity management. Clinicians strive to optimize outcomes from toxin injections. One potential complication is toxin spread beyond the intended muscle, which can lead to unwanted weakness. The utilization of ultrasound allows direct visualization of target muscles and identification of toxin leakage from the target muscle. Ultrasound evaluation of clinical factors that correlate to toxin leakage have not been studied. To identify cases of botulinum toxin injectate leak beyond the targeted muscle during ultrasound-guided spasticity injections and associate cases of leak with predictive clinical factors, which include muscle size, fibroadipose changes, and number of previous injections. This was a prospective observational study. An outpatient clinic in an academic medical center. Patients who demonstrated wrist flexor spasticity warranting intervention were invited to participate. Patients received standard-of-care spasticity management with injection of onabotulinumtoxinA into the flexor carpi radialis muscle based upon clinical presentation and prescribing guidelines. Ultrasound video was recorded, and a blinded review was conducted by the study team. The primary outcome measure was visualized leak of injectate on recorded ultrasound video. Documented leak was then associated with clinical factors including diameter of the flexor carpi radialis, volume of injectate used, history of prior injections, and fibrotic change of the muscle. The study included 54 patients, 77.8% of whom had an underlying diagnosis of cerebrovascular accident. Injectate leak was observed in 18.5% of injections and could not be confirmed in 9.3% of injections. Multivariable analysis demonstrated increased odds of leak with higher Modified Heckmatt Scale score. No statistically significant increase in leak was noted with higher volume of injectate or smaller muscle diameter. Extramuscular leak of botulinum toxin injection may be associated with fibroadipose muscle change.

Muscular Hypertrophy and its Relation to Strength Performance: A Physics-Based Analysis of Conceptual Inaccuracies

ABSTRACT The interchangeable use of terms such as muscle mass, volume, cross-sectional area, and thickness in discussions on the physiology of muscle hypertrophy has led to misconceptions in research and practice. This review aims to highlight the improperness of this approach and highlights the overlooked parameter of muscular density (MD). The hypothesis is that muscle density acts as a mediator, leading to inevitable muscle enlargement in long-term strength training. It is proposed that research in muscular adaptations to training should implement measures of MD to complement measurements of muscle size. This article aims to refine the understanding of muscular adaptations and optimize training strategies for athletes and fitness enthusiasts.

Effects of Resistance Training Volume on Physical Function, Lean Body Mass and Lower-Body Muscle Hypertrophy and Strength in Older Adults: A Systematic Review and Network Meta-analysis of 151 Randomised Trials.

The optimal prescription and precise recommendations of resistance training volume for older adults is unclear in the current literature. In addition, the interactions between resistance training volume and program duration as well as physical health status remain to be determined when assessing physical function, muscle size and hypertrophy and muscle strength adaptations in older adults. This study aimed to determine which resistance training volume is the most effective in improving physical function, lean body mass, lower-limb muscle hypertrophy and strength in older adults. Additionally, we examined whether effects were moderated by intervention duration (i.e. short term, < 20weeks; medium-to-long term, ≥ 20weeks) and physical health status (i.e. physically healthy, physically impaired, mixed physically healthy and physically impaired; PROSPERO identifier: CRD42023413209). CINAHL, Embase, LILACS, PubMed, Scielo, SPORTDiscus and Web of Science databases were searched up to April 2023. Eligible randomised trials examined the effects of supervised resistance training in older adults (i.e. ≥ 60years). Resistance training programs were categorised as low (LVRT), moderate (MVRT) and high volume (HVRT) on the basis of terciles of prescribed weekly resistance training volume (i.e. product of frequency, number of exercises and number of sets) for full- and lower-body training. The primary outcomes for this review were physical function measured by fast walking speed, timed up and go and 6-min walking tests; lean body mass and lower-body muscle hypertrophy; and lower-body muscle strength measured by knee extension and leg press one-repetition maximum (1-RM), isometric muscle strength and isokinetic torque. A random-effects network meta-analysis was undertaken to examine the effects of different resistance training volumes on the outcomes of interest. We included a total of 161 articles describing 151 trials (n = 6306). LVRT was the most effective for improving timed up and go [- 1.20 standardised mean difference (SMD), 95% confidence interval (95% CI): - 1.57 to - 0.82], 6-min walk test (1.03 SMD, 95% CI: 0.33-1.73), lean body mass (0.25 SMD, 95% CI: 0.10-0.40) and muscle hypertrophy (0.40 SMD, 95% CI: 0.25-0.54). Both MVRT and HVRT were the most effective for improving lower-limb strength, while only HVRT was effective in increasing fast walking speed (0.40 SMD, 95% CI: - 0.57 to 0.14). Regarding the moderators, our results were independent of program duration and mainly observed for healthy older adults, while evidence was limited for those who were physically impaired. A low resistance training volume can substantially improve healthy older adults' physical function and benefits lean mass and muscle size independently of program duration, while a higher volume seems to be necessary for achieving greater improvements in muscle strength. A low volume of resistance training should be recommended in future exercise guidelines, particularly for physically healthy older adults targeting healthy ageing.

Bioavailable testosterone and androgen receptor activation, but not total testosterone, are associated with muscle mass and strength in females.

Testosterone, the major androgen, influences the reproductive and non-reproductive systems in males and females via binding to the androgen receptor (AR). Both circulating endogenous testosterone and muscle AR protein content are positively associated with muscle mass and strength in males, but there is no such evidence in females. Here, we tested whether circulating testosterone levels were associated with muscle mass, function, or the muscle anabolic response to resistance training in pre-menopausal females. Twenty-seven pre-menopausal, untrained females (aged 23.5 ± 4.8 years) underwent a 12-week resistance training programme. Muscle strength, size, power, and plasma and urine androgen hormone levels were measured. Skeletal muscle biopsies were collected before and after the training programme to quantify the effect of resistance training on AR content and nuclear localisation. Primary muscle cell lines were cultured from a subset (n=6) of the participants' biopsies and treated with testosterone to investigate its effect on myotube diameter, markers of muscle protein synthesis and AR cellular localisation. Physiological levels of total testosterone were not associated with muscle mass or strength at baseline or with the changes in muscle mass and strength that occurred in response to resistance training in our cohort of pre-menopausal females. In contrast, bioavailable testosterone and the proportion of nuclear-localised AR were positively associated with skeletal muscle mass and strength in pre-menopausal females. In vitro, supra-physiological doses of testosterone increased myocyte diameter, but this did not occur via the Akt/mTOR pathway as previously suggested. Instead, we show a marked increase in AR nuclear localisation with testosterone administration in vitro. KEY POINTS: Total circulating testosterone was not related to muscle mass or strength before or after resistance training in pre-menopausal females. Bioavailable testosterone was positively related to exercise-induced muscle hypertrophy in pre-menopausal females. In vivo nuclear localisation of the androgen receptor was positively related to muscle mass in pre-menopausal females at baseline, but not to resistance training-induced hypertrophy. Testosterone treatment induced androgen receptor nuclear translocation but did not induce mTOR signalling in primary skeletal myocytes cultured from pre-menopausal female muscle.

The Role of Cystic Fibrosis Transmembrane Conductance Regulator in Skeletal Muscle Contractile Function

Purpose: Genetic mutations in cystic fibrosis (CF) result in CF transmembrane conductance regulator (CFTR) dysfunction. CFTR is expressed in human skeletal muscle; its effect on skeletal muscle abnormalities is unknown. The study objective is to investigate the role of CFTR in skeletal muscle contractile function. Methods: We conducted a prospective, cross-sectional study comparing 34 adults with minimal and 18 with residual function CFTR mutations, recruited from Toronto Adult CF Centre, St. Michael's Hospital, Unity Health Toronto. Quadriceps, biceps brachii, and handgrip strength was measured with dynamometers; leg muscle power with the stair climb power test. Quadriceps muscle contractility was determined by quadriceps muscle strength normalized to quadriceps muscle size, measured with ultrasound images. Multivariable regression was used for analysis. Results: People with residual function CFTR mutations had higher quadriceps muscle torque normalized to quadriceps layer thickness and to rectus femoris cross-sectional area by 27.5 Nm/cm [95% CI (2.2, 52.8) Nm/cm, P = .034] and 5.6 Nm/cm2 [95% CI (0.3, 10.9) Nm/cm2, P = .041], respectively, compared with those with minimal function CFTR mutations. There were no differences in quadriceps muscle torque (P = .58), leg muscle power (P = .47), biceps brachii muscle force (P = .14), or handgrip force (P = .12) between the 2 mutation groups. Conclusions: CFTR protein may play a role in muscle contractility, implying a limited capacity to exert muscle force per unit of muscle size in people with CF. This suggests that building a greater muscle mass through resistance exercises focusing on muscle hypertrophy in exercise prescription may improve muscle strength in people with CF.

7945 Modelling the Factors Associated With Sexual and Mood Symptoms Within the First Year of Anabolic-Androgenic Steroid Cessation in Men

Abstract Disclosure: B. Grant: None. J. Kean: None. N.L. de Silva: None. O. Quinton: None. P. Bassett: None. J. McVeigh: None. A. Lingford-Hughes: None. S. Minhas: None. S. Bhasin: None. W.S. Dhillo: None. C.N. Jayasena: None. Context: Anabolic-androgenic steroids (AAS) are misused by millions of men worldwide to boost muscle size and physical performance. Recent studies have quantified the recovery of cardiovascular markers and testicular function following AAS cessation. Qualitative studies demonstrate that low mood, anxiety, suicidal ideation, and sexual dysfunction are also common following AAS cessation. However, no previous study has focused on quantifying symptoms within the first year of AAS cessation, nor investigated independently associated factors for these symptoms. Methods: Cross-sectional, observational study of 165 men in 3 groups; non-AAS (n=43); current-AAS (n=76); past-AAS ≤1 year (n=46). All participants completed questions on substance misuse, Beck Depression Inventory-II (BDI-II), International Index Erectile Function-15 (IIEF-15), General Anxiety Disorder (GAD-7), Quality-of-life (SF-36), and underwent fasting, morning blood sampling with urine toxicology. Results: As expected, current-AAS had lower gonadotropins and elevated serum total testosterone compared with past-AAS and non-AAS. Sexual function measured using IIEF-15 was impaired in men stopping AAS &amp;lt;1year (past-AAS) compared with current AAS users: (1) total: 69.0 [95% CI 64.0, 71.0], current-AAS; 61.0 [95% CI 56.0, 66.0], past-AAS; p=0.077; (2) erectile function: 30.0 [95% CI 29.0, 30.0], current-AAS; 28 [95% CI 21.0, 29.0], past-AAS; p=0.015; (3) sexual desire: 9.0 [95% CI 8.0, 10.0], current-AAS; 6.0 [95% CI 5.0, 8.0], past-AAS; p&amp;lt;0.0001; (4) overall satisfaction: 10.0 [95% CI 8.0, 10.0], current-AAS; 7.0 [95% CI 7.0, 8.0], past-AAS; p=0.002. Multivariable analysis suggested that psychiatric comorbidity (coefficient -6.5 [95% CI -13.0, -1.3] p=0.03) and AAS cessation (coefficient -10.8 [95% CI -5.6, -17.2]; p&amp;lt;0.001) were associated with lower total IIEF-15 scores.Depression scoring was worse in the past-AAS group compared with non-AAS: BDI-II 4.0 [95% CI 2.0, 7.0], non-AAS; 7.0 [95% CI 4.0, 16.0], past-AAS; p=0.0448. Multivariable analysis suggested that psychiatric comorbidity (OR 2.39 [95% CI 1.60, 3.57]; p&amp;lt;0.001) and lower serum total testosterone (OR 0.85 [95% CI 0.88, 0.94]; p=0.002) were associated with higher BDI-II scores.Energy and fatigue measured using SF-36 was lower in the past-AAS group compared with non-AAS: 70 [95% CI 65, 75], non-AAS; 60 [95% CI 50, 65], past-AAS; p=0.0498. No significant differences in anxiety scoring were detected. Discussion: We report the first, detailed quantification and modelling of symptoms in men currently misusing and stopped AAS within the previous year. These data reveal potentially treatable factors to improve symptoms of AAS cessation if proven within interventional studies. Presentation: 6/2/2024

7945 Modelling the Factors Associated With Sexual and Mood Symptoms Within the First Year of Anabolic-Androgenic Steroid Cessation in Men

Abstract Disclosure: B. Grant: None. J. Kean: None. N.L. de Silva: None. O. Quinton: None. P. Bassett: None. J. McVeigh: None. A. Lingford-Hughes: None. S. Minhas: None. S. Bhasin: None. W.S. Dhillo: None. C.N. Jayasena: None. Context: Anabolic-androgenic steroids (AAS) are misused by millions of men worldwide to boost muscle size and physical performance. Recent studies have quantified the recovery of cardiovascular markers and testicular function following AAS cessation. Qualitative studies demonstrate that low mood, anxiety, suicidal ideation, and sexual dysfunction are also common following AAS cessation. However, no previous study has focused on quantifying symptoms within the first year of AAS cessation, nor investigated independently associated factors for these symptoms. Methods: Cross-sectional, observational study of 165 men in 3 groups; non-AAS (n=43); current-AAS (n=76); past-AAS ≤1 year (n=46). All participants completed questions on substance misuse, Beck Depression Inventory-II (BDI-II), International Index Erectile Function-15 (IIEF-15), General Anxiety Disorder (GAD-7), Quality-of-life (SF-36), and underwent fasting, morning blood sampling with urine toxicology. Results: As expected, current-AAS had lower gonadotropins and elevated serum total testosterone compared with past-AAS and non-AAS. Sexual function measured using IIEF-15 was impaired in men stopping AAS &amp;lt;1year (past-AAS) compared with current AAS users: (1) total: 69.0 [95% CI 64.0, 71.0], current-AAS; 61.0 [95% CI 56.0, 66.0], past-AAS; p=0.077; (2) erectile function: 30.0 [95% CI 29.0, 30.0], current-AAS; 28 [95% CI 21.0, 29.0], past-AAS; p=0.015; (3) sexual desire: 9.0 [95% CI 8.0, 10.0], current-AAS; 6.0 [95% CI 5.0, 8.0], past-AAS; p&amp;lt;0.0001; (4) overall satisfaction: 10.0 [95% CI 8.0, 10.0], current-AAS; 7.0 [95% CI 7.0, 8.0], past-AAS; p=0.002. Multivariable analysis suggested that psychiatric comorbidity (coefficient -6.5 [95% CI -13.0, -1.3] p=0.03) and AAS cessation (coefficient -10.8 [95% CI -5.6, -17.2]; p&amp;lt;0.001) were associated with lower total IIEF-15 scores.Depression scoring was worse in the past-AAS group compared with non-AAS: BDI-II 4.0 [95% CI 2.0, 7.0], non-AAS; 7.0 [95% CI 4.0, 16.0], past-AAS; p=0.0448. Multivariable analysis suggested that psychiatric comorbidity (OR 2.39 [95% CI 1.60, 3.57]; p&amp;lt;0.001) and lower serum total testosterone (OR 0.85 [95% CI 0.88, 0.94]; p=0.002) were associated with higher BDI-II scores. Energy and fatigue measured using SF-36 was lower in the past-AAS group compared with non-AAS: 70 [95% CI 65, 75], non-AAS; 60 [95% CI 50, 65], past-AAS; p=0.0498. No significant differences in anxiety scoring were detected. Discussion: We report the first, detailed quantification and modelling of symptoms in men currently misusing and stopped AAS within the previous year. These data reveal potentially treatable factors to improve symptoms of AAS cessation if proven within interventional studies. Presentation: 6/2/2024

Evaluation of the reliability of measuring lower back muscles cross-sectional area based on manual segmentation within multi-level MRI images

IntroductionManual segmentation of paraspinal muscle cross-sectional area (CSA) is widely used to assess related health disorders. This study aimed to evaluate the reliability of this segmentation process for each paraspinal region of interest across the three intervertebral levels commonly used for segmentation (L3/4, L4/5, and L5/S1). MethodsAxial-T2-weighted MRI images for 238 patients were divided among five raters (47 ± 1 cases each). To conduct the intra-rater reliability study, the CSA of each paraspinal lumber muscle (psoas major (PM), multifidus (MF), and erector spinae (ES)) and the intervertebral disc (ID) were manually segmented twice on all targeted levels before being assessed for each region per rater. The Inter-rater reliability was determined by comparing the results of different readers who segmented the same dataset. The Intraclass Correlation (ICC) and Coefficient-of-Variation percentage (CV%) were reported for each analysis. ResultsLow intra- and inter-rater variability (CV%<11) was found for each reader in each region and intervertebral level. The inter-rater reliability was excellent (ICC>0.9) for the PM, ID, and ES at L3/4. However, it was very good for MF at all levels and ES at L4/5, L5/S1 (ICC range: 0.82–0.88) affected by the fat-infiltration nature of the ES and MF muscles, their proximity to each other, and their smaller size (correlation between muscle size and ICC = 0.6, P < 0.01). The ID segmentation has the lowest CV (<3 %) and excellent ICC (>0.93). ConclusionManual paraspinal muscle segmentation using axial-T2-weighted MRI is reliable at all commonly segmented intervertebral levels. However, the reliability level can be degraded by the presence of high-fat infiltrate, unclear muscle boundaries, and muscle size. Implications for practiceFollowing consistent guidelines can help improve segmentation results. The IDs can be used as reliable internal references.