Impairments in microvascular perfusion that occur as a result of capillary rarefaction or reduced insulin mediated dilation of terminal arterioles have been proposed to limit nutrient and insulin delivery to skeletal muscle in sedentary individuals, obesity, metabolic syndrome and ageing, via a mechanism involving reductions in endothelial NO production. As such the mechanisms that underlie these impairments, and how lifestyle interventions influence them, are of great scientific and clinical significance. Current knowledge on the enzymes that determine NO bioavailability is primarily based on measurements in isolated blood vessels from animal models. A lack of suitable techniques has meant there is a paucity of data regarding the mechanisms that lead to impaired microvascular perfusion in human skeletal muscle. As such our lab has recently developed immunofluorescence microscopy methods which allow quantitation of the protein content and phosphorylation state of enzymes within the endothelium of the microvasculature of human muscle (1).Using these techniques our lab has demonstrated that the microcirculation in human muscle is highly responsive to increases in physical activity with substantial changes in capillary density and content and activity of endothelial enzymes that control muscle perfusion occurring. In support of this, endurance training (ET) in lean healthy individual results in increased capillarization and elevated eNOS protein content (2). Interestingly, ET in obese individuals causes similar increases in capillarization and eNOS content, but also results in decreased NADP(H)oxidase content, which, is not apparent in lean individuals. Such adaptations are not restricted to endurance-type activities. High intensity interval training (HIT) induces comparable improvements in capillarization and endothelial enzymes to ET in both lean (1) and obese individuals (unpublished data). However, 6wks of HIT in lean individuals increased eNOS protein content of the muscle microvascular endothelium more than ET (2; P < 0.05). These findings add to the growing support that HIT is an effective time-saving training method. Furthermore, unpublished data suggest that resistance training induces smaller improvements in endothelial enzymes than ET and HIT. It is becoming increasingly apparent that precise regulation of skeletal muscle perfusion by the microvasculature is crucial for maintaining healthy skeletal muscle function. As such interventions aimed at improving microvascular perfusion are crucial, with the above data suggesting that exercise training is an essential lifestyle modification capable of maintaining or improving skeletal muscle endothelial function. However, further research is necessary to fully elucidate the microvascular adaptations which occur following exercise training, and what form of training is optimal as a therapeutic strategy.