Altitude is generally described as 1200m or higher above sea level. On ascent to altitude, atmospheric pressure is reduced, and therefore air molecules are more spread out than at sea level. This means that although the percentage of oxygen within the air does not change, the partial pressure is reduced, decreasing the amount of oxygen that is available for use by the body.
This reduction in oxygen levels is the cause of mountain sickness on sudden exposure to altitude, and also causes a reduction in VO2 max (maximal oxygen consumption) and exercise performance.
Does altitude affect CrossFit performance?
In 2017 the CrossFit south regional was held in San Antonio, Texas, at an altitude of 198m. In 2018 it moved to Salt Lake City, Utah, which sits at an altitude of 1288m. It took place in the first week of the regionals calendar in both years.
In 2017 in San Antonio the male winner of the south regional achieved times 3% slower than the average of the winners of the other seven regionals across the six workouts. In two events, he achieved an above-average time; in four events, he was below average. In 2018, after the move to Salt Lake City, the male winner of the south regional achieved scores 9% slower than the average of the winners of the other regionals.
There was a similar pattern seen in the women. In Texas in 2017, the female winner achieved times within 1% of the average of the other regional winners that year. She did better than average in four events and worse in two. In 2018 in Salt Lake City, the female winner of the south regional achieved times 14% slower than the average of the other regionals winners – a considerable difference.
In 2018 for both the male and female south regional winners every event over the weekend was slower than the average of the other regional winners.
There are obviously a number of different factors that could have come into play to affect these results, but it is difficult to deny that the change in altitude is likely to have had some impact.
What is altitude training?
The use of altitude training is common in sport, particularly in the endurance world. Over time, prolonged exposure to lower partial pressures of oxygen stimulates a multitude of adaptations within the body. It is these adaptations that altitude training aims to capitalise on.
It was initially thought that the main adaptation that occurs is an increase in the number of red blood cells, and therefore the oxygen-carrying capacity of blood. The drop in arterial oxygen saturation causes hypoxia (low oxygen levels) within the kidneys, which stimulates them to produce the hormone erythropoietin (EPO). EPO acts to stimulate the production of red blood cells within the bone marrow. However, improvements in sea-level performance have been demonstrated in athletes after altitude training, even in the absence of an increase in red cell mass. (1)
This implies that other mechanisms are also playing a part. Hypoxia appears to affect cell signalling by reducing the breakdown of a transcription factor called hypoxia-inducible factor 1 (HIF-1). HIF-1 activates EPO and transferrin, a substance involved in iron metabolism, which is vital for haemoglobin production. It stimulates enzymes involved in carbohydrate metabolism, muscle lactate metabolism and carbonic anhydrase, which is involved in the regulation of pH. It stimulates the growth of new blood vessels (angiogenesis), and signals enzymes that produce vasodilators such as nitric oxide. (2)
Each of these actions in isolation or combination may contribute to the improvement in exercise performance at sea level following altitude training.
Altitude training can take a number of different forms. Traditional training, where the athlete lives and trains at altitude can cause problems, including:
- shortness of breath
- nausea and vomiting
- significant weight loss (particularly lean body mass)
- sleep disturbances
These all act to inhibit performance.
The reduced partial pressure of oxygen at altitude and subsequent reduction in VO2 max alongside these symptoms mean that training cannot be performed to the same intensity that it is at sea level. This results in a decrease in training load and therefore a reduction in stress and subsequent adaptation to training.
Some coaches and athletes overcome these issues by adopting what is called a ‘live high, train low’ form of altitude training. The athlete lives at high altitude (or in high altitude simulation) to obtain the physiological adaptations described above but will travel to a lower altitude to train, enabling maintenance of higher training loads.
Would altitude training improve CrossFit performance?
There are no studies specifically looking at altitude training for CrossFit or functional type fitness. Instead, we can look at some of the components that are important to CrossFit that have been studied to see how these are affected. (19)
A systematic review of 20 studies investigating the effects of altitude training on sea-level performance showed that the live high, train low method resulted in improvements in VO2 max. (3)
Fifteen elite male swimmers were tested for squat jump height and swimming start performance before and after a 17-day training camp at moderate altitude. The swimmers showed significant improvements in both jump height and start performance following the camp. (4) There was no control group in this study, so we cannot be sure if the improvements were attributable to altitude or just the training itself regardless of elevation.
Two studies have been carried out testing short distance running performance or speed with altitude. The first, on five national level sprinters who trained at 1860m for two weeks, showed an increase in 150m running speed after the two weeks, but no change in 300m or blood lactate levels (indicating no change in anaerobic capacity). (5)
The second study was carried out under the live high, train low model with eight 400m runners living in an altitude house (sea level pressure, but with a reduced oxygen percentage) for ten days, and training at sea level. This study demonstrated improved 400m performance after the ten days compared to a control group, increased speeds at certain lactate concentrations, and a decrease in resting blood pH. These changes in the acid-base balance and lactate metabolism might be responsible for the improvement in sprint performance. (6)
It is thought that resistance training with hypoxia causes a reduction in oxygen concentration within the muscle tissue, leading to greater production of metabolites and anabolic hormones, and accelerated recruitment of type II motor units. These changes impose greater stress on the tissue, therefore leading to more significant adaptation and strength gains. There is some mixed evidence for this.
In one study, low-resistance exercise (6 sets of 25 repetitions at 30% 1RM, three times/week for four weeks) combined with hypoxia (12% inspired oxygen, ∼4000m) had no additional effect on maximal strength compared to identical exercise completed under normal conditions. (7)
In contrast, another research group reported improvements in knee flexor/extensor cross-sectional area, maximal voluntary contraction and max reps at 20% 1rm following five weeks training in hypoxic conditions (athlete oxygen saturation 80%). (8)
One study in female netball athletes tested resistance training under hypoxic conditions – five weeks of training low-load resistance exercise (20% of 1RM) of the knee flexor and extensor muscles combined with hypoxic air (athlete oxygen saturation 80%). This training not only improved muscle strength (15%) and hypertrophy (6%) but also induced faster (4%) 5m and 10m sprint times. (9)
It is important to note that none of these strength studies were actually carried out at altitude, the training was carried out in hypoxic conditions.
There are clearly many other aspects of fitness that have not yet been investigated, and further research needs to be done to ascertain how altitude training may affect these. Even in endurance sports where the use of altitude training is well established, there remains little consensus on the most efficient training regime of duration, elevation, actual altitude vs simulation, etc. The evidence we have so far does seem to imply that altitude training could improve a number of the key components of functional fitness. As the sport of CrossFit develops with increases in funding and more athletes becoming professional, it may be that we see the introduction of altitude training camps for elite athletes, as we do in so many other sports.