Congrats on making it to Week 3 of your training, and for being determined to push thru it, even though you missed a few runs! Make a promise to yourself to stick to the remainder of the schedule, and you will have no problem! Also, working in some cross training on your days off is a perfect way to catch back up, and to maximize your body's ability to handle the increase in mileage later on.
Jumping on the bike is a great way to cross-train, and as a matter of fact, I just got back from a spin class at the gym :-) I recommend that you go to a cycling class from time to time because you will push yourself so much harder in a group setting with an instructor. This is why I also like mixing up my cross training days with other cardio classes such as yoga and kickboxing. I would recommend an activity like one of these on one of your cross training days, and reserve the other day for strength building.
Since running is such an intensive cardio workout, you have to build up your body strength and endurance in order to push it farther and longer. This can be done in a gym weight training with free weights, or at your home or a park utilizing body resistance workouts, such as lunges, squats, tricep dips, pull-ups, etc. If you legs are sore, save them for your next run, and instead concentrate on your arms and abs. Either way, you will feel stronger on your next run, and your endurance will go through the roof!
I would also recommend throwing in some speed workouts from time to time. Exercises such as stairs, tempo and fartlek runs will not only improve your time, but it will help prepare you for courses that are may have hills, and teach your body how to recover quicker.
This is what I would recommend, and what is working for me. If you need some suggestions of workouts, or other information on running, check out Runpals.com!
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