Atmospheric pressure decreases with increases in altitude, which makes it harder for our bodies to pull oxygen from the surrounding air. The higher we go, the harder it becomes to extract oxygen which in turn decreases the amount of oxygen carried by our blood to our muscles and organs. Our brains will be sensitive to the lower oxygen content in our blood and reduce our muscle recruitment, which in turn decreases our power output. The threshold for performance decrements has been suggested to be around 1000m above sea-level, with further decreases in endurance capacity of roughly 1% per 100 m above this threshold. There is large individual variation in the response to altitude exposure with certain athletes experiencing greater performance decrements than others. An athlete’s response to altitude may depend on their genetic disposition, training status, diet, recovery and previous exposure to altitude.
If we are exposed to altitude long enough (>2 weeks), physiological adaptations occur which reduce the effect of altitude on performance. Our muscle cells develop more mitochondria, which are responsible for producing the energy needed for muscle contractions, and we produce more haemoglobin and red blood cells to increase our oxygen carrying capacity. These adaptations to altitude form the foundation of the “live high-train low (LHTL)” training intervention, whereby elite athletes live at moderate altitudes of between 2000 and 3000m for a period of 3-4 weeks, but still train regularly below 1000m. This training model allows elite athletes to be exposed to high altitudes for long enough for the beneficial physiological adaptations to occur, but still train at the high-intensities needed for peak performance.
However, the LHTL model is traditionally used to improve performance at sea level and not altitude.
The most effective method of optimising performance at altitude is to spend an adequate amount of time at the altitude where the competition will take place. The amount of time required to achieve optimal acclimatisation is dependent on the altitude, with higher altitudes requiring longer periods of exposure. General recommendations for racing at low to moderate altitudes (<3000m) are to live at the competition altitude for a period of 2 weeks prior to competition. Obviously, this is highly impractical for most athletes, especially sub-elite competitors who have full-time jobs. So how can these cyclists reduce the negative effects of altitude?
Over the last two decades numerous devices have been developed to simulate altitude while at sea-level. These include; nitrogen tents which athletes sleep in to simulate the LHTL model, hypoxic (low oxygen) breathing systems and hypoxic training centres. A recent review of the scientific literature suggests that training in a hypoxic environment may be more beneficial than living at a simulated altitude. This type of training is referred to as intermittent hypoxic training (IHT) or the ‘live low-train high’ (LLTH) model.
This relatively new training method is fast receiving attention as an effective method to possibly increase performance at sea-level and acclimatise to altitude. What is interesting is how the training changes the athlete’s physiology. The exposure to altitude during IHT is not long enough to cause the same adaptations seen following chronic altitude exposure (LHTL), but rather improves the efficiency and working capacity of the muscles. The proposed benefit of this type of training is the addition of another stimulus, hypoxia (reduced oxygen availability), compared to training at sea-level alone. There are several scientific studies that have reported improved endurance performance at simulated altitude following a few weeks of IHT.
In a study performed on trained runners, including IHT training resulted in improved performances at simulated altitude compared to normal sea-level training. To date, this is the only study, completed using trained endurance athletes, examining the effect of IHT on performance at altitude. Although further research is required to confirm these findings, this is a promising and potentially useful tool for coastal-based athletes to prepare for competition at altitude. If you are planning on competing at a moderate or high altitude, it may be worthwhile considering incorporating some IHT as part of your training program.