How to Pace a Trail Ultra

Ask a hundred ultra runners why their race went badly and most will describe a nutrition failure, a stomach that shut down, a cramp, a bad patch that never ended. Watch the data and the same story appears in nearly all of them: they went out too hard, and everything else followed.

Pacing is the master variable. Fueling problems are frequently pacing problems - you cannot digest at an intensity above your gut's tolerance. Cramping is frequently a pacing problem. The bad patch at 60 km is frequently a bill from kilometre 12.

Distance is not the unit

A 50K with 500 m of gain and a 50K with 3,000 m of gain are different events by hours. Any pacing plan built on kilometres will be wrong by an amount roughly proportional to the vertical.

A serviceable first estimate: convert climbing to flat-equivalent distance by adding one kilometre for every 100 m of gain.

• 50 km with 2,000 m gain → 50 + 20 = 70 flat-equivalent km
• 100 km with 5,000 m gain → 100 + 50 = 150 flat-equivalent km

Then apply an ultra pace to that number - typically 60-75% of your flat marathon pace for a 50K, slower for longer events - and add time for aid stations, technical terrain, night sections, and heat.

This is rough. It is also far better than assuming a mountain 50K takes 20% longer than a road 50K. For a real estimate, feed the course GPX to a grade-adjusted predictor, which handles the gradient distribution properly rather than treating all climbing as equivalent.

Sanity-check against reality. Look up last year's results for your race. Find finishers whose recent times at other distances resemble yours, and see what they ran. Field data on the actual course beats any model.

Build a segment plan, not a finish time

A single goal time is not actionable at kilometre 40. What you want is a table of segments - usually aid station to aid station - with a target elapsed time for each.

For each segment, note:

• Distance and vertical gain
• Target elapsed time at arrival
• What you eat and drink in that segment
• What you do at that aid station (refill, swap, nothing)

Print it. Put it in your vest pocket. Being able to look at a card at hour seven and see "you are 12 minutes behind plan and that is fine" is worth a surprising amount.

Two rules for building the numbers:

Weight the effort toward the second half. Plan the first half at roughly 48-49% of your total time, so a small positive split is your worst case and a negative split is achievable. Almost nobody negative splits an ultra; planning to means you probably run something close to even, which is the actual goal.

Add time to the late segments. A 10 km segment at hour two and the same 10 km at hour ten are not the same segment. Add 10-20% to your late-race segment estimates depending on distance - more for 100 milers, less for 50Ks.

The first third

The most useful piece of advice in ultrarunning is also the most ignored: the first third of the race should feel too easy.

Not "controlled". Not "comfortable". Slightly embarrassing. You should be letting people go past and feeling faintly foolish about it.

Two concrete checks in the first two hours:

• Can you speak a complete sentence? On every climb, in every section. If not, back off. There is no exception to this in the first half of an ultra.
• Are you hiking things you could run? On any climb over about 15%, you should be hiking early even when running feels possible. Running the early climbs is the classic way to arrive at the halfway point with quads that are already spent.

The physiological reason: at higher intensities you burn a greater proportion of carbohydrate, your gut's ability to absorb what you eat drops, and eccentric damage accumulates faster. Going out hard does not just cost you time later - it degrades your ability to fuel, which then costs you more time later.

Pacing the climbs

Climbs are where races are lost, because they are where the effort creep is invisible. On a climb your pace is already slow, so you have no feedback telling you that you have gone anaerobic.

Steer by breathing. Full sentences in the first half; short sentences at worst in the second half. If your breathing rhythm shortens on a climb early in the race, you are spending capital you will want later.

Heart rate is a poor guide here - it lags gradient changes by 30-60 seconds and drifts upward through the day regardless of effort. There is a longer treatment of that problem, but the short version is: use it as a ceiling, not a target.

Power, if you use it, works well for climbs precisely because it does not lag.

Pacing the descents

Two errors, in opposite directions.

Error one: banking time on early descents. The first big descent of a long race feels free. Your legs are fresh, the effort is low, gravity is helping. It is not free - it is a loan against your quadriceps at a terrible interest rate. Run the first descents at maybe 80% of what feels available.

Error two: braking down every descent out of caution. Constant braking is more damaging than controlled fast descending, because you spend longer under eccentric load and land with straighter legs. Relaxed, short-strided, higher-cadence descending is both faster and cheaper than tense heel-braking.

The rule of thumb: descend at an effort where you could hold a conversation and where your legs feel like they are cycling rather than absorbing.

Aid stations

Aid station time is a large and invisible fraction of an ultra. Ten stations at six minutes each is an hour.

• Know before you arrive what you need. Decide in the last kilometre.
• Refill, grab, go. Sitting down is a decision, not an accident - make it deliberately if you make it at all.
• Eat while walking out, not standing still.
• Budget the time honestly in your plan. Two minutes for a quick refill, five to eight for a full reset with a crew or drop bag. Do not pretend you will be faster than you will be.

When the plan meets reality

You will fall behind your plan. Something will go wrong. Here is the triage.

A bad patch. Almost always one of four things: you are underfuelled, you are dehydrated, you went out too hard, or your blood sugar dipped. Take 40-60 g of carbohydrate, drink, walk for ten minutes, and reassess. The great majority of bad patches resolve within 20-30 minutes if you feed them. Do not make decisions during one.

You are 30 minutes behind at halfway. Recalculate from your current position rather than trying to reclaim time. Chasing a lost goal time in the second half of an ultra is how a hard day becomes a DNF. Set a new realistic target and race that.

You are 20 minutes ahead at halfway. This is worse than being behind. You have almost certainly gone out too hard. Deliberately slow down, eat, and expect to give the time back.

Your stomach shuts down. Usually intensity-related. Slow down, switch to fluid carbohydrate and something bland, and keep taking small amounts. Stopping fueling entirely turns a bad hour into a DNF.

A cut-off is closing. Do the arithmetic properly rather than panicking - work out the pace you actually need, not the pace you fear you need. Then decide whether to spend the effort or accept the outcome.

A worked plan

A 100 km alpine race, 5,000 m gain, runner targeting 15 hours.

Note the first segment is 13% of the time for 14% of the distance, and the last is 13% of the time for 15% of the distance on much easier terrain. That is the shape of a well-paced race: give away a little early, take it back late.

After the race, the most useful thing you can do is look at what actually happened rather than what you remember. The race report analyzer takes your FIT and GPX files and produces segment-by-segment pacing and drift analysis - which usually shows the mistake was made three hours before it hurt.