To 'chow bears' is to become very physically tired when exercising. The phrase came about due to the feeling of 'having a bear on your back.' Obviously this would slow you down somewhat and make you feel a bit exhausted. To be 'chowing bears' would be to start feeling this sensation.
Often occurs when performing cardiovascular exercise the day after a big night, or when exercising after a few fags or pints.
"Wow bro, I'm chowing serious bears after that run!"
"Ya no me too, I'm chowing bears after I chowed that gap in the line. Mondo. Think I'm gonna need to be substituted soon."
"Coach, I chowed bears, please get me off the field!"
When you are writing a particularly challenging exam/test paper and you have to leave out one or more entire sections because they are so hard or you ran out of time. If this happens to you, you have 'chowed section.'
Geez man, I'm really chowing section in this standard grade maths paper!