Circular motions are fine , but not alot of pressure . Let the tips of the brush do the work..
I have found the Mike's Natural soap tins to be awesome for loading a brush using painting strokes. No need for circles with the nice wide, flat cake.
Hypothetically speaking. I'm certain that actual badgers and boars both, would enjoy swirling around in shave products and/or the whiskers on my face.
If you want ultimate brush longevity, this prohibition on circular strokes is sound advice. It comes from the preeminent Simpsons brushmaker of the family era, Stan Archer, and was oft-repeated by David Carter of pre-Vulfix Simpsons. I'm not sure if Mark Watterson or Gary Young could give any hard evidence either, but I doubt they would disagree. Mr. Archer's point was that it is the twisting of the hair strands against each other that was particularly rough on the hairs and knot. I would suggest this is even more critical in high-lofted brushes. Gently combing out your brushes may help realign the strands and keep them from being chronically twisted.
These brushes are made for swirling, and that's just what they'll do
One of these days these brushes are gonna swirl all over you
I've never seen ill effects of using a circular motion to apply lather.