Mary Boudreau Conover BSNed 

“When you hold your breath, you can’t breathe.”   I saw that written once on a CrossFit white board. Of course, I thought it was so silly as to be hilariously funny and I’m still laughing.   

However, it made me wonder if all of us who have internalized the commands of: “Big breath! Hold it! Exhale!”  know precisely why those commands are important.  It may be that we only know half of why they are important.  That “half” would clearly be: “Strengthen your core!”  Expanding our lungs and holding it--in tandem with seriously engaging the abs—supports a solid body core and protects us from injury.   

The other half is cardiovascular and has to do with blood pressure (BP), heart rate, cardiac contractility, and conduction velocity between atria and ventricles.  For the squat it is a little different.   

This well known lifting ritual—inhale-hold-exhale—benefits you, the weightlifter, not only by enhancing your core strength, but also by helping to keep you from feeling wiffy at the end of the lift. 

 The big held breath.  Holding the breath with expanded lungs abruptly places pressure on sensitive receptors, known as baroreceptors, located mainly in the walls of the carotid sinus and the aortic arch.  This pressure causes sympathetic deactivation and vagal activation, which in turn sends an urgent message to the brain and from there to the heart and peripheral arteries to lower the BP, slow the heart rate, and decrease cardiac contractility--NOW.  

The blood pressure is lowered by vasodilatation and a decrease in ventricular contractility. The heart rate is slowed because of vagal stimulation to the sinus node, a group of cells located at the top of the right atrium that serves as the natural pacemaker of the heart.   

The exhale.  But what about when you exhale and stop fooling those sensitive pressure-receptors?  When you exhale, the pressure on the baroreceptors abruptly ends and they instantly swing into action to lower your BP and heart rate.  They do this by slowing their firing rate and thus allowing the sympathetic nerves to dominate.  Your heart increases its rate and contractility and your peripheral arterial system contracts, returning your blood pressure to normal, ready for the next rep.   

Are you making too many demands on the responsiveness of your nervous system?  Certainly not. You were made for this.  

Squat.  A different thing happens with a deep squat.  When you’re deep in the hole, the blood is squeezed out of your legs and butt, sending more blood to the heart and brain and blood pressure rises.  As you rise out of the squat, the venous pool of blood in your butt and legs returns and your BP goes down—predictably.  Should that ever be a problem (feeling wiffy---light-headed, tiny faeries floating around) when squatting, standing up quickly, or at the sight of blood, etc just cross your legs at the ankles and tighten the leg, butt and ab muscles, or of course—squat again!  No one will know.  Or at CrossFit, flop on the floor; no one will notice!    

Full bore WOD.  When CrossFitters finish an intense WOD they are usually laid out on their backs, one bent leg, arms flung east and west, not talking, mouth open and gasping.  That’s exactly the right thing to do.  During intense exercise your BP is high, but post-exercise BP drops significantly and syncope can result if you are standing.  If you must stand post WO use the leg cross and muscle tightening maneuver.   

Everyday activity.  When you are not requiring dynamic responses from your baroreceptors because of abrupt changes in blood pressure, they are still working for you, over-powering sympathetic nerve activity and maintaining a prevailing steady state of vagal efferent activity (messages sent from the brain to target organs, in this case--the heart and peripheral arteries).  This elegant system quietly takes care of you throughout all of your varied daily activities.  For example, when you rise from a sitting or lying down position gravity would demand that the blood pressure in your upper body decrease, but the reflexes of the baroreceptors maintain a relatively constant arterial pressure for most people.  However, some will need to do the ankle cross, tight legs, butt, ab maneuver. 

Summary.  We have complicated bodies, but we can be satisfied with our basic understanding of the simple physiological truth that our baroreceptors will efficiently manage our blood pressure, heart rate, and cardiac contractility when we are lifting heavy as long as we help it along.  Big breath!  Hold it!  Exhale!