The Running Series · No.04
The Long Run
The Anchor of a Marathon Week
Sunday's long run goes 16 miles and feels strong. Monday the legs are heavy, Tuesday they are still heavy, and Wednesday's workout gets cut short because nothing is firing. By Thursday everything feels normal again, which lines up nicely with an easy run on Saturday and another long run on Sunday.
Run that pattern for twelve weeks and the long run has quietly consumed the rest of the training. You end up with three usable days a week, and the session that was supposed to build your durability has become the reason nothing else gets built.
The long run is the most important session in a marathon block and also the easiest one to get wrong, usually because people treat it as a weekly test of what they can survive rather than as a weekly stimulus that has to fit inside a functioning week.
The short version
- It is the most important session, and the easiest to get wrong. Treat it as a stimulus that fits the week, not a survival test.
- It trains fatigue resistance, fuel efficiency, and structural tolerance, none of which involve speed.
- Aim for about 25 to 30 percent of your weekly volume, and judge it by what Monday feels like.
- Rehearse fueling and gear every time. Race day should be the twelfth run on that plan, not the first.
What it is actually training
There are three things going on, and none of them involve speed.
Fatigue resistance
As you run, the muscle fibers you started with gradually deplete their glycogen, and your body progressively recruits additional fibers to keep the work going. Spending extended time on your feet teaches your body to manage that handoff more smoothly, and how well you manage it is largely what determines whether mile 22 goes well or falls apart.
Fuel efficiency
You store enough glycogen for somewhere between 90 minutes and two hours of running, while your fat stores are effectively unlimited for these purposes. Long, easy running shifts the balance of fuel use toward fat at any given pace, which spares glycogen and pushes back the point at which you run out. That is driven by duration rather than intensity, which means running your long run faster actually works against the thing it is meant to develop.
Structural tolerance
Bone, tendon, and fascia adapt to load slowly, and the long run represents the largest single dose of that load in your week.
How long it should be
A useful guideline is 25 to 30 percent of your weekly volume, so if you are running 30 miles a week your long run belongs somewhere around 8 to 10 miles rather than 18.
When you push well past that ratio, the long run stops being one session inside a balanced week and starts being the week itself, with everything else reduced to recovery from it. Most marathon plans peak the long run somewhere between 18 and 22 miles, and very few runners need more than that. Covering the full 26 in training costs recovery you cannot really afford and teaches you very little that 20 miles did not already.
How fast it should be
Conversational for the bulk of it, with any faster work confined to specific segments you have planned in advance.
The honest test is what Monday looks like. If Monday is a normal easy day, your long run is doing its job. If Sunday regularly costs you both Monday and Tuesday, something needs adjusting, and it is usually one of three things: the run is too long relative to your current weekly volume, you are running it too fast, or you are underfueling it. Frequently it is some combination of all three. Sorting that out is worth doing before you add another mile.
Fueling
Once you are past 75 to 90 minutes, you want carbohydrate coming in, generally somewhere in the range of 30 to 60 grams per hour taken at regular intervals rather than waiting until you feel empty. By the time you actually feel empty you are already well behind, and no amount of gel is going to catch you up quickly enough to matter.
The more important point is that your gut is trainable and genuinely needs the training. Your tolerance for taking in carbohydrate while running improves with repeated exposure, which means race day should be roughly the twelfth time you have used that specific product at that specific rate rather than the first. The same logic applies to shoes, socks, shorts, and anything else that will be in contact with your skin for three hours.
When to add structure
If you are newer to running
Keep the whole thing easy and use walk breaks freely. They are a legitimate tool rather than a sign of failure, and taking them lets you accumulate more total time on your feet with less accumulated damage, which is the entire point of the session.
If you have a year or two in
Once the long run feels routine, you can finish the last 20 to 30 minutes at a moderate effort. That gives you a manageable dose of the specific skill of running well when you are already tired.
If you are inside a race-specific block
Building goal-pace segments into the run makes sense, something along the lines of three sets of two miles at race pace with easy running between them. What you are rehearsing is the exact sensation of holding your number on legs that have already been working for a while, which is precisely what race day is going to ask of you.
One last thought
If those race-pace segments require an interval-level effort to hit, then your goal pace is not really your goal pace yet. It is a hope. Finding that out in August leaves you plenty of time to adjust, whereas finding it out at mile 18 in October does not.
More in the series