00:00
One thing you always have to be cognizant of when you are doing either isometric exercise or
isotonic exercise is what you are doing with your breath. It's very easy to hold your breath
during these maneuvers causing the strain-like response. We call this a Valsalva maneuver and
it's a forced expiration against the closed glottis, a bearing down movement. As you do that
response, you get corresponding changes in blood pressure. There are four different phases
associated with the Valsalva or breath hold like that. First you get an increase in blood
pressure then you get a decrease in blood pressure as the baroreflex kicks in and then once
you release that bearing down or the holding your breath, you get a reflex increase in blood
pressure and then it comes back to normal. So why this is important is because your blood
pressure response to exercise is affected by your breath when you're doing that particular
exercise. So let's look now more closely what happens if you do resistance exercise without
holding your breath. During resting conditions, we have this kind of boxes that we're going to
use for blood pressure. The top part of the box is your systolic blood pressure, the bottom
portion of the box is your diastolic blood pressure and that red line that's mean arterial
blood pressure. So we have blood pressure now plotted on the Y axis and first you're in resting
conditions meaning that maybe you're on a weight machine but you haven't actually done any
work yet. If you do light to moderate exercise, you have an increase in systolic blood pressure,
increase in diastolic blood pressure and an increase in mean pressure. If you do moderate to
vigorous exercise with resistance training, you get even larger increases in systolic blood
pressure, diastolic blood pressure and mean pressure. So simply doing anaerobic exercise that
involves resistance work increases your blood pressure acutely while you're doing that
activity. That's important concept to keep in mind if you already have someone who is
hypertensive and you're worried about further increasing their blood pressure. Now why do
we get these blood pressure responses to resistance exercise? Well the first is very simple. It
is you're thinking about doing the exercise. That is called central command or feed forward
mechanism and it's simply your drive to want to do that exercise. Simply by thinking about
doing it you are committing yourself to start to have increases in heart rate and blood
pressure in anticipation of that result of exercise. There are also some feedback components
The baroreceptor's feedback, if there is an increase in blood pressure you get a corresponding
change in heart rate. Chemoreceptors are also involved. If you start to utilize or build up
too much carbon dioxide, that will also feed in to this exercise pathway causing an increase in
blood pressure. Finally probably the most important for the resistance exercises associated
with isometric or isotonic exercise are the skeletal muscle afferents. These are class III and
class IV muscle afferents that respond to the local milieu of things like hydrogen ions, local
metabolites, things that will engage a muscle afferent. If you know that your muscles are
increasing their activity, then you'll want to respond by increasing perfusion to them. How
does the body increase perfusion? By increasing delta P or the driving pressure. So if you have
a greater blood pressure response, you should be able to perfuse those muscles. All of these
feedback mechanisms as well as the feed forward mechanisms integrate together in the
brainstem to give a coordinated response to resistance exercise.