Basic mechanisms
Possible mechanisms linking blood pressure, physical
activity and fitness have been reviewed elsewhere.
8,10,11 It is likely that the sympathetic nervous
system is involved. A meta-analysis of 13 study
groups from nine randomised controlled training
studies showed a highly significant weighted net
reduction of plasma noradrenaline of 29% (15;42)
(Po0.001).9 In addition, the lack of an effect on
blood pressure during sleep, when sympathetic
activity is low, indirectly supports the involvement
of the sympathetic nervous system in the hypotensive
effect of training. The renin–angiotensin–
aldosterone system is also potentially important
through its effects on blood volume and arterial
pressure.10 More recently, it has been suggested that
improvement of endothelial function contributes to
the reduction of blood pressure after training.12–14 It
is likely that the lowering of blood pressure by
training is multifactorial and further studies are
needed to elucidate the mechanisms.