Pacing. Sounds easy enough, but ask any runner and it can often be the bain of their existence. Before the dawn of wrist-bound GPS watches, you practically had to be a mathematician to calculate your pace as you ran.
I got smart for one marathon several years ago (I thought) and decided to print out one of those cool wrist pacing bands. I had read where if you covered it with clear packing tape before attaching it around your wrist, it would keep the moisture (sweat) out. Well, I didn't have any clear packing tape, but I did have clear Contact paper. Sounds like a good substitute, right? WRONG! Evidently Contact paper is porous and packing tape is not. So, halfway through the marathon I looked down at my wrist band. Under the contact paper was a swirl of colors. Basically I had a lava lamp on my wrist. Looked really pretty, but didn't do a dang thing for helping me keep up with my pace. Live and Learn.
Non runners and new runners often think that the second half of a race should be faster than the first half—a negative split. That may be doable in a shorter race, but more than likely with 5K, 10K, and even half marathon races, runners are shooting for even splits. Even splits can be a tall order for a full marathon but it can be done. Some running experts say that it may be more realistic, espeically for a lesser experienced runner to shoot for the second half being about 5-mins slower than the first half.
To prepare for even marathon splits or splits that are somewhat close to each other, the key really is doing race-pace runs during your training along with your tempo and long slow runs. The tempo runs help push out your lactate threshold and increase your VO2Max, making you a stronger more efficient runner. The long slow runs, help build your mileage and your muscular endurance. In most training plans you run short-and-fast and you run long-and-slow, but you don't get to run at the pace you'll be running for 26.2 miles. Seems odd to have a goal race pace, but to never run it in your training.. I think sticking in some runs that allow you to run at pace will better prepare you for the race and better prepare you for your pacing during the race.
With my runners, I have them run some of their longer tempo runs (7 or 8 miles) at race pace. They begin and end with a 1-mile warm-up/cool-down followed with the tempo miles in between. It's also a good idea to take some of those long runs and instead of running them at a minute slower than race-pace try running them at 20 to 30 seconds slower than race pace. Another good strategy is to position a mid-mileage run (say maybe 14 or 15 miles) and run it at race pace (making sure to begin with a 1-mile easy warm-up). I've also discovered that adding some speed later in a long run is an effective strategy. For example, ramp up the pace to race pace or faster for the last two miles of your long run. This helps teach your body to know that it can "pull-out" some reserves at the end of the race. If you do this in your training, it won't surprise or shock your brain/body if you do it during the race.
The long slow run is important and the bulk of your long runs need to be done in this fashion, but ramping up the pace on a select few of these long runs can really help prepare you mentally and physically for running those even splits (or close to even splits) on race day.