We just came off the Olympics in Rio. Think about our 100m athletes. How long do you think they warm-up before a race that lasts only 10 seconds? Can you believe about an hour! Even our marathon athletes will warm-up for 2-3 miles before their race! You would think with 26.2 miles, there would be more than enough time to ease into their race pace but nope, they understand they need to spend a couple miles getting their system prepped to race.
The body does not respond very well going from inactivity to intense activity. The cardio-vascular, respiratory, musculo-skeletal, and neurological and metabolic energy pathways need to be gradually stimulated in order to perform at an optimal level. You need to lubricate your joints, warm your muscles and connective tissue and slowly wake up your breathing and cardio systems.
Muscles that are warm have a much better ability to extract and utilize oxygen to produce energy. As muscles warm up, the enzyme activity level is increased. This means that fats and sugars are broken down more rapidly, and more energy will be produced. This will of course, enhance your performance.