I'm in shape.
Round.
I think people use it under a variety of situations. For instance, if someone has a lean body with toned muscles, they are probably likely to be told they are in shape. They could be all pumped up and have poor cardiovascular fitness, though. Equally someone could have good endurance while doing cardiovascular events but also be overweight, obese, fat, whatever....and could be called in shape for their endurance.
I think of it as a general term that is generally meaningless. People tell me that I'm in shape and I don't think I'm in shape at all......to each his own. I'm workin on it, though.....
b