Im 20 now, at 16 I was running 3 miles in 21 min for a national Kickboxing tournament. Since College I have put on a good bit of weight( about 35 lbs) and now if I try to run more than a mile my calves and thighs just give out. So I end up with a 12 min. LSD run (pathetic, I know). I need some advice on how to build back up to a 3 mile run (hell, even a 2 mile run). My calves don't bother me during sprint work ( 100 yds x 6 with 1 min rest between sprints. So I am a bit perplexed as to why I have the big buildup during LSD runs. Thanks peoples.