use security assist to create a login system
once the user logs in, they could go to a page to submit a run
you would need a table to contain:
and other information about the run.
when the user logs in, their ID is stored in a session.
use a form top collect the distance and insert to a database table with the data and the usersID
then you could use sum() like you suggested to return the total runs for a specific uer,