Heart rate is one of the fundamental parameters of trail training. If it is misinterpreted or misused, the risk of compromising your progress or accumulating unnecessary fatigue is significant. It is therefore essential to learn how to manage your heart rate in trail.
The specifics of heart rate in trail
Heart rate is rarely stable in trail. Unlike road running, changes in elevation, terrain technicality, and arm use cause constant variations in intensity. The heart rate spikes quickly on climbs and tends to drop on descents. Rough trails place demand on the muscles, and frequent accelerations cause heart rate to fluctuate. Finally, the constant engagement of the arms and upper body increases energy demand and oxygen requirements.
Another phenomenon adds to terrain-related variations: cardiac drift. Even when maintaining a constant intensity, heart rate gradually increases over the hours. This rise is explained in particular by the duration of effort, elevation gain, heat, dehydration, and accumulated muscle fatigue, especially on descents. The weight of carried equipment can also have an impact on heart rate. Overpacked trail packs increase the effort required and can accelerate cardiac drift on long outings.
How to define and use your heart rate zones?
Several heart rate indicators are useful in trail. Max HR (maximum heart rate) corresponds to the maximum number of beats your heart can reach during a very intense effort. Many runners estimate it with the formula Max HR = 220 − age. However, it can vary for each runner, and a stress test remains more precise.
The RHR (resting heart rate) corresponds to the number of beats per minute measured upon waking. Tracking it helps evaluate training progress and detect signs of fatigue.
Heart rate zones allow you to plan your trail training. Base endurance is a zone in which your breathing remains comfortable. Generally, it is around 60 to 75% of Max HR. It helps develop your aerobic endurance, your ability to use fat as fuel, and your resistance to fatigue over long distances. This is therefore the zone in which the majority of your training volume should be completed.
Another zone to work on in trail is the anaerobic threshold. This is the maximum effort intensity you can sustain for an extended period without extreme fatigue setting in. Located around 80 to 95% of Max HR, it allows you to maintain a higher pace on runnable sections, be more efficient on long climbs, and delay the onset of fatigue. Threshold sessions typically represent a small proportion of total training volume in trail.
Heart rate in trail is a valuable indicator. However, it is influenced by many factors and should not replace RPE (Rate of Perceived Exertion). Your sensations remain essential for correctly interpreting heart rate data.
Managing your cardio according to the terrain
Terrain is one of the main factors driving heart rate variation in trail. On climbs, HR can rise very quickly due to increased energy demand. Trying to maintain the same pace as on flat ground often leads to exceeding your target zone. To stay within the desired intensity, it is better to accept slowing down or hiking in trail, especially on the steepest gradients.
On descents, many runners expect their heart rate to drop quickly. Yet HR can remain elevated. First, because the cardiovascular system needs time to recover from sustained effort. Second, because muscles work in eccentric contraction to control speed on the way down. Despite a lower cardiovascular demand than on climbs, HR can therefore remain relatively high, especially on broken or highly technical terrain.
To manage your cardio effectively in trail, several accessories can be used. The chest belt is the reference tool for trail runners. It directly measures the electrical activity of the heart and therefore offers excellent accuracy. The optical wrist sensor analyses variations in blood flow beneath the skin. While more convenient, it is less reliable during rapid changes in intensity.
What mistakes should you avoid?
Analysing heart rate in trail is very useful, but you should not become a slave to your watch. Heat, fatigue, altitude, elevation, and hydration all strongly influence heart rate data. Constantly trying to stay within a precise zone can therefore become counterproductive. What matters most is knowing how to interpret that data in context.
Heart rate is strictly individual. Comparing it with others is a real mistake. Even at an equivalent level, trail runners can show very different values. Some naturally have a higher heart rate than others for the same effort. What matters is focusing on how it changes relative to your own benchmarks.
Finally, rest must not be neglected. A resting heart rate that is consistently higher than usual can signal incomplete recovery, lack of sleep, the onset of illness, or excessive fatigue build-up. In that case, it is better to temporarily ease off your training.
Analysing heart rate in trail is an excellent tool to guide training. To be truly meaningful, however, it should not be used in isolation. Terrain, conditions on the day, and your sensations remain essential for correctly interpreting heart rate data.
Photo credits: Delphine Daniélou
