Capt. Ken O'Donnell of the Concord said about 12:25 p.m. on Thursday, a 20-year-old woman fell while jogging along Thoreau Street and Sudbury Road.
O'Donnell said the department got a call that "someone collapsed and was laying down."
O'Donnell said the woman fainted and doubled over near O'Donnell said she was wearing jogging attire.
"When we got there, people were around her, assisting her," O'Donnell said.
The woman was conscious and alert, he said.
She was transported by the fire department to Emerson Hospital as a precaution, O'Donnell said.
Police officers directed traffic around the accident scene on the busy streets.