What follows isn't strictly about running (shirtless or otherwise), but the moral I would draw therefrom is what justifies its inclusion here.
I was on my way to lunch the other day, the sun burning high in the sky, when I passed three or four boys - they couldn't have been more than fourth-graders - just concluding a game of basketball. They had all stripped to the waist and seemed in the highest of spirits as they ceded the court to a female foursome.
Perhaps 30 minutes later, I was retracing my steps after my meal when I saw that three different boys were now playing. Their shirts were still on, but plastered with perspiration - and the expressions were grim as the ball was passed and shot. In sum, the trio seemed less to be enjoying some healthful exercise as trying to complete an onerous assignment from school.
Now, it may seem like a stretch for me to say this, but I'd go as far as to say that had the troika eased up a bit and peeled off their upper-body attire, they would have enjoyed their workout a lot more. The sun would have warmed them less aggressively and perhaps that indefinable camaraderie that animates shared shirtlessness would have taken hold, making for a spring in step and lightness in heart. And this thought, at least, is easily transposed to running or jogging: Many a time, I've seen a plodder soldiering along bathed in sweat, his shirt literally a-swimming - and pitied him for his refusal to embrace shirtless freedom (I'll admit that, as a man, such sentiments pretty much never strike me when passing a similarly-suffering woman - though intellectually, I hold jogbra-ness to be equally liberating).
The vignette is not quite exhausted. The happier boys I had earlier encountered, as it happened, had still been in evidence as I strolled by after lunch. They were still shirtless and now lounging about in a nearby hut, chatting up a storm with the girls who had taken their place after their game. Now, one can sometimes read screeds online by women who insist that shirtlessness is rude, inconsiderate and lower than robbing the blind. But these schoolgirls must have missed that lecture. The interaction of these youngsters seemed completely natural; the girls themselves were in shorts and T-shirts, but the boys' bare-chestedness was not being held against them. And it leads me to suspect that the great mass of people are similarly free of such prejudices - and so understand that someone shirtless in the name of exercise (whether that be running or some other form) is likely as decent and approachable as the next person.
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!