The Original 13 Week Sprint Training Plan Question

For biking it is very simple...more saddle time! (making sure the bike fit is decent as well does not hurt.)

For running try going slow and/or doing a combination of running and walking to build endurance (3' running 1' walking repeat etc...) until you can move up to slow running and then just put in smart miles and workouts. It is really easy to hurt yourself with bad form/to much volume when just starting running though so that is really where you need to take it easy and listen to your body (sore knees/hips, shin splints, Planter Faciatus (sp?)...Etc)

As for the x's not sure, might mean do what you can here, fill it in and use that as a starting place to build from?

Good Luck!

Thank you....

If you read the description it sounds like X should be a number you are comfortable with and increasing each week prior to starting the actual 13 week plan.  If you can already swim and bike 20-30 minutes per time a couple times a week then just start the 13 week plan.