How old are you?
Look at supplementation as the way to give your body everything it needs in order for it to create all of the pharmacological goodies you need such as human growth hormone and testosterone. Good quality vitamins (endurance training drains your body of key nutrients), essential amino acids (whey proteins) and essential fatty acids (flax and other oils) will put your body on the right track. Train hard, eat smart, and believe rest as important as the other two, and your body will support you.
I don't believe on precursors (the theory that if you flood your body with the precursors of hormones your body will produce more of them). For instance, one of the precursors of testosterone is common fat. I don't recall any particular study but I seriously don't think that overweight people suffer from too much testosterone....
Endurance training is more about training your mind than your body. If you learn how to transcend missery, you will progress faster and become stronger than people with better genetic make up.