I've come across some sites that advertise or document activities at 'running camps'. I've not personally attended one, having never taken the sport up that seriously, but on the 'Photos' sections I've noted something very telling:
These folks, when they go for their training runs, fall heavily into the 'who needs a shirt?' category.
Among males, a good 80 per cent overall are shirtless as they pad along. Among females, over 50 per cent are in their jogbras, which as you may recall qualifies as 'honorary shirtlessness' in my book. Numerous large groups of males are to be found running along with not even one member clad in a constrictive upper-body garment. Mostly, none of them is even carrying a shirt in his hand or tucked into his shorts, so it is clear everyone had started off confidently bare-chested.
The first thing one might conclude is that, when there is 'safety in shirtless numbers', the natural upshot amongst runners is to shed shirt and run free. For those of us, then, it may often be the inhibiting effect of running alone or with someone who doesn't make the first move to strip to the waist that keeps us all 'topped-up'. Ironically, of course, it would seem then if we take the initiative to take off our shirts, it is at least possible that our running partners, or others in the vicinity, might feel more comfortable following suit.
May 2015: First up, though I still try to put up blog content whenever I can, it has been easier to more regularly visit the the Twitterverse. Follow me at @barethomas10 and let's keep the shirtless running flag flying. Of course, the blog still attracts very interesting comments, and good discussion. Keep it up.
Second, in the years since this venture launched, and as shirtless running among women has gone increasingly mainstream, the term "jogbra" has clearly declined in use. I will thus prefer "sportsbra" henceforth - as has already been the case on Twitter, and in recent posts here.
I continue to welcome guest posts (sent to email@example.com) on any related topic, including from those who would discourage stripping to the waist. I am myself of course a fervent convert to the joys of running bare. But let all voices be heard!