When it comes to strength training (or any strenuous activity such as shoveling snow for example), breathing properly is a very important technique!
You should always be exhaling as you contract and inhaling when going back to rest. Never hold your breath during the contraction stage of any exercise. When you hold your breath while exerting force, the Valsalva maneuver comes into play.
Basically, when you hold your breath during exertion the glottis is closed against pressure and this can lead to a dramatic increase in blood pressure. When you combine high-intensity workouts with a Valsalva maneuver, your blood pressure can approach dangerous levels, especially in individuals with already high blood pressure levels and other high-risk individuals. Breathing is very important!
Josh Anderson is an AFAA Certified Personal Fitness Trainer and the CEO of Always Active Athletics.