In a race, walk before you have to
Having paced a number of marathons, I tend to pass runners that are walking from mile 20 onwards. These runners have the haunted look of total exhaustion, and often find it very hard to start running again.
If you have to walk in a race due to exhaustion or muscle fatigue, it is too late to get much benefit from the walking break. Taking a walking break before you are forced to walk will allow your muscles to bounce back. The walk can be anything from a few seconds at Aid Stations to a structured run/walk plan. Anecdotal evidence suggests that walking for 2-4 minutes is a good approach.
1 Will it make me slow?
People often try to avoid walking because of the time they will lose. However, a short walking break reduces your overall pace by only a small amount. Being forced to walk the last miles from exhaustion will cost a lot more time, as well as suffering.
If you walk for 2 minutes at 20 min/mile, you will cover 0.1 mile. If you had been running at 7 min/mile, that would have taken 42 seconds rather than 120. Therefore the cost is 78 seconds, which is not an outrageous amount of time. Given the way the muscles can bounce back in those two minutes, the break can pay for itself.
It is not clear to me if the optimum marathon strategy is to run the whole race at a reasonably even pace, or if it is faster to take Walking Breaks. I have seen no research or evidence one way or another.
3 Getting running again
Running again after a walking break can be painful, but the pain should only last a few dozen steps.
4 Are walking breaks right for you?
If you have never run a marathon, but are planning on a sub-4 marathon, I would suggest adding in about 3 Walking Breaks. If you think you will be slower than 4 hours, you may want to consider a few more.
If you are an experienced marathon runner, you should know if Walking Breaks are right for you. If you've been forced to walk at the end of a race, then you should add them in. If you can run the whole race, but your pace plummets at the end, consider adding them in or joining a pace group. If you can run the whole race at an even pace, or negative splits, Walking Breaks may or may not make you faster.
5 Is it a 'real' marathon if you walk?
Everyone has an opinion on this, and there is no 'right' answer. However, believing that walking in a marathon is not a 'real' marathon means when Bill Rodgers won the 1975 Boston marathon in 2:09:55, it was not a 'real' marathon as he stopped five times . That does not make sense to me. The goal of the race is to complete the distance as fast as possible. If it is faster to walk/run than to run, that is the optimum strategy. If the race has a long enough cut off to allow walking the whole race, then the walkers are fulfilling the rules of the race and are just as valid. If you don't like that, start a race with a shorter cut off; I've heard that some African races close the finish after 2:30 ;}