Endurance exercise improves health partly though improvements in skeletal muscle function. Mitochondrial biogenesis is one of the mechanisms that underpin the positive health benefits of endurance exercise. Endurance-exercise and energy sensitive pathways signal to promote transcriptional processes that initiate the adaptive response. Thus the aim of this thesis was to further understand the regulation of post-exercise signalling within skeletal muscle, with specific focus on the activation of energy-sensitive mitochondrial biogenic signalling pathways. It was demonstrated that muscle-specific knockout of p53 does not impair mitochondrial protein content or enzyme activity within mouse skeletal muscle. In human skeletal muscle, fasting and fasted-exercise augment CREB\(^S\)\(^e\)\(^r\)\(^1\)\(^3\)\(^3\) and AMPK\(^T\)\(^h\)\(^r\)\(^1\)\(^7\)\(^2\) phosphorylation, while the mRNA expression of \(PDK4\) but not \(PPARGC1A\) is also increased in the fasted state. Finally, one week of nicotinamide riboside supplementation did not alter skeletal muscle mitochondrial respiration and whole-body substrate utilisation at rest or during endurance exercise, while SIRT1 and 3 activity and \(PPARGC1A\) mRNA expression at rest and following endurance-exercise are also unaffected by nicotinamide riboside supplementation. Overall, this thesis contributes novel data to the understanding of metabolism and skeletal muscle signalling following endurance exercise and how nutrition and endurance exercise could be integrated to optimise specific adaptations.

The principle aims of this thesis involved the development of methods to measure enzymes that determine nitric oxide (NO) production (eNOS) and quenching (NAD(P)Hoxidase) within the microvasculature of skeletal muscle, and the use of these techniques to investigate metabolic syndrome and various training modes. Chapter 2 describes the development of reliable methods to analyse enzymes responsible for NO bioavailability within the endothelium of skeletal muscle microvessels. Chapter 3 suggests that impaired eNOS ser1176 phosphorylation is instrumental to the reductions in insulin sensitivity of obese Zucker rats. Chapter 4 reveals that 6 weeks endurance training (ET) and sprint interval training (SIT) in sedentary males induce similar increases in capillary density, and that SIT is more effective than ET at increasing eNOS content. Chapter 5 fails to observe a change in any measure of microvascular structure or function following 6 weeks resistance training in sedentary males. Chapter 6 suggests that 4 weeks of constant-load SIT is an effective intervention to improve the content of endothelial enzymes controlling NO bioavailability in obesity. In conclusion this thesis describes novel techniques which will be valuable tools for future research into microvascular function, and suggests that SIT may be an effective time efficient strategy to improve microvascular function.

The menopause is associated with a deficiency of reproductive hormones, and accompanied by a significant loss of bone mass. This bone loss is accelerated within the first five years post-menopause. Muscle strength at this time would have important clinical implications for correcting imbalance and preventing falls. The aim of the studies within this thesis were to 1) determine the rate and time course of force loss of the quadriceps muscle group over 12 months in three groups of women with varying hormonal status 2) establish the role of oestrogen in this weakness and 3) investigate the effectiveness of hormone replacement therapy (HRT) in maintaining muscle function. The reliability of an isokinetic dynamometer and a strain gauge assembly was examined initially to determine the inherent variability of muscle function assessment. Strength of the knee extensors measured on the isokinetic dynamometer was deemed reliable in middle-aged women, although at 1.05 rad/s more practice trials were needed to attain peak torque. Measurements of the knee flexors were highly variable. Maximal voluntary isometric contractions were repeatable using the strain gauge system, for both the knee extensors and first dorsal interosseus (FOI) muscle. There was greater variability in force production generated from electrically stimulated contractions. Maximal strength of the knee extensors declined by 9.3-4.6 and I0.3?3.1% (mean?SE) for dynamic (1.05 radls) and isometric strength respectively over 9 months in hypoestrogenic post-menopausal women. There were no changes at higher angular velocities, or for handgrip strength. These results support the role of reproductive hormones in influencing force production, which is further endorsed by the observation that females on HRT did not experience a reduction in strength over this time. The force loss was significant only when the post-menopausal and HRT group were compared (p < 0.05). The postmenopausal group were within I to 3 years past the menopause, the time period in which bone loss is rapid. This rapid loss of strength would therefore be expected to level out, similarly to bone. The menopause is an oestrogen-deficient and progesterone-deficient endocrinopathy. It is not possible to identify which hormone, if not both, is responsible for these observed changes in strength. To explore the relationship between acute changes in oestrogen and progesterone and strength, maximal force production of the quadriceps and first dorsal interosseus (FOI) was measured across the menstrual cycle. Maximal strength of the quadriceps was lowest prior to the surge in luteinizing hormone (LH) and reached its peak mid-luteal, a difference of 12.6?4.3% (mean?SE). These changes were significantly different (p < O.OS). From these results, there does not appear to be a role of unopposed oestrogen influencing force production but the pattern of strength changes implicates progesterone. There were no corresponding fluctuations in strength of the FOI, which remained relatively stable across the menstrual cycle. The contractility and fatigue resistance of the quadriceps did not differ significantly between any phase (p > O.OS).The difficulty in isolating oestrogen during the menstrual cycle does not render this a good model to assess its effects upon force production. Maximal strength and fatiguability of the FDI were examined in young women undergoing in vitro fertilisation (IVF) treatment when acute, massive changes in oestrogen are induced. There were no differences in muscle function of the FDI when assessed under very low or high oestrogen changes (p > O.05). The independent effects of oestrogen upon muscle function were not demonstrated here. Hormone replacement therapy is the most efficacious treatment for preventing menopausally-related bone loss. The results from the longitudinal study suggest that HRT confers protection against muscle weakness as a consequence of ovarian failure. Whether HRT maintains or restores strength was examined in the FDI of post-menopausal women (n=9). The oestrogen only and oestrogen-progestogen phases were compared with baseline measurements. A positive change in strength was observed, although this did not reach significance (p < O.1). The increase in strength (15.2±20.6%) between baseline and the oestrogen-progestogen phase of HRT corroborates the involvement of progesterone in determining muscle function. The findings suggest that the menopause is associated with a loss of strength, prevented by the administration of HRT. Oestrogen alone does not influence force production, although progesterone is implicated. This has important ramifications in hysterectomised women who are prescribed preparations containing oestrogen only.