I'm with Lynn on this one, while we teach not holding your breath, the truth is we do it to keep new divers from doing something dumb. Holding your breath is a problem IF 2 other conditions are met at the same time, your lungs are completely full and you are ascending. Think about the physics involved. First off, for the air in your lungs to expand (and rupture your lungs), you MUST be ascending, if you are holding position the air in your lungs is a constant volume or if descending it's contracting- neither of which is a problem. Only when you ascend does it expand and cause a problem if it has no escape. In addition, the rate of accent also comes into play because the air expansion rate is relative to your accent rate. If you are ascending so fast that a second or 2 pause in breathing is going to be dangerous, then you are already in big trouble to start with because you are already ascending way way to fast and holding a full breath is the last thing you should be doing......in fact your lungs need to be fully deflated to help reduce your positive buoyancy and slow your accent.
That said, a couple of breathing techniques will do the job much better and there is no need to hold your breath. Both of these methods require you to be truly neutral, proper weighting helps make them more effective and easier to accomplish.
1: Breathing off the top/bottom of your lungs. To ascend/ go positive, you slowly inhale fully followed by a somewhat quicker exhale but instead of exhaling fully, you exhale about half of your lung volume, repeat as needed. To descend/go negative you do the opposite, fully exhale slowly and following it with a half breath inhaled at a faster rate.
2:Varied rate normal breathing - With this method you change the cadence of parts of your breathing cycle to accomplish an overall positive or negative buoyancy. To ascend/go positive you ssslowly inhale deeply then exhale at a faster rate, maybe 2 or 3 times faster followed by another long sssslow inhale, to descend you just switch which part of the cycle is long and slow with the shorter, faster one.
A couple of key factors in buoyancy control that many fail to realize are buoyancy adjustments are NOT instantaneous, they take time to take effect and that they are additive- the positive portions of several deep breaths add together to give you a larger effective change. I see these 2 effects getting new divers in trouble all the time. They add air to their BC, nothing happens so they do it again, nothing happens so they do it yet again, usually more this time, all of which takes 2 or 3 seconds. It's about then that the lag and additive nature of buoyancy kick in and they are quickly headed up. Buoyancy control is the art of diving and it requires slow gentle actions and the patience to wait for them to take effect.