I found this out the hard (?) way this morning. As I started my practice this morning, I couldn't help thinking about Grimmly's recent posts about the length of the inhalation and exhalation, and paid more attention to my breathing. It turns out that I start out with fairly long breaths in Suryas A and B. And then, for some inexplicable reason, once I get into Trikonasana, my breaths suddenly start getting shorter. Not sure why I do this; it's not as if the standing postures are particularly physically challenging. Anyway, I noticed this tendency, and tried to compensate by deliberately making my breaths longer. Boy, did that make Virabhadrasanas A and B harder; my thighs were positively burning. Turns out I have been slacking in the standing postures without even being aware of it.
The interesting thing is, once I got into primary (starting from Paschimottanasana), my breath automatically regained the length it had in the Suryas without any effort on my own. Curious, don't you think?
In any case, I have Grimmly to thank for bringing my attention to these fluctuations of my breath during practice. Moral of the story? I don't know... do not be dismissive of other blogger's musings about practice?