Quadriceps Cross-sectional Area Research Articles

Clinical evaluation of fully automated thigh muscle and adipose tissue segmentation using a U-Net deep learning architecture in context of osteoarthritic knee pain

ObjectiveSegmentation of thigh muscle and adipose tissue is important for the understanding of musculoskeletal diseases such as osteoarthritis. Therefore, the purpose of this work is (a) to evaluate whether a fully automated approach provides accurate segmentation of muscles and adipose tissue cross-sectional areas (CSA) compared with manual segmentation and (b) to evaluate the validity of this method based on a previous clinical study.Materials and methodsThe segmentation method is based on U-Net architecture trained on 250 manually segmented thighs from the Osteoarthritis Initiative (OAI). The clinical evaluation is performed on a hold-out test set bilateral thighs of 48 subjects with unilateral knee pain.ResultsThe segmentation time of the method is < 1 s and demonstrated high agreement with the manual method (dice similarity coeffcient: 0.96 ± 0.01). In the clinical study, the automated method shows that similar to manual segmentation (− 5.7 ± 7.9%, p < 0.001, effect size: 0.69), painful knees display significantly lower quadriceps CSAs than contralateral painless knees (− 5.6 ± 7.6%, p < 0.001, effect size: 0.73).DiscussionAutomated segmentation of thigh muscle and adipose tissues has high agreement with manual segmentations and can replicate the effect size seen in a clinical study on osteoarthritic pain.

Muscle Strength, Size, and Composition Following 12 Months of Gender-affirming Treatment in Transgender Individuals.

As many sports are divided in male/female categories, governing bodies have formed regulations on the eligibility for transgender individuals to compete in these categories. Yet, the magnitude of change in muscle mass and strength with gender-affirming treatment remains insufficiently explored. This study explored the effects of gender-affirming treatment on muscle function, size, and composition during 12 months of therapy. In this single-center observational cohort study, untrained transgender women (TW, n = 11) and transgender men (TM, n = 12), approved to start gender-affirming medical interventions, underwent assessments at baseline, 4 weeks after gonadal suppression of endogenous hormones but before hormone replacement, and 4 and 12 months after treatment initiation. Knee extensor and flexor strength were assessed at all examination time points, and muscle size and radiological density (using magnetic resonance imaging and computed tomography) at baseline and 12 months after treatment initiation. Thigh muscle volume increased (15%) in TM, which was paralleled by increased quadriceps cross-sectional area (CSA) (15%) and radiological density (6%). In TW, the corresponding parameters decreased by -5% (muscle volume) and -4% (CSA), while density remained unaltered. The TM increased strength over the assessment period, while the TW generally maintained their strength levels. One year of gender-affirming treatment resulted in robust increases in muscle mass and strength in TM, but modest changes in TW. These findings add new knowledge on the magnitude of changes in muscle function, size, and composition with cross-hormone therapy, which could be relevant when evaluating the transgender eligibility rules for athletic competitions.

Ultrasonography to measure quadriceps muscle in critically ill patients: A literature review of reported methodologies.

Muscle wasting in the intensive care unit (ICU) is common and may impair functional recovery. Ultrasonography (US) presents a modern solution to quantify skeletal muscle size and monitor muscle wasting. However, no standardised methodology for the conduct of ultrasound-derived quadriceps muscle layer thickness or cross-sectional area in this population exists. The aim of this study was to compare methodologies reported for the measurement of quadriceps muscle layer thickness (MLT) and cross-sectional area (CSA) using US in critically ill patients. Databases PubMed, Ovid, Embase, and CINAHL were searched for original research publications that reported US-derived quadriceps MLT and/or CSA conducted in critically ill adult patients. Data were extracted from eligible studies on parameters relating to US measurement including anatomical location, patient positioning, operator technique and image analysis. It was identified that there was a clear lack of reported detail and substantial differences in the reported methodology used for all parameters. A standardised protocol and minimum reporting standards for US-derived measurement of quadriceps muscle size in ICU is required to allow for consistent measurement techniques and hence interpretation of results.

Anatomical and Neuromuscular Determinants of Strength Change in Previously Untrained Men Following Heavy Strength Training.

This study examined whether changes in strength following a moderate-duration strength training program were associated with changes in specific combinations of anatomical and neuromuscular variables. 36 men (18–40 y) completed 10 weeks of lower-limb heavy resistance (6-RM) strength training. Measurements included cross-sectional area (CSA), fascicle length (lf) and fascicle angle (θf) from proximal, middle and distal regions of the four quadriceps components; agonist (EMG:M), antagonist (EMG) muscle activities and percent voluntary quadriceps activation (%VA; interpolated twitch technique); patellar tendon moment arm distance; and maximal isometric, concentric and eccentric (60° s–1) torque. Multiple regression models were developed to quantify the relationship between the change in maximum torque and the changes in combinations of anatomical and neuromuscular variables. The best model for each contraction mode was determined using Akaike’s Information Criterion (AICc), an information-theoretic approach for model selection. Strength increased significantly following training (mean range = 12.5–17.2%), and moderate relationships were observed between modeled data (using best-fit prediction models) and the change in torque for each contraction mode. The change in isometric torque was best (although weakly) predicted by the linear combination of the change in proximal-region vastus lateralis (VL) CSA and fascicle angle (R2 = 0.27, p < 0.05; AICcwi = 0.52, i.e., the probability the model would be selected as the “best model”). The models best predicting the change in concentric and eccentric torque both included the combination of the change in quadriceps (i.e., mean of all muscles) EMG:M and the change in vastus intermedius fascicle angle combined with either a change in proximal-region VL (R2 = 0.40, p < 0.001; AICcwi = 0.15) or whole quadriceps (R2 = 0.41, p < 0.001; AICcwi = 0.30) CSA (concentric and eccentric, respectively). Models incorporating the change in proximal CSA typically received substantial support (AICC < 2) for concentric torque prediction models, and the change in % VA and pre-training moment arm distance had substantial support for use in eccentric torque prediction models. In conclusion, adaptations varied between individuals, however strength training programs targeted to improve a group of variables that particularly includes agonist muscle activation might yield the greatest improvements in concentric and eccentric knee extension strength, whereas proximal muscle size and fascicle angle appear most important for isometric torque improvements.

Resistance Training Increases Muscle Strength and Muscle Size in Patients With Liver Cirrhosis

Cirrhosis is often complicated by reduced muscle mass and strength, which limits the ability to perform daily activities and affects quality of life. Resistance training can increase muscle strength and mass in elderly and chronically ill patients. We performed a randomized controlled trial to investigate whether resistance training increases muscle strength and size in patients with compensated cirrhosis. We performed a prospective study of 39 patients with cirrhosis (Child-Pugh class A or B) seen at an outpatient clinic in Denmark from January 2015 through March 2017. Participants protein intake and activity levels were registered daily. Participants were randomly assigned (1:1) to a group that performed 36 1-hour sessions of physical exercise (supervised progressive resistance training for 1 hour, 3 times weekly for 12 weeks) or a control group (no change in daily activity level). Maximal muscle strength was measured as the peak torque in isokinetic knee extension and muscle size was measured as the cross-sectional area of the quadriceps muscle, assessed by magnetic resonance imaging of the thigh. The exercise group increased their muscle strength by 13% (from a mean 119 Nm to 134 Nm)-an 11 Nm greater gain in mean strength than that of the control group (P = .05). The exercise group increased their quadriceps cross-sectional area by 10% (from a mean 58.5 cm2 to 64.6 cm2)-a 4.4 cm2 greater gain than that of the control group (P < .01). The exercise group had significant increases in whole-body lean mass and body cell mass, and significant increases in 6-minute walking distance and the mental component summary of the short form-36 questionnaire. Adverse events were minor and equal between groups. In a randomized trial of patients with compensated cirrhosis, we found that 12 weeks of supervised progressive resistance training increased muscle strength and size and had beneficial effects on general performance measures, compared with patients who did not change their daily activity routine (control subjects). ClinicalTrials.gov no: NCT02343653.

Changes in Muscle Power and Muscle Morphology with Different Volumes of Fast Eccentric Half-Squats.

The aim of the study was to evaluate power performance and muscle morphology adaptations in response to 5 weeks of fast-eccentric squat training (FEST) performed twice per week, with three different training volumes. Twenty-five moderately trained females were assigned into three groups performing eight repetitions of FEST of either four sets (4 × 8 group; N = 9), 6 sets (6 × 8 group; N = 8) or eight sets (8 × 8 group, N = 8). Before and after the intervention, countermovement jumping height (CMJh) and power (CMJp), half squat maximal strength (1-RM), quadriceps cross-sectional area (QCSA) and vastus lateralis (VL) architecture and fiber type composition were evaluated. Significant increases (p < 0.05) were found for all groups, with no differences among them in 1-RM (4 × 8: 14.8 ± 8.2%, 6 × 8: 13.1 ± 9.2% and 8 × 8: 21.6 ± 7.0%), CMJh (4 × 8: 12.5 ± 8.5%, 6 × 8: 11.3 ± 9.3% and 8 × 8: 7.0 ± 6.2%), CMJp (4 × 8: 9.1 ± 6.0%, 6 × 8: 7.1 ± 5.2% and 8 × 8: 5.0 ± 3.9%) and QCSA (4 × 8: 7.7 ± 4.7%, 6 × 8: 9.0 ± 6.8% and 8 × 8: 8.2 ± 6.5%). Muscle fiber type distribution remained unaltered after training in all groups. VL fascicle length increased and fascicle angle decreased only in 6 × 8 and 8 × 8 groups. In conclusion, four sets of eight fast-eccentric squats/week increase lower body power and strength performance and maintain type IIX muscle fibers after 5 weeks, at least in moderately trained females.

Dose-Response Relationship Between Neuromuscular Electrical Stimulation and Muscle Function in People With Rheumatoid Arthritis.

Neuromuscular electrical stimulation (NMES) is a viable intervention for improving impaired muscle function in individuals with rheumatoid arthritis (RA). However, there is limited evidence about the dose-response relationship between NMES and muscle function in these individuals. The objectives of this study were to investigate the dose-response relationship between NMES and muscle function in individuals with RA and to establish the minimal NMES training intensity for promoting improvements. This study was a secondary analysis of data obtained before and after an NMES intervention in a randomized study. The study took place at a research clinic. Only adults diagnosed with RA were included. The intervention consisted of 36 NMES treatment sessions for the quadriceps muscles over 16 weeks. Muscle function was measured before and after the intervention; quadriceps cross-sectional area and muscle quality were assessed using computed tomography, and strength was measured with an isokinetic dynamometer. NMES training intensity was calculated as a percentage by dividing NMES-elicited quadriceps muscle torque by the maximum voluntary isometric contraction. Improvements in muscle function were calculated using paired-sample t tests. The dose-response relationship was determined using curve estimation regression statistics. The minimum NMES training intensity was defined as that sufficient to significantly improve all muscle function measures. Twenty-four people (48 legs) participated (75% women; mean [SD] age = 58 [8] years; mean body mass index=32 [7] kg/m2). Quadriceps cross-sectional area, muscle quality, and strength improved after the intervention. Associations between NMES training intensity and muscle quality (r2=0.20) and strength (r2=0.23) were statistically significant, but that between NMES training intensity and muscle cross-sectional area was not (r2=0.02). The minimum NMES training intensity necessary to improve all measures of muscle function ranged from 11% to 20% of the maximum voluntary isometric contraction. The relatively small sample size was a limitation. The minimum NMES training intensity for significant gains in muscle function was ∼15%. Higher NMES intensities may promote better muscle quality and strength in individuals with RA.

Progression of Blood Flow Restricted Resistance Training in Older Adults at Risk of Mobility Limitations.

Blood flow restriction (BFR) resistance training leads to increased muscle mass and strength but the progression leading to adaptations may be different as strength gains are often to a lesser magnitude than high-load (HL) training. The impact of training loads and repetitions on older adults’ muscle mass and strength following BFR or HL training was evaluated. Twenty-one older adults (67–90 years) classified as being at risk of mobility limitations were randomly assigned to HL (n = 11) or BFR (n = 10) knee extension (KE) and flexion (KF) training twice per week for 12 weeks. Strength was measured with 10-repetition maximum (10-RM) tests and isometric contractions. Cross-sectional area (CSA) of the quadriceps and hamstrings was measured. HL and BFR interventions increased 10-RM KF and isometric strength (P < 0.05) and hamstrings CSA increased an average of 4.8 ± 5.9% after HL and BFR training (time main effect P < 0.01). There were no differences between the training groups (time x group interactions P > 0.05). The rate of progression of KF training load and repetitions was comparable (time × group interactions of each variable P > 0.05). The groups averaged an increase of 0.50 ± 25 kg⋅week-1 and 1.8 ± 0.1.7 repetitions⋅week-1 of training (time main effects P < 0.05). The HL training group experienced greater improvements in KE 10-RM strength than the BFR group (60.7 ± 36.0% vs. 35.3 ± 25.5%; P = 0.03). In both groups, isometric KE strength increased 17.3 ± 18.5% (P = 0.001) and there were no differences between groups (P = 0.24). Quadriceps CSA increased (time main effect P < 0.01) and to similar magnitudes (time x group interaction P = 0.62) following HL (6.5 ± 3.1%) and BFR training (7.8 ± 8.2%). The HL group experienced accelerated progression of load when compared to BFR (0.90 ± 0.60 kg⋅week-1 vs. 30 ± 0.21 kg⋅week-1; P = 0.006) but was not different when expressed in relative terms. BFR training progressed at a rate of 3.6 ± 1.3 repetitions⋅week-1 while the HL group progressed at 2.2 ± 0.43 repetitions⋅week-1 (P = 0.003). HL training led to greater increases in KE 10-RM and it may be attributed to the greater load and/or faster rate of progression of the load throughout the 12-week training period and the specificity of the testing modality. Incorporating systematic load progression throughout BFR training periods should be employed to lead to maximal strength gains.

Combining Whey Protein Isolate with Eccentric Training Improved Quadriceps Strength in Patients with ACL Rupture (P12-024-19)

ObjectivesAnterior cruciate ligament (ACL) rupture results in significant quadriceps weakness, which will then cause abnormal gait and knee instability. Eccentric training (ET) can produce larger effects on muscle strength than concentric training, which may be further augmented by protein supplement. This study was to examine the effects of combining whey protein supplement with preoperative isokinetic ET on quadriceps strength and function after ACL rupture. MethodsThirty-seven male subjects aged 18–40 years with ACL rupture were randomly assigned to isokinetic ET (IET, N = 19) group or isokinetic ET with whey protein isolate (IET + WP, N = 18) group. Both groups received preoperative isokinetic ET for six weeks, containing 3–4 sets per day with 8–10 repetitions for each set, twice a week. Subjects in IET + WP consumed whey protein isolate 22 g per day. Cross-Sectional Area (CSA) of quadriceps was scanned by MRI, and strength and knee function were measured before and after the trials. ResultsAfter intervention, CSA of the involved quadriceps increased by 3.7% (NS) in IET and 7.6% (P = 0.012) in IET + WP. The ratio of side-to-side increased by 3.9% (NS) in IET and 4.8% (P = 0.002) in IET + WP. The peak torque of quadriceps during eccentric contraction at 60 degree/s, concentric contraction at 60, 180 and 300 degree/s increased by 27.9% (P < 0.001), 35.9% (P < 0.001), 34.3% (P = 0.002) and 27.3% (P = 0.003) in IET, and increased by 44.2% (P < 0.001), 42.3% (P < 0.001), 37.4% (P = 0.002) and 36.7% (P < 0.001) in IET + WP, respectively, with no differences between the two groups. Lysholm and IKDC2000 knee function score in IET + WP increased by 24.7% (P = 0.001) and 12.9% (P = 0.001). ConclusionsCombining whey protein supplement with ET tends to be more effective on improving CSA of quadriceps, knee function and quadriceps strength when compared to ET alone after ACL rupture, even though the results did not reach statistical differences. Funding SourcesThe research was supported by The National Key Research and Development Program (No.2016YFD0400603).

Associations Between Muscle Morphology Measured with Ultrasonography and Self-Reported Function Following Anterior Cruciate Ligament Reconstruction

Deficits in quadriceps function are common in patients who sustain an anterior cruciate ligament (ACL) injury and undergo subsequent ACL reconstruction (ACLR). Quadriceps atrophy is among the notable changes in muscle tissue after ACLR. The relationship between muscle morphology and self-reported function should be established so treatment options can be targeted to improve function after ACLR. PURPOSE: (1) To evaluate rectus femoris (RF) cross-sectional area (CSA) and intramuscular fat percent (PF) in the injured and uninjured limb from 9 weeks post ACLR to return to activity (RTA) and (2) identify associations between injured limb quadriceps CSA, PF and self-reported function. METHODS: 28 individuals with primary unilateral ACLR (Age=16.6±2.7; Weight=71.8±17.7; 64% female; 18 bone-patellar tendon-bone; 2 quadriceps tendon; 5 hamstring tendon) were recruited for this study. RF was imaged at 15cm proximal of superior border of the patella. Quadriceps CSA and PF of the injured and uninjured limb were used for analysis. Self-reported function was evaluated using the International Knee Documentation Committee score (IKDC). Paired-samples t-tests were used to compare inter-limb differences in CSA and PF and changes from 9 weeks to RTA. Partial correlations adjusting for sex were used to analyze the relationship between RF morphology and IKDC scores. RESULTS: Injured limbs had smaller RF CSA at each time point (4.5±1.6cm2 vs 5.2±1.9cm2, p<.01 and 5.2±1.9cm2 vs 5.6±2.1 cm2, respectively) compared to the uninjured limb. Injured limb CSA increased at RTA (4.5±1.6cm2 vs 5.2±1.9cm2, p<.01) while the uninjured limb did not (p=0.12). No differences in PF were found between limbs (p=0.18, and p=0.43, respectively) or time point (p=0.67, and p=0.92, respectively). After adjusting for sex, larger injured limb CSA was associated with higher IKDC scores at 9 weeks and trended toward significance at RTA (r=0.32, p=0.05, and r=0.26, p=0.09, respectively). Injured limb PF was negatively associated with IKDC scores at both time points (r=-0.55, p=<.01, and r=-0.39, p=0.02, respectively). CONCLUSIONS: Inter-limb differences in RF muscle CSA are not ameliorated at RTA. RF CSA and PF are associated with self-reported function in individuals with ACLR and should be treatment targets to improve patient function following injury.

Cigarette Smoking Is Associated With Lower Quadriceps Cross-sectional Area and Attenuation in Older Adults.

In addition to well-established links with cardiovascular and respiratory diseases, cigarette smoking may affect skeletal muscle; however, associations with quadriceps atrophy, density, and function are unknown. This study explored the associations of current and former smoking with quadriceps muscle area and attenuation as well as muscle force (assessed as knee extension peak torque) and rate of torque development-a measure of muscle power in older adults. Data from 4469 older adults, aged 66-95 years at baseline in the Age, Gene/Environment Susceptibility-Reykjavik Study with measurements of thigh computed tomography, isometric knee extension testing, self-reported smoking history, and potential covariates were analyzed. Sex differences were observed in these data; therefore, our final analyses are stratified by sex. In men, both former smokers and current smokers had lower muscle area (with β= -0.10, 95% confidence interval [CI] = -0.17 to -0.03 and β = -0.19, 95% CI = -0.33 to -0.05, respectively) and lower muscle attenuation (ie, higher fat infiltration, β = -0.08, 95% CI = -0.16 to -0.01 and β = -0.17, 95% CI = -0.34 to -0.01, respectively) when compared with never smokers. Smoking status was not associated with male peak torque or rate of torque development. In women, current smoking was associated with lower muscle attenuation (β = -0.24, 95% CI = -0.34 to -0.13) compared to never smoking. Among female smokers (current and former), muscle attenuation and peak torque were lower with increasing pack-years. Results suggest that cigarette smoking is related to multiple muscle properties at older age and that these relationships may be different among men and women. This article presents novel data, as it examined for the first time the relationship between smoking and computed tomography-derived quadriceps muscle size (cross-sectional area) and attenuation. This study suggests that current cigarette smoking is related to higher muscle fat infiltration, which may have significant health implications for the older population, because of its known association with poor physical function, falls, and hip fractures.

Blood Flow Restriction Does Not Attenuate Short-Term Detraining-Induced Muscle Size and Strength Losses After Resistance Training With Blood Flow Restriction.

Teixeira, EL, de Salles Painelli, V, Silva-Batista, C, de Souza Barros, T, Longo, AR, Lasevicius, T, Schoenfeld, BJ, Aihara, AY, and de Almeida Peres, B. Blood flow restriction does not attenuate short-term detraining-induced muscle size and strength losses after resistance training with blood flow restriction. J Strength Cond Res 35(8): 2082-2088, 2021-After a short-term resistance training with blood flow restriction (BFR), we investigated the effects of 12 days of detraining (DET), without an exercise stimulus, on quadriceps cross-sectional area (QCSA) and muscle strength (1 repetition maximum [1RM]), with 1 leg receiving daily intermittent BFR during DET vs. the same nonexercise condition without BFR (CON) in the contralateral leg. Both subjects' legs were evaluated for QCSA and 1RM before (PRE) and after (POST) both legs being unilaterally submitted to 3 weeks (4 days per week) of low-load (3 sets of 15 repetitions, 30% 1RM) resistance training with BFR. The DET period started immediately after POST, where each leg was randomly submitted to a daily intermittent BFR protocol or CON, without any associated exercise stimulus. Quadriceps cross-sectional area and 1RM were reassessed after DET. Both legs at CON and BFR conditions increased QCSA (6.3 and 6.8%, respectively; both p < 0.0001) and 1RM (9.5 and 10.1%, respectively; both p < 0.05) from PRE to POST. Both legs at CON and BFR conditions reduced QCSA (-4.6 and 4.9%, respectively; both p < 0.0001) and 1RM (-9.0 and -8.2%, respectively; both p < 0.05) from POST to DET, with no significant differences between conditions (p > 0.05). We conclude that muscle strength and hypertrophy gains obtained in 3 weeks of resistance training with BFR are not maintained after 12 days of DET. Moreover, the application of BFR, without an associated exercise stimulus, does not attenuate such losses.

Muscle mass and strength gains following 6 months of resistance type exercise training are only partly preserved within one year with autonomous exercise continuation in older adults.

Although resistance type exercise training (RT) effectively increases muscle mass and strength in older individuals, it remains unclear whether gains in muscle mass and strength are maintained without continued supervised training. We assessed the capacity of older individuals to maintain muscle mass and strength gains one year after partaking in a successful RT program. Fifty-three healthy older adults performed a 24-wk supervised RT program. Upon the cessation of the training program, participants were not provided with any advice or incentives to continue exercise training. One year after completion of the training program, all participants were contacted and invited back to the laboratory to assess anthropometrics, body composition (DXA), quadriceps muscle cross-sectional area (CSA) (CT-scan), muscle strength (1RM knee extension/leg press), and muscle fiber characteristics (muscle biopsy). Following primary analyses on all participants that responded to the invitation (n = 35), participants were divided into two groups: individuals who had continued to perform exercise training on an individual basis (EXER group; n = 16) and individuals who had not continued to perform any regular exercise (STOP group; n = 19) after completing the RT program. The initial increases in quadriceps CSA (+506 ± 209 and +584 ± 287 mm2) and knee extension strength (+32 ± 12 vs +34 ± 10 kg) after the 24-wk RT program did not differ between the STOP and EXER group (all P > 0.05). One year after discontinuation of the RT program, participants had lost muscle mass (P < 0.01), with a greater decline in quadriceps CSA in the STOP vs EXER group (-579 ± 268 vs -309 ± 253 mm2, respectively; P < 0.05). Muscle strength had decreased significantly compared to values after completing the RT program (P < 0.01), with no differences observed between the STOP vs EXER group (knee extension: -21 ± 8 vs -18 ± 8 kg, respectively; P > 0.05), yet remained higher compared with values before the RT program (P < 0.05). Though prolonged RT can effectively increase muscle mass and strength in the older population, muscle mass gains are lost and muscle strength gains are only partly preserved within one year if the supervised exercise program is not continued.

Clinical validation of fully automated segmentation of thigh muscle and adipose tissue cross sectional areas using maching learning with a convolutional neural network

Clinical validation of fully automated segmentation of thigh muscle and adipose tissue cross sectional areas using maching learning with a convolutional neural network

Blood Flow Restriction Therapy Versus Standard Care for Reducing Quadriceps Atrophy After Anterior Cruciate Ligament Reconstruction.

Clinical Scenario: Quadriceps atrophy and weakness are common after anterior cruciate ligament reconstruction (ACLR). Blood flow restriction (BFR) therapy, alone or in combination with exercise, has shown some promise in promoting muscular hypertrophy. This review was conducted to ascertain the extent to which current evidence supports the use of BFR for reducing quadriceps atrophy following ACLR in comparison with standard care. Clinical Question: Is BFR more effective than standard care for reducing quadriceps atrophy after ACLR? Summary of Key Findings: The literature was searched for studies that directly compared BFR treatment to standard care in patients with ACLR. Three level I randomized control trial studies retrieved from the literature search met the inclusion criteria. Clinical Bottom Line: Reviewed data suggest that a short duration (13d) of moderate-pressure BFR combined with low-resistance muscular training does not appear to measurably affect quadriceps cross-sectional area. However, a relatively long duration (15wk) of moderate-pressure BFR combined with low-resistance muscular training may increase quadriceps cross-sectional area to a greater extent than low-resistance muscular training alone. The results of the third randomized control trial suggest that employing BFR while immobilized in the early postoperative period may reduce quadriceps atrophy following ACLR. Additional data are needed to establish if the benefits of BFR on quadriceps atrophy after ACLR outweigh the inherent risks and costs. Strength of Recommendation: All evidence for this review was level 1 (randomized control trial) based on the Centre for Evidence-Based Medicine criteria. However, the findings were inconsistent across the 3 studies regarding the effects of BFR on quadriceps atrophy resulting in a grade "B" strength of recommendation.

Structural differences in the diaphragm of patients following controlled vs assisted and spontaneous mechanical ventilation.

Ventilator-induced diaphragm dysfunction or damage (VIDD) is highly prevalent in patients under mechanical ventilation (MV), but its analysis is limited by the difficulty of obtaining histological samples. In this study we compared diaphragm histological characteristics in Maastricht III (MSIII) and brain-dead (BD) organ donors and in control subjects undergoing thoracic surgery (CTL) after a period of either controlled or spontaneous MV (CMV or SMV). In this prospective study, biopsies were obtained from diaphragm and quadriceps. Demographic variables, comorbidities, severity on admission, treatment, and ventilatory variables were evaluated. Immunohistochemical analysis (fiber size and type percentages) and quantification of abnormal fibers (a surrogate of muscle damage) were performed. Muscle samples were obtained from 35 patients. MSIII (n = 16) had more hours on MV (either CMV or SMV) than BD (n = 14) and also spent more hours and a greater percentage of time with diaphragm stimuli (time in assisted and spontaneous modalities). Cross-sectional area (CSA) was significantly reduced in the diaphragm and quadriceps in both groups in comparison with CTL (n = 5). Quadriceps CSA was significantly decreased in MSIII compared to BD but there were no differences in the diaphragm CSA between the two groups. Those MSIII who spent 100h or more without diaphragm stimuli presented reduced diaphragm CSA without changes in their quadriceps CSA. The proportion of internal nuclei in MSIII diaphragms tended to be higher than in BD diaphragms, and their proportion of lipofuscin deposits tended to be lower, though there were no differences in the quadriceps fiber evaluation. This study provides the first evidence in humans regarding the effects of different modes of MV (controlled, assisted, and spontaneous) on diaphragm myofiber damage, and shows that diaphragm inactivity during mechanical ventilation is associated with the development of VIDD.

Muscle-Derived Stem Cell-Enriched Scaffolds Are Capable of Enhanced Healing of a Murine Volumetric Muscle Loss Defect.

Volumetric muscle loss secondary to traumatic or surgical causes can lead to functional and aesthetic impairments. The authors hypothesize that an implantable muscle-derived stem cell-enriched collagen scaffold could significantly augment muscle regeneration in a murine model of volumetric muscle loss. Murine muscle-derived stem cells were isolated using a modified preplating technique and seeded onto type 1 collagen scaffolds to create the muscle-derived stem cell-enriched collagen scaffolds. Murine rectus femoris defects of 5 mm were created and randomized to one of three conditions (n = 6 per group): untreated controls, collagen scaffold only, and muscle-derived stem cell-enriched collagen scaffolds. In vivo muscle healing was quantified using micro-computed tomography. Muscle explants were analyzed using standard histology and whole-mount immunofluorescence at 8 weeks. In vivo experiments demonstrated significantly greater quadriceps cross-sectional area in the muscle-derived stem cell-enriched collagen scaffold group compared with controls on micro-computed tomography (0.74 ± 0.21 versus 0.55 ± 0.06 versus 0.49 ± 0.04 ratio of experimental to naive quadriceps cross-sectional area; p < 0.05). Muscle explants of the muscle-derived stem cell-enriched collagen scaffold group demonstrated significantly higher cellular density compared with controls (1185 ± 360 versus 359 ± 62 versus 197 ± 68 nuclei/high-power field; p < 0.01). Immunofluorescence for laminin and myosin heavy chain confirmed formation of organized muscle fibers within the defect of the muscle-derived stem cell-enriched collagen scaffold group only. However, appreciable confocal colocalization of myosin heavy chain with green fluorescent protein expression was low. The results of this study indicate that muscle-derived stem cell-enriched scaffolds significantly improved skeletal muscle regeneration in a murine muscle defect model. Based on the low fluorescent colocalization, host progenitor cells appear to contribute significantly to intradefect myogenesis, suggesting that deployment of a viable muscle-derived stem cell-enriched scaffold stimulates a regenerative mitogen response in native tissues.

Type 1 Muscle Fiber Hypertrophy after Blood Flow-restricted Training in Powerlifters.

To investigate the effects of blood flow-restricted resistance exercise (BFRRE) on myofiber areas (MFA), number of myonuclei and satellite cells (SC), muscle size and strength in powerlifters. Seventeen national level powerlifters (25 ± 6 yr [mean ± SD], 15 men) were randomly assigned to either a BFRRE group (n = 9) performing two blocks (weeks 1 and 3) of five BFRRE front squat sessions within a 6.5-wk training period, or a conventional training group (Con; n = 8) performing front squats at 60%-85% of one-repetition maximum (1RM). The BFRRE consisted of four sets (first and last set to voluntary failure) at ~30% of 1RM. Muscle biopsies were obtained from m. vastus lateralis (VL) and analyzed for MFA, myonuclei, SC and capillaries. Cross-sectional areas (CSA) of VL and m. rectus femoris were measured by ultrasonography. Strength was evaluated by maximal voluntary isokinetic torque (MVIT) in knee extension and 1RM in front squat. BFRRE induced selective increases in type I MFA (BFRRE: 12% vs Con: 0%, P < 0.01) and myonuclear number (BFRRE: 18% vs Con: 0%, P = 0.02). Type II MFA was unaltered in both groups. BFRRE induced greater changes in VL CSA (7.7% vs 0.5%, P = 0.04), which correlated with the increases in MFA of type I fibers (r = 0.81, P = 0.02). No group differences were observed in SC and strength changes, although MVIT increased with BFRRE (P = 0.04), whereas 1RM increased in Con (P = 0.02). Two blocks of low-load BFRRE in the front squat exercise resulted in increased quadriceps CSA associated with preferential hypertrophy and myonuclear addition in type 1 fibers of national level powerlifters.

Dietary feeding pattern does not modulate the loss of muscle mass or the decline in metabolic health during short-term bed rest.

Short periods of bed rest lead to the loss of muscle mass and quality. It has been speculated that dietary feeding pattern may have an impact upon muscle protein synthesis rates and, therefore, modulate the loss of muscle mass and quality. We subjected 20 healthy men (age: 25 ± 1 yr, body mass index: 23.8 ± 0.8 kg/m2) to 1 wk of strict bed rest with intermittent (4 meals/day) or continuous (24 h/day) enteral tube feeding. Participants consumed deuterium oxide for 7 days before bed rest and throughout the 7-day bed rest period. Prior to and immediately after bed rest, lean body mass (dual energy X-ray absorptiometry), quadriceps cross-sectional area (CSA; CT), maximal oxygen uptake capacity (V̇o2peak), and whole body insulin sensitivity (hyperinsulinemic-euglycemic clamp) were assessed. Muscle biopsies were collected 7 days before, 1 day before, and immediately after bed rest to assess muscle tracer incorporation. Bed rest resulted in 0.3 ± 0.3 vs. 0.7 ± 0.4 kg lean tissue loss and a 1.1 ± 0.6 vs. 0.8 ± 0.5% decline in quadriceps CSA in the intermittent vs. continuous feeding group, respectively (both P < 0.05), with no differences between groups (both P > 0.05). Moreover, feeding pattern did not modulate the bed rest-induced decline in insulin sensitivity (-46 ± 3% vs. 39 ± 3%; P < 0.001) or V̇o2peak (-2.5 ± 2.2 vs. -8.6 ± 2.2%; P < 0.010) (both P > 0.05). Myofibrillar protein synthesis rates during bed rest did not differ between the intermittent and continuous feeding group (1.33 ± 0.07 vs. 1.50 ± 0.13%/day, respectively; P > 0.05). In conclusion, dietary feeding pattern does not modulate the loss of muscle mass or the decline in metabolic health during 1 wk of bed rest in healthy men.

Neurostructural correlates of strength decrease following total knee arthroplasty: A systematic review of the literature with meta-analysis.

Recent literature suggests that alterations in both neural and structural components of the neuromuscular system are major determinants of knee extensor muscle weakness after total knee arthroplasty (TKA). Therefore, the goal of this study was to investigate the maximal voluntary strength (MVS), voluntary muscle activation (VMA), and the cross-sectional area (CSA) of the muscle, up to 33 months after the TKA. We searched relevant scientific databases and literature for outcomes of interest, including quadriceps MVS, VMA, and CSA. Ten studies met the inclusion criteria and involved a total of 289 patients. The quality of the studies was evaluated by Methodological Index for Non-Randomized Studies (MINORS). Results showed that quadriceps MVS markedly declines in the early postoperative period, after which it slowly and linearly recovers over time. However, the same phenomenon was not observed for VMA and CSA, which were not significantly altered after the TKA. Furthermore, a meta-regression analysis revealed that the change in VMA accounted for 39% of the relative change in quadriceps strength (R2=0.39; p=0.015) in the early postoperative period. Patients treated with TKA had considerable weakness of the quadriceps muscle, which was detectable up to 3 months after surgery. Although the change in VMA largely explains quadriceps weakness, this change and CSA differences were not significant, suggesting that other neural correlates, such as hamstrings coactivation, might alter quadriceps muscle function. Thus, more attention should be paid to address VMA failure and coactivation of antagonist muscles. More comprehensive rehabilitation approaches may be required to target the whole neural circuit controlling the motor action.