Before Runkeeper was highlighted they were somewhere around 25th place in category Health and fitness in the Android Market. Now they are on site and three at the time of writing they are on site looking at the total number of 288 applications. Google itself selects which apps they will highlight. How this process works is unclear, but itself does Google always know she is looking for high quality apps.
The substantial increase in the number of downloads may also have to deal with that more people have sought Runkeeper and similar apps because they have good intention to increase their sports in 2012. With RunKeeper to keep track of how much distance you travel while running or cycling, the more calories you've burned during a workout and much more. Since the beginning of last year's app has become free.