Contingency Management (CM) is highly effective in promoting recovery from substance use disorders, but benefits tend to attenuate over time when CM is discontinued. Identifying modifications of CM delivery that can extend its benefits is an important goal. The goal of this study is to evaluate the use of reinforcements to increase physical activity, specifically walking. The study provides a standard CM intervention to promote walking for three weeks. After three weeks, a progressively increasing variable interval schedule of reinforcement will be evaluated for increasing the durability of effects of the initial CM intervention. We hypothesize that Variable Interval Prize Contingency Management will result in greater adherence to a walking goal of 10,000 steps per day at Week 15 and Week 24 compared to the Control Condition.

Inclusion Criteria:

• age > 18 years
• currently not physically active
• Physically able and willing to walk 10,000 steps per day

Exclusion Criteria:

• psychiatric or physical illness that could interfere with participation