Breathing — it's something that we should absolutely not take for granted.
With the assistance of our diaphragm, upper shoulder muscles and abdominal muscles, we inspire (inhale) air and exchange it at the "terminal ends" of our circulatory and respiratory pathways. Doing this allows our heart to drive oxygen-rich blood to the muscles that really need it.
Body physiology can be highly complicated on the working end of things, even when the activity is simple in nature. Although breathing would be deemed an involuntary (happening without having to think about it or control it) activity, in resistance training of any kind, it is the timing of one's breathing that becomes more critical.
It is human nature to "bear down" or hold one's breath anytime the human body anticipates resistance or impact. The act of holding one's breath during or immediately prior to exertion is how the body stabilizes itself in anticipation of a load or resistance it must overcome.
The medical term assigned to this activity of trying to force air through the nose or closed pathway is called the Valsalva maneuver. On the positive side, this maneuver stabilizes the spine when lifting heavy loads or when having to overcome a mechanical disadvantage when lifting a heavy object.
Conversely, the Valsalva maneuver (reflex) can be responsible for the increased pressure in the chest that slows down the return of blood to the heart and can increase both ocular (eye) and cerebral vascular (brain blood vessels) pressure.
Generally speaking, when an individual engages in a resistance movement, it behooves them to exhale throughout the resistant or "positive" phase of the movement. During this phase, the muscles that do the work (primary movers) are shortening. It is also during this phase that an individual is most susceptible to holding their breath.
In most instances, the muscle lengthening, or "negative" cycle of the resistance movement, is when the inhale should occur as the body prepares to send more oxygen to the muscles that will be contracting for another forceful repetition.
Applying the age-old adage that "the exception proves the rule," there are times when it behooves the individual who is performing resistance work to hold their breath through the most difficult aspect of the lifting motion and exhale only when the weight is returning to it's original position in the lift. Usually, this is recommended when the spine does not have the support of a weight bench or chair that can stabilize the body during the lift.
In other words, the Valsalva maneuver is necessary to stabilize the spine by tightening all the muscles around it.
Most often, this technique is employed when performing an Olympic lift (you need not be an Olympian to do this) where a significant amount of weight is elevated so high above the center of a person's gravity that the Valsalva is the only way to stabilize the spine. Exhaling in these movements is frequently performed once the weight has reached its apex or end-point in the lift and is then returned to its starting position.
While proper lifting mechanics are always an end-goal for all those who lift weights, great care should be taken in learning to implement breath control and the consequent effect it can have on both strength and health.
Bill Victor is the owner of Victor Fitness System Professional Fitness Trainers, Flashpoint Athletic Speed & Agility Specialists, and Performance Nutrition Consultants. He can be reached at firstname.lastname@example.org and online at http://theflashpoint.org and http://VictorFitnessSystems.com.