That's right thugspliter, the pump is just the response of your body forcing blood to the muscle helping it contract. Cortisol is a stress hormone produced from just that "STRESS". Cortisol is catabolic which means it breaks down tissue. That is why it's so important to replenish your glycogen (carbs) quickly following your workout, and then within 90 minutes consume your high quality protein. Cortisol levels are elevated and stay that way if you don't feed the muscle cells, and SLEEP.