Whether training affects transmural capillary distribution is similarly unclear.Lower values were found in subendocardium and higher values in subepicardium in treadmilltrained rats, rats. Despite the conflicting reports on the effect of exer cise on capillary growth, maximal coronary blood flow are higher in the hearts of trained than untrained animals.However, increased blood flow might be due to changes in larger vessels in the vascular tree found coronary blood flow in trained pigs to be higher in subepicardium and similar in subendocardial layers while CD was lower in both regions and linked increased coronary flow with higher arteriolar density on training.Moreover, blood flow in creases in relation to increased heart rate, but CD was decreased in rats with increased heart rate. What the stimulus is for capillary growth or why it is absent under various conditions is not at all clear.Although there is a very good correlation between CD and volume density of mitochondria in hearts of differ ent species, indicating an adaptation of the capillary bed to oxidative capacity, training of various intensity in rats failed to change mitochondrial content that a lower heart rate re sulting from training could contribute to capillary growth due to an increased capillary wall tension during prolonged diastole when capillaries are wider than in systole where the find ings on capillary proFosfomycin calcium liferation are unequivocal.No pro liferation has been found in adult or older rats or in the larger animals studied so far.The role of various growth factors or mechanical effects of cardiac contraction in capillary growth is a matter for further investigation.The use of muscle biopsies in conjunction with elec tron microscopy and modern histochemical techniques has enabled the effects of different types of training to be studied in various muscles of men and women of dif ferent ages.In general, endurance training leads to in creased capillarization, which is usually preceded by or parallels increased oxidative capacity assessed either by the activity of oxidative Anagrelide enzymes. Increased CD is, as in other situations, sometimes linked with decreased fiber diam eters in endurance training linked with fiber hypertrophy.Capillary growth occurs in most cases to a similar degree in men and women. Although most studies were performed on vastus lateralis trained by bicycling, other activities like swim ming led to increased capillariza tion in the active deltoid muscle.Increased capillariza tion in endurance training was usually linked with a change of muscle composition with fast glycolytic fibers changing into fast oxidative. Several studies re ported increased CD even when muscle fiber areas did not change, indicating true capillary growth, being greater around slow and fast oxidative than around glycolytic fibers. This is not surpris ing, since fast fibers are only activated during supra maximal contraction of very short duration or heavy resistance train ing, on the other hand, did not lead to increased capil larization or even a decrease in the oxidative capacity in muscles involved in these types of training.Animal experiments are in agreement with the find ings in humans described an increased number of capillaries surround ing oxidative fibers in guinea pigs and rats trained on a treadmill.