need wager ideas

my cousin and i have decided to create a series of wagers to help motivate us into losing weight.

we're doing it in 5lb increments.
whoever loses 5lbs first is the winner, then we take one day off and start anew from where we are for the next 5lb "race."

wager #1: the loser has to buy the winner's coupon inserts.

wager #2: the loser has to pay for the winner's mani/pedi.

we're taking turns picking the wager.

here is where i need a little help.

i want to have a side bet going on. i want to put as a challenge to work on our upper body, since women tend to have weaker upper bodies.

the challenge is to see who can do ONE legit pull-up... military style. but i don't know what to wager. i want it to be beefy enough to entice both of us to try it.

what would you suggest?
thanks in advance for any ideas or thoughts