Altigraph · How to read an elevation profile

How to read a race elevation profile before race day

Every race website shows one: a jagged line, distance along the bottom, altitude up the side. Most people glance at it, spot the big bump, and move on. Read properly, the same picture tells you where the race is decided, where to hold back, and where a steady effort will pass everyone who did not look. Here is how to read it in five minutes, and what the picture will not tell you.

Start with three numbers, not with the shape

1. Total climbing against distance. Divide the metres of ascent by the kilometres: metres climbed per kilometre. It is the single figure that says whether a course is flat, rolling or a mountain run, and it lets you compare two races of different lengths. A course you already know is the best reference: work out its ratio once, and every new course reads against it.
2. Where the climbing sits. The same 400 m of ascent is a different race if it is all in the first 5 km, spread evenly, or stacked in the last quarter. Early climbing tempts you to burn matches before the flat; late climbing punishes anyone who ran the flat too fast. Note the kilometre of the top of the last real climb: that is the point where you can finally commit.
3. The steepest 100 m. An average gradient hides walls. A climb that averages 5 % but holds a 14 % stretch is not run like a steady 5 %: on that stretch running may be slower than a brisk walk. Knowing where the wall is, and that it is short, is what keeps you calm on it.

Altigraph gives the three straight away: total ascent and distance in the header, the table of sections with the kilometre where each climb starts and ends, and for each one the average gradient and the steepest 100 m. The page on GPX profiles explains how the ascent is computed and why the organiser's figure is usually a little higher.

Why the picture exaggerates

An elevation profile is never drawn to scale. The horizontal axis covers kilometres, the vertical axis covers a few hundred metres: to make anything visible, the vertical is stretched, often by a factor of ten or more. That is why a 4 % slope looks like a wall on the chart, and why the same course looks brutal on one website and gentle on another. Read the gradient in percent, never the angle of the line. An 8 % gradient is 8 m gained for every 100 m travelled, whatever the drawing looks like.

Two more things move the shape without changing the course. Smoothing: every tool filters GPS jitter before drawing, and each filters its own way, so small bumps appear on one profile and vanish on another. The altitude source: a route drawn online carries terrain-model altitudes, smooth and consistent; a track recorded by a watch carries the sensor's, with its wobble. Neither is the truth, and the difference between them can exceed the height of a small climb.

The profile is a map of effort, not of beauty: hover it, read the numbers under your finger, and let the shape go.

Turn the curve into sections, and the sections into a plan

Nobody runs a profile; you run a sequence of pieces. Cut the course where the gradient changes sign and give each piece one intention:

• Climbs: hold an even effort, and let the pace fall. Breathing and heart rate are the guide; the watch pace on a climb means nothing on its own. Most running apps show a "grade adjusted pace" for exactly this reason: it estimates what the effort would have been worth on the flat.
• Descents: they are not free. A long descent costs the legs (braking, impact) more than the lungs, and the bill arrives on the next flat section. On a road race, a controlled descent is where you recover; on a trail, it is where the race is often won or lost, by footing rather than fitness.
• Flats and false flats: a 1 to 2 % rise over several kilometres does not look like a climb on the profile, and it does not feel like one at first, but it slows you all the same. When a flat section feels harder than it should, look at the gradient before doubting yourself.

Then write the plan on the course itself: "km 6 to 8, climb, hold back; km 8 to 11, descent, relax the shoulders; km 14, the wall, 300 m, walk if needed; from km 15, all in." Altigraph's table gives you those kilometre marks, and the shareable image of the profile fits on a phone screen, or on a strip of tape on your forearm.

Compare, do not guess

A profile only speaks when set against one you know. Load the race you did last month and the one you are preparing side by side: same total ascent, but where does it sit? Same distance, but how much steeper is the worst stretch? Altigraph compresses the whole profile into its link, so two tabs are enough to compare, and the link can be sent to a training partner without a file or an account.

Five checks the week before

1. Metres climbed per kilometre, and how it compares with a course you know.
2. The kilometre where the last real climb tops out.
3. The steepest 100 m: where, how long, how steep.
4. The longest descent, and what comes right after it.
5. Any false flat longer than a kilometre.

Write the five answers down. On race morning they are worth more than any pace chart, because they are about this course and nobody else's.

Published 21 September 2026. How Altigraph cuts a route into sections (100 m sliding gradient, 1.5 % threshold, pieces under 150 m merged) is described on the GPX profile page and in the questions on the home page.