If I decide to go for it, Higdon Int. 2 seems like the easy winner on a few fronts. It's the right number of weeks. I've used his plans before. There's 2 rest days. No crazy mileage. I'd probably shift the rest day to a Tuesday or Thursday so I could match DD's days off school. It just hurts my brain to see that the *only* speedwork is 400m repeats (alternating with "tempo" runs) AND he doesn't tell you what to do for recovery between repeats (walk? jog?) or how long that recovery interval should be.
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But is it aggressive enough? Should I be doing 2 speed sessions/week?
Enter Higdon Advanced. 2 Speed sessions (repeats or hills AND a tempo run) every week. Only 1 day off, and 1 XC day. Not gonna lie....this one looks like I would want to curl up and die by week 7. More risk, more potential reward? But I also wonder if I *started* with advanced and it was too much, it would be a rather easy change to drop down to Int 2, instead of the other way around. Or if I would just crash and burn into a whimpering pile of mush. Could be one of the stupidest things I've ever done to my body. Or it could work.
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It sounds like you're on a pretty compressed timeline. Do you have the time to do some focused speed work before starting a training plan, or given the timeline would this just be it?
I know it can be tough to gain speed aggressively through a single training plan. Either the target paces start out discouragingly fast (even if you can hit them, barely, the workout is
way too hard to safely sustain), or else you have to sort of stair-step up every few weeks (e.g. your goal 5k pace may be 9:45/mi, but if you can only hit 10:35/mi at first, you do that and try to bump up 0:10/mi every couple of weeks as conditioning improves).
Assuming I only had the 12 weeks, I would
personally do a hybrid of the two plans, with two speed workouts per week, but maybe not the added long run mileage of the Advanced plan (at least for the first half). The important thing is to see if you can start to hit those target paces
at all. My goal would be to build speed as quickly as I possibly could without injuring myself, then focus on building endurance and sustaining that speed. Endurance is critical to success, but if you are dead-set on a certain pace, it doesn't matter that much if you can sustain a slower pace.
Since the pace goals are so aggressive, I do think the Tempo runs would be a helpful complement to the intervals, so you can train for 5k speed in short bursts, but also translate that into sustained speed for 2-4 miles at a time. It also gives you a good check-in. If you can't hit your goal pace on a 3- or 4-mile tempo run halfway through, that's potentially an off-ramp. If you can, then you have to focus on building endurance.
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A bit of personal experience -- I started running again in November after almost a year of little-to-no exercise, just putting in 10-15 miles/week. I started a 16-week marathon training plan on 1/1, so I'm basically 12 weeks in.
My first two weeks, I ran two 2-mile Tempo runs with an average speed of 10:40/mile and an average heart rate of 172bpm. Oof.
I the last two weeks, I ran 6- and 7-mile Tempo runs with an average speed of 10:10/mile and an average heart rate of 156bpm. Yay!
For the first four weeks, I was running 3-4 times per week, with one speed workout and only 15 total miles.
For the last four weeks, I've been running 6-7 times per week, with two speed workouts and 35-45 total miles. I think both the speed workouts
and the high volume of easy miles were both really really beneficial for me.
Since I was starting from a pretty low base of mileage and conditioning, I saw pretty dramatic results in a pretty short timeframe. On January 1, my 'easy' pace was a sometimes difficult 14:30-15:00 min/mile, and I would've struggled to finish a HM in much less than 3 hours. After the last 12 weeks, I'm certain I could run a sub-2:22 HM this weekend.
But it's taken a LOT of work -- 333 miles in the last 11 weeks -- and I was starting from a very low base level of fitness. You may be in better starting shape than I was and have less room for easy improvement, or you may not have the time to put in the easy mileage that you need to build aerobic capacity.
But I thought that might be a helpful reference point as you consider how to proceed.