The health benefits of exercise have been known as early as the 5th century. Since then many studies have corroborated these benefits involving both animal and human subjects. But still, the scientific community is uncertain on whether exercise intensity or volume is more important for health benefits. Some studies indicate that vigorous intensity with low volume is adequate to improve whole-body insulin sensitivity and organ metabolism, while others indicate that moderate intensity and high volume exercise is required to achieve these benefits. 

In this thesis, I have investigated the effects of two weeks of low volume and high intensity sprint interval training (SIT) and high volume and low intensity moderate intensity continuous training (MICT) on the liver, pancreas, and intestine in untrained healthy subjects and subjects with type 2 diabetes or prediabetes using a wide range of imaging modalities. Hepatic and pancreatic fat was measured using magnetic resonance spectroscopy (MRS). The hepatic, pancreas, and intestinal insulin-stimulated glucose and fasting free fatty acid uptake was measured using positron emission tomography (PET). Lipoprotein subfraction composition was analyzed with nuclear magnetic resonance (NMR) and gut microbiome was analyzed with 16S rRNA gene sequencing. 

Both SIT and MICT reduced the liver and pancreatic fat content in subjects with high hepatic and pancreatic fat content. They also improved the lipoprotein subfraction profile with increasing the lipoproteins associated with protecting against diabetes and reducing the ones associated with acquiring diabetes. Moreover, both training modes also changed the gut microbiota profile with increasing microbes associated with protection against obesity. However, only MICT improved the hepatic and intestinal insulin-stimulated glucose and reduced fasting free fatty acid uptake. 

In conclusion, two weeks of exercise improves fat content, lipoprotein, and the gut microbiota profile regardless of training intensity or volume; however, the changes in the liver and intestinal substrate uptake depend on exercise volume rather than intensity. This suggests that, in the short-term, MICT might be more beneficial in improving internal organ metabolism than SIT.