Hikers who are gaining experience often set their sights on more ambitious summits. Yet the effects of altitude on the body should not be underestimated. To prepare as well as possible for a high-mountain outing, a few precautions are worth taking. Cimalp shares its best advice for hiking at altitude.
The effects of altitude on the body
Thinning air
Hiking at altitude has significant effects on the body. Indeed, the higher you go, the lower the atmospheric pressure. Blood oxygenation is reduced and the body enters a state of hypoxia. You may then experience breathing difficulties and a drop in physical performance.
Above 2,500 metres, you may also experience the first symptoms of Acute Mountain Sickness (AMS). When the body fails to adapt quickly to altitude, headaches, nausea, insomnia or loss of appetite can occur.
Lower temperatures
At altitude, temperature drops by an average of 6°C for every 1,000 metres of elevation gain. It can therefore be cold, even in the height of summer. The cold is felt even more at night, where the temperature difference with daytime is often very pronounced. The sensation of cold is also amplified by the wind, which can be particularly strong on exposed sections. The Windchill effect can then increase the loss of body heat.
Solar radiation and UV
In the mountains, solar radiation is much stronger. UV intensity increases by around 10% for every 1,000 metres. Snow or light-coloured rock reflection further increases exposure. As a result, you risk sunburn, heatstroke or snow blindness.
Accelerated dehydration
Hiking at altitude causes a drop in air humidity. This phenomenon is linked to hygrometry. The higher you go, the lower the air humidity level. This dry air then causes water to evaporate through breathing and perspiration. Even without visibly sweating, you lose a lot of fluid and risk accelerated dehydration.
Other effects of altitude
On top of all these factors, hiking at altitude can have other effects on the body. You may notice a reduced appetite, disrupted sleep, or increased fatigue linked to slower muscle recovery.
The acclimatisation phase at altitude
Understanding acclimatisation
Acclimatisation during a high-altitude hiking trip is essential. The body needs to adapt to the lack of oxygen. To compensate, it must increase its breathing and heart rate, then produce more red blood cells. This process takes time, however.
Ascend gradually
To give the body time to adjust to altitude, it is important to ascend gradually. Above 2,500 metres, it is advisable to follow the "Climb high, sleep low" rule — that is, to climb during the day but sleep no more than 300 to 500 metres higher than the previous night.
Overexertion is also not advisable. Acclimatisation is faster when you conserve your energy. Avoid intense effort at the start of the hike and rest whenever possible. For every 1,000 metres of altitude gained, we recommend taking a rest day.
Staying hydrated and fuelled
To stay in good physical shape, hydration and nutrition are paramount at altitude. Every day, drink at least two litres of water to compensate for fluid loss caused by low humidity. Don't wait until you're thirsty. Instead, aim to drink regularly and in small quantities. This way you'll stay hydrated throughout the day.
When it comes to food, try to eat enough, particularly carbohydrates and proteins. This will give you sufficient energy and support red blood cell production.
Monitor your symptoms
AMS is common at altitude, but particularly dreaded by hikers. While the first signs usually fade quickly, they can sometimes worsen. Certain symptoms such as breathing difficulties even at rest, extreme fatigue, vomiting, severe headaches or hallucinations should put you on alert.
If AMS persists, you must descend as quickly as possible. The main risk is the development of pulmonary or cerebral oedema, which constitutes a life-threatening emergency.
Understanding acclimatisation duration
From the first hours at altitude, the body begins to adapt. A full acclimatisation, however, takes several days to several weeks, depending on the individual, the duration and the target altitude.
If you climb to below 3,000 metres, you should acclimatise within just a few days. Between 4,000 and 5,000 metres, it generally takes two weeks. Finally, a hiking trip to above 5,000 metres requires several weeks of acclimatisation.
Equipment for hiking at altitude
Technical clothing
To dress well at altitude, the three-layer principle is ideal. For the base layer, go for thermal underwear in merino wool or synthetic fabric. They keep you warm while wicking away perspiration.
For your mid layer, choose fleece jackets or hiking down jackets. They are perfect for retaining heat in cold conditions. Finally, choose hardshell jackets as your outer layer. They offer ideal protection against rain, wind and snow. For trousers, go for a model with a water-repellent finish.
Grippy footwear
Trekking shoes must be chosen with care. At altitude, trails are often steeper, so good ankle support is essential. Look for a high-cut model. Also choose a grippy and rigid sole for better grip.
Depending on the season, also consider waterproofing, breathability and a degree of insulation. In the event of snow at altitude, crampon-compatible footwear is also recommended.
Accessories
Several accessories are essential for good protection. Against UV rays, equip yourself with category 3 or 4 sunglasses, high-protection sunscreen (SPF 50+), a cap or hat. To combat the cold, bring gloves, a beanie or headband, a buff or neck gaiter, and technical socks.
Hiking poles are recommended for better stability. They also relieve the joints on both ascents and descents. The backpack should finally be suited to hiking, with a comfortable carrying system.
Safety equipment
A hiking first aid kit is essential at altitude. You can supplement it with a distress whistle, a survival blanket and a head torch with spare batteries.
For navigation equipment, bring a map and compass, a GPS, and an altimeter. This will allow you to track elevation gain and manage acclimatisation as effectively as possible. A mobile phone with a power bank or a VHF radio are essential for contacting the emergency services.
Practical accessories
A few other practical accessories can round out your kit. You can bring a pair of binoculars, a field guide and a camera. They will let you observe the wildlife and flora and keep precious memories.
You now know everything you need to about hiking at altitude. For a successful outing, make sure you plan your route carefully and check the mountain weather forecast. You'll be set to head out in the best possible conditions.
