Tapering Is Comprehensive
It’s probably intuitive to you that resting before a race involves cutting back on both aspects of training load: mileage and intensity. One issue marathoners often encounter is the phenomenon I call “frisky legs.” A couple of weeks into a more prolonged taper but with a week or so remaining before the marathon, you are likely to be feeling the beneficial physical effects of taking it easier, and as a result of feeling fresher than you have in months, you may be seduced into running faster on your daily runs, and especially in your final few programmed workouts, than you should. Like much in life, what feels great at the time may come at a cost. I speak from experience: In 2002 I was getting ready for the Vermont City Marathon and had a solid shot at a PR based on a number of key sessions in the month or two beforehand. Four days before the race, I set out to run a four-miler at goal marathon pace. Instead, I felt so fantastic that I pulled out most of the stops in the last two miles and in the last 5K of the workout I came perilously close to my PR at the time. That was almost surely one reason I fell well short of expectations in the marathon.
In any case, be sure to not only keep your mileage totals modest but take special care to keep your easy runs extremely easy. If this means hooking up with someone much slower than you for runs in the last two or three weeks, or running on a treadmill with the belt speed set at a very modest pace, by all means go for it. It’s worth the added reach.