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Although regular aerobic exercise has been shown to lower arterial blood pressure in older adult humans with essential hypertension, the mechanisms responsible for this hypotensive effect remain largely unknown.To examine the hypothesis that the reduction in arterial blood pressure in older hypertensive humans with regular exercise is accompanied by evidence of a change in arterial structure.We measured peak limb vascular conductance, a well-established noninvasive measure of arterial structure, both in the forearm (untrained limb) and in the calf (exercise-trained limb) of 22 older adults (aged 51–74 years) with stage 1 or 2 essential hypertension. Eleven subjects walked 3–4 days/week at a mild exercise intensity (45% of heart rate reserve) for 6 months. Eleven other subjects served as nonexercising controls.Maximal oxygen consumption of subjects in the exercise group increased by 17% (P < 0.05) with no change in body mass and body fat. Systolic and diastolic arterial blood pressures at rest were reduced by 7 ± 4 and 5 ± 2 mmHg, respectively (P < 0.05). There were roughly 20% increases in peak forearm blood flow and peak forearm vascular conductance (both P < 0.05). Similar increases in peak calf blood flow and vascular conductance were observed (both P < 0.01). There were no significant changes in any of these variables over the same time period for the nonexercising controls.The decrease in resting blood pressure in older adults with stage 1 or 2 essential hypertension in response to regular aerobic exercise is associated with an increase in peak limb vascular conductance, which could be due in part to favorable changes in arterial structure. These exercise-induced functional and, possibly, structural changes are not confined to the exercise-trained limbs, but rather are more systemic in nature. These apparent beneficial changes in limb vasodilatory capacity and vascular structure can be produced with a mode, intensity, and frequency of aerobic exercise that can be tolerated and is commonly performed by older adults.