Q: I have recently been reading up on a plant training whereby the branch is twisted in opposite directions until you hear a snap. It said this breaks the plant fibers and causes them to rebuild and create a stronger branch with better buds. Is this correct? Would this technique be safe to use while in flower? - Alex L.
A: Alex, be careful where you get you information. There is a lot of misinformation out there that can be harmful to your plants and garden. The best sources for information on cannabis cultivation are usually not books about marijuana, but text books on plant biology, plant science and botany that never even mention the cannabis. Remember, your cannabis plants are no different from any other plant and there is no refuting science.
With that said, let me correct the erroneous information you read. The technique you described is often referred to as "super cropping" and it can be a very effective technique in creating fuller, bushier plants with additional colas. The reason for this has nothing to do with breaking and rebuilding the plant's tissue fibers. That occurs in humans when we exercise -- specifically in heavy weight training. But the goal of super cropping is the same as other pruning techniques such as topping or FIMing -- which is to release plant hormones that encourage more vigorous plant growth and development.
An example of "topping" a plant by removing the top terminal shoot.
Specifically, the pruning techniques rely on the release of plant auxins to spur new growth and plant structuring. Some growers will prefer super cropping over topping or FIMing because cutting a branch is an irreversible operation. Therefore, it is better to start by cutting less -- or in this case not at all -- especially if you’re new to the practice.            
With that said, an important concept that needs to be understood when learning about pruning is the term apical dominance. Apical dominance resides in the terminal (or top) shoot of a plant and it is what guides the upward direction of plant growth. It's also closely associated with the center or main stem or trunk. Apical dominance is governed by the production of plant hormones (auxins) that are developed in the terminal shoot. The auxin inhibits the growth of other lateral shoots below. The removal of the terminal shoot lowers certain auxins throughout the plant, which allows the lower lateral shoots to produce new, vigorous growth.
An example of FIMing a top shoot by removing 80 percent and leaving 20 percent of the shoot.
To answer the second part of your question about pruning during flowering the answer is a resounding no. Do not deploy any of these types of pruning techniques during flowering. Reserve pruning for the vegetative phase of plant development. Depending on plant's size when you trigger flowering, you may be able to get away with some pruning during the first week or two of flowering, but it is not recommended. If you veg for four weeks, begin pruning a week or two after rooting clones or transplanting seedlings, but if your are triggering flowering after only two weeks of veg, you might try week one or week two of flower, but never later.
It is advisable to begin your pruning program as early as possible to structure and develop your plant's form early, but be sure to not interfere with the flowering phase once it begins. Once flowering starts, your plant needs all its energy for bud and resin development. Pruning during flowering (other than leaves) can result in lower yields and potency or, even worse, causing the plant to hermaphrodite.
Best of luck in your endeavors to everyone and remember to stay safe and secure!