How to pace an ultra

There are a few different strategies people use when pacing an ultra , which do you think is the best ?

  1. Go hard from the start and get as many miles covered before the legs force you to shuffle to the finish.
  2. Go easy at the start and aim to pick it up in last half.
  3. Aim to run same pace ( relative to the terrain) for the entire race.
  4. None of the above

Before I answer that lets look at some of the pacing strategies of the elites and see what  we can learn.

In this study looking at 100km road runners in the world championships, they found that the top runners slowed 15% from their initial starting speed and the slower runners slowed down significantly more.

The study grouped finishers into groups of 10 ( A to G) according to finish time. It’s very obvious to see that all groups slowed down – the faster runners less so. Groups G and F started way too fast relative to their fitness.

What about in 100 mile flat races ? 

Here is a strata plot of Zach Bitters 100 mile US record.  Just as in the 100km  you can see  a drop in pace occur – in this case around 75 miles .

What about in 24 hour races ?

This study looked at exactly that and concluded, “…. fastest runners start at lower relative intensities and display a more even pacing strategy than slower runners.”

The graph  below shows the normalised mean running speed to allow comparison between groups



Group 1 which started with the slowest relative speed ended with most distance; 180.5km, Group 2  ran 142.4km, Group 3; 122.1km and Group 4; 97.2km.  [NOTE Group 1 didn’t start at the slowest speed – but their speed was closest to their overall speed than the others- the other 3 groups started much faster relative to their mean running speed over the 24 hours.]

It looks like we all get slower but the faster finishers slow down less and also start at a pace that is relatively easier for them than the slower runners.

The take-home – start easy and slow down as little as possible. But how easy is easy?  ( Read on )

Does the same apply in trail ultras  ?

Until recently it has been impossible to determine objective pacing strategies for trail races due to the constantly changing speeds that a trail forces you to make. With the advent of power meters,  we can now measure power throughout a race and power can be determined independently of the terrain – ie the speed you end up running at say 200 Watts will vary depending on the terrain but the effort remains the same.

I’ve had quite a few runners use power meters in races which has allowed me to see what has worked best in terms of pacing. Note although I’ll be discussing power you don’t have to have a power meter to benefit from this discussion – we are looking at pacing and I’ll relate back to running without power meters later so bear with me 

Let’s have a look at some runners that had good races to see what the reduction in power looks like.

Here is what it takes to run 9.24 at the UTA 100. The red line represents run power.


From start to finish there is a reduction of 15% which corresponds exactly to what the study on 100km road runners found.

Below is another runner who had a great race, running just over 15 hours in the UTA100 with a reduction in power of 16%.

In the HK100 this runner went just under 16 hours with a reduction in power of 18%.


What about when a race doesn’t go so well ?

In this race, also at the HK100, the runner lost 35% of initial power and finished well behind expectations.


What does all that tell us other than to have a good race you shouldn’t slow down that much – which of course is obvious?

What about those athletes that finish strong, catching athletes in the back half of a race? Do they speed up?

Below is Sunmaya Budhas power when she stormed home to almost snatch the win in the 2022 CCC race as she  ran the second fastest time in history.  She lost 13%  of her  initial power.


So even when making up time on the race leader (who set a course record) she still slowed down.


The advantage of power is we can look at what intensity the athletes started at and determine at what power  intensity leads to the least reduction in power and therefore fastest possible finish time.

Let’s revisit each of the athletes above and talk about intensity.

The 9.24 UTA runner ran his long runs leading into the race at around   225-235W . His starting power was 6-10% higher than long run power.

The 15 hour UTA runner started at 178W and her longest training runs were around 165-175W . She started 3-7% faster than long run pace.

The sub 16 hour HK100 runner started at 149W and her long runs were around 132W .  She started 11% faster

The last athlete who didn’t have a good race,  started at 250W and his long runs were around 215-220W ie 12-14% faster

For those that understand the concept of Functional Threshold (FTP) power or Critical power (CP)  the starting percentages were as follows

9.24 UTA – 79%

15 hour UTA- 84%

sub 16 HK100- 81%

15 hour HK100- 90%

Sunmayas CCC – 83%

The higher the percentage of threshold you start the more slow down there is. ( Which when you think about it makes perfect sense – if you start a 100km at say 10km pace you are going to see a much bigger slow down than if you started it at marathon pace ).  The data suggests that for a 100km trail race starting at 80-85% of threshold yields the best results for races lasting 10-15 hours. For longer races  it will be less than that , for 15-20 hour races 75-80% and for even longer closer to 70%

For those that don’t use power think of it as a percentage of your threshold – i.e. hardest pace you can maintain for approx 45-60 minutes and your long run pace is  70-80% of that pace/ effort.

What does that all mean in terms of paces?

Let’s use 6 min per k as a benchmark to see what the above actually looks like

If your long run speed was typically 6 min ks on the flats then I suggest you start at most between 3-5% faster ( unless you are elite in which case can start 6-10% faster ). That equates to  5:42-5:49 minutes per k pace.

A 15 % reduction of that pace means at the end you should be running at approx 6:36 pace

I’m confused by all the numbers – what does all that mean?

Simply put – to run your best 100km start at a pace a fraction faster than your long run pace and try and slow down as little as possible,  accepting that slow down is inevitable. For longer races start at a pace that’s easier than your usual long run pace.

Now that sounds easy but there are a few problems in the execution of that strategy.

With fresh legs the 5:42-49min ks you were running in long runs feels very very slow. Add in adrenalin, competition and all of a sudden you are running sub 5:30 pace and feeling great . Until of course it all catches up with you and your pace drops to well over 7 min ks. You ask yourself why the legs won’t allow you to run any faster when the initial pace felt so easy – but it actually wasn’t.

The advice to find a pace that feels easy at the start and then slow down a little more is sound advice if you don’t have access to a power meter to give you more objective data.

How to pace the last half of an ultra

Pacing the last half is easy. If you have paced the first half well then it’s just a matter of trying to keep the pace up as much as possible but accepting it will gradually slow down and the perceived effort in trying to minimise that slow down will rise as the race continues.

What about uphill and downhill – how should we pace those?

Should you hike or run uphill? 

With power it’s easy – if you can’t run uphill below your power target then hike. Without power, you need to use perceived effort. I see way too many runners pushing too hard uphill and then needing a period of recovery afterward to recover from the effort of climbing. During that period they lose any advantaged gained from pushing harder uphill. When you get to the top of a hill you should be able to resume running either on the flat or downhill at your usual pace without any recovery period. If you were running a flat race you would aim for even effort but for some reason when it comes to hilly races people think it’s ok to push a bit harder uphill as they can recover on the downhill. In almost all cases you’ll lose more time on the downhill recovering than you gained on the uphill.

So if you feel your effort level rising as you climb then slow down. If you cant run up the hill with the same effort as you were running on the flat then switch to a hike.

What about downhills?

Running downhills will usually feel a little easier cardiovascular wise but your heart and lungs aren’t usually the limiting factor in the latter stages of an ultra, your legs are. So downhills should be approached with the idea of minimising the load on your quads. That doesn’t necessarily mean slowly – sometimes the braking forces needed to run slowly downhill are higher than running a little faster,  allowing gravity to help and using high cadence short strides to minimise quad damage.


Other factors  that affect pacing 


The above assumes you have trained sufficiently for the race, it assumes you have got a few 4+ hour long runs in and have had consistent weekly training for a number of months, if you are going in underdone then you’ll need to go even slower at the start – ie usual long run pace or even  slower .

Specificity of training 

If your training hasn’t been that specific – eg you haven’t done many stairs or hills for a race that has lots of stairs or hills then again your starting pace will have to be lower to allow for the greater fatigue that will occur due to the unfamiliar nature of the course.


If it’s hot and or humid you’ll need to start slower again ( unless your training has been in same conditions as the race and you are acclimatised)


Unless you provide your muscles with enough fuel then the best pacing strategy in the world is not going to help. What we often see is if you go out too fast you are more likely to have nutrition issues as the faster pace makes it harder for your stomach to digest what you are putting into it.

Going back to the original question;  How to pace an Ultra ? 

Which is the best option

a) Go hard from the start and get as many miles covered before the legs force you to a shuffle to the finish

b) Go easy at the start and aim to pick it up in last half

c)  Aim to run same pace ( relative to the terrain)  for the entire race

d) None of the above

The answer is d) none of the above

The correct answer – start easy and minimise the slow down !

Option 2 is the closest but the idea of picking the speed up in the last half of an ultra is fantasy. You will certainly feel an increased effort level but the pace will be slower.


NOTE – for those that use power – the above is a very simplified version of power in ultras in order to make it understandable and relatable for those not using power – for a more complete discussion on setting power targets for trail races have a look here.