Boston-based RunKeeper has begun displaying offers from brands to its users as they reach certain milestones in their fitness regimens. RunKeeper is seeking to make the program appear as native as possible to its application to avoid the semblance of traditional mobile advertising. 

?We had been thinking for a long time about the business model and when we would invest in monetization,? said Jason Jacobs, CEO and founder of RunKeeper. ?We didn?t want to just do advertising. We didn?t want to do anything to disrupt the user experience.? 

RunKeeper counts 34 million users around the world. The app allows users to track their runs, walks and other workouts using the GPS in their phones and by logging their activities. 

After logging a workout in the app and hitting certain milestones, such as a best new pace, users will be rewarded in a way that is meant to appear serendipitous. The rewards will all be fitness-related, from brands that include Pebble, Chobani, Propel Fitness Water, Quaker Oats and P&G Secret Deodorant. Users can also be rewarded with free song downloads sponsored by brands. 

RunKeeper will seek to identify key milestones in its users? fitness regimens and then display rewards from sponsor brands. The brands pay Kiip on what it calls a cost-per-engagement basis, and revenues are shared with RunKeeper. 

The rewards will vary from brand to brand. In some cases a reward might be a free product, or a discount on a service, Mr. Jacobs said. 

Kiip, which originated as a rewards distributor for gaming apps, has evolved to serve other types of apps, such as those used for recipes and fitness. The company integrated with the AllRecipes.com app earlier this year, for example. 

The rewards are designed to surprise users, said Brian Wong, CEO of Kiip, based in San Francisco. 

?It?s not about dangling a carrot in front of people to get them to achieve certain milestones,? he said. ?That attracts the wrong kinds of users.? 

Mr. Wong said RunKeeper and Kiip worked together to ensure that the rewards appear native to the app.

RunKeeper plans to continue testing and monitoring how its users react to the rewards, but initial testing was positive, the company said. It is restricting the rewards to certain key milestones at first, but will consider expanding it further, Mr. Jacobs said. 

If all goes according to plan, the rewards will be popping up on users? screen right as they are feeling the elation of having completed a good workout. 

RunKeeper does not want to crash that high by inundating its users with banner ads and other traditional mobile advertising media.

?We our curator?s eye, we want to be careful how we present this to our users,? said Mr. Jacobs. ?We are going to be careful to partner with appropriate brands, and we are going to be careful about which rewards we will put in front of our users.?