What are your runs like in the week leading up to your A marathon? And how much biking and swimming could I do in the week leading up to the race without hurting my marathon result?
I roughly followed the taper in the Pfitzinger and Douglas book Advanced Marathoning for London in April, with a fair degree of success. I think I was doing the 85 mile week plan, although this was higher than most of my miles leading up to the taper, so this may have been on the high side.
There was a mix of steady, threshold, intervals (3x1 mile @ 5k pace being a key one 10 days out) and a race the week before and I came home in a fairly respectable 2:27:56, for a 7 minute PB, so something seemed to have worked. Not sure how much part the taper played though. I haven’t raced a tri for a few years now, but I’d be happily getting some time in on the bike in that period assuming it wasn’t too intense. Swimming too, making sure I wasn’t too fatigued overall.
Cheers, Rich
Not sure what fast is to you, but I like the 60% two weeks out and 40% one week out model.
I like keeping the same number of activities, but no intensity in swim / bike. A few 400’s and some striders in my run leading up to race day.
Good enough for a BQ.
I do think taper is individual. I like to stay active. I cannot say that my legs feel particularly fresh on race day, but the endurance is there. I have felt fresh at other races and maybe that leads me to over cooking it early, but I don’t race as well. I think key is to shed as much fatigue and lethargy as possible without losing too much fitness. How you get there will take some experimenting.
YMMV
It’s hard to post after 2:27 guy 
I’m slower, just sub-3 most of the times.
Every training week has about 3 quality running sessions: 2 shorter intensive stuff and a long run.
Taper is 2 weeks and the sessions look like this:
2 weeks out:
- 5x1 mile @MP
- no second quality session, just 6 miles aerobic
- 13 miles long run
1 week out: - 3x1 mile @MP
- no or minimum running last 3 days
- marathon
I tend to overpush myself so a conservative taper works better.
Would some intensity in a swim, or a hard 90 min bike midweek, affect my marathon?
Intensity in the swim earlier in the week is probably okay. I wouldn’t go hard on the bike the week of as you will end up with some lingering fatigue.
What is your goal in the marathon; Finish or maximize performance? If it’s the latter then no, stop the swim and bike BS and focus on running.
I prefer a 3 week peaking period to a 1 or 2 week. Here’s how my last one went.
Saturday 22 days out, 21 mile run at 6:58 pace
21D: 35 minutes very easy
20D: 70 minutes at 7 flat + 25 minutes easy
19D: 5 x 1 mile at threshold (5:40s) + 4 miles quick in the afternoon
18D: 2 very easy runs totaling 10 miles
17D: 8 miles at 7:00 pace
16D: 8 x 400 in 75s
15D: 1:45 long run at 6:55pace
14D: 30 minutes very easy
13D: 2 runs totaling 10 miles at 7:00 pace (7 + 3)
12D: 12 miles with 8 miles at MP (6:00)
11D: two very easy runs of 3 miles each
10D: 40 minutes very easy
9D: 2 runs totaling 10 miles at 7:00 pace (6+4)
8D: 12 miles at 6:55 pace
7D: Rest
6D: 3 miles at 7:00 pace
5D: 3 x 2k at threshold
4D: 25 very easy minutes
3D 2 runs totaling 6 miles at 7:00 pace (3 + 3)
2D 30 minutes easy
1D: 1 mile easy, 1 mile at MP, 1 mile easy
0D: 26.2 miles in 2:39
As you can see I bring the mileage down but I keep intensity.
Threshold intervals, short intervals of maybe 3 min x 4 sets max.
Race effort run of 6 to 7 miles.
2 days out off day.
Day before 2 to 3 mile tempo.
If the marathon is my A race, I usually remove swimming and biking the week before to rest up.
I don’t have detailed guidance like those above . I’m decently fast as an age grouper and BQ, but I’m not anywhere near your speed.
I find almost no crossover fatigue from swimming to running and only a little from biking as long as keep the biking within reason. In fact I feel like cycling keeps my legs loose during the taper and keeps my taper tantrums in line too. LT and sweet spot intervals are more fatiguing than spinning or short VO2 max intervals. Of course the leg crushing group ride with multiple sprints and hills climbs leaves me shredded for 1-2 days.
My Boston plan this year,
5 and 4 weeks out: peak mileage at 50ish MPW. During marathon season I get to 11-12 hours/week of training, ~ 6 of it running
2 weeks out: Run 37 miles with a VO2 set, hill reps, EZ run and a marathon pace run (12 miles with 5 at MP)
Bike 4 hours: spin, spin, 30min VO2 set, EZ MTB day
1 week out: R: 20 miles with hill reps, short MP set, VO2 set, race prep
bike: 3 hours : EZ road ride, higher cadence set on the trainer
Boston: run fast enough not to freeze !