In adults it is known that endurance training can reduce both systolic and diastolic blood pressure by approximately 10 mmHg in individuals with moderate essential hypertension, but exercise does not seem to have an effect on subjects with severe hypertension.
However, the mechanisms responsible for the decrease in blood pressure with physical activity have yet to be determined. A reduced cardiac output is mentioned as a reason for the fact that activity lowers blood pressure, although this cardiac output reducing effect of physical activity is not found in all studies. If there is no influence on cardiac output, then the blood pressure decreasing effect may be caused by a reduction in peripheral vascular resistance, which may be due to a reduction of sympathetic nervous system activity.
In addition, the relation between physical activity and blood pressure can be caused by the anxiety-reducing effect of physical activity. It is questionable, however, if this mechanism is also present in children and adolescents.
It appears that essential hypertension may begin early in life and that detection and treatment of possible blood pressure abnormalities at young ages is important. There is, however, no direct evidence that elevated blood pressure in children is related to CVD later in life. There is also not much evidence that physical activity has beneficial effects on blood pressure in children and adolescents. There are many cross-sectional studies investigating this relationship, but again the best evidence comes from longitudinal studies and well-controlled intervention studies.
In the CATCH study, a 30-month multidisciplinary intervention in order to improve physical activity among more than 4000 children and adolescents did not have any effect on blood pressure (Webber et al 1996). It is argued that, as in adults, the possible lowering effect of physical activity on blood pressure only holds for children and adolescents with hypertension and not for young people with normal blood pressure values.
This implies that this effect is difficult to observe in population studies in children with low incidence of hypertension. It should also be kept in mind that the effect of reducing blood pressure in hypertensive children and adolescents is probably only true for high intensity aerobic type physical activity and not for normal (or habitual) physical activity.
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