Mobile Supportive Teams for Reinforcing Increased Daily Exercise Study

Inclusion Criteria: Participants must: * be at least 18 years of age * be insufficiently physically active (\< 150 minutes per week of moderate-intensity equivalent aerobic physical activity as measured by waist-worn accelerometer (research grade physical activity measurement device) - i.e., sum of time spent in minutes of moderate-intensity activity plus twice the minutes spent in vigorous-intensity activity \< 150 minutes per week) * be part of a self-selected team of 3-8 individuals each of whom also meet all other eligibility criteria (members of the same household are only eligible to participate if they are on the same team - limit one team per household) * have access to a smartphone (Android or iphone operating system-based) with an internet connection * report being able to walk at least ¼ mile without stopping * be able to provide informed consent * complete all screening and baseline questionnaires and activities Exclusion Criteria: * participating in another physical activity study or program * are pregnant, breastfeeding, less than 6 months post-partum, or plan to become pregnant during the time frame of the investigation * report a medical condition that would affect the safety and/or efficacy of a physical activity program (e.g., terminal illness; uncontrolled heart condition, dementia, bulimia nervosa or binge eating disorder, other significant psychiatric problems, or use of insulin) * report conditions that in the judgment of the Principal Investigator would render them unlikely to be able to independently follow the intervention protocol for 3 months, including conditions which might compromise their ability to engage independently with the intervention website materials and wearable physical activity tracker, as well as complete online questionnaires and adhere to wearing an accelerometer