Don’t lean over with your arms on your knees. This shows your opponent you are tired.
No matter how tired you get, keep your head up and your shoulders back.
This will give the impression of strength, both mental and physical.
There is also the metaphorical meaning of letting your head drop or having your head down, signifying acceptance of defeat.
Keeping your head up displays a willingness to face your troubles.
Show strength – feel strong.