have positive impacts on aging by helping to decreasing the shortening of telomeres. Effects on metabolic processes In addition to restructuring the muscular and skeletal system to better handle mechanical stress, physical exercise also affects gene expression with respect to metabolism. The effects are widespread and can affect anything from muscle growth to aerobic stamina to diabetes and other metabolic disorders. In general, even a small amount of exercise can induce hypomethylation of the whole genome within muscle cells. This means that many regulatory genes can be turned on for pathways like muscle repair and growth. The intensity of the exercise directly correlates to the amount of promoter demethylation, so more strenuous exercise activates more genes. MicroRNAs (miRNAs) interfere with mRNA that is present and render it unusable and therefore decrease the product of that mRNA. MiRNAs regulate many physiological processes, such as inflammation, angiogenesis (the creation of blood vessels), as well as ischemia (the restriction of blood flow within the vessels) prevention. Aerobic exercise reduces the overall number of various miRNAs within the skeletal muscle that produce negative effects. Stimuli that cause the body to enter an anabolic, or constructive, phase, such as resistance training as well as the correct diet, has also shown a reduction of miRNAs. This reduction may actually play a role in the growth of the muscle cell. Class IIa Histone deacetyltransferases (HDACs) are highly expressed within human skeletal muscles. Exercise helps to reduce their activity, especially at promoters, which affects gene expression. In mice, this regulation of HDAC5 has been shown to increase the amount of type I fibers in muscle. Type I fibers are slow twitch, endurance fibers. This data agrees with human data that says the amount of type I fibers is positively correlated with the maximal aerobic capacity. It also suggested that the amount of type 1 fibers is correlated with a histone acetyltransferase (HAT) that is involved in osteoblast differentiation and bone formation. Diabetes Individuals with type II diabetes have hypermethylation of several genes within the muscle, like peroxisome proliferator-activated receptor gamma (PPAR-γ) and coactivator 1 alpha (PGC-1α). The hypermethylation of these genes decreases the expression of both mitochondrial DNA as well as PGC-1α mRNA. Exercise is a way to prevent and treat these effects by helping to hypomethylate PPAR-γ and PGC-1α. Additionally, exercise also increases expression of glucose transporter type 4 (GLUT4), which will also help with diabetes symptoms.