I believe that building mileage for a marathon is the biggest robber of performance. Training for weeks and weeks plus adding mileage leaves a person worn out. Weeks and weeks of long runs add to this exhaustion.
I consider a long run to be over 15 miles in length. When the length starts approaching 20 miles even more stress is added to your training. I prefer to run long runs two weeks in a row. Resting the third week and taking one additional day of complete rest.
Example: Week 1 - Sunday Long
Week 2 - Sunday Long
Week 3 - Sunday Rest, Monday Rest
The next controversial topic is how far to run? My own experience from running 15 marathons has taught me that I need to run one 23 or 24 mile long run in training approximately three weeks before the actual race. I recommend this because, of the confidence that I receive and the time spent on my feet. Every time I tried to run just 20 mile long runs I always hit the wall at 20 miles. Going beyond 20 miles and increasing to 23 or 24 miles always prevented the wall form happening.
Pacing for marathon long runs should be very comfortable. The reason for your marathon long runs is purely aerobic. Other aspects of your marathon training will address marathon pacing etc. I recommend using a heart rate monitor for all training, especially during long runs. Keep your heart rate below 75% of maximum. Going above 75% will lengthen the recovery time of your long run.
How many long runs? I prefer to train 20 weeks for a marathon. I don't believe training plans less than this are very effective. The body needs time to adapt and become stronger. Most injuries incurred during shorter training plans are caused by adding to much stress in a short amount of time.
I will not begin my marathon training until I have finished training for a half marathon in the early spring. After running a half marathon my long runs will be over 15 miles. This is a good point to begin adding runs over 18 miles. I will try to run 6 or 7 long runs of 20 miles during marathon training. My last long run of 23 or 24 miles will be done three weeks before marathon race day. Then I will begin my taper.
Every marathon runner or coach has his or her own theory about the longest run during marathon training. Some argue that 20 miles in long enough. Others argue running up to 30 miles. And some even say that 15 miles is long enough. Which theory is correct?
In my own opinion the two greatest coaches are Arthur Lydiard and Jack Daniels. These two coaches never had their runners run longer than 22 miles. My interpretation of their coaching system is that they based this distance on the length of time that a marathoner would run during the actual race. During marathon training a distance of 22 miles ran at slower than marathon pace would equal the time running the actual marathon.
My own theory about marathon training follows a similar pattern. I try to lengthen my long run in minutes to the amount of time that I project to be my finishing time. For example if my projected marathon goal is 3 and ? hours. My longest run will be 3 and half hours at my long distance heart rate of between 60 and 75% mhr 3 weeks before the marathon.
Two drawbacks to this theory are under estimating your finishing time and running longer than three hours. Figuring out your estimated finishing time can be a challenge. There are many ways to estimate your finishing time. My personal choice is to take my latest half marathon finishing time and double it and add one half hour. For those whose finishing time projects out to be longer than 3 hours I would not run longer than 3 and a half hours.
A suggestion about longs runs during marathon training. When your long run time starts approaching three hours allow 14 to 21 days between these efforts. Three hour runs take a lot out of you both physically and mentally. Extra time is needed for the body and mind to adapt to these difficult efforts.
My theory about long runs during marathon training has helped to me set my own personal best times in the marathon. I believe this will allow you to reach your own marathon goals also.