Trail running: finding the hardest climb of your run and what its numbers tell you

I.Three ways to be « the hardest »

A four-hour trail outing with four cols, and the question that comes up at the debrief: which one hurt the most? Without precise figures, the answer depends on when you ask — the runner just after the finish, his legs the next day, his memories three weeks later. Three different answers for the same outing.

The reason is simple: « the hardest » is not a single notion. It covers at least three distinct criteria that don't necessarily designate the same climb:

• The longest — the one that lasts the most, that accumulates the most positive elevation gain. The endurance climb.
• The steepest — the one with the highest average gradient. The strength climb.
• The latest in the fatigue curve — not necessarily the longest or the steepest, but the one that lands when the legs are already cooked. Its difficulty is relative to what came before.

Depending on the criterion, you'll land on three different climbs. Pulling the figures lets you settle the question with knowledge.

II.Spotting the candidates on the elevation profile

Before isolating anything, open the track in a GPX analyser and look at the elevation profile. The peaks are obvious: three or four bumps stand out on the silhouette. Three patterns come up often:

• The long, progressive climb — on the profile, a steady inclined ramp, no jolts. Typical of a mid-mountain col.
• The short, brutal pitch — an almost vertical line on the profile, little horizontal amplitude, lots of vertical. Typical of a technical section.
• The saw-tooth succession — close-spaced bumps with short descents between. Trickier to analyse: do you isolate each bump, or the whole sequence?

At this stage, you measure nothing yet. You simply note: « these three or four climbs are my candidates. »

III.Four numbers that decide

With the candidates spotted, time to measure. Four numbers are enough to rank them with nuance — each lights up a different corner of the difficulty.

VAM (vertical ascent in metres per hour) is the reference measure. It tells you how many metres of climb you absorb in an hour, independently of horizontal distance. A climb you went up at 900 m/h is more brutal than one at 700 m/h, no matter their respective lengths.

Net gradient (as a percentage) clarifies the physical character of the climb. At equal VAM, a steeper climb demands more force per stride and less cardio; a gentler climb demands more duration and more cardio. Not the same fatigue.

Average heart rate tells you what the heart actually took. It's what reveals cumulative fatigue: a moderate climb mid-race can show a higher average HR than a harder climb early on, simply because the legs were already warm and the heart wasn't « slowing down » between efforts anymore.

Duration serves to weight. At similar VAM and HR, twenty minutes leave a stronger memory imprint than ten.

For what each measure says in detail, see our guide to the twelve measures.

IV.The step-by-step method

With the candidates spotted and the key figures in mind, the analysis becomes mechanical:

1. Load your .gpx file into GPXchunk. Nothing is sent to a server, everything stays in the browser.
2. Identify 3 or 4 candidates on the elevation profile (the visible bumps).
3. For each candidate, drop the two handles at the start and end of the climb — either on the profile, or by typing kilometre bounds.
4. Note the four key figures: VAM, net gradient, average HR, duration.
5. Compare climb by climb.

Free segment isolation is exactly what this kind of question needs — you're not trying to publish a segment, you're trying to understand what happened.

V.A 30-km trail, four climbs, and their figures

Take a concrete case. A 30-km trail, four hours and thirty minutes of running, 1 200 metres of total elevation gain spread across four main climbs. Once isolated in GPXchunk, they yield this:

• Climb A (km 8 → 10.5) — 200 m gain over 2.5 km, average gradient 8 %, duration 17 min. VAM 705 m/h, average HR 158 bpm.
• Climb B (km 14 → 17) — 380 m gain over 3 km, average gradient 12.7 %, duration 28 min. VAM 814 m/h, average HR 163 bpm.
• Climb C (km 22 → 24) — 240 m gain over 2 km, average gradient 12 %, duration 18 min. VAM 800 m/h, average HR 168 bpm.
• Climb D (km 27 → 28) — 200 m gain over 1.2 km, average gradient 16.7 %, duration 11 min. VAM 1 091 m/h, average HR 175 bpm.

Which is the hardest? Depends on the criterion:

• Longest, most gain → B (28 min, 380 m).
• Steepest, highest VAM → D (16.7 %, 1 091 m/h).
• Highest average HR → D (175 bpm), followed by C (168 bpm) — the two late climbs, where cumulative fatigue speaks.

The longest is not the hardest. Nor is the steepest. It's by combining VAM, gradient and heart rate that you decide.

Final reading: B is the endurance trial — the longest, the biggest energy drain. D is the peak trial — the most brutal, the most demanding on legs and heart in the instant. Two climbs that hurt differently, that you'd confuse without the numbers.

VI.Why note it, outing after outing

Doing this sorting once is a curiosity. Doing it on every outing turns it into a training tool.

First for tracking progress: the same climb, run several weeks apart, yields a comparable VAM. If it goes up, you're improving in climbing efficiency. If it stays the same while average HR drops, your cardio is building. Three comparable outings are enough to see a trend.

Then for course reconnaissance: a .gpx track received from a friend who has already run the route — isolate his climbs, read their VAMs, and you know in advance which one will blow you up, and where to save energy. More precise than a generic comment « it climbs hard at km 24 ».

Finally for understanding a bad day: « I cracked on climb D » becomes measurable. HR running away fifteen minutes from the end, VAM collapsing on the second third — the figures tell the story the legs forgot.