Christiansen, Danny (2018) Promoting training adaptation in human skeletal muscle by blood flow restriction and cold-water immersion: with special emphasis on K+ regulation and Na+,K+-ATPase abundance in different fibre types. PhD thesis, Victoria University.

Abstract

The molecular signals underlying improvements in the skeletal muscle capacity for K+ regulation and Na+,K+-ATPase expression in humans are poorly understood. Further, fibre-type-specific regulation of Na+,K+-ATPase isoforms by exercise training appears inadequately explored. This thesis investigated in humans possible mechanisms regulating the muscle’s capacity for K+ regulation and Na+,K+-ATPase-isoform expression in different fibre types with exercise training and presents a novel method for fibre type identification of single muscle fibres. Molecular signals (oxidative stress, hypoxia, lactate, AMPK- and Ca2+-signalling) were modulated by exercising with and without blood flow restriction (BFR), and in systemic hypoxia, and changes in expression of Na+,K+-ATPase genes were examined by RT-PCR. In another experiment, an intra-subject design was used, where one leg trained with and the other leg without BFR, along with measurement of thigh K+ release. Effects of cold-water immersion on training-induced adaptations in Na+,K+-ATPase isoforms were also examined. The reliability and validity of dot blotting for fibre-type determination of single muscle fibres were evaluated by use of western blotting. Key findings were that increased oxidative stress, AMPK signalling, and disturbance of ionic and redox homeostasis are positively associated with training-induced increases in the capacity for K+ regulation and Na+,K+-ATPase-isoform expression. In contrast, the level of hypoxia and lactate concentration, and modulation of CaMKII signalling, was not related to the regulation of Na+,K+-ATPase-isoform expression. Fibre type-dependent adaptations of Na+,K+-ATPase expression were associated with improvements in K+ regulation and exercise tolerance. In addition, dot blotting was valid and reliable for fibre type determination of single muscle fibres. In conclusion, this thesis has identified key mechanisms underlying, and a novel strategy (BFR training) to augment, training-induced improvements in K+ regulation by human skeletal muscle and presents a valid and reliable method for easy and rapid fibre type determination of individual muscle fibres.

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