In one embodiment, a method for generating a message to a friend of a user is provided, comprising: processing activity data of a first user measured by an activity monitoring device to update a value of an activity metric for the first user； identifying a change in an inequality relationship between the value of the activity metric for the first user and a value of the activity metric for a second user； in response to identifying the change in the inequality relationship, prompting the first user to generate a message to the second user.
