Catalyst Athletic - Greg Everett
At this point, everyone reading this I'm sure has at least a pretty good idea of how to breath (or not) during heavy lifting. However, I do see and hear some interesting interpretations, so I want to get a few things straight.
First, it's important that when you get a breath prior to a lift, you're getting a complete one; that is, you're pulling the diaphragm down, expanding the abdomen, and filling the lungs entirely. Many people, often inadvertently, fill only the chest. This fails to establish a strong base and largely defeats the purpose of the breath. Expand, fill and then tighten down without trying to hollow or suck in your abs. I find it helps to thing of pushing the abs down. This will further pressurize, tighten up all the trunk musculature, but also maintain a broad base for better stability.
This breath should be taken and the trunk set before any lifting begins. This is particularly important for the jerk. Often athletes will initiate the lift while finalizing the inhale. This prevents complete stabilization and can throw off balance considerably. Get your air, tighten down, settle into position, and only then initiate the lift. When doing multiple consecutive reps, get a new breath for each one; don't try to do a heavy set of 5 squats on a single breath. Moreover, if you're doing heavy reps, take your time between each one. Don't feel like you have to bang out 5 reps in 5 seconds. Take a few breaths at the top between each one - I promise it still counts as one set.
There are a couple reasons dizziness or light-headedness can occur. The most common is during the front squat or the clean: the athlete is not properly racking the bar and the pressure is compressing the carotid arteries, reducing blood flow to the brain. This will not only cause dizziness, but can very easily cause unconsciousness if not responded to quickly enough - it only takes about 3-4 seconds of occlusion before you're out. Keep the shoulders forward and slightly up and pull the head straight back - the bar should not be in contact with the clavicles, and should not be cutting your head off.
The other reason, which occurs independently of bar placement or even exercise, is stimulation of the vagus nerve by holding the breath and/or bearing down. Both of these actions, particularly together, can cause a reduction in heart rate and blood pressure. This reduction can be significant enough to cause dizziness and unconsciousness. You can easily feel the effect of holding your breath on heart rate: Find your pulse, feel it for a while, then keep your fingers on it while you hold your breath for a few seconds; you'll feel an almost immediate reduction in pulse rate. These things are a couple of a collection of vagal manuevers used in medicine to control tachycardia.
If during any exercise you start to feel dizzy, develop tunnel vision or the like, immediately stop and take a knee. Occasionally you will recover enough to complete the lift, but if you're light-headed enough, your judgment will no longer be sufficient to determine whether or not you're able to, and this is when you get yourself into trouble. I have seen more than one lifter pass out during a clean recovery; luckily, none of these have resulted in serious injury, but the potential for injury should be obvious. Don't be stupid