The Types of Runs

What is going on underneath

When you run at a low, conversational intensity, your body is doing a lot of quiet work that you cannot feel happening. It is growing additional capillaries around the muscle fibers you are using, which gives oxygen more routes for delivery. It is increasing both the number and the size of the mitochondria inside those fibers, and since mitochondria are where oxygen actually gets converted into usable energy, having more of them raises how much work you can do aerobically. Your heart is adapting too, filling more completely between beats and pushing more blood with each contraction. And your muscles are gradually getting better at pulling energy from fat, which matters enormously over long distances because you carry a nearly unlimited supply of fat and only a couple of hours' worth of stored carbohydrate.

Almost none of that responds to how hard you are running. It responds to how much time you spend running, which is why easy mileage is not the warm-up act before the real training happens. For most runners it is the majority of the training.

Hard running does something different. When you are working close to the limit of how quickly your body can take in and use oxygen, repeatedly visiting that limit is what nudges it upward over time, and you are also recruiting the faster muscle fibers that stay more or less dormant at easy effort. Your nervous system gets better at firing those fibers in a coordinated way, which shows up as smoother, more economical running at speed.

Sitting between those two is threshold effort, which is the pace where you produce lactate at roughly the same rate you can clear it. Go a little above that line and lactate starts accumulating faster than you can deal with, so you are eventually forced to slow down. Training right around that line pushes it outward, and moving that line is what allows you to hold a faster pace for a long time without falling apart, which is more or less the definition of marathon fitness.

So you have three different adaptations that each require a different kind of effort to access, and the single moderate loop touches none of them cleanly. That is why the plateau happens.

The runs themselves

Easy runs

RPE about 3 to 4, where you can hold full conversational sentences without gasping. This is where the aerobic work actually gets done, through accumulated volume rather than through effort, and it should make up the bulk of your week. The most common mistake is running these a bit too fast because slow feels unproductive, but the slowness is genuinely the mechanism.

Recovery runs

Easier still, around RPE 2 to 3, short and deliberately gentle. They keep blood moving and maintain your running frequency on days when your body cannot absorb any real work. If it feels slightly annoying to hold back that much, you have the effort about right.

Long runs

Mostly easy effort and typically 25 to 30 percent of your weekly volume. They build fatigue resistance and train fuel efficiency in a way that shorter runs cannot, which makes them the anchor of a marathon week.

Progression runs

Start easy and finish moderate or harder, with each third quicker than the last. What they train is the specific ability to raise your output on legs that are already tired, which is exactly what the closing miles of a marathon will ask of you.

Fartlek

Alternating faster and easier blocks without a stopwatch, so you might run hard to the next light post and easy to the one after that. Because the recovery lasts as long as you need it to, it is the friendliest possible introduction to intensity.

Tempo & threshold runs

RPE 6 to 7, comfortably hard, where you can manage short phrases but not full sentences. This is the session that moves the lactate line outward, and for anything from a 10k to a marathon it tends to return more fitness per unit of effort than anything else you could do.

Intervals

Harder still, RPE 8 to 9, where you can get out a word or two at most. They work the top end of your oxygen uptake and improve how economically you move at speed, and they have the pleasant side effect of making threshold pace feel considerably more manageable afterward.

Strides

Short accelerations, usually four to eight repetitions of around 20 seconds, run fast but relaxed with full recovery between each one, tacked onto the end of an easy run. Because the recovery is so generous, they barely register as fatigue, which makes them the safest way to keep some speed in a program.

Hill repeats

Hard effort at a lower impact cost, since running uphill naturally shortens your stride and reduces landing forces while still driving your heart rate up. That makes them useful for anyone whose joints are not quite ready for flat speed work. Jog the downhills rather than racing them, since the descent is where most of the damage happens.

Race-pace runs

Rehearsal, using the exact pace you are targeting along with the gear and fueling you plan to use. They only make sense once you have a goal and a date on the calendar.

How much of this applies to you

The menu above is the same for everybody. How much of it belongs in your week is not.

If there is one idea worth carrying away from all of this, it is that the answer to a plateau is rarely running harder across the board. More often it is running the easy days genuinely easy so that one or two days a week can be genuinely hard.