Trail and fell running
Woodland one minute, open moor the next, four hours out, and a pack strap working away at your shoulders the whole time. Trail exposure is patchy, and patchy is harder to plan for.
Trail running alternates between shaded woodland and completely open ground, which makes the exposure intermittent and therefore easy to underestimate. The plan has to be built for the open sections and worn through the shaded ones, because nobody stops at a treeline to change anything, and the pack straps add friction lines that running otherwise lacks.
A trail run is not one exposure environment, it is several, visited in an order set by the route. Twenty minutes under trees, then an hour across open moor, then a descent through a plantation, then a long exposed ridge. The load is not constant and neither is the perception of it, which is exactly why it gets misjudged.
Two things make the trail case different from road running. The first is duration: trail and fell sessions routinely run to three, four or more hours, which puts them in the highest band on this site. The second is the pack. Almost every long trail run involves carrying something, and a vest pack introduces friction lines that a road runner does not have.
| Surface | Angle to the sun | Exposed for | What removes protection | Control that holds |
|---|---|---|---|---|
| Shoulders | Near horizontal, and directly under the pack straps | 4h+ | Pack strap movement over hours, sweat, a shirt riding up | A short sleeve top under the pack. Product cannot survive a strap |
| Back of the neck | Steep, and worse when climbing with the head down | 4h+ | Collar, pack, sweat, and the rider never sees it | A cap with a neck flap, or a collar |
| Face and forehead | High, unshaded on the open sections | 4h+ | Sweat drainage on climbs, wiping | A peak and a brow band. This is where the eyes problem lives |
| Forearms | Rotating, with poles held forward on the climbs | 4h+ | Pole straps, sleeve edge, vegetation | Sleeves, which also deal with bracken, gorse and nettles |
| Calves and shins | Facing forward and sideways on ascent | 4h+ | Very little friction | Applied product holds here, or gaiters and longer socks |
| Lips | Presented forward, wind-dried as well as sun-exposed | 4h+ | Drinking, eating, wiping, wind | A lip product used at every checkpoint or drink |
Intermittent cover is a planning problem
The mistake is straightforward. You set off through woodland, the shade is pleasant, the decision about sleeves and hats is made in that environment, and then you spend three hours in the open. Nobody stops at the edge of a treeline to reconsider, partly because the transition is gradual and partly because you are running.
The fix is to plan against the most exposed part of the route rather than the start of it. Look at the map before you go and identify the longest continuous open section. That section sets the requirement. Everything else is worn in comfort through the shade, which is a small price.
There is a related trap on descents. People often start a long descent by removing a hat or pushing sleeves up, because the effort drops and the wind picks up. On an open descent, at speed, facing into the light, that is the moment the face and forearms take the most and receive the least protection.
The pack strap problem
A running vest pack sits on the shoulders and upper chest and moves with every stride for hours. It is the highest-repetition friction source in any sport covered on this site, simply because of stride frequency multiplied by duration. Under the strap, nothing applied survives, and at the strap edge you get the worst combination: partial shading and constant abrasion, which produces the sore, chafed, sunburned line that trail runners recognise immediately.
The answer is cloth under the strap. A short sleeve top rather than a vest removes the problem at the shoulder entirely, and it is a change most trail runners make eventually anyway for chafing reasons.
Fell running in rain and cloud does not remove the exposure. Thin cloud transmits a substantial amount of ultraviolet, and hill days often begin in cloud and finish in clear air above it.
Being wet from rain is also not the same as being wet from sweat: rain arrives from outside and runs off, sweat arrives from underneath and lifts. On a long day in poor weather you are getting both at once, plus pack friction, plus four hours.
Altitude, aspect and reflection on the hill
British hills are not high by international standards, but ultraviolet does increase with elevation, and the ground surface on a fell is often pale scree, wet rock or, in spring, snow. Aspect matters too: a south-facing slope in the middle of the day is a fundamentally more exposed environment than a north-facing one, and route choice determines which you spend your hours on.
Spring is the underestimated season here. The sun climbs quickly from March onwards, snow may still be lying, the air is cold enough that nobody is thinking about sun, and hill days are long. It is a combination that catches out a great many people every year and it is covered in more detail in the terrain section.
| Session | Band | The exposure feature | What to fix first |
|---|---|---|---|
| Woodland loop | 60-120 | Mostly shaded, dappled light | Little needed beyond a normal application |
| Open moor or ridge | 2-4h | No shade at all for the whole section | Cover and a hat, decided before leaving |
| Long mountain day | 4h+ | Altitude, reflection, changeable weather, poles | Full cover plus a plan for the descent |
| Ultra or race | 4h+ | Fixed duration, checkpoints as the only stops | Front-load, then a fixed routine at each checkpoint |
| Recce in poor weather | 2-4h | Cloud gives a false sense of safety | Check the forecast index rather than the sky |
Everything here assumes you already have the hill day right: navigation, weather, spare layers and someone knowing your route. Sun protection sits inside that, not instead of it. For heat illness, the NHS has guidance, and 999 is the number if somebody is seriously unwell.
A workable trail plan
- Look at the route and find the longest open section. That sets what you wear.
- Apply before you dress, including ears, the back of the neck and the backs of the hands.
- Wear a cap with a peak, and a collar or neck cover if the day is bright.
- Wear a short sleeve top rather than a vest if you are carrying a pack.
- Carry a lip product where you can reach it without stopping.
- Reapply face, ears and neck at a checkpoint, summit or genuine stop, and not otherwise.
The recurring theme in trail running is that everything gets decided at the car park and nothing gets revisited. Which means the car park decision is the whole plan, and it should be made against the most exposed part of the day rather than against how it feels standing in the shade next to the boot.
Questions
Is a vest pack worse than a rucksack for this?
Both create friction lines, but a running vest moves with every stride, so the repetition count over four hours is very high. The practical answer for either is a sleeve under the strap, which also reduces chafing.
Do I need sun protection on a cloudy hill day?
Thin and broken cloud transmits a substantial amount of ultraviolet, and hill days frequently start below cloud and finish above it in clear air. The forecast index is a better guide than what the sky looks like from the car park.
Does running under trees count as protection?
Dappled shade reduces exposure but does not remove it, and the proportion of a trail route that is genuinely shaded is usually smaller than it feels. Plan against the open sections, because those are where the load accumulates.
Should I use poles differently in strong sun?
Poles hold the forearms forward and upward for long periods on climbs, which increases what those surfaces receive, and pole straps add a friction line at the wrist. Sleeves solve both without changing anything about how you use them.
What about the tops of the feet in trail shoes?
Low-cut shoes and short socks leave a strip across the top of the foot facing almost straight up for hours, and it is a surface almost nobody treats. It is one of the more common places people burn on a long summer hill day.
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