Increase In Muscle Cross-sectional Area Research Articles

A novel computational framework for the estimation of internal musculoskeletal loading and muscle adaptation in hypogravity.

Introduction: Spaceflight is associated with substantial and variable musculoskeletal (MSK) adaptations. Characterisation of muscle and joint loading profiles can provide key information to better align exercise prescription to astronaut MSK adaptations upon return-to-Earth. A case-study is presented of single-leg hopping in hypogravity to demonstrate the additional benefit computational MSK modelling has when estimating lower-limb MSK loading. Methods: A single male participant performed single-leg vertical hopping whilst attached to a body weight support system to replicate five gravity conditions (0.17, 0.25, 0.37, 0.50, 1 g). Experimental joint kinematics, joint kinetics and ground reaction forces were tracked in a data-tracking direct collocation simulation framework. Ground reaction forces, sagittal plane hip, knee and ankle net joint moments, quadriceps muscle forces (Rectus Femoris and three Vasti muscles), and hip, knee and ankle joint reaction forces were extracted for analysis. Estimated quadriceps muscle forces were input into a muscle adaptation model to predict a meaningful increase in muscle cross-sectional area, defined in (DeFreitas et al., 2011). Results: Two distinct strategies were observed to cope with the increase in ground reaction forces as gravity increased. Hypogravity was associated with an ankle dominant strategy with increased range of motion and net plantarflexor moment that was not seen at the hip or knee, and the Rectus Femoris being the primary contributor to quadriceps muscle force. At 1 g, all three joints had increased range of motion and net extensor moments relative to 0.50 g, with the Vasti muscles becoming the main muscles contributing to quadriceps muscle force. Additionally, hip joint reaction force did not increase substantially as gravity increased, whereas the other two joints increased monotonically with gravity. The predicted volume of exercise needed to counteract muscle adaptations decreased substantially with gravity. Despite the ankle dominant strategy in hypogravity, the loading on the knee muscles and joint also increased, demonstrating this provided more information about MSK loading. Discussion: This approach, supplemented with muscle-adaptation models, can be used to compare MSK loading between exercises to enhance astronaut exercise prescription.

Therapeutic Consequences of Targeting the IGF-1/PI3K/AKT/FOXO3 Axis in Sarcopenia: A Narrative Review.

The high prevalence of sarcopenia in an aging population has an underestimated impact on quality of life by increasing the risk of falls and subsequent hospitalization. Unfortunately, the application of the major established key therapeutic-physical activity-is challenging in the immobile and injured sarcopenic patient. Consequently, novel therapeutic directions are needed. The transcription factor Forkhead-Box-Protein O3 (FOXO3) may be an option, as it and its targets have been observed to be more highly expressed in sarcopenic muscle. In such catabolic situations, Foxo3 induces the expression of two muscle specific ubiquitin ligases (Atrogin-1 and Murf-1) via the PI3K/AKT pathway. In this review, we particularly evaluate the potential of Foxo3-targeted gene therapy. Foxo3 knockdown has been shown to lead to increased muscle cross sectional area, through both the AKT-dependent and -independent pathways and the reduced impact on the two major downstream targets Atrogin-1 and Murf-1. Moreover, a Foxo3 reduction suppresses apoptosis, activates satellite cells, and initiates their differentiation into muscle cells. While this indicates a critical role in muscle regeneration, this mechanism might exhaust the stem cell pool, limiting its clinical applicability. As systemic Foxo3 knockdown has also been associated with risks of inflammation and cancer progression, a muscle-specific approach would be necessary. In this review, we summarize the current knowledge on Foxo3 and conceptualize a specific and targeted therapy that may circumvent the drawbacks of systemic Foxo3 knockdown. This approach presumably would limit the side effects and enable an activity-independent positive impact on skeletal muscle.

NOX2 deficiency exacerbates diet-induced obesity and impairs molecular training adaptations in skeletal muscle

The production of reactive oxygen species (ROS) by NADPH oxidase (NOX) 2 has been linked to both insulin resistance and exercise training adaptations in skeletal muscle. This study explores the previously unexamined role of NOX2 in the interplay between diet-induced insulin resistance and exercise training (ET). Using a mouse model that harbors a point mutation in the essential NOX2 regulatory subunit, p47phox (Ncf1*), we investigated the impact of this mutation on various metabolic adaptations. Wild-type (WT) and Ncf1* mice were assigned to three groups: chow diet, 60% energy fat diet (HFD), and HFD with access to running wheels (HFD + E). After a 16-week intervention, a comprehensive phenotypic assessment was performed, including body composition, glucose tolerance, energy intake, muscle insulin signaling, redox-related proteins, and mitochondrial adaptations. The results revealed that NOX2 deficiency exacerbated the impact of HFD on body weight, body composition, and glucose intolerance. Moreover, in Ncf1* mice, ET did not improve glucose tolerance or increase muscle cross-sectional area. ET normalized body fat independently of genotype. The lack of NOX2 activity during ET reduced several metabolic adaptations in skeletal muscle, including insulin signaling and expression of Hexokinase II and oxidative phosphorylation complexes. In conclusion, these findings suggest that NOX2 mediates key beneficial effects of exercise training in the context of diet-induced obesity.

Effects of free weight and body mass-based resistance training on thigh muscle size, strength and intramuscular fat in healthy young and middle-aged individuals.

What is the central question of this study? How do free weight resistance training (RT) and body mass-based RT for 8weeks compare for isometric muscular strength, muscle size and intramuscular fat (IMF) content in the quadriceps femoris? What is the main finding and its importance? Free weight and body mass-based RTs could induce muscle hypertrophy; however, decreased IMF content was observed following the body mass-based RT alone. The objective of this study was to investigate the effects of free weight and body mass-based resistance training (RT) on muscle size and thigh intramuscular fat (IMF) in young and middle-aged individuals. Healthy individuals (aged 30-64years) were assigned to either a free weight RT group (n=21) or a body mass-based RT group (n=16). Both groups performed whole-body resistance exercise twice a week for 8weeks. Free weight resistance exercises (squats, bench press, deadlift, dumbbell rows and back range) involved 70% one repetition maximum, with three sets of 8-12 repetitions per exercise. The nine body mass-based resistance exercises (leg raise, squats, rear raise, overhead shoulder mobility exercise, rowing, dips, lunge, single-leg Romanian deadlifts and push-ups) included the maximum possible repetitions per session, which were performed in one or two sets. Mid-thigh magnetic resonance images using the two-point Dixon method were taken pre- and post-training. The muscle cross-sectional area (CSA) and IMF content in the quadriceps femoris were measured from the images. Both the groups showed significantly increased muscle CSA post-training (free weight RT group, P=0.001; body mass-based RT group, P=0.002). IMF content in the body mass-based RT group significantly decreased (P=0.036) but did not significantly change in the free weight RT group (P=0.076). These results suggest that the free weight and body mass-based RTs could induce muscle hypertrophy; however, in healthy young and middle-aged individuals, decreased IMF content was induced following the body mass-based RT alone.

Myofiber hypertrophy adaptations following 6 weeks of low-load resistance training with blood flow restriction in untrained males and females.

The effects of low-load resistance training with blood flow restriction (BFR) on hypertrophy of type I/II myofibers remains unclear, especially in females. The purpose of the present study is to examine changes in type I/II myofiber cross-sectional area (fCSA) and muscle CSA (mCSA) of the vastus lateralis (VL) from before (Pre) to after (Post) 6 wk of high-load resistance training (HL; n = 15, 8 females) and low-load resistance training with BFR (n = 16, 8 females). Mixed-effects models were used to analyze fCSA with group (HL, BFR), sex (M, F), fiber type (I, II), and time (Pre, Post) included as factors. mCSA increased from pre- to posttraining (P < 0.001, d = 0.91) and was greater in males compared with females (P < 0.001, d = 2.26). Type II fCSA increased pre- to post-HL (P < 0.05, d = 0.46) and was greater in males compared with females (P < 0.05, d = 0.78). There were no significant increases in fCSA pre- to post-BFR for either fiber type or sex. Cohen's d, however, revealed moderate effect sizes in type I and II fCSA for males (d = 0.59 and 0.67), although this did not hold true for females (d = 0.29 and 0.34). Conversely, the increase in type II fCSA was greater for females than for males after HL. In conclusion, low-load resistance training with BFR may not promote myofiber hypertrophy to the level of HL resistance training, and similar responses were generally observed for males and females. In contrast, comparable effect sizes for mCSA and 1-repetition maximum (1RM) between groups suggest that BFR could play a role in a resistance training program.NEW & NOTEWORTHY This is the first study, to our knowledge, to examine myofiber hypertrophy from low-load resistance training with blood flow restriction (BFR) in females. Although this type of training did not result in myofiber hypertrophy, there were comparable increases in muscle cross-sectional area compared with high-load resistance training. These findings possibly highlight that males and females respond in a similar manner to high-load resistance training and low-load resistance training with BFR.

Lumican, an Exerkine, Protects against Skeletal Muscle Loss.

Exerkines are soluble factors secreted by exercised muscles, mimicking the effects of exercise in various organs, including the muscle itself. Lumican is reportedly secreted from muscles; however, its roles in skeletal muscle remain unknown. Herein, we found that lumican mRNA expression in the extensor digitorum longus was significantly higher in exercised mice than in unloading mice, and lumican stimulated myogenesis in vitro. Additionally, lumican knockdown significantly decreased muscle mass and cross-sectional area (CSA) of the muscle fiber in the gastrocnemius muscle of exercised mice. Lumican upregulated phosphorylation of p38 mitogen-activated protein kinase (MAPK) and a p38 inhibitor near completely blocked lumican-stimulated myogenesis. Inhibitors for integrin α2β1 and integrin ανβ3 also prevented lumican-stimulated myogenesis. Systemic lumican treatment, administered via the tail vein for 4 weeks, significantly increased relative muscle masses by 36.1% in ovariectomized mice. In addition, intramuscular lumican injection into unloaded muscles for 2 weeks significantly increased muscle mass by 8.5%. Both intravenous and intramuscular lumican treatment significantly increased muscle CSA. Our in vitro and in vivo experiments indicate that lumican is a muscle-secreted exerkine that affords protection against muscle loss by activating p38 MAPK via integrin receptors.

Effects of Blood Flow Restriction Combined With Resistance Training or Neuromuscular Electrostimulation on Muscle Cross-Sectional Area.

Low-load resistance training (LL) and neuromuscular electrostimulation (NES), both combined with blood flow restriction (BFR), emerge as effective strategies to maintain or increase muscle mass. It is well established that LL-BFR promotes similar increases in muscle cross-sectional area (CSA) and lower rating of perceived exertion (RPE) and pain compared with traditional resistance training protocols. On the other hand, only 2 studies with conflicting results have investigated the effects of NES-BFR on CSA, RPE, and pain. In addition, no study directly compared LL-BFR and NES-BFR. The aim of the study was to compare the effects of LL-BFR and NES-BFR on vastus lateralis CSA, RPE, and pain. Individual response for muscle hypertrophy was also compared between protocols. Intrasubject longitudinal study. University research laboratory. Fifteen healthy young males (age = 23 [5]y; weight = 77.6 [11.3]kg; height = 1.76 [0.08]m). Vastus lateralis CSA was measured through ultrasound at baseline (pre) and after 20 training sessions (post). The RPE and pain responses were obtained through modified 10-point scales, handled during all training sessions. Both protocols demonstrated significant increases in muscle CSA (P < .0001). However, the LL-BFR demonstrated significantly greater CSA changes compared with NES-BFR (LL-BFR = 11.2%, NES-BFR = 4.6%; P < .0001). Comparing individual increases in CSA, 12 subjects (85.7% of the sample) presented greater muscle hypertrophy for LL-BFR than for the NES-BFR protocol. In addition, LL-BFR produced significantly lower RPE and pain responses (P < .0001). The LL-BFR produced significantly greater increases in CSA with significant less RPE and pain than NES-BFR. In addition, LL-BFR resulted in greater individual muscle hypertrophy responses for most subjects compared with NES-BFR.

Body Composition Predictors of Adverse Postoperative Events in Patients Undergoing Surgery for Long Bone Metastases.

Introduction:Body composition assessed using opportunistic CT has been recently identified as a predictor of outcome in patients with cancer. The purpose of this study was to determine whether the cross-sectional area (CSA) and the attenuation of abdominal subcutaneous adipose tissue, visceral adipose tissue (VAT), and paraspinous and abdominal muscles are the predictors of length of hospital stay, 30-day postoperative complications, and revision surgery in patients treated for long bone metastases.Methods:A retrospective database of patients who underwent surgery for long bone metastases from 1999 to 2017 was used to identify 212 patients who underwent preoperative abdominal CT. CSA and attenuation measurements for subcutaneous adipose tissue, VAT, and muscles were taken at the level of L4 with the aid of an in-house segmentation algorithm. Bivariate and multivariate linear and logistic regression models were created to determine associations between body composition measurements and outcomes while controlling for confounders, including primary tumor, metastasis location, and preoperative albumin.Results:On multivariate analysis, increased VAT CSA {regression coefficient (r) (95% confidence interval [CI]); 0.01 (0.01 to 0.02); P < 0.01} and decreased muscle attenuation (r [95% CI] −0.07 [−0.14 to −0.01]; P = 0.04) were associated with an increased length of hospital stay. In bivariate analysis, increased muscle CSA was associated with increased chance of revision surgery (odds ratio [95% CI]; 1.02 [1.01 to 1.03]; P = 0.04). No body composition measurements were associated with postoperative complications within 30 days.Discussion:Body composition measurements assessed using opportunistic CT predict adverse postoperative outcomes in patients operated for long bone metastases.

Intrinsic contractile dysfunction in a surgical model of muscle hypertrophy

Synergistic ablation (SA) is widely used to induce muscle hypertrophy in rodent studies. However, it has been demonstrated that SA-induced compensatory hypertrophy induces increases in maximum isometric force that are smaller in magnitude than the increase in muscle cross-sectional area, suggesting a reduction in the specific force production due to intrinsic contractile dysfunction in the hypertrophied fibers. Here, by using the mechanical skinned fibers, we investigated the mechanisms behind the reduction in specific force in the compensatory hypertrophied muscles. Rats had unilateral surgical ablation of the gastrocnemius and soleus muscles to induce the compensatory hypertrophy in the plantaris muscles. Two wk after surgery, the mean fiber diameter was increased by 19% in the SA group compared with the contralateral control (CNT) group. In contrast, compared with the CNT group, both the depolarization-induced force (-51%) and the Ca2+-activated maximum specific force (-32%) were markedly reduced in skinned fibers from the SA group. These deleterious functional alterations were accompanied by decreases in the amount of DHPRα1, RYR, junctophilin 1, and SH3 and cysteine-rich domain 3 (STAC3) in SA muscles. Thus, these data clearly show that SA induces not only an increase in skeletal muscle fiber hypertrophy but also leads to a reduction in the intrinsic contractile dysfunction due to the excitation-contraction uncoupling and impaired force-generating capacity.

Comparative analysis of Dipodomys species indicates that kangaroo rat hindlimb anatomy is adapted for rapid evasive leaping.

Body size is a key factor that influences antipredator behavior. For animals that rely on jumping to escape from predators, there is a theoretical trade-off between jump distance and acceleration as body size changes at both the inter- and intraspecific levels. Assuming geometric similarity, acceleration will decrease with increasing body size due to a smaller increase in muscle cross-sectional area than body mass. Smaller animals will likely have a similar jump distance as larger animals due to their shorter limbs and faster accelerations. Therefore, in order to maintain acceleration in a jump across different body sizes, hind limbs must be disproportionately bigger for larger animals. We explored this prediction using four species of kangaroo rats (Dipodomys spp.), a genus of bipedal rodent with similar morphology across a range of body sizes (40-150g). Kangaroo rat jump performance was measured by simulating snake strikes to free-ranging individuals. Additionally, morphological measurements of hind limb muscles and segment lengths were obtained from thawed frozen specimens. Overall, jump acceleration was constant across body sizes and jump distance increased with increasing size. Additionally, kangaroo rat hind limb muscle mass and cross-sectional area scaled with positive allometry. Ankle extensor tendon cross-sectional area also scaled with positive allometry. Hind limb segment length scaled isometrically, with the exception of the metatarsals, which scaled with negative allometry. Overall, these findings support the hypothesis that kangaroo rat hind limbs are built to maintain jump acceleration rather than jump distance. Selective pressure from single-strike predators, such as snakes and owls, likely drives this relationship.

Chronic Sequelae After Muscle Strain Injuries: Influence of Heavy Resistance Training on Functional and Structural Characteristics in a Randomized Controlled Trial

Background: Muscle strain injury leads to a high risk of recurrent injury in sports and can cause long-term symptoms such as weakness and pain. Scar tissue formation after strain injuries has been described, yet what ultrastructural changes might occur in the chronic phase of this injury have not. It is also unknown if persistent symptoms and morphological abnormalities of the tissue can be mitigated by strength training. Purpose: To investigate if heavy resistance training improves symptoms and structural abnormalities after strain injuries. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A total of 30 participants with long-term weakness and/or pain after a strain injury of the thigh or calf muscles were randomized to eccentric heavy resistance training of the injured region or control exercises of the back and abdominal muscle. Isokinetic (hamstring) or isometric (calf) muscle strength was determined, muscle cross-sectional area measured, and pain and function evaluated. Scar tissue ultrastructure was determined from biopsy specimens taken from the injured area before and after the training intervention. Results: Heavy resistance training over 3 months improved pain and function, normalized muscle strength deficits, and increased muscle cross-sectional area in the previously injured region. No systematic effect of training was found upon pathologic infiltration of fat and blood vessels into the previously injured area. Control exercises had no effect on strength, cross-sectional area, or scar tissue but a positive effect on patient-related outcome measures, such as pain and functional scores. Conclusion: Short-term strength training can improve sequelae symptoms and optimize muscle function even many years after a strain injury, but it does not seem to influence the overall structural abnormalities of the area with scar tissue. Registration: NCT02152098 (ClinicalTrials.gov identifier).

Exercise-induced fluid shifts are distinct to exercise mode and intensity: a comparison of blood flow-restricted and free-flow resistance exercise.

MRI can provide fundamental tools in decoding physiological stressors stimulated by training paradigms. Acute physiological changes induced by three diverse exercise protocols known to elicit similar levels of muscle hypertrophy were evaluated using muscle functional magnetic resonance imaging (mfMRI). The study was a cross-over study with participants (n = 10) performing three acute unilateral knee extensor exercise protocols to failure and a work matched control exercise protocol. Participants were scanned after each exercise protocol; 70% 1 repetition maximum (RM) (FF70); 20% 1RM (FF20); 20% 1RM with blood flow restriction (BFR20); free-flow (FF) control work matched to BFR20 (FF20WM). Post exercise mfMRI scans were used to obtain interleaved measures of muscle R2 (indicator of edema), R2' (indicator of deoxyhemoglobin), muscle cross sectional area (CSA) blood flow, and diffusion. Both BFR20 and FF20 exercise resulted in a larger acute decrease in R2, decrease in R2', and expansion of the extracellular compartment with slower rates of recovery. BFR20 caused greater acute increases in muscle CSA than FF20WM and FF70. Only BFR20 caused acute increases in intracellular volume. Postexercise muscle blood flow was higher after FF70 and FF20 exercise than BFR20. Acute changes in mean diffusivity were similar across all exercise protocols. This study was able to differentiate the acute physiological responses between anabolic exercise protocols. Low-load exercise protocols, known to have relatively higher energy contributions from glycolysis at task failure, elicited a higher mfMRI response. Noninvasive mfMRI represents a promising tool for decoding mechanisms of anabolic adaptation in muscle.NEW & NOTEWORTHY Using muscle functional MRI (mfMRI), this study was able to differentiate the acute physiological responses following three established hypertrophic resistance exercise strategies. Low-load exercise protocols performed to failure, with or without blood flow restriction, resulted in larger changes in R2 (i.e. greater T2-shifts) with a slow rate of return to baseline indicative of myocellular fluid shifts. These data were cross evaluated with interleaved measures of macrovascular blood flow, water diffusion, muscle cross sectional area (i.e. acute macroscopic muscle swelling), and intracellular water fraction measured using MRI.

A Comparison of the Effect of Strength Training on Cycling Performance between Men and Women.

During the last decade numerous review articles have been published on how concurrent strength and endurance training affect cycling performance. However, none of these have reviewed if there are any sex differences in the effects of concurrent training on cycling performance, and most research in this area has been performed with male cyclists. Thus, the aim of the current paper is to review the scientific literature on the effect of concurrent training on cycling performance in male and female cyclists with a special emphasis on potential sex differences. The results indicate that both male and female cyclists experience a similar beneficial effect from concurrent training on cycling performance and its physiological determinants compared to normal endurance training only. Some data indicate that women have a larger effect on cycling economy, but more studies are needed to explore this further. Furthermore, the adaptations to strength training thought to be responsible for the beneficial effects on cycling performance seem to be very similar between men and women. Interestingly, increased muscle cross-sectional area in the main locomotor muscles seems to be an important adaptation for improved performance, and, contrary to popular belief, cyclists should aim for increased muscle cross-sectional area when adding strength training to their normal training. We conclude that both male and female cyclists can improve their cycling performance by adding strength training to their normal training.

Volume of Gluteus Maximus and Minimus Increases After Hip Arthroscopy for Femoroacetabular Impingement Syndrome

To investigate the change in muscle volume around the hip in patients with femoroacetabular impingement (FAI) after arthroscopy and evaluate other factors related to muscle change. We performed a retrospective review of magnetic resonance imaging data of patients with FAI who underwent hip arthroscopy. Magnetic resonance imaging was obtained pre- and postoperatively. The cross-sectional area (CSA) of muscles were determined on axial images. The Wilcoxon signed-rank test was used to determine the differences between pre- and postoperative hip muscle CSA. The correlations of change in muscle CSA with age, sex, body mass index, pain level, preoperative symptom duration, follow-up time, and multiple validated patient-reported outcomes were also analyzed with a Spearman rank correlation test. Fifty-one patients with a mean age of 36.5 ± 5.6 years were included and analyzed. The follow-up was 26.6 ± 0.5 months (range, 24-40 months), and 27 (52.9%) were women. Patients with FAI showed increased hip muscle CSA of gluteus maximus (P= .002) and gluteus minimus (P= .001). Post- compared with preoperative, the value for the change in medius CSA was underpowered, and no differences in other hip muscle CSAs were observed. The increased muscle CSA of the gluteus maximus was significantly correlated with the improvement of modified Harris Hip Score (ρ= 0.404; P= .003). The increased muscle CSA of the gluteus minimus was significantly correlated with the improvement of pain Visual Analog Scale (ρ= 0.452; P= .001). Age, body mass index, sex, symptom duration, and follow-up time were not significantly correlated with change in muscle CSA. Patients with FAI have a significantly increased postoperative muscle CSA of the gluteus maximus (7.8%) and the gluteus minimus (11.6%) compared with preoperative values. The increased muscle CSA of the gluteus maximus and gluteus minimus was significantly correlated with improvement in modified Harris Hip Score and pain Visual Analog Scale, respectively. The increase of muscle volume may be associated with the improvement of subjective function and pain relief. Level IV, therapeutic case series.

Quantitative Muscle MRI Depicts Increased Muscle Mass after a Behavioral Change in Myotonic Dystrophy Type 1.

Background Patients with myotonic dystrophy type 1 (DM1) increased their physical activity and exercise capacity following a behavioral intervention. However, it is unknown what is altered in muscles of patients with DM1 as a result of this intervention. The increased exercise capacity suggests that decelerated fat infiltration or increased muscle cross-sectional area (CSA) could be involved. Purpose To assess the effect of this activity-stimulating behavioral intervention on the lower extremity muscles of patients with DM1 with longitudinal quantitative muscle MRI. Materials and Methods In this prospective trial, participants with DM1 were randomized to a behavioral intervention (n = 14) or continued regular care (standard care; n = 13); no age-matched pairing was performed. Participants underwent MRI of the lower extremities at baseline and 10-month follow-up (January 2015 to March 2016). Fat fraction (FF), muscle CSA, and muscle water T2 (T2water) as markers for fat infiltration, muscle mass, and alteration in tissue water distribution (edema), respectively, were assessed with a chemical shift-encoded Dixon sequence and multiecho spin-echo sequence. Longitudinal within-group and between-group changes were assessed with paired-samples t tests and multivariable regression models. Results A total of 27 patients with DM1 (15 men) were evaluated. Patient age was comparable between groups (intervention, 45 years ± 13 [standard deviation]; standard care, 5 years ± 12; P = .96). Muscle CSA increased 5.9 cm2 ± 7.8 in the intervention group during the 10-month follow-up (P = .03) and decreased 3.6 cm2 ± 7.2 in the standard care group (P = .13). After 10 months, the mean difference between the groups was 9.5 cm2 (P = .01). This effect was stronger in muscles with baseline FF below the mean ± standard deviation of unaffected volunteers (-0.4 cm2 ± 0.15; P < .001). FF increased 0.9% ± 1.0 in the intervention group (P = .02) and 1.2% ± 1.2 for standard care (P = .02), with no between-group difference (P = .56). T2water did not change significantly in either group (intervention, P = .08; standard care, P = .88). Conclusion A behavioral intervention targeting physical activity increased lower extremity muscle cross-sectional area in patients with myotonic dystrophy, preferentially in healthy-appearing muscle. © RSNA, 2020 Online supplemental material is available for this article.

Zilpaterol hydrochloride lowers marbling score by dilution of marbling and depression of intramuscular adipocyte volume in M. longissimus dorsi of beef steers

We hypothesized that zilpaterol hydrochloride (ZH) depresses marbling scores in beef cattle by dilution of the intramuscular (i.m.) adipose tissue in the longissimus thoracis (LT) by increased muscle cross-sectional area. Crossbred steers were treated with ractopamine hydrochloride (RH; 28 d) or ZH (20 d) or no β-adrenergic agonist (CON). ZH increased LT cross-sectional area (P < .001) and depressed rib fat depth (P < .001), USDA marbling score (P < .05), percent LT lipid (P < .02), total lipid in a 2.54 cm-thick LM steak (P < .05) and most LT lipid fatty acids (P ≤ .05),but had no effect on mean i.m. adipocyte volume (P = .15). ZH increased the relative volume proportion of smaller i.m. adipocytes (250 to 500 pL) and decreased the proportion of larger i.m. adipocytes (2000 and 3000 pL) (P < .05). We conclude that ZH reduces marbling score both by dilution of the marbling and a depression of i.m. adipocyte relative volumes.

Muscle Cross-sectional Area Improves With Home-based Training During Metastatic Castration-resistant Prostate Cancer

PURPOSE: Exercise training improves regional body composition in localized prostate cancer, but it is unknown if training has similar effects in advanced disease. Goals of this analysis were to determine changes in leg muscle cross-sectional area (CSA) and quality (MQ) values following home-based exercise training during metastatic castration-resistant prostate cancer (mCRPC) and to compare CSA values to healthy controls (CON). METHODS: Sedentary mCRPC patients undergoing androgen deprivation therapy (ADT) including next generation androgen receptor signaling inhibitors (n = 17, age = 71y ± 8, BMI = 32.0 kg/m2 ± 6.5) underwent CSA and MQ analyses using B-mode ultrasound for the vastus lateralis (VL) muscle before and after a 12-week home-based exercise protocol. Age- and BMI-matched CON (n = 17, age = 69y ± 2, BMI = 32.8kg/m2 ± 6.5) completed baseline scans only. RESULTS: At baseline, VL CSA was lower in mCRPC (9.12cm2+ 3.15) relative to CON (36.55cm2 ± 7.04, p<0.001, d=4.95). For mCRPC patients, the 12-week intervention did not change VL MQ, but increased CSA by 15.2% following the intervention (pre: 8.28cm2 ± 2.85, post: 9.54 ± 3.56, p<0.001, d= 0.39) with no change in MQ. CONCLUSIONS: Patients undergoing ADT for advanced prostate cancer exhibit lower muscle size compared to CON; however preliminary results suggest that home-based exercise training induces a moderate degree of regional muscle hypertrophy. The finding of regional hypertrophy is consistent with work conducted in patients with localized disease on ADT and may be an important outcome to monitor if increases in muscle CSA translate into improvements in physical function and quality of life. Supported by Physical Activity and Cancer Survivorship Pilot Funding.

Benefits of higher resistance-training volume are related to ribosome biogenesis.

For individuals showing suboptimal adaptations to resistance training, manipulation of training volume is a potential measure to facilitate responses. This remains unexplored. Here, 34 untrained individuals performed contralateral resistance training with moderate and low volume for 12weeks. Moderate volume led to larger increases in muscle cross-sectional area, strength and type II fibre-type transitions. These changes coincided with greater activation of signalling pathways controlling muscle growth and greater induction of ribosome synthesis. Out of 34 participants, thirteen displayed clear benefit of MOD on muscle hypertrophy and sixteen showed clear benefit of MOD on muscle strength gains. This coincided with greater total RNA accumulation in the early phase of the training period, suggesting that ribosomal biogenesis regulates the dose-response relationship between training volume and muscle hypertrophy. These results demonstrate that there is a dose-dependent relationship between training volume and outcomes. On the individual level, benefits of higher training volume were associated with increased ribosomal biogenesis. Resistance-exercise volume is a determinant of training outcomes. However not all individuals respond in a dose-dependent fashion. In this study, 34 healthy individuals (males n=16, 23.6 (4.1)years; females n=18, 22.0 (1.3)years) performed moderate- (3 sets per exercise, MOD) and low-volume (1 set, LOW) resistance training in a contralateral fashion for 12weeks (2-3 sessionsper week). Muscle cross-sectional area (CSA) and strength were assessed at Weeks 0 and 12, along with biopsy sampling (m. vastus lateralis). Muscle biopsies were also sampled before and 1h after the fifth session (Week 2). MOD resulted in larger increases in muscle CSA (5.2 (3.8)% versus 3.7 (3.7)%, P<0.001) and strength (3.4-7.7% difference, all P<0.05. This coincided with greater reductions in type IIX fibres from Week0 to Week12 (MOD, -4.6 percentage points; LOW -3.2 percentage points), greater phosphorylation of S6-kinase1 (p85 S6K1Thr412 , 19%; p70 S6K1Thr389 , 58%) and ribosomal protein S6Ser235/236 (37%), greater rested-state total RNA (8.8%) and greater exercise-induced c-Myc mRNA expression (25%; Week2, all P<0.05). Thirteen and sixteen participants, respectively, displayed clear benefits in response to MOD on muscle hypertrophy and strength. Benefits were associated with greater accumulation of total RNA at Week2 in the MOD leg, with every 1% difference increasing the odds of MOD benefit by 7.0% (P=0.005) and 9.8% (P=0.002). In conclusion, MOD led to greater functional and biological adaptations than LOW. Associations between dose-dependent total RNA accumulation and increases in muscle mass and strength point to ribosome biogenesis as a determinant of dose-dependent training responses.

Temporal increase in muscle cross-sectional area as an acute effect of resistance exercise in resistance-trained and untrained individuals

The purpose of this study was to compare the temporal increase in muscle cross-sectional area (CSA) as the acute response of resistance exercise (RE) between resistance-trained and untrained groups and investigate the factors that affect the muscle CSA. Resistance-trained ( n = 14) and untrained ( n = 14) subjects performed four kinds of triceps brachii RE. Muscle CSA and intracellular hydration (IH), were measured prior to and 5-, 30-, and 60-minute after RE. Pearson's correlation coefficient was calculated to clarify the relationships among percent increases in muscle CSA and IH, area under the Oyx-Hb curve, blood lactate concentration, and % maximum voluntary contraction (MVC)-root-mean-square (RMS) of electromyogram (EMG). At 5-minute after RE, muscle CSA increased significantly to 120.2 ± 6.3% in the resistance-trained group and 105.5 ± 2.3% in the untrained group ( p < .01). However, neither group showed a significant difference between the values before and 30-minute after RE. In the resistance-trained group, there was a significant increase in IH at 5-minute post-RH ( p < .01), and correlations were found between percent increases in muscle CSA and IH ( r = 0.70, p < .01), area under the Oxy-Hb curve ( r = 0.77, p < .01), and % MVC-RMS of EMG ( r = 0.72, p < .01). The findings of this study suggest that measurements of muscle CSA in studies of muscle hypertrophy should be performed 30-minute or more after the last resistance exercise session, and muscle pump exercises should be conducted just before participation in bodybuilding, and physique contests.

Low-load blood flow restriction elicits greater concentric strength than non-blood flow restriction resistance training but similar isometric strength and muscle size.

Low-load venous blood flow restriction resistance training (RT + BFR) has been demonstrated to increase muscle strength to a greater degree than low-load non-BFR resistance training (RT) during isotonic training, but no previous investigations have examined RT + BFR versus RT during isokinetic training. The purpose of the present study was to examine the effects of 4 weeks of isokinetic low-load RT + BFR versus low-load RT on indices of muscle strength, muscle size, and neural adaptations. Thirty women (mean ± SD; 22 ± 2years) participated in this investigation and were randomly assigned to 4 weeks of either RT + BFR (n = 10), RT (n = 10), or control (n = 10) group. Resistance training consisted of 75 reciprocal forearm flexion-extension isokinetic muscle actions of the forearm flexors performed at a velocity of 120°s-1. Concentric peak torque increased to a greater extent for RT + BFR after 4 weeks (36.9%) compared to RT (25.8%), but there were similar increases in isometric torque (23.3-42.1%). For both RT + BFR and RT, there were similar increases in muscle cross-sectional area and muscle thickness of the biceps brachii after 2 weeks (11.3-14.3% and 12.4-12.9%, respectively) and 4 weeks (18.7-21.9% and 19.0-20.0%, respectively). There were similar increases in mechanomyographic amplitude, mechanomyographic mean power frequency, and electromyographic mean power frequency, but no changes in electromyographic amplitude for all conditions (including control). These findings indicated that low-load RT + BFR elicited greater increases in concentric strength than low-load RT, but elicited comparable increases in isometric strength and muscle size. There were also no differences in any of the EMG and MMG responses among conditions.