I recently ran the Ultra-Trail Kosci 100 in the Snowy Mountains in Australia. The race starts at Perisher Village at 1720m, climbs to the top of Mt Kosciuszko at 2228m and stays above 1600m for the first 60km of the race.  I found this race a lot harder than I was expecting, and every runner I spoke to in the following days said the same thing.

Everyone found it hard, most people were slower than they thought they would be, and almost everyone suffered some sort of nutrition or GI issue.

The most likely factor that caused these problems is the altitude. When you are running at 1600m you have to run significantly slower than usual to keep your relative effort/exertion the same. By “significantly”, I mean something in the vicinity of 30sec – 1 min / km slower than normal.

What happens when you run at 1600m?

When running at 1600m, your body has to work harder to get enough oxygen into your bloodstream due to the thinner air and reduced oxygen availability. This makes running feel more difficult and more tiring. Your heart has to beat faster to pump more blood, and your breathing becomes deeper and more frequent to try to take in as much oxygen as possible.

Even with the increase in both heart rate and breathing rate, your muscles still receive less oxygen, which means your body has to rely on less efficient energy systems. This can lead to feeling fatigued sooner than you would at lower altitudes, especially during longer runs like ultra trail races.

Over time, your body can adapt to the challenges of altitude, but these changes don’t happen overnight. One of the main adaptations is an increase in the production of red blood cells, which helps carry more oxygen through your body. However, it usually takes several days or weeks of staying at altitude for these changes to kick in fully.

Running at altitude can make it feel like it is warmer than you would expect. This happens because the air is less dense, which makes it harder for your body to lose heat through convection. Combined with the extra effort required to run in thinner air, this makes running at altitude feel harder, both physically and mentally.

Altitude can also suppress your appetite, so is important to focus on eating enough food, especially energy-dense options, to fuel your performance.

To perform well at altitude, it is crucial to adjust your expectations and pacing. You will need to slow down to account for the lower oxygen levels and the increased strain on your body.

How can you acclimatise to running at high altitudes?

The following training strategies can help to improve your performance running at altitude.

1. Prepare Physically
  • Boost Aerobic Fitness: Focus on building a strong aerobic base through low-intensity, long-duration training runs before the event. A higher fitness level helps mitigate the drop in performance due to reduced oxygen availability.
2. Adjust Pacing and Effort
  • Start Slower: At altitude, your body tires more quickly due to lower oxygen levels. Begin the race at a conservative pace to avoid early fatigue.
  • Use Perceived Effort: Rely on how you feel rather than trying to maintain sea-level paces. Your heart rate will naturally be higher, so focus on sustainable effort.
3. Prioritise Hydration
  • Stay Well-Hydrated: Thinner air increases fluid loss through breathing, so drink more than usual. Start the race fully hydrated and continue drinking consistently throughout.
  • Electrolytes: Include electrolytes to maintain balance, especially if you sweat heavily.
4. Optimise Nutrition
  • High-Calorie Carbs: Altitude can suppress your appetite. Try eating small amounts frequently to help keep your energy levels stable.
  • Iron Levels: Ensure adequate iron intake in the weeks leading up to the event to support red blood cell function, which is critical for oxygen transport.
5. Mental Strategies
  • Mindset and Focus: Expect the race to feel harder and embrace the challenge. Knowing what to expect can prevent frustration.
  • Break the Race into Sections: Focus on short-term goals during the run to stay motivated and avoid feeling overwhelmed.