No, silly. Not that kind of LSD. Take your mind out of the gutter. To a runner, LSD means "long, slow distance" running. You begin your run slow. As in really slow. Your feet land with softness and a spring. Your breathing is slow. Your heart rate is under control.
Performing exercise at an aerobic level of intensity is the key to developing your aerobic system. By using the LSD method, I have discovered that though I am running slower I am running farther -- without taking any rest breaks. Today I had planned to get in, maybe, 4-5 miles. I ended up feeling so good I stopped at 10.
I ran the entire time. Movement was bliss, with legs and lungs taking me for a delightful run.
Someone has said, "Running may not add years to your life but there's no doubt it will add life to your years." I can heartily agree.