In Charles Dickens's novel David Copperfield, the fictional character, Wilkins Micawber, makes an astute observation that applies to not only incomes but pacing as well:
"Annual income twenty pounds, annual expenditure nineteen pounds nineteen and six, result happiness. Annual income twenty pounds, annual expenditure twenty pounds nought and six, result misery." ~ Wilkins MicawberThe scenario:
You are standing on the starting line, blood rushing through your veins, legs jumpy with anticipation, bouncing foot to foot - champing at the bit - and gun fires. You cross the mats, press the start button on the Garmin, and take off with the flow of runners.
What could be more natural. Running. With energy. With speed. Light on your feet. Breath...and feet...and legs...and heart...all so there in the moment. You feel so freaking good.
And then you take a quick glance at your wrist. Your aimed for pace is 8:15, but Mr. Garmin seems to indicate that you are at about 7:50. "Sweet", you think. "I'm ahead of pace and I feel great. I feel so flipping great!! This is my day. I am going to crush that PR." And so it goes for the first 6 miles, where you begin to feel that perhaps you pushed it a bit too fast. So you pull in on the reigns and settle into your projected 8:15 pace, for, oh, maybe another 10 miles. And then you start noticing that your pace begins to drop. You try harder, but your legs just don't respond. Now you're at 8:40 and struggling to maintain that. At mile 21 your pace drops to 9:10, then 9:20...you walk/run your way to the finish painfully cramped from the waist down...You feel like you're crawling and you can not will your legs to move any faster.
How could something that began so gloriously end in ignominious defeat??
So let's talk marathon pacing (this applies to shorter distances as well - but for different and the same reasons). Generally your optimal marathon pace (MP) is very close to, but slightly above, your lactate-threshold (LT) pace. Why? Well, two reasons really:
1) Once you drop down below to your LT pace certain things begin happening, metabolically, in your muscles increasing acid concentration and interfering with energy production. Stay just above (a bit slower then) LT and that lactate is used to produce more ATP, the energy source you need to keep muscles contracting. Lactate is a fuel, but if there's too much produced at once, then it can not be taken up fast enough and accumulates in your muscles. THIS is the big problem. Lactate is not the enemy. Too much lactate too fast is the enemy. That accumulating lactate creates an acidic environment that physically damages your muscles and interferes with the process of muscle contraction.
2) When you stay just above LT, you can use both fat and glycogen for energy production. Go under LT, and you predominantly rely on glycogen which is a very limited fuel source. If you can stay in the zone where fat and glycogen are used, sparing the limited glycogen for as long as possible, then you are less likely to bonk at mile 17, or 20, or 22...So, let's return to our runner above. Let's say that she runs just 5 seconds per mile faster than LT for the first 6 miles of her marathon - what happens? Well, the environment of her muscles is now acidic and that shuts down the enzymes needed for ATP production. What does she FEEL: heavy and tight. And now she must work harder to maintain the pace that would have felt doable had she not begun this whole metabolic process. She has also burned through precious glycogen at a higher rate than she needed to. So, she will run out earlier in the race. The result: The seconds she "banked" during the early stages of the race will be lost many times over during the later stages of the race.
Training of course should aim to lower the pace at which you can run before hitting LT (that is you should be training to improve your LT pace + training your fat burning metabolism), and your race pace should be determined with that in mind. But it is crucial that you stay above that place where bad things begin to happen (and you will not feel the deleterious effects until AFTER it is too late). And the fact is that most of us have experienced the consequences of going out too fast, and yet we continue to do it. It takes discipline and understanding to do the right thing, especially when everyone around you is doing the wrong thing (going out too fast). BUT I guarantee, if you heed this warning, you will be passing all those suffering through the later stages of their race, and best of all you will feel stronger and more capable than you ever have before!