The investigators are interested in using social norms to motivate people to sign up for a 100-day exercise challenge and exploring how to make social norms messages more effective.

The investigators are interested in using social norms to motivate people to sign up for a 100-day exercise challenge and exploring how to make social norms messages more effective. Specifically, the primary purposes of this study are to test (a) whether social norms messages (i.e., information about how many people have signed up for the challenge) can increase signup rates and eventually lead people to exercise more and (b) whether such messages become more effective when they highlight different types of motivations (intrinsic vs. extrinsic motivations). Through a partnership with a university, the investigators are running a large-scale, randomized field controlled trial aimed at increasing sign-ups for the challenge and exercise frequencies during the challenge.

Benefits-eligible employees at the partner university are randomly assigned to one of four experimental conditions and receive the corresponding version of email message encouraging them to sign up for the challenge.

(1) In the control group, the email does not mention the number of people who have signed up. (2) In the norm condition, the email mentions the number of people who have signed up. (3) In the norm and health motive condition, the email mentions the number of people who have signed up, and highlights that the challenge is designed to help people to stay fit in a fun way. (4) In the norm and reward motive condition, the email mentions the number of people who have signed up, and highlights that the challenge is designed to help people to stay active and earn rewards.

The investigators hypothesize that Groups 2, 3, and 4 will have a higher sign-up rate and higher exercise frequencies on average than Group 1, because positive social norms should motivate people to engage in the target, desirable behavior. Also, the investigators will compare sign-up rates and exercise frequencies between Groups 2, 3, and 4 to examine whether highlighting intrinsic and extrinsic motives can further increase sign-up rates and overall exercise frequencies than only giving social norms information.

All benefits-eligible employees at the partner university for whom the Human Resource (HR) office has an email address on record receive invitation emails from HR. The invitation emails that contain the interventions are sent out one week AFTER the registration period has started, because HR needs to know how many people sign up in the first week and use this information to create a social norms message. Employees who sign up for the challenge during the first week of the registration period (i.e., prior to the implementation of the interventions) cannot be affected by the interventions. Thus, the investigators decide in advance that these employees will be excluded from analysis.

Employees will receive two emails that are sent eight days apart from each other. Thus, the investigators plan to examine both the sign-up rates within one week after each email goes out and the overall sign-up rates throughout the 50-day registration period.

The investigators plan to explore moderators based on (a) employees' demographics (age, gender, ethnicity, position), (b) employees' participation in previous challenges, and (c) employees' health condition and fitness level prior to the challenge (such as how actively they have been participating in other wellness activities, their health statistics).

Inclusion Criteria:

• All benefits-eligible employees at partner university for whom the Human Resource office has an email address on record

Exclusion Criteria:

• Employees who sign up for the challenge prior to the implementation of the interventions will NOT be included in the analysis.

(The interventions are implemented one week after the registration period has started. The partner university has to send invitation emails to all benefits-eligible employees with an email address on record, including those who already signed up. However, employees who already signed up cannot be affected by the interventions and thus will be excluded from the analysis.)