It probably started as an attempt to increase his size, and then somebody caught him at it so he had to come up with a quick excuse:
First Man caught standing in shed, with weights tied: "Uh, it's chi-gung! You wouldn't understand..."
Other Man: "Ohhhh, Chi-gung, 'eh? Let me try. I bet you I can hold up more weight than you!"
First man: "I double-dog dare you!"