I wear a sports bra under a sleeveless t-shirt (DRI-FIT fabric) and running shorts (also same fabric). Although truthfully, I wish I could just wear only the sports bra and shorts b/c the heat has been awful lately. Sometimes after I come back, I'm sweating like crazy. Running minus the shirt would keep me considerably cooler.

My question is this: Is it appropriate for a 39 year old who has two kids but a decent body to wear JUST the sports bra or is that a look for a much younger woman?

I've seen women do both and I'm confused as to what is the proper running attire rules, lol.

Any thoughts from the runners on the board?

erm if you're comfortable with just the sport bra and shorts, go for it.
I don't think there's really a rule thing with what you're going to wear for running, personally.
i'm 24 and i wouldn't go for that look, just because im not comfortable w/ it, not really because i mind people's thoughts

If you're comfortable with it, go for it!

Especially if you're running outside, no one really sees you for a long enough period of time really to judge anyways. I bet you look great so I see absolutely no problem with it if you're comfortable with it!

When I am close to goal, I will be wearing a sports bra jogging. I am looking foward to no more short sleeve shirt tan lines from jogging.

If you're comfortable, go for it.

Where I run outside, wearing only a bra is asking to get cat-called and harrassed. YMMV.

I wear a dollar store sports bra, a cotton t-shirt or tank top, and swishy fabric shorts.

What ever keeps you happy and comfy..... I've always been a singlet and shorts girl, but I don't see why your age has to come into it at all.......

If you feel comfortable then go for it and be proud of what you have

Haha...the tan lines - I can definitely relate to that.

As far as the cat calls, I doubt they'd harass me once they see I'm close to 40 and the bra has a tendency to squish my breasts down and flatten them so it's not like I'm a Playboy Bunny running and bouncing everywhere, lol.

Plus the bras I have look like you could wear them alone b/c they have subtle patterns on them.

I guess it's a matter of preference. Maybe I will but not on the weekend because everyone's out and about, lol. I will agree that running outside is different than running on a treadmill at a gym. No one sees you for very long.

If the temperature is above 95 degrees, there's no question in my mind - bra only and no shirt. It's way too hot at that point.