The trial will be conducted over two, 3-month periods. For the first 3 months, there will be 3 groups: Group 1 will receive the Twitter intervention and a "Fitbit" triaxial pedometer to track their steps throughout the day; Group 2 will receive the Fitbit pedometer only; Group 3 will be a waitlist control, and receive an online Center for Disease Control (CDC) website on physical activity and walking improvement.