Often I would begin to feel better at mile 2 and even better at mile 3 if it was a longer race like a 10 miler. But when racing a 5K or shorter there's no time for feeling lousy – you've got to be 'on it' from the gun.
Perhaps you've noticed this, too?
This phenomena is not solely reserved for races, either. Have you ever started your run and felt absolutely gassed, only to rally 10-20 minutes later and finish feeling strong and rejuvenated?
The answer is an effective warm-up. By warming up to meet the demands of the workout or race, you'll hit your first split very comfortably, relaxed, and confident.
Generally you'll want to address these three areas: dynamic mobility, the aerobic system, and the neuromuscular system.
Dynamic Mobility First
You don't have to get real fancy here, just do a few moves that take your body's joints through a full range and multiple planes of motion. The lunge matrix works well, for example.
The typical runner runs and sits. So, not much movement side-to-side or rotation. The dynamic warm up may be the only time during the day where you're really exploring these planes and so just from an injury prevention standpoint it's important to include them in your routine.
The Progressive Aerobic Warm Up
If you've ever felt truly lousy in the first few minutes of a run and then “miraculously” better as you continued, consider your pace. I see it EVERYDAY in the gym. Guy hops on treadmill sets the speed to 7.0 and he's off! No doubt his legs feel heavy and breathing is labored as his body attempts to switch over from 'sedentary mode' to to 'aerobic mode'.
Give your body's systems a chance to recalibrate and adjust. Simply start your run by walking, then shuffling, then jogging, THEN running. No predetermined times here - just listen to your body and it will naturally and gradually increase the pace as your aerobic system revs up.
“The Shorter The Race, The Longer The Warm-up.”
If you're going to do some high intensity training or racing, then you need more than dynamic mobility and a progressive aerobic warm up run. You'll feel best if you engage your neuromuscular system a bit more by doing some running at race pace or faster.
Racing a 5K? After the warm up walk/jog/run, do several 'strides' to ignite your nervous system. These should be building to slightly faster than race pace. No need to set any PRs here, just looking to wake that system up with some progressively faster 20sec strides.
==>Now, here's the part that most people ordinarily wouldn't do, but I promise it works. Bang out a quarter mile at race pace. Really sense into the pace and how sustainable it feels. Practice being relaxed and economical.
Allow about 5 minutes to go by between the end of the warm up and the race. But not too much time or you'll lose the benefit!
Now, when you start the race, your body will feel the familiar. You will have JUST practiced what you are doing. Your energy systems all say, “GO”. No more sucking wind in the first mile :-)