Abstract High intensity interval training (HIIT) improves cardiorespiratory fitness (VO2max), but its impact on metabolism remains unclear. We hypothesized that 12-week HIIT improves insulin sensitivity in people with or without type 2 diabetes (T2D, NDM). However, despite identically improved VO2max, mainly insulin-resistant persons (T2D, IR NDM) responded with improved insulin sensitivity and circulating small extracellular vesicles (SEV), along with reduced myocellular protein kinase Cε activity (T2D) or inflammation (IR NDM). These changes related to the SEV proteome, characterized by downregulated phospholipase C pathway (T2D) and upregulated antioxidant capacity (IR NDM). Thus, SEV cargo likely contributes to modulating exercise responsiveness in humans.