Type-2 diabetes is a major health problem worldwide and the prevalence keeps surging. Exercise and diet interventions are first-line procedures in diabetes prevention and management. However, the predisposition to the development of insulin resistance and the action needed to stay healthy may differ markedly at the individual level. To understand this, we must address the diversity in skeletal muscle composition - the primary glucose-disposal organ. The current project aims to determine the role of inter-individual skeletal muscle diversity in insulin resistance. Skeletal muscle is a heterogeneous tissue consisting of a mixture of fibers broadly defined as slow and fast fibers. Whereas the average skeletal muscle consists of a roughly even mixture of each type, a large proportion of individuals display a predominantly fast or slow muscle composition (=myotype). While fast myotypes may excel in sprint-like sport events, fast fibers retain an inferior glucose-handling capacity and poor insulin sensitivity leading to the question: Is insulin-resistance the heavy toll for speed? Using our own novel non-invasive approach for myotype determination, we will address this relationship with an unprecedented statistical power followed up by mechanistic and translational research in distinct slow and fast myotype groups. The results can establish an important determinant of type-2 diabetes development and by early preventive screening allow targeted exercise and diet counterresponses.