Muscles, Volume 2, Issue 2 (June 2023) – 9 articles

This study aimed to examine the chronic effect of a stair climbing–descending exercise (ST-EX) program on glycemic control in individuals with type 2 diabetes (T2D). Sixteen T2D participants were randomly divided into two groups and followed up over 12 weeks: they either performed regular ST-EX after meals at home (n = 8) or maintained their daily routine (CON; no training) (n = 8). The participants in the ST-EX group were instructed to perform a minimum of 12 sessions/week of ST-EX for more than three days/week. One session of ST-EX consisted of two repetitions of 3 min bouts of climbing to the second floor, followed by walking down to the first floor. Fourteen participants completed the study (seven for each group). The decrease in glycoalbumin levels was significantly greater in the ST-EX group (mean value: −1.0%) than in the CON group (+0.4%). Moreover, the knee extension force increased greatly in the ST-EX group (+0.2 Nm/kg) compared with that in the CON group (−0.1 Nm/kg), with no significant change in the skeletal muscle mass. Performing regular ST-EX after meals may be an effective strategy to improve glycemic control and lower-extremity muscle strength in individuals with T2D. Full article

Strenuous exercise involving eccentric muscle actions induces skeletal muscle damage resulting in delayed onset muscle soreness (DOMS). Antioxidant supplementation, such as astaxanthin (AX), may alleviate muscle injury following intense exercise. The purpose of this study was to investigate the effect of a four-week course of AX supplementation at 12 mg/day⁻¹ on subjective markers of DOMS, recovery, and performance after a bout of muscle damaging eccentric exercise. Nineteen resistance-trained men (mean ± SD: age, 22.6 ± 2.2 y) completed a between-group design with a four-week supplementation period of 12 mg/day⁻¹ of either AX or a placebo. Subjects completed four trials, with trials One and Three designed to induce muscle damage, consisting of a one repetition maximum test (1RM) for leg-press, followed by five sets of ten repetitions at 65% of 1RM. Trials Two and Four were performance trials, conducted 48 h later and consisting of repetitions to failure at 65%, 70%, and 75% of 1RM. Subjective markers of DOMS and recovery were collected at multiple timepoints post-trial for trials One and Three. Although performance was not affected (p > 0.05), AX supplementation significantly decreased subjective markers of DOMS (p = 0.01) compared to the placebo. The results demonstrated that AX may enhance recovery by reducing DOMS without detriment to performance in resistance-trained men. Full article

The aim of the study was to analyze muscle activation in the three positions of the deadlift (DL). Twenty male participants (33.4 ± 3.9 years; 42.2 ± 9.1 months of experience with DL; 91.0 ± 14.8 kg; and 1.78 ± 0.06 m) pulled a bar through isometric actions in three DL positions: lift-off, mid-pull, and lockout. Isometric strength, knee angle, and activation of the rectus femoris (RF), biceps femoris (BF), lateral gastrocnemius (GAL), and erector spinae (ERE) muscles were collected. The analysis of variance showed that the maximum isometric force presented differences between the positions (p = 0.001; η² = 0.973) considered large with higher values at the mid-pull position. Interactions were found between muscles and position (p = 0.001; η² = 0.527) considered large. The RF and ERE showed greater activation in the lift-off position, while in the mid-pull position, there was greater activation of the BF and GAL muscles. The DL positions produce different activations in the bi-articular and uni-articular muscles. The lift-off requires more activation from the RF and ERE positions. The mid-pull position, despite generating greater force, presented greater activations in the BF and GAL. The ERE showed higher activations as the external torque was greater. Full article

Exercise-induced muscle injury and the subsequent release of Damage-Associated Molecular Patterns (DAMP) result in soreness and inflammation. Dietary supplements may accelerate the rate of recovery by supporting resolution of inflammation. The purpose of this study was to determine if methylsulfonylmethane (MSM) supplementation (30 d prior to exercise and during recovery) altered mRNA expression in LPS-exposed blood leukocytes after a bout of downhill running. Exercise consisted of 60 min of downhill running (−15% grade). Blood (baseline, pre-exercise, 4, 24, 48, and 72 h post-exercise) was diluted (1:10) and combined with LPS (20 µg/mL) for 24 h. Total RNA was isolated from leukocytes and analyzed for 574 immune-associated mRNA (Nanostring nCounter; ROSALIND.BIO). Data were expressed as log2 fold change from baseline for each condition (MSM and placebo). Compared to placebo, MSM supplementation was associated with an improved inflammation response (15 mRNA) and viral immune response (2 mRNA). The largest number of changes were found at 4 and 24 h post-exercise. The key finding in the present study is that MSM supplementation can improve inflammation management and the innate immune response after exercise. Full article

The skeletal muscle is a highly plastic tissue that shows a remarkable adaptive capacity in response to acute and resistance exercise, and modifies its composition to adapt to use and disuse, a process referred to as muscle plasticity. Heat shock proteins (HSPs), a class of evolutionarily conserved molecular chaperones, have been implicated in the regulation of skeletal muscle plasticity. Here, we summarize key findings supporting the notion that HSPs are important components required to maintain skeletal muscle integrity and functionality. HSPs participate in the transcriptional program required for myogenesis and are activated following muscle exercise and injury. Their dysfunction, either as a consequence of improper expression or genetic mutations, contributes to muscle atrophy and leads to the development of myopathies and peripheral motor neuropathies. Denervation/reinnervation and repeated rounds of nerve degeneration/regeneration have been observed in motor neuropathies, suggesting that an imbalance in HSP expression and function may impair the repair of the neuromuscular junctions. Boosting HSP activity may help preventing muscle atrophy by promoting muscle differentiation and helping the repair of NMJs. Boosting HSP function may also help to combat the development of rhabdomyosarcoma (RMS), a highly aggressive type of pediatric soft tissue sarcoma whose cells have skeletal muscle features but are unable to fully differentiate into skeletal muscle cells. Full article

We describe two cases of myofibrillar myopathies, due to different gene mutations. The first was a girl with cardiomyopathy and sensory axonal neuropathy that underwent cardiac transplantation at 15 years and suffers from rotatory scoliosis due to BAG3 mutation. The second is a male patient, with evident limb-girdle weakness since age 3. Two muscle biopsies were performed at ages 3 and 15, with muscle MRI, and LDB3 gene sequence analysis also carried out. Muscle biopsies revealed the presence of dystrophic changes in the first biopsy and myopathic abnormalities in the second, and the MRI images of the lower limbs showed an asymmetrical involvement in the thigh of quadriceps muscles and in the calf of gastrocnemius muscles. The patient was responsive to treatment with an intermittent steroid regimen and muscle-strengthening exercises. Considerations on both muscle–bone interaction and psychological and socioeconomic conditions are carried out for both cases. Full article

Limb-girdle muscular dystrophies (LGMDs) represent a group of muscle diseases due to monogenic mutations encoding muscle proteins that are defective for heterozygous and homozygous mutations prevalent in certain regions. Advances in knowledge of their pathophysiology have shed light on these rare diseases, which were, until recently, difficult to diagnose. This paper has described the process of diagnosis in autosomal recessive limb-girdle dystrophy that in Tunisia are due to the c.521del mutation in gamma-sarcoglycanopathy and to ethnically specific mutations in other countries such as Italy. The epidemiology, pathophysiology clinical features, and the main socioeconomic needs as well as research progress are discussed. We discuss an Italian case for its psychosocial impact and socioeconomic consideration and compare this case with Tunisian patients. Full article

Musculoskeletal health is directly linked to independence and longevity, but disease and aging impairs muscle mass and health. Complete repair after a pathological or physiological muscle injury is critical for maintaining muscle function, yet muscle repair is compromised after disuse, or in conditions such as metabolic diseases, cancer, and aging. Regeneration of damaged tissue is critically dependent upon achieving the optimal function of satellite cells (muscle stem cells, MSCs). MSC remodeling in muscle repair is highly dependent upon its microenvironment, and metabolic health of MSCs, which is dependent on the functional capacity of their mitochondria. Muscle repair is energy demanding and mitochondria provide the primary source for energy production during regeneration. However, disease and aging induce mitochondrial dysfunction, which limits energy production during muscle regeneration. Nevertheless, the role of mitochondria in muscle repair likely extends beyond the production of ATP and mitochondria could provide potentially important regulatory signaling to MSCs during repair from injury. The scope of current research in muscle regeneration extends from molecules to exosomes, largely with the goal of understanding ways to improve MSC function. This review focuses on the role of mitochondria in skeletal muscle myogenesis/regeneration and repair. A therapeutic strategy for improving muscle mitochondrial number and health will be discussed as a means for enhancing muscle regeneration. Highlights: (a). Mitochondrial dysfunction limits muscle regeneration; (b). Muscle stem cell (MSC) function can be modulated by mitochondria; (c). Enhancing mitochondria in MSCs may provide a strategy for improving muscle regeneration after an injury. Full article

This study examines the relationships between ultrasonography measurements of skeletal muscle size and echo intensity (EI) with muscle strength and local muscle endurance in a habitually resistance-trained population. Twenty young, healthy participants underwent imaging of the biceps brachii in the sagittal and transverse planes and with the extended field of view (EFOV) technique. Linear regression was used to examine measures of muscle thickness (MT), muscle cross-sectional area (mCSA), EI, and corrected EI (cEI) in each scanning plane for their associations with strength (1RM biceps curl) and local muscle endurance (4x failure @ 50%1RM). The strongest predictor of 1RM strength and local muscle endurance was sagittal MT (adj. R² = 0.682) and sagittal cEI (adj. R² = 0.449), respectively. Strength and transverse MT (R² = 0.661) and the EFOV mCSA (R² = 0.643) demonstrated a positive relationship. Local muscle endurance and cEI in the transverse plane (R² = 0.265) and the EFOV scan (R² = 0.309) demonstrated a negative relationship. No associations were shown with uncorrected EI. While each scanning plane supports the muscle size-strength and echogenicity-endurance relationships, sagittal plane imaging demonstrated the strongest associations with muscle fitness. These findings provide important methodological insights regarding ultrasound imaging and muscle fitness relationships. Full article