There is a common belief that training for an ultra marathon is just about logging many, many easy miles. And whilst volume is a big factor, for sure, it is not the only one.
BLUF: Ultra training is not volume or intensity. It is building enough aerobic durability while using the smallest effective dose of intensity to raise your ceiling, without wrecking your recovery.
Where the belief comes from
The logic seems sound. You are racing at a slow pace, sometimes for many hours, so surely you should train slowly for many hours too.
And there is real truth in there. The foundation of any ultra plan is aerobic volume. Time on feet builds durability, fat-burning efficiency, tendon and connective tissue resilience, and the mental patience the distance demands.
Most runners, if anything, do not run easy enough on their easy days. So the message to "slow down and build volume" is a good one for a lot of people.
But it gets stretched too far. It becomes "all my running should be slow", and that is where performance quietly leaks away.
Race pace is not the same as training intensity
Here is the mistake I see most often. People confuse the pace they will race at with the intensity they should train at.
Your ultra pace may be slow. That does not mean all your training should be.
So, what that means is this: if you only ever train at, or below, your race effort, you never develop the qualities that sit above it. And those qualities are the ones that make your race effort feel easier when the day comes.
What intensity actually gives you
Used deliberately and proportionately, higher-intensity work does a lot of useful things for an endurance athlete. Here is what to focus on:
- Running economy. How much energy you burn to hold a given pace. Improve it and every mile costs you less. This is arguably the biggest lever for an ultra runner.
- Leg speed and mechanics. Strides and short efforts keep your stride from collapsing into a slow shuffle. Better mechanics hold up longer under fatigue.
- Cardiovascular capacity. The size of the engine. A bigger ceiling means your steady effort sits at a lower percentage of your maximum.
- Fatigue resistance. Threshold and tempo work teaches your body to clear and tolerate the by-products of harder effort, so you hold form deeper into a race.
- Confidence. Knowing you can push and recover changes how you feel about a bad patch at hour six.
The key message here is not "run hard all the time". It is that a small, well-placed amount of intensity punches well above its weight.
You are not only training for the finish line
Now for the part people forget. The chances are you are not just training for an ultra. You are training for life, and for longevity.
One of the strongest markers of long-term cardiovascular health is your VO2 max, roughly a measure of how much oxygen your body can use at maximum effort. It is a good proxy for the size and health of your aerobic engine.
A large observational study published in JAMA Network Open found that higher cardiorespiratory fitness was associated with significantly lower long-term mortality, with no observed upper limit to the benefit (Mandsager et al., 2018). In plain terms: fitter tended to mean longer-lived, across the population they studied.
I want to be honest about what that does and does not prove. It is an association, not a guarantee, and it does not mean intensity is the only way to get fitter. Easy aerobic training absolutely improves VO2 max, particularly if you are less trained to begin with.
But as your fitness develops, easy miles alone tend to stop moving the needle. Appropriately prescribed higher-intensity work is usually a more powerful stimulus for pushing that ceiling higher. So the same intensity that helps your race also helps the version of you that is still running in thirty years.
How to use intensity without breaking yourself
Alright, so how do you actually apply this? The principle is minimum effective dose. Enough to raise the ceiling, not so much that it eats your recovery or your consistency.
Here is a simple way to think about the balance:
- Keep the base big and genuinely easy. The large majority of your weekly volume, most guides land somewhere around 80 percent, should be comfortable, conversational running. Easy means easy.
- Add one, sometimes two, quality sessions a week. That is usually plenty alongside high volume. More than that and you are borrowing from recovery.
- Vary the type of intensity. Threshold or tempo for fatigue resistance. Hill reps for strength and economy. Short intervals for cardiovascular capacity. Strides for leg speed. You do not need all of them every week.
- Make it specific closer to race day. Long runs with tempo blocks, or effort on tired legs, bridge the gap between fitness and race demands.
- Respect the recovery. Intensity only works if you absorb it. If a hard session is bleeding into your easy days, the balance is wrong.
For example: a runner building towards a 50k might do one weekly threshold or hill session, a handful of strides after an easy run, and then protect the rest of the week for volume and recovery. That is it. Not complicated, but deliberate.
The reframe
So, to bring it back to the core point.
Volume builds the engine's durability. Intensity raises its ceiling. You want both, in the right proportions, for the right reasons.
If your entire ultra plan is long, slow running, you are probably leaving performance on the table, and you may be leaving some long-term health benefit there too. That being said, the answer is not to go and thrash yourself. It is to add intensity like seasoning: small, deliberate, and in the right places.
Better to be consistently good than sporadically great. Do that, and you build a body that can perform on race day, and for a long time after it.
If you have any questions, queries or concerns about how to fit this into your own training, don't sit on them, let me know.