User device position indication for security and distributed race challenges

A mobile computing device includes a processor configured to receive position information from a position sensor and a display controlled by the processor. The device also includes a storage medium accessible to the processor and bearing instructions which, when executed by the processor, cause the processor to receive user input to challenge a friend's mobile device to an exercise, upload the challenge to a server, and receive a signal from the server indicating the challenge is accepted. The instructions cause the processor to upload to the server position information at a predetermined start time and receive from the server map information presenting a position of the mobile device and a position of the friend's mobile device. Further, the instructions cause the processor to receive updates of the map information including updates of the position of the mobile device and the position of the friend's mobile device periodically during the exercise.