Genotypes and phenotypes: implications of exercise on the inter-individual differences in biological responses

The increase in inactivity and sedentary behaviours has been linked to an increase in people becoming overweight and obese, which leads to serious complications, such as type 2 diabetes, stroke, heart disease, and cancers. Exercise training has been proven to improve the health-related components of fitness, for example endurance, strength, and power and helps tackle these health risks. However, a large proportion of people do not engage in exercise, with a lack of understanding on how to implement exercise efficiently to maximise people’s improvements in these components of health-related fitness. Research evidence has shown that exercise genetics play a large role in how people adapt and respond to specific types of exercise training differently. Yet, it is unclear which specific genes are of interest and if this applies to the untrained population, as most research is in elite and well-trained athletes. The aims of this thesis were to first examine the literature-based evidence on the components of health-related fitness responses to different exercise training programmes and the time-courses of these. Secondly, to assemble a list of commonly reported candidate genes and assess the association of these genes to the components of fitness, which has not been done previously. Correlation coefficient showed that training load was significantly associated with the improvements in cardiorespiratory fitness, muscular strength, and anaerobic peak power (R2 = 0.86, 0.50, 0.90, respectively) across 18 studies. Additionally, there were still large inter-individual differences in the improvements of these three phenotypes, even with matched training load and volume. The second review found that certain exercise genes explained up to 72% of this variability. Following these two reviews, training load, habits, and volume were collected via questionnaires in 661 participants from the UK population and compared with the results from the literature review. The findings were then applied in a group of previously untrained participants during a field-based training study. These participants were then genotyped to identify if there were real-world application with exercise training and genetic information to improve health and fitness phenotypes. The results uncovered that training programmes are complex, due to a mixture of training modes, changes in the programme, and progression. Nevertheless, results found that training in endurance improved participants V̇O2max significantly, yet there were still large differences between participants improvements. Eta-squared (η2) found that a large proportion of this was explained by allele-specific genotypes (53.5%), establishing the association between genotypes and the improvements in cardiorespiratory fitness.