I believe everyone has a kick, we all have the creatine phosphate system that gives us this quick burst of energy. Its there and I'm sure in a mile this system is not depleted. How do you access this while tired? Well its a survival instinct, perhaps shorten your cadence to trigger it, Fight to the end or Flight accept defeat. At the end I think this comes down to how strong you are mentally. Being fit is one thing but if you're weak minded you will likely allow others to outkick you.