Interesting that very few of these life hacking blog posts attempt to draw a distinction between different types of exercise. A marathon (or training for one) is a very different form of stress to a low-rep high-intensity power or oly lifting session, and I would expect their neurological effects to be miles apart.
Regarding the endorphin hypothesis, there's another parallel hypothesis which is that the good feelings of exercise are just a symptom of oxygen deprivation in the brain:
Altitude-chamber tests have shown that as oxygen deprivation
increases, some victims experience a sense of increasing
well-being, even euphoria, while they’re losing the ability
to function in a thoughtful, coordinated manner.
I saw recently a show on Discovery about the rescue swimmer training program and they mentioned that euphoria is one of the symptoms of oxygen deprivation. At one moment one of the candidates stayed too much under water and fainted, yet when they pulled him outside, he had a grin on his face and looked euphoric.
I have trained in swimming for a big part of my youth, not competition but skills. When practicing swimming under water all teachers were certain to warn us to not push too far. If you are reaching your limits there is a small window where you don't feel anything anymore, which you can possibly ignore by a feeling of "I can do this", which makes you euphoric as well. Combined with lack of oxygen the euphoria will actually put your life at risk while your down there being happy...
Regarding the endorphin hypothesis, there's another parallel hypothesis which is that the good feelings of exercise are just a symptom of oxygen deprivation in the brain:
Source: http://www.planeandpilotmag.com/pilot-talk/ntsb-debriefer/a-...