12th Century medicine

bleeding

Bleeding was a common practise to let off the energy of young men. For example, a literary hero Guingamor is to go hunting but:

Ses nies estoit ce jor seingniez,	His nephew [Guingamor] had been bled that day
Si estoit auques desetiez,	And so was feeling rather indisposed.

- Guingamor line 25-26 (trans. Weingartner)

So Guingamor stays at home and plays chess.