Any pistol over 20 ounces will "flop" around on you when you run. Someday you will leave it at home.
If you like the PPK then check out the Sig 232 with the two tone finish. The slide will be stainless and the frame aluminum. That should keep the rust bunnies at bay for a while. I have a .380 Sig 232, and it is a quality rig. The .380 cartridge is pretty weenie, though. I prefer the trigger and sights on the Sig to the Walther.
A small 9mm is an option. Many people have had good luck with Kahrs, but I have not. There is a rumor about Keltec making a small 9mm and introducing it at the SHOT show, but I don't know if that rumor is just smoke or not.
A .38 special J frame is also a consideration. The .357 Magnum versions sound great- and they are-in theory. I found the sensation of firing a scandium .357 J Frame(loaded with magnums) to be similar to being smacked in the hand by an iron pipe. Five times. Then reload...
A fag bag is probably the best way to carry concealed while you are exercising. I hate the things, but they work. Choose carefully, as they are all a pain in the ass- literally. The bag will move on you and cause heat rash, so you may have to do some customization with non-chafing materials.
A good can of pepper mace might be a good addition. Dogs will definately ruin your day and it is nice to have options.
Speaking of options, have you considered hanging out on your couch with your AR-15 on your lap, speed eating pork rinds and watching the Shopping Channel? How the hell you expect to become a full fledged internet commando if you are going to EXERCISE? Yeesh.