Im not looking to bulk up, jet get cut, get rid of fat so I can get a 6pack, etc etc.. I am doing lifting, but at the end of the workout, I use the rest of my energy on running. I have been a lazy bastard for around 3 years, surprisingly im pretty muscular still, but my endurance has diminished to almost nothing. I am slowly building it back up. Today was a milestone for me since I joined the gym a month ago, I did an entire mile (80%running, 20% walking) all in one sitting. My heart rate gets up to around 180, im 18 years old, 180lbs, 5'10". Should I simply keep running until I cant stand anymore? Eventually I would like to run 2 miles nonstop.