The skeletal muscle fibre is a syncitium where each myonucleus regulates the gene products in a finite volume of cytoplasm i.e., the myonuclear domain (MND). A novel image analysis algorithm applied to confocal images, analyzing MND size and myonuclear spatial distribution in 3-dimensions in single skeletal muscle fibres has been used in this project. The goal was to explore the modulation of myonuclei count and MND size in response to muscle adaptation processes. The effects of ageing, gender, hormones, muscle hypertrophy and body size were investigated on MND size. A strong linear relationship was found between MND size and body size in the muscle fibres from mammals representing a 100,000-fold difference in body size. Independent of species, MND size was highly dependent on MyHC isoform type and mitochondrial contents of skeletal muscle fibres. In hypertrophic mice, a significant effect of MND size on specific force and myosin content was observed. This effect was muscle fibre type-specific and shows that the bigger MNDs in fast-twitch EDL muscle fibres are optimally tuned for force production while smaller MNDs in slow-twitch soleus muscle fibres have a much more dynamic range of hypertrophy without functional compromise. This indicates a critical volume individual myonuclei can support efficiently for a proportional gain in muscle fibre force and size. In human muscle fibres, spatial organization of myonuclei was affected by both ageing and MyHC isoform expression. In fibres expressing type I MyHC isoform, an increased MND size variability and myonuclear aggregates were observed in old age although average MND size was unchanged. In contrast, in type IIa fibres, the average MND size was smaller reflecting smaller size of muscle fibres. Those changes may influence the transcriptional activity per myonucleus and/or local cooperatively of myonuclei in a gender and muscle fibre-type specific manner. Finally, hormone replacement therapy was shown to negate menopause-related functional impairment in skeletal muscle fibres. The positive effect on force was due to quantitative effect in fibres expressing fast myosin isoform while the effect was both quantitative and qualitative in fibres expressing slow myosin isoform. The effect on MND size was fibre type dependent and was achieved by significantly reducing domain size in slow- but not the fast-twitch muscle fibres. Together, our data suggest that modulation of myonuclei count and MND size is a mechanism contributing to remodelling of skeletal muscle in muscle adaptation process. These findings should be considered when developing therapeutic approaches towards restoring muscle mass and strength in muscle wasting conditions.

The purpose of this study was to evaluate the manual and automatic analysis methods for force-time curve analysis of the isometric mid-thigh pull (IMTP) test. The visual analysis, first derivative analysis and threshold analysis methods were used to analyse onset time and time-specific forces at 50 ms, 90 ms, 200 ms and 250 ms on the force-time curve. Ninety-three collegiate sports athletes’ trials were selected and analysed by each method. The visual analysis method was set as the reference method for paired comparisons with the first derivative analysis method and threshold analysis method. Onset time comparisons revealed that the first derivative analysis method was comparable with the visual analysis method with average difference at about 30 ms. Results from the weighted least products regression analysis and the Bland-Altman analysis showed that large fixed bias confounded by proportional bias existed in the threshold analysis method, and time-specific force variables obtained from the first derivative analysis method were closer to those from the visual analysis method when compared with the threshold analysis method. These findings suggest that the first derivative analysis method could be an effective tool for force-time curve analysis of the IMTP test.

Title: Relationship between selected specific and general indicators of strength in water slalom competitors in category C1 Objectives: The aim of the study was to find out the relationship between the maximum strength tests at the gym and the explosive force test when paddling on flat water. Another aim of the thesis was to compare the measurement with results in selection races to Czech national team 2018. Methods: The test battery for general force tests included the bench press test, the attachment on the bench, the one arm attachment on the bench and the one arm pull up on the bar. To test the explosive force on a flat water we used a three-axis piezoelectric load cell 9137. Dewesoft Sirirus and Dewesoft, Dewetron, were used to diagnose the course of force. Correlation analysis was used to determine the relationship between the measurements. The degree of dependence was determined by the correlation coefficient value. Results: A strong dependence rate (r = ≥ 0.7) was demonstrated in the water test and the one arm attachment on the bench. There was no evidence of a strong degree of dependence on bench - press exercises (r = 0,63), the attachment on the bench (r = 0,58)and the one arm pull up on the bar (r = 0,04). The paddlers who achieved the best results in specific and general strength...

E3-Ubiquitin-Ligasen übertragen Ubiquitin auf die von ihnen gebundenen Substratproteine. Durch diese Ubiquitinierung werden Proteine für den kontrollierten Abbau im Ubiquitin-Proteasom-System markiert. Dieser Prozess beeinflusst aber auch die Aktivität verschiedener Signalwege, die Lokalisation von Proteinen oder die strukturelle Integrität zellulärer Komponenten. MuRF1, MuRF2 und MuRF3 sind E3-Ubiquitin-Ligasen, die hauptsächlich in quergestreifter Muskulatur exprimiert werden. Von MuRF1 ist bereits bekannt, dass es u. a. über die Ubiquitinierung von Myosinen und deren anschließender Degradation an der Entwicklung der Herz- und Skelettmuskelatrophie beteiligt ist. Da das Wissen über MuRF2 und MuRF3 in diesem Zusammenhang noch begrenzt ist, sollte die Auswirkung der kombinierten Keimbahndeletion von MuRF2 und MuRF3 in einem Mausmodell untersucht werden. Der Doppelknockout (DKO) von MuRF2 und MuRF3 führte zu Veränderungen der Morphologie und der Funktionsfähigkeit der Skelett- und Herzmuskulatur. In Skelettmuskelfasern kam es zur Ablagerung myosinhaltiger Proteinaggregate, zu einer Zunahme an langsam kontrahierenden Muskelfasern sowie zum Auftreten von Myozyten mit zentral gelegenen Nuclei als Anzeichen von Regenerationsprozessen. Isolierte Skelettmuskeln von DKO-Mäusen entwickelten eine geringere maximale spezifische Kraft als Muskeln aus Kontrolltieren. Ihre Herzen waren morphologisch unauffällig. Dennoch waren die Kontraktion des linken Ventrikels und das Schlagvolumen reduziert. Darüber hinaus zeigten isolierte Kardiomyozyten Beeinträchtigungen der Kontraktionsfähigkeit und der Kalziumströme in vitro. Eine massenspektrometrische Untersuchung ergab, dass in den Muskeln der MuRF2/3-DKO-Mäuse im Vergleich zu den Kontrollmäusen 12 Proteine in erhöhter Menge vorhanden waren. Eine Anreicherung von MAPKAP-K3, einem dieser Proteine, und von MAPKAP-K2 konnte im Western Blot von Proteinlysaten aus Skelettmuskeln und dem Herz der MuRF2/3-DKO-Mäuse detektiert werden. / E3 ubiquitin ligases attach the small modifier ubiquitin to their substrate proteins. This ubiquitin-tag not only marks proteins for the proteasome dependent degradation, but also influences the activity of signalling pathways, the localisation of proteins or the structural integrity of cellular components. MuRF1, MuRF2, and MuRF3 are E3 ubiquitin ligases predominantly expressed in striated muscles. MuRF1 is involved in cardiac and skeletal muscle atrophy by mediating proteasome-dependent degradation of myosins. The knowledge about MuRF2 and MuRF3 in this context is limited. Therefore, a mouse model was used to analyse the impact of the combined deletion of MuRF2 and MuRF3. The double knockout (DKO) of MuRF2 and MuRF3 influenced the structure and function of skeletal and cardiac muscle. Skeletal muscle fibres exhibited myosin-containing protein aggregates, a fibre-type shift towards slow fibres, and myoycytes with central nuclei which is an indication of regeneration. Maximal force development was reduced in isolated hindlimb muscles M. soleus and M. extensor digitorum longus of MuRF2/3-DKO mice. Hearts were morphologically normal. No protein aggregates or signs of fibrosis were detected. However, heart performance was impaired. The contractibility of the left ventricle and the ejection fraction were reduced. Isolated cardiomyocytes showed a diminished contractibility. Furthermore, their speed of contraction and relaxation was reduced and they had impaired calcium transients. Mass spectrometric analysis of muscle lysates identified 12 enriched proteins in MuRF2/3-DKO muscles. Western Blot analysis confirmed that MAPKAP-K3, one of these proteins, and MAPKAP-K2 were enriched in lysates of skeletal muscles and left ventricles of MuRF2/3-DKO mice. Further investigations will show how MAPKAP-K2- and MAPKAP-K3-signalling pathways are involved in the development of the MuRF2/3-DKO-phenotype.

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