In the final two weeks prior to your marathon, you will need to reduce your volume and intensity a bit to bring about an optimum peak. This is the time to get extra sleep, plenty of good nutrition, and run as relaxed in your workouts as possible.
Reduce your volume with two weeks to go by about 20% (of maximum mileage for this training period), but still include your normal workout frequency and intensity. This week, the chief goals are to maintain your thresholds, sharpen-up with a few quicker sessions, and allow any micro-damage to your muscles to heal.
Try to complete your last focused long run 12-14 days prior to your competition. Do this run in your planned race outfit and shoes to see how they perform in a race simulation. Also, practice your pre-run and mid-run nutrition at this time.
Research what is available on the race course, and try to purchase that product to use in your last longer workouts.
The below plan would be prime for the two runners listed with two weeks to go before a big marathon. One is a beginning runner who has never completed a marathon before, one is for a marathon veteran seeking a PR.
First or Second Year Runner, Limited Background in Formal Training
Time Goal– 4hrs
Long Run (15mls in Race Gear w/ Fueling; two-weeks to race)
Easy 45min Run, 8x 12sec Max Hill Sprints
WU, Tempo Run (6mls @ Goal Marathon Pace), WD
Easy 50min Run
Highly Competitive Runner, Extensive Background in Formal Training
Time Goal– 2:40
WU, 12mls @ Goal Marathon Pace, WD (two weeks to race; run in race gear w/ fueling)
Mod 50min, Short Hill Sprints
WU, 5x 1600m @ Half-Marathon-10K Pace w/ 400m Recovery Jogs, WD
Very Easy 30min
Easy 60min, Light Strides