Why is it harder to run at high altitude? Well lets clarify what high altitude is. For most runners, it’s more than 5000 feet above sea level. To me, since I live at 4500 feet, it’s around 8500-9000 feet where it starts to impact my running.
What happens? Everyone knows there is less oxygen at higher altitudes so your heart and lungs have to work harder to deliver the same amount of oxygen to your working muscles. This means an increase in your heart rate and breathing at your normal pace when you are at high altitude for your body.
What does this mean? You have to slow down. Depending on how much it is effecting you, the distance of your race, and the terrain, you may have to slow down quite a bit such as a minute to two minutes per mile slower. The longer your body is in motion the easier it is for your heart rate and breathing rate to be impacted at normal pace. Also you may do fine running flat at 10,000 feet (me) but climbing is definitely more difficult.
What can you do if you train below 5000 feet and are registered to run something at or over 5000 feet? First, don’t set high expectations, especially if this is your first race at altitude. Second, train and race on effort not on pace. Your body doesn’t care about pace. It cares about the effort it is putting out. Third, try to find out if your body responds better to arriving 3-4 days early to acclimatize or within 24 hours of the race before the altitude starts effecting you.
The ideal situation would be for you to be able to consistently train at altitude such as once a week. Sporadic training only gives you a difficult training run and no benefit to training your body. It may help train your mind to know what to expect preventing a freak out on race day. Another training strategy is to increase the intensity of some of your runs. By doing this, you mimic (not perfectly) the increased effort your body will experience at altitude.
The other thing to be aware of is making sure you fuel and hydrate properly at altitude. Your body is working harder which means you are going to need more fuel and more water during the race.
What about the other way around? If you train at high altitude and then move to sea level, everyone thinks you’ll have more oxygen and should be much faster. But this may not be the case. The reason is, although you have more oxygen it doesn’t equal leg turn over. In order to run faster, you also have to train your legs to turn over more quickly. To do this, you need to do speed work. If you want to be able to run a 7 minute mile then you need to train at a 7 minute mile even if you are going from high to low elevation.