If you want to challenge another Litesport user, you can send a match to compete after completing a workout. From the results screen after your workout, click on "Create Match" near the bottom of your results, then select the Litesport profile you want to match with on the right-hand side of the menu. Click the user you would like to send a match to, and click "Send Match" at the bottom. You will then get a "Match Sent" confirmation: