The five of you push hard, but only you girls are trying hardest. Mark jumps ahead mid way through, leaving you behind Maddi, only by a hair. Behind you, Liz and then Amanda, push on, but know without saying that Maddi or yourself should be the winners, with Maddi's nearly flat chest and your small one.
With each step, the battle between you two gets fiercer, but with a final heave you pass over the finish line seconds before Maddi and the others. You snap at Marcus a couple times and direct his attention to your chest as you look down, severely out of breath. Your breasts balloon out wards stretching the limits of your once supportive running shirt, the bases running out where the garment met your chest.
"See?" you say to Mark. "It does work, but to keep it temporary, we made the time limit a week at most."
"Oh, my god!" Mark gasped. "Can I feel them?" he asked tentatively.
You laugh and say "Go ahead, if it convinces you." in truth, the situation turned you on more than a little bit. He walked up and reached out for them, squeezing them softly. You found yourself relieved as you saw how close your shirt was to breaking that you had not worn a sports bra today. You guessed fairly securely that your breasts had grown to at least a mid D cup, if not more.
"So mark," an out of breath Amanda asked. "You ready to start betting with us? you can make the next bet."