As USA Track and Field Level 3 Endurance Coach(there are less two dozen in the entire country) and a USATF Level 1 School Instructor who has studied distance running for over 28 years I would say the answer is very simple. Running is a neuromuscular skill like swimming, serving a tennis ball, hitting a golf ball, throwing a ball, or high jumping, etc. While I certainly agree you should have good one leg strength and best be able to walk for a fairly long distance. As I have taught every athlete I have trained you must always work on your endurance, speed, strength. coordiation, and flexibility at all times. Starting out as a new runner you must start with drill work to teach your body the correct way to run and to run for very short distances working on correct form and stopping when you start losing your form, recover and run again. Soon you will be able to run well for a fairly long distance. I am sure many are thinking it just running I am pretty good and it came to me by just running. Then think about this after the disaster that was Sydney in 2000 for American distance runners, USATF High Performance which had been video taping athletes in every event area except the distance events since 1983, decide to video tape our best male distance runners at the 2003 USATF National Outdoor Track and Field Championships. They record the finals of all events 800m to 10,000m(10K). 60 athletes in total were rated on their biomechanics as poor, fair, average, good, or excellent. 36 were poor, 21 fair, and 3 were average. After this America’s top coaches as well as USATF High Performance focus on two things, improving running form and developing the ability to sprint. The ability to sprint is the foundation to good running form since the transition from distance running to sprinting should be smooth and effortless.