running cross country & swim

If you plan to run XC next season then by all means start running now. A couple of things to do first. Get in touch with the coach and get an idea of what the team will be running in weekly miles when school starts. Your coach might even have a summer schedule to give you. If they give you info, then disregard the rest of this post and listen to your coach.

If you are not a runner, start slow and build throughout the summer. Run every other day easy. Maybe 2 to 3 miles. Do not worry about time, only the distance. Get up every morning and run at the same time regardless of the weather. On the days you are not running you should be cross training. Swimming, because you mentioned that as another sport as well as bike riding. Rides should be triple the time you are running up to a max of 90 minutes. You should also start a body weightlifting program. Push ups, pull ups and core.

First thing to do is run a time trial. If you are going to be a freshman next year, run either a 1600 meter or 3200 meter on the track to get a base line of your speed, pace and time. Every 3 or 4 weeks you should repeat this time trial to see how much progress is being made.

Go easy the first 4 weeks then one week of only cross training. Then for the next 4 weeks add extra miles and extra days. Your goal is to be running 6 days with 1 day of active recovery. I don't know your age or grade you will be in next year, so I'm unable to recommend a weekly mileage. Keep in mind that some schools are very involved in XC and the mileage and programs are intense. Our 7th graders will run 30 miles a week and the 8th graders will go 40 miles a week. (boys program)

You asked if it will be miserable. Yes, but in a good way. By suffering more in the summer, you will suffer later in the season. If you're doing the sport right when racing, you will be suffering, wishing for the finish line to come sooner and should be completely out of gas in the end. XC is a team sport. Your place is worth points. So if you're dogging it, you're hurting your team.

Will it slim you down? Yes. Runners are fit. Not all runners start off that way. Some are just like you. The ones that persevere, don't quit and believe in themselves come out on the other side for the best. Keep in mind that "hard work is hard", (Nike quote).

Hope some of this helps. Good luck and have fun.

at 175 and 155lbs - you may also want to look at recomp - following a structured lifting plan - it will help lose what you are describing as chubby - and help in running/swimming strength/endurance (I know it has for me)