This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Insulin resistance, defined as an impairment in insulin's ability to stimulate peripheral glucose uptake, as well as suppress hepatic glucose output and lipolysis, are major characteristics of impaired glucose tolerance (IGT) and type 2 diabetes. The mechanisms by which insulin resistance develops are unclear. Skeletal muscle is the major tissue responsible for insulin action on peripheral glucose uptake, and therefore has been implicated as a primary site for the development of insulin resistance. Intramuscular triglyceride (IMTG) content and turnover, specifically, have been the topics of considerable recent interest as the amount of IMTG correlates strongly with insulin sensitivity. Substantial data exists that healthy men and women may use IMTG differently, especially during exercise. We speculate that this gender-dependent mechanism for IMTG use is lost in the development of IGT. Our first aim will describe IMTG content and turnover at baseline and during acute exercise in men and women with IGT. The second and third aims of the study will attempt to explain the mechanisms by which men and women lose the ability to turnover IMTG once they develop IGT. We hypothesize that women rely on oxidative capacity of muscle, whereas men rely on the activation of PPAR target genes, as these have been shown in animal studies. To differentiate these mechanisms, men and women with IGT will be randomized to either an exercise training program (to increase oxidative capacity) or fibrate therapy (to activate PPAR for 12 weeks. Will we combine blood and tissue sampling, stable isotope methodology, and measures of insulin sensitivity in pursuit of these aims? Better understanding the role of IMTG content and turnover in the development of insulin resistance in men and women may guide our therapy in the prevention and treatment of diabetes.