We all feel amazing at mile 6.
Yet the all too common and seemingly inevitable occurs.
The slowing of pace during the second half of a marathon.
It is almost universally experienced by distance athletes. If you've covered 26.2 miles, you have likely dealt with this yourself. Luckily a single strategy can generally overcome this obstacle. But, what causes this slowing, and how can we deal with it?
If you cover the first 13.1 miles too quickly, that mistake now has another 13.1 miles to express itself. If you run the first 13.1 miles too slowly, you have a second 13.1 miles to fix that mistake.
The first part of remedying an issue is to find the cause. Be that an injury or a poor race performance. When looking at a significant slowing of pace during a marathon, the causes generally come down to only a few things.
Starting with training and fitness. Simply put, many people are under-trained when they step foot at the starting line of a marathon. It is a grave error to underestimate the distance and overestimate your fitness. This can include anything from a lack of consistent training volume to not enough time spent at race pace during training.
The second half of a marathon is almost always going to be warmer than the first half. Depending on the temperature, this can cause both an increase in perceived effort and slowing of pace.
Something else that cannot be helped is a second half of the route being more difficult than the first half. This is the case at events such as Boston, Grandfather Mountain Marathon, and the Seattle Marathon.
Poor nutrition can mean either taking in too many calories, too few calories, or the wrong type. This is likely the most difficult factor to control because nutrition depends so much on all other race factors.
Using tools such as the McMillan Running Calculator, you can estimate times at various distances based on a recent race. This does not mean that if you run a 45 minute 10k last week, you can run a 3:31 marathon next week. Among other things, that 3:31 equivalent assumes similar race conditions and proper training for the distance.
When it comes down to it, the chief reason for excessive fatigue and a drastic slowing of pace during the second half of a marathon is poor pacing early on. This can mean you went out too fast for your fitness level, for the weather, or for the terrain.
It is also important to realize that pacing trumps all of the above issues. If the weather is excessively warm as was the case at the 2012 Boston Marathon, if you are under trained, if the second half of the course is hillier...all of that can be remedied by running the first half slower. You cannot eat or fuel your way out of running the first 13.1 miles too fast.
The goal should not always be the same split or a negative split, but not having a drastic slowing of pace will always be beneficial. An often suggestion strategy is to aim for a constant pace over the 26.2 miles with a gradually increasing level of perceived effort.