<qa>  What is the relationship between cardiovascular fitness, physical activity and cardiovascular health?Substantial evidence supports a favorable relationships between cardiovascular fitness, physical activity and cardiovascular health. In particular, it is well established that increased levels of physical activity result in favorable improvements in lipid and carbohydrate metabolism. There is also evidence that increased physical activity and cardiovascular fitness have beneficial effects on cardiovascular health independent of the effects on specific cardiovascular risk factors. One hypothesis proposes that the beneficial effects of regular exercise in humans is mediated through peripheral mechanisms, in particular through the chronic adaptations in skeletal muscle to habitual exercise. The exercise exposures required to achieve health benefits in humans are poorly defined and the mechanisms through which these beneficial adaptations occur are poorly understood. The study will investigate the peripheral biological mechanisms through which chronic physical activity alters carbohydrate metabolism and lipid metabolism, resulting in improvements in these parameters of cardiovascular health and fitness in humans. 