I like to run and try to get out 4 times a week. I buy good shoes and have no knee problems (I actually know more people in MA that have knee problems than runners that do). I am training distance right now, but if I were running just for MA, I would be doing a 5K plan that has short to mid mileage, tempo and hills built into the schedule. You get down to doing a low 20 something in the 5K and you will be kicking it (pun intended) in your classes. I never could get the knack of swimming, I even tried last summer and took some lessons. It's too bad you can't use a snorkel in triathalons or I would be all over it. I limit my carbs to natural carbs, try to eat protein based meals especially after the long runs occasionally throwing in a protein shake after a strenuous workout.