Muscles, Volume 2, Issue 4 (December 2023) – 8 articles

This study evaluated muscle composition, quality, and strength of non-weight bearing and weight bearing muscles between males and females. Twenty-eight, healthy males (n = 14; mean ± SD; age = 25.1 ± 4.2 years; height = 181.9 ± 10.6 cm; weight = 91.6 ± 17.2 kg) and females (n = 14; age = 25.0 ± 3.4 years; height = 165.9 ± 6.9 cm; weight = 66.0 ± 10.2 kg) underwent body composition assessment to estimate body fat (%BF) and total-body, arm, and leg fat-free mass (TFFM, ArmFFM, and LegFFM, respectively) and muscle composition via B-mode ultrasound to measure muscle cross-sectional area (mCSA), echo intensity (EI), and thickness (mT) of four muscles [rectus femoris (RF), vastus lateralis (VL), flexor digitorum superficialis (FDS), and flexor carpi radialis (FCR)]. Additionally, upper- [handgrip strength (HG)] and lower-body [leg extension (LE)] maximal strength were measured, recorded, and expressed relative to FFM to determine muscle quality (MQ) for the dominant arm and leg, respectively. Males had greater TFFM, ArmFFM, and LegFFM (p < 0.001), mCSA for RF, VL, FCR, and FDS (p < 0.001), and mT for RF, VL (p < 0.001–0.006). Females had greater EI for RF, VL, and FDS (p = 0.003–0.01). Negative correlations were identified between EI and MQ for all muscles in males and females, however, no significance was determined. Despite the sex differences in absolute strength and size, muscle quality (relative strength) was not different for the upper nor lower body. Full article

Several reports have provided evidence that there are genetic variants of genes such as MSTN, BDRKB2, ACTN3 and ADRB2 that are involved in a better response to adaptation during resistance or strength training, while other genes such as GRB14, AGT and END1 are reported to be associated with the risk of suffering from some diseases such as diabetes, hypertension or obesity. A cross-sectional study from a Mexican Mestizo population was performed to estimate the frequency of 10 gene variants in 8 genes involved in athletic performance or chronic degenerative diseases, MSTN (rs1805085, rs1805086), BDKRB2 (rs1799722), FST (rs1423560), ACTN3 (rs1815739), ADRB2 (rs1042713, rs1042714), GRB14 (rs8192673), AGT (rs699) and EDN1 (rs5370), and to compare frequencies from 26 populations reported in the Database of 1000 Genomes project. Genotype frequencies fitted the Hardy–Weinberg equilibrium, except for MST rs1805086 and FST rs1423560, and our study revealed significant differences in the distribution of frequencies of some of these gene variants among populations reported in the 1000 Genomes Project. Our findings provide insights regarding the genetic background of our population, and future case–control studies can be carried out with more accurate sample sizes for genetic association studies. Our results may be also useful in recognizing the roles and mechanisms contributing to athletic performance and/or chronic degenerative diseases in Mexicans. Full article

Skeletal muscle MRI studies in limb-girdle muscular dystrophy (LGMD) have increased over the past decades, improving the utility of MRI as a differential diagnostic tool. Nevertheless, the relative rarity of individual genotypes limits the scope of what each study can address, making it challenging to obtain a comprehensive overview of the MRI image of this splintered group. Furthermore, MRI studies have varied in their methods for assessing fat infiltration, which is essential in skeletal muscle MRI evaluation. It stayed problematic and impeded attempts to integrate multiple studies to cover the core MRI features of a distinct LGMD. In this study, we conducted a systematic review of LGMD in adults published until April 2023; 935 references were screened in PubMed and EMBASE, searches of the gray literature, and additional records were added during the screening process. Finally, 39 studies were included in our final analysis. We attempted to quantitatively synthesize the MRI data sets from the 39 individual studies. Finally, we illustrated ideal and simple MRI muscle involvement patterns of six representative LGMD genotypes. Our summary synthesis reveals a distinct distribution pattern of affected muscles by LGMD genotypes, which may be helpful for a quick first-tier differential diagnosis guiding genetic diagnostics. Full article

Electromyographic biofeedback (EMG-BF) is a technique that can contribute to the improvement of muscle tone and control in the rehabilitation process after injury. The aim of this research was to determine the effectiveness of EMG-BF in increasing the electromyographic activity of the vastus lateralis after knee injury. The sample consisted of four individuals who had undergone surgery or rehabilitation to resolve either a partial meniscal tear or a patellar tendon strain. The intervention consisted of a program of ten sessions of EMG-BF work. Twelve trials were performed in each session, in which participants were instructed to target the muscle tension produced by the vastus lateralis of the uninjured hemilateral limb. Of the twelve trials in each session, the first three and the last three were performed without feedback, and the intermediate six with feedback. The recording of muscle activity was performed using CY-351/2 Mioback equipment, which allowed the amplitude of the electromyographic signal to be evaluated. The results indicated that the sample analyzed reached greater amplitude during the biofeedback trials, both for the maximum (Z = −13.43, p < 0.001, Cohen’s d = 0.64, 95% CI (0.27, 1.01)) and mean (Z = −7.26, p < 0.001, Cohen’s d = 0.24, 95% CI (−0.12, 0.60)) values. The amplitude also increased throughout the ten sessions, both for the maximum (Z = −3.06, p < 0.01, Cohen’s d = 1.37, 95% CI (0.29, 2.45)) and mean (Z = −3.06, p < 0.01, Cohen’s d = 1.20, 95% CI (0.34, 2.08)) values. Thus, the results highlight the efficacy of this technique in improving muscle activity, suggesting that it is a useful therapeutic procedure in injury recovery. Full article

Firefighters are at a higher risk for experiencing back pain due to the nature of their job, but physical fitness may help to reduce this risk. Therefore, the primary purpose of this study was to determine if a correlation between subjective back pain severity and core muscular endurance exists in firefighters. A secondary purpose was to determine if age or body composition were correlated with back pain severity. This cross-sectional study was performed at a fire department during their Physical Fitness Assessment Program and included 72 male firefighters. Measures included weight, body fat percentage, maximal plank hold times for core muscular endurance, and the Oswestry Low Back Pain Disability Questionnaire. A Pearson product correlation analysis was performed between back pain score and each of the following variables: body fat percentage, BMI, age, and plank hold times. A second set of correlation coefficient analyses was performed between the same variables exclusively in subjects who reported back pain. This study found that, within this population of firefighters, there was no significant correlation between back pain and plank times or body composition variables, although there was a trend toward significant correlations between BMI and body fat percentage when only subjects with back pain were considered. Full article

The heart is composed of muscle cells called cardiomyocytes, including a specialized population named pacemaker cells that form the cardiac conduction system (CCS), which is responsible for generating the action potential dictating heart contractions. Failure of the CCS system leads to cardiac arrhythmias, which require complicated therapies and often the surgical implantation of electrical pacemakers. However, recent research has focused on the development of novel therapies using biological pacemakers that aim to substitute electrical devices. While most signaling pathways and transcription factors involved in the development of the pacemaker cells are known, the upstream regulatory networks need to be predicted through computer-based databases, mathematical modeling, as well as the functional testing of the regulatory elements in vivo, indicating the need for further research. Here, we summarize the current knowledge about the vertebrate myocardial CCS system and the development of the pacemaker cells, as well as emphasize the areas of future research to clarify the regulation of muscle pacemaker cells and the ease of development of biological therapies. Full article

Ketone salt (KS) supplementation induces temporary nutritional ketosis to achieve potential exercise performance and health benefits. Racemic KS includes both D/L isomers of β-hydroxybutyrate, yet commercially available measurement devices (i.e., blood meters) only measure the D variant. The aim of this study was to investigate the efficacy of a blood meter to measure serum β-hydroxybutyrate in comparison with gas chromatography–mass spectrometry (GC-MS) before and 30 min after consuming a placebo or racemic KS. In this triple-blinded cross-over study, 16 healthy adults were administered either a placebo or KS drink, and the circulating β-hydroxybutyrate concentration was measured at baseline (PRE) and 30 min following consumption (POST) using a blood ketone meter and by GC-MS. Compared to the placebo, both GC-MS and the blood meter obtained significantly greater β-hydroxybutyrate levels from PRE to POST time-points after consuming KS. Additionally, GC-MS results showed significantly higher levels of β-hydroxybutyrate with both the placebo and KS at PRE and POST time-points, as compared to the blood meter. These results indicate that (1) even in the absence of KS, the blood meter yields significantly lower β-hydroxybutyrate values than GC-MS, and (2) the inability of the blood meter to measure L-β-hydroxybutyrate values POST KS warrants the further development of publicly available ketone measurement apparatuses. Full article

Background: Loop diuretics (LDs) are used to treat various health conditions including heart failure (HF), liver cirrhosis, and chronic kidney disease (CKD). Sarcopenia is a skeletal muscle health issue related to the depletion and decrease of muscle mass and strength, leading to adverse outcomes including frailty syndrome, functional decline, falls, hospitalizations, augmented length of hospital stay, and increased morbidity and mortality. Methods: This study investigated the probable association between LD use and sarcopenia via conducting a non-systematic review of the existing literature. Results: In subjects with non-dialysis-dependent chronic kidney disease (NDD-CKD), an augmented risk of sarcopenia is significantly associated with LD use. Interestingly, in patients with HF treated with LDs, thigh and arm circumferences were significantly small, which is indicative of skeletal muscle wasting. Additionally, in anorexic subjects who are more likely to be on diuretic medication, suffering also from cachexia, a higher prevalence of sarcopenia was demonstrated. In cirrhotic subjects, the treatment dosage of LDs was inversely correlated with the skeletal muscle area per year (ΔSMA). Nevertheless, in subjects with liver cirrhosis treated with LDs, who were divided into those with and those without muscle cramps, the presence of sarcopenia was similar. Conclusions: Further investigation is imperative to validate potential interplay between LDs and sarcopenia. Full article