So im training for my senior year hs xc season and Ive been doing all of the usual recomendations such as raising mileage and what not and Im trying to get every edge I can get seeing its my last season. So I do this workout in my pool where I swim freestyle completely underwater on one breath any where from 30 to 60 meters then take a minute rest then do anywhere from 6 to 20 reps depending on the distance of each rep, and Im trying to make these workouts further and have more repeats as the summer progresses, its almost like a speed work session just with swimming under water and it feels like it too. So am I wasting my time essentially just holding my breath or am I actually improving myself as a runner by improving my economy and anaerobic strength?