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When the Lights Go Out

“Passing out” under heavy weight should not be taken lightly.


Call it “passing out,” “blacking out” or “fainting,” but no matter what you call this physiological phenomenon, it can be a nemesis for a CrossFitter. Indeed, a significant percentage of CrossFitters will experience a “lights out” moment at some point in their training career, and it can be very dangerous.

In sports science, we refer to this phenomenon as exercise-induced syncope, and we know the general pathology — insufficient blood (and with it oxygen) to the brain. But the specific physiological cause or set of causes in CrossFit movements is not clear. So here are the major players and possible ways to deal with them:

The Valsalva Maneuver During a heavy lift like a clean, lifters often close their glottis (“hold their breath”) in order to create intrathoracic pressure, thereby stabilizing the upper spine. However, this pressure also significantly decreases blood flow back to the heart from the lower extremities. When this thoracic pressure persists for a few seconds or more, the brain suffers from lack of oxygen, and down the lifter can go.

Solution: After holding your breath at the bottom of a move, purse your lips and let small amounts of air out until you reach the rack position.

Carotid Artery Pressure Direct pressure on the carotid can occur when the bar rests high in the front-rack position for too long. To be clear, the bar does not directly apply pressure to the carotid. The bar presses back on the area of the carotid called “the superior carotid triangle” — particularly the sternocleidomastoid and omohyoideus muscles in the neck — and that pressure reduces blood flow to the brain.

Solution: Keep the bar on the clavicles. The longer you stand, the greater the chance of getting dizzy. On a clean-and-jerk, don’t pause too long. Simply ascend, set and jerk.

Vasovagal Response If lifters are excessively excited (too “psyched up”) before a lift, this arousal can actually serve as a trigger to the vagus nerve, which is a parasympathetic nerve, meaning its job is to slow things down. The problem is that the vagus nerve affects heart rate. So heart rate slows, blood pressure drops, and athletes can begin to feel lightheaded.

Solution: Approach a big lift with adequate physical preparation and a clear head; avoid getting caught up in overly emotional arousal.

Nutritional Status If athletes are dehydrated and/or low on blood sugar — both of which are often consequences of dieting — a blackout could be on the way. In dehydration, syncope is usually the result of reduced blood pressure. In the case of low blood sugar, the brain lacks necessary energy to function properly. However, dehydration and low blood sugar often go together, and their detrimental effects can be cumulative.

Solution: Stay well-hydrated before and during your workout. Do not train on an empty stomach or expect PRs when dieting.

Orthostatic Hypotension This condition, also called “postural hypotension,” is the proverbial “head rush” one may get from standing up too quickly. While it may be considered a simple consequence of blood fighting gravity (the blood pools in the lower extremities upon standing, as in the clean), the truth is that some people are more susceptible than others to this phenomenon.

Solution: Having considered the other causes above, keep track of your syncope episodes. If they persist, orthostatic hypotension can be treated pharmaceutically, and a medical professional should intervene.