From now to Nov. 11, Exchange shoppers can vote with their feet in the 'Exchange and Under Armour Freedom Challenge: Army vs. Air Force.' Participants cast their ballots by logging workouts at MapMyFitness.com in support of either service branch. Whichever branch gets the most workouts logged at the end of the challenge will be declared the winner. Participants could win an Under Armour or AAFES Exchange gift card. To participate, visit MapMyFitness.com or download the MapMyFitness mobile app, find "Army vs. Air Force" under "Challenges" and select which branch you would like to support. Then, log your workouts at MapMyFitness.com or by using the MapMyFitness mobile app. The Challenge is open to shoppers age 18 and older.