Sagacity is more about mind than body. You've probably heard someone be called a sage, meaning that the person has developed much wisdom and good judgment from experience. Sagacity is also a noun. The word refers to insight built from information taken in and mentally processed over many years.
Is sagacity a medical condition?
James Fenimore Cooper wrote in The Last of the Mohicans:
Had any of the Hurons turned to look behind them, they would have seen the animal watching their movements with an interest and sagacity that might easily have been mistaken for reason.
And in Fyodor Dostoevsky's The Idiot:
One of the murderers suddenly changed into a woman before your very eyes; then the woman was transformed into a hideous, cunning little dwarf; and you believed it, and accepted it all almost as a matter of course — while at the same time your intelligence seemed unusually keen, and accomplished miracles of cunning, sagacity, and logic!
Charles Dickens used the word in his novel, Bleak House:
He was really very kind and gentle, and as he stood before the fire warming his boots and rubbing his face with his forefinger, I felt a confidence in his sagacity which reassured me.