David's Girl again, after a half marathon, your joints and muscles ache for at least two days. Its normal. Its called DOMS. The process of taxing your body and then recovery is how you bring about physical changes in it. It really is no pain, no gain.
Reading this thread, I can't help notice a few other things. Firstly, overweight people, rather than complying with the fat, happy stereotype, often seem quite unhappy with their weight. Or at least talk about it an awful lot. They also think they have the monopoly on physical struggles. And are people supposed to be extra nice to them and avoid upsetting them, while they tend to come out with relatively abusive comments to slimmer people without thinking ("thin", "thin faced", "men prefer curvy women", etc).
I don't know why I can't emphathise enough with fat people. I don't know why they can't empathise enough with slim people who exercise either. I suspect though its because I feel that being overweight is something you can do something about yourself in many cases, while there a lot of people out there who suffer illness and physical ailments that they cannot do anything about. I certainly find it easier to empathise with someone who is suffering with cancer, for example. I honestly don't find overweight people that interesting. I don't insult them when I see them (and wish that they'd extend me the same courtesy). I also wonder though whether the people that do comment on them do it out of concern and also because they don't want to identify with them as they don't want to be overweight themselves?
Stands back, waiting for sarcastic, quickly followed by smug comments and accusations of being "angry" and "lacking empathy".