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Background: Post-COVID condition (PCC) affects ~10% of SARS-CoV-2–infected individuals and manifests as persistent symptoms such as fatigue, exercise intolerance and muscle weakness. This study aimed to assess the skeletal muscle of these patients and compare them with healthy controls.

Methods: Biopsies were obtained from the vastus lateralis muscle of 28 nonhospitalised PCC patients without concomitant diseases (75% women, mean age 46.4 ± 10.4 years) and 28 age- and sex-matched healthy controls (79% women, mean age 46.6 ± 8.7 years). The analysis included morphological and pathological alterations, fibre type composition, fibre cross-sectional area, capillarisation, number of myonuclei, presence of developmental myosin, CD68+ cells, macroautophagy markers, mitochondrial respiration, lipidomics and RNA sequencing.

Results: PCC patients, compared to controls, had a higher percentage of angulated fibres (median [IQR] 0.43 [0.00–3.20] vs. 0.00 [0.00–0.00]; p < 0.001), small, rounded fibres (0.21 [0.00–1.20] vs. 0.00 [0.00–0.00]; p < 0.001) and fibres expressing fetal myosin (0.26 [0.00–1.15] vs. 0.00 [0.00–0.17]; p = 0.015). Semiquantitative analysis showed nuclear clumps (18/27, 66.6%), hypertrophic fibres (9/27, 33.3%) and fibrosis (22/27, 81.4%) in PCC patients. Fibre cross-sectional area was significantly lower in PCC patients (4031 ± 1365 vs. 4982 ± 1463 μm2; p = 0.018), largely driven by differences in type 2 fibre size (3533 ± 1249 vs. 4275 ± 1646 μm2; p = 0.068) than type 1 fibre size (4553 ± 1422 vs. 4932 ± 1380 μm2; p = 0.325). There was a significantly lower number of myonuclei per fibre in PCC (3.4 ± 1.1 vs. 4.1 ± 1.0; p = 0.012), but no difference in the presence of CD68+ per fibre (0.28 ± 0.15 vs. 0.22 ± 1.0; p = 0.115). No group differences were observed in macroautophagy markers LC3B (0.0032 ± 0.0007 vs. 0.0030 ± 0.0006; p = 0.232) or p62 (0.0072 ± 0.0023 vs. 0.0079 ± 0.0016; p = 0.814). Capillary-to-fibre ratio in PCC patients was lower for both type 1 (2.2 ± 0.7 vs. 2.6 ± 0.9; p = 0.044) and type 2 fibres (1.8 ± 0.6, vs. 2.2 ± 0.8; p = 0.022). Mitochondrial respiration was 11–28% lower in PCC patients, although not statistically significant. Lipidomics showed a lower number of phospholipids, and RNA sequencing revealed downregulation of eight metabolic pathways, primarily related to oxidative phosphorylation in PCC patients compared to controls (FDR < 0.05).

Conclusions: Nonhospitalised patients with PCC show signs of morphological and pathological muscle changes suggestive of degeneration and regeneration. The smaller overall fibre size, lower number of phospholipids, reduced mitochondrial oxidative capacity and lower capillarisation in these patients may be a consequence of reduced physical activity levels. The presence of clusters of atrophied angular and round-shaped fibres, signs of inflammation and fibrosis and increased expression of fetal myosin may reflect myopathic and neurogenic post-viral effects. Trial Registration: ClinicalTrials.gov Identifier: NCT05445830.

Background: Desmin is a major cytoskeletal protein considered ubiquitous in mature muscle fibers. However, we earlier reported that a subgroup of muscle fibers in the soft palate of healthy subjects and obstructive sleep apnea patients (OSA) lacked immunoexpression for desmin. This raised the question of whether these fibers also lack messenger ribonucleic acid (mRNA) for desmin and can be considered a novel fiber phenotype. Moreover, some fibers in the OSA patients had an abnormal distribution and aggregates of desmin. Thus, the aim of the study was to investigate if these desmin protein abnormalities are also reflected in the expression of desmin mRNA in an upper airway muscle of healthy subjects and OSA patients.

Methods: Muscle biopsies from the musculus uvulae in the soft palate were obtained from ten healthy male subjects and six male patients with OSA. Overnight sleep apnea registrations were done for all participants. Immunohistochemistry, in-situ hybridization, and reverse transcription–quantitative polymerase chain reaction (RT–qPCR) techniques were used to evaluate the presence of desmin protein and its mRNA.

Results: Our findings demonstrated that a group of muscle fibers lacked expression for desmin mRNA and desmin protein in healthy individuals and OSA patients (12.0 ± 5.6% vs. 23.1 ± 10.8%, p = 0.03). A subpopulation of these fibers displayed a weak subsarcolemmal rim of desmin accompanied by a few scattered mRNA dots in the cytoplasm. The muscles of OSA patients also differed from healthy subjects by exhibiting muscle fibers with reorganized or accumulated aggregates of desmin protein (14.5 ± 6.5%). In these abnormal fibers, the density of mRNA was generally low or concentrated in specific regions. The overall quantification of desmin mRNA by RT–qPCR was significantly upregulated in OSA patients compared to healthy subjects (p = 0.01).

Conclusions: Our study shows evidence that muscle fibers in the human soft palate lack both mRNA and protein for desmin. This indicates a novel cytoskeletal structure and challenges the ubiquity of desmin in muscle fibers. Moreover, the observation of reorganized or accumulated aggregates of desmin mRNA and desmin protein in OSA patients suggests a disturbance in the transcription and translation process in the fibers of the patients.

Background: Beyond being a pulmonary disease, chronic obstructive pulmonary disease (COPD) presents with extrapulmonary manifestations including reduced cognitive, cardiovascular, and muscle function. While exercise training is the cornerstone in the non-pharmacological treatment of COPD, there is a need for new exercise training methods due to suboptimal adaptations when following traditional exercise guidelines, often applying moderate-intensity continuous training (MICT). In people with COPD, short-duration high-intensity interval training (HIIT) holds the potential to induce a more optimal stimulus for training adaptations while circumventing the ventilatory burden often associated with MICT in people with COPD. We aim to determine the effects of supramaximal HIIT and MICT on extrapulmonary manifestations in people with COPD compared to matched healthy controls.

Methods: COPD-HIIT is a prospective, multi-centre, randomized, controlled trial with blinded assessors and data analysts, employing a parallel-group designed trial. In phase 1, we will investigate the effects and mechanisms of a 12-week intervention of supramaximal HIIT compared to MICT in people with COPD (n = 92) and matched healthy controls (n = 70). Participants will perform watt-based cycling two to three times weekly. In phase 2, we will determine how exercise training and inflammation impact the trajectories of neurodegeneration, in people with COPD, over 24 months. In addition to the 92 participants with COPD performing HIIT or MICT, a usual care group (n = 46) is included in phase 2. In both phases, the primary outcomes are a change from baseline in cognitive function, cardiorespiratory fitness, and muscle power. Key secondary outcomes include change from baseline exercise tolerance, brain structure, and function measured by MRI, neuroinflammation measured by PET/CT, systemic inflammation, and intramuscular adaptations. Feasibility of the interventions will be comprehensively investigated.

Discussion: The COPD-HIIT trial will determine the effects of supramaximal HIIT compared to MICT in people with COPD and healthy controls. We will provide evidence for a novel exercise modality that might overcome the barriers associated with MICT in people with COPD. We will also shed light on the impact of exercise at different intensities to reduce neurodegeneration. The goal of the COPD-HIIT trial is to improve the treatment of extrapulmonary manifestations of the disease.

Introduction: Resistance training (RT) is a key component of pulmonary rehabilitation for people with COPD; however, whether the effects of RT could be optimized by utilizing the exercise principle of non-linear periodization is yet to be determined.

Method: An international multicenter RCT was conducted across three countries. Fifty-seven people with COPD (70+7 yrs, FEV1% 49+21, 58% male) were randomized to 8 weeks of RT designed per current COPD guidelines to improve muscle strength or to non-linear periodized resistance training (NLPRT) designed to improve muscle strength [4 weeks] but also muscle endurance [4 weeks]. Outcomes included muscle strength, muscle endurance, functional exercise capacity (1-minute sit-to-stand [1-STS], endurance shuttle walk test [ESWT], Unsupported Upper Limb Exercise test [UULEX]), and disease-specific quality of life (QoL). Intention-to-treat (ITT) analysis was utilized, and Cohen's D Effect Sizes [ES] were calculated.

Result: ITT analysis demonstrated that NLPRT resulted in more pronounced effects on muscle strength (+33% vs. +21%, ES 0.928), muscle endurance (+147% vs. +50%, ES 1.080), ESWT (+168m vs. +36m, ES 0.592), 1-STS (+4 STS vs. 1 STS, ES 0.864), UULEX (+142sec vs. + 42sec, ES=0.819) (all p<0.05) when compared to RT. Both NLPRT and RT resulted in clinically relevant improvements in QoL without differences between modalities.

Conclusion: These results indicate that 8 weeks of NLPRT yields significantly better outcomes in various dimensions of muscle function and functional capacity when compared to 8 weeks of traditional RT. Consequently, this suggests a potential need for reevaluating and updating current RT guidelines to incorporate these findings.

Vocal signals, including human speech and birdsong, are produced by complicated, precisely coordinated body movements, whose execution is fitness-determining in resource competition and mate choice. While the acquisition and maintenance of motor skills generally requires practice to develop and maintain both motor circuitry and muscle performance, it is unknown whether vocal muscles, like limb muscles, exhibit exercise-induced plasticity. Here, we show that juvenile and adult zebra finches (Taeniopygia castanotis) require daily vocal exercise to first gain and subsequently maintain peak vocal muscle performance. Experimentally preventing male birds from singing alters both vocal muscle physiology and vocal performance within days. Furthermore, we find females prefer song of vocally exercised males in choice experiments. Vocal output thus contains information on recent exercise status, and acts as an honest indicator of past exercise investment in songbirds, and possibly in all vocalising vertebrates.

In the current study, we compared muscle morphology in three advanced aging cohorts that differed in physical function, includ-ing a unique cohort of lifelong endurance athletes. Biopsies from the vastus lateralis muscle of seven lifelong endurance athletes (EAs) aged 82-92 yr, and 19 subjects from the Uppsala Longitudinal Study of Adult Men (ULSAM) aged 87-91 yr were analyzed. ULSAM subjects were divided into high-(n = 9, HF) and low-(n = 10, LF) function groups based on strength and physical function tests. The analysis included general morphology, fiber type and cross-sectional area, capillarization, deficient cytochrome c oxi-dase (COX) activity, number of myonuclei and satellite cells, and markers of regeneration and denervation. Fibers with central nuclei and/or nuclear clumps were observed in all groups. EA differed from LF and HF by having a higher proportion of type I fibers, 52% more capillaries in relation to fiber area, fewer COX-negative fibers, and less variation in fiber sizes (all P < 0.05). There were no differences between the groups in the number of myonuclei and satellite cells per fiber, and no significant differ-ences between LF and HF (P > 0.05). In conclusion, signs of aging were evident in the muscle morphology of all groups, but neither endurance training status nor physical function influenced signs of regeneration and denervation processes. Lifelong en-durance training, but not higher physical function, was associated with higher muscle oxidative capacity, even beyond the age of 80.NEW & NOTEWORTHY Here we show that lifelong endurance training, but not physical function, is associated with higher mus-cle oxidative capacity, even beyond the age of 80 yr. Neither endurance training status nor physical function was significantly associated with satellite cells or markers of regeneration and denervation in muscle biopsies from these very old men.

The middle ear muscles have vital roles, yet their precise function in hearing and protection remains unclear. To better understand the function of these muscles in humans, the morphology, fiber composition, and metabolic properties of nine tensor tympani and eight stapedius muscles were analyzed with immunohistochemical, enzyme-histochemical, biochemical, and morphometric techniques. Human orofacial, jaw, extraocular, and limb muscles were used as references. The immunohistochemical analysis showed that the stapedius and tensor tympani muscles were markedly dominated by fibers expressing fast contracting myosin heavy chain MyHC-2A and MyHC-2X (79 ± 6% vs. 86 ± 9%, respectively, p = 0.04). In fact, the middle ear muscles had one of the highest proportions of MyHC-2 fibers ever reported for human muscles. Interestingly, the biochemical analysis revealed a MyHC isoform of unknown identity in both the stapedius and tensor tympani muscles. Muscle fibers containing two or more MyHC isoforms were relatively frequently observed in both muscles. A proportion of these hybrid fibers expressed a developmental MyHC isoform that is normally absent in adult human limb muscles. The middle ear muscles differed from orofacial, jaw, and limb muscles by having significantly smaller fibers (220 vs. 360 μm², respectively) and significantly higher variability in fiber size, capillarization per fiber area, mitochondrial oxidative activity, and density of nerve fascicles. Muscle spindles were observed in the tensor tympani muscle but not in the stapedius muscle. We conclude that the middle ear muscles have a highly specialized muscle morphology, fiber composition, and metabolic properties that generally showed more similarities to orofacial than jaw and limb muscles. Although the muscle fiber characteristics in the tensor tympani and stapedius muscles suggest a capacity for fast, fine-tuned, and sustainable contractions, their difference in proprioceptive control reflects different functions in hearing and protection of the inner ear.

Objective: Previous reports of muscle changes in the upper airways of obstructive sleep apnea (OSA) patients have primarily been attributed to acquired nerve lesions due to snoring vibrations. The aim of this study was to investigate whether alterations reflecting muscle fiber injuries also occur in the upper respiratory tract of snoring and OSA patients and if these changes relate to upper airway dysfunction.

Methods: Muscle changes in biopsies from the soft palate of 20 patients suffering from snoring and OSA were investigated with enzyme, immunohistochemical, and morphometric techniques. Biopsies from eight healthy non-snoring subjects were used as controls. Swallowing dysfunction was assessed with videoradiography.

Results: Fourteen patients had various degrees of swallowing dysfunction. The muscle samples from all the patients showed changes typical for both motor-nerve lesions and muscle fiber injuries. The most common alterations reflecting myopathy were fibers having aggregates and disorganization of cytoskeletal proteins (15.5 ± 10.7%). Other changes were fibers with vacuole-like structures (5.0 ± 4.4%), centrally positioned myonuclei (7.9 ± 4.8%), subsarcolemmal accumulations of nuclei, and various forms and sizes of ring fibers, that is, fibers where the myofilaments were disorganized peripherally (2.8 ± 2.8%).

Conclusion: The results show that muscle changes mirroring both myopathy and neuropathy co-exist in the upper airway of snoring OSA patients. These findings suggest muscle weakness as a contributing factor to the upper airway dysfunction in OSA patients.

Background: Training volume is paramount in the magnitude of physiological adaptations following resistance training. However, patients with severe COPD are limited by dyspnea during traditional two-limb low-load/high-repetition resistance training (LLHR-RT), resulting in suboptimal training volumes. During a single exercise session, single-limb LLHR-RT decreases the ventilatory load and enables higher localized training volumes compared with two-limb LLHR-RT.

Research Question: Does single-limb LLHR-RT lead to more profound effects compared with two-limb LLHR-RT on exercise capacity (6-min walk distance [6MWD]), health status, muscle function, and limb adaptations in patients with severe COPD?

Study Design and Methods: Thirty-three patients (mean age 66 ± 7 years; FEV1 39 ± 10% predicted) were randomized to 8 weeks of single- or two-limb LLHR-RT. Exercise capacity (6MWD), health status, and muscle function were compared between groups. Quadriceps muscle biopsy specimens were collected to examine physiological responses.

Results: Single-limb LLHR-RT did not further enhance 6MWD compared with two-limb LLHR-RT (difference, 14 [–12 to 39 m]. However, 73% in the single-limb group exceeded the known minimal clinically important difference of 30 m compared with 25% in the two-limb group (P = .02). Health status and muscle function improved to a similar extent in both groups. During training, single-limb LLHR-RT resulted in a clinically relevant reduction in dyspnea during training compared with two-limb LLHR-RT (–1.75; P = .01), but training volume was not significantly increased (23%; P = .179). Quadriceps muscle citrate synthase activity (19%; P = .03), hydroxyacyl-coenzyme A dehydrogenase protein levels (32%; P < .01), and capillary-to-fiber ratio (41%; P < .01) were increased compared with baseline after pooling muscle biopsy data from all participants.

Interpretation: Single-limb LLHR-RT did not further increase mean 6MWD compared with two-limb LLHR-RT, but it reduced exertional dyspnea and enabled more people to reach clinically relevant improvements in 6MWD. Independent of execution strategy, LLHR-RT improved exercise capacity, health status, muscle endurance, and enabled several physiological muscle adaptations, reducing the negative consequences of limb muscle dysfunction in COPD.

BACKGROUND AND HYPOTHESIS: Isolated malleus shaft fractures are rare cases. A commonly reported cause is a finger pulled out from a wet outer ear canal after a shower or bath. The objective was to investigate experimentally the mechanism and forces needed to establish an isolated malleus shaft fracture.

METHODS: Ten fresh-frozen human temporal bones were adapted to allow visual inspection of the structures involved while negative pressure trauma was applied. Thirty malleus bones were broken and the required forces were measured. Measurements from 60 adult test subjects were used to create mathematical and physical models to calculate and measure the forces necessary for generating trauma. To calculate the maximum muscle force developed by the tensor tympani muscle, the muscle area and fiber type composition were determined.

RESULTS: The temporal bone experiments showed that applied negative pressure in a wet ear canal could not fracture the malleus shaft with only passive counterforce from supporting structures, although the forces exceeded what was required for a malleus shaft fracture. When adding calculated counteracting forces from the tensor tympani muscles, which consisted of 87% type II fibers, we estimate that a sufficient force is generated to cause a malleus fracture.

CONCLUSION: The combination of a negative pressure created by a finger pulling outward in a wet ear canal and a simultaneous counteracting reflexive force by the tensor tympani muscle were found to be sufficient to cause an isolated malleus fracture with an intact tympanic membrane.