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Exercising at Altitude

and the incredible adaptations the body goes through

By Jessica Kelner, D.O. - August 1, 2018

Exercising at altitude is no easy feat. At higher altitudes, there is less oxygen available in the air that you breath, which makes it harder for your body to get the oxygen it needs to perfuse your tissues with oxygen. If you add exercising to the mix, this places an even higher oxygen demand on your muscles and tissues requiring even more oxygen. 
Acclimatization to high altitude involves the body adapting to hypoxia (lower levels of oxygen in the air). The human body is quite incredible with its ability to adapt to new environments. There is a series of metabolic and musculocardio-respiratory adaptations that affect how oxygen is used by the body. These adaptations start immediately upon ascent to higher altitude and continue for months after (assuming you stay at the higher altitude elevation).
During the initial exposure, the body’s number one priority is making sure you get enough oxygen.  The body begins to increase ventilation as well as cerebral blood flow when hypoxia is the greatest. This assures that your brain has enough oxygen (very important).  This increased ventilation can lead to an increased loss of body water (which can lead to dehydration). The body’s sympathetic nervous system starts to kick into overdrive (it is essentially freaking out that it doesn’t have enough oxygen). The hypoxia induces immunosuppression, increased oxidative stress (can cause tissue damage), increased dehydration, and decreases overall training intensity. It also will affect sleep quality and cognitive performance. You may not be able to sleep well or may have periods of time while your sleeping that you may experience apneic breathing (when you stop breathing in your sleep). Bottom line, you will be able to breathe, but may not feel so hot.
Over the next few days, the body starts the process of making more hemoglobin (this is the molecule that carries oxygen in the blood). Cardiac output (overall blood volume pumped from the heart) decreases, there is an increase in your heart rate (heart beats per minute) and the stroke volume (the amount of blood pumped out each time the heart beats) decreases.  After a few more days, you start to gain improvements in the structural and biomechemical properties of muscle tissue, as well as an elevated buffering capacity (body’s ability to deal with acidic environments).  The sympathetic nervous systems production of catecholamines (such as epinephrine) that induces glycogen depletion in muscles. This means your immediate energy storage that is found in muscle is going to be temporarily reduced.
Within weeks of living at higher altitude, the body increases mobilization of free fatty acids (energy storage from fat), increases mitochondria (the cells that make energy for you), and increases oxidative enzyme activity. Due to the increased sympathetic nervous system functioning, there is a decrease in appetite, which at times can lead to an energy deficit.  This can be particularly dangerous if you are also trying to exercise at the same time.   The energy deficit can cause muscle loss, but there is also a potential for deregulation of anabolic signaling (these are hormones that help build muscle).
From the first day through the first few days of arriving at higher altitude, there are risks of developing Acute Mountain Sickness (AMS), High Altitude Pulmonary Edema (HAPE), High Altitude Cerebral Edema (HACE), cardiac arrhythmias and cerebral hypoxia. If not recognized and treated these syndromes can be potentially fatal.
Acute Mountain Sickness (AMS) occurs in 10-30% of people that ascend in altitude.  It usually occurs over 7,000 feet, but can occur in sensitive people not acclimatized at as low as 5,000 ft. This can be compounded by cold and element exposure.  The symptoms of AMS are nausea, headache, poor sleep, cough, dyspnea on exertion (shortness of breath), and mental status changes.  AMS can be treated by descending in elevation and oxygen when needed.
High Altitude Cerebral Edema (HACE) and High Altitude Pulmonary Edema (HAPE) are much more serious complications from high altitude exposure.  Due to the pressure changes that altitude has on the body, with increasing altitude, there can be a shift of fluids from the capillaries (small blood vessel networks) into the brain (HACE) or the lungs (HAPE).  This causes fluid to build up in the brain or lungs and can be very dangerous and life threatening.  High Altitude Cerebral Edema (HACE) is rarely seen below 13,000 feet and High Altitude Pulmonary Edema (HAPE) is rarely seen below 9,000 feet.
The body has an incredible ability to not only adapt to new environments, but excel at functioning and living in them.  Exercising and living at higher altitude is something that has been used by many competitive athletes to attempt to gain an advantage during competition. 
High altitude training is one of the effective strategies for improving aerobic exercise performance at sea level via altitude acclimatization, thereby improving oxygen transport and/or utilization.  Training at altitude can induce high altitude acclimatization, thereby increasing respiratory frequency, accelerating heart rate, elevating hemoglobin level and red cell volume, enhancing capillary density, and reducing blood lactate concentration, which can further improve the function of cardiovascular system, local blood supply, lactic acid tolerance capacity, and maximal oxygen consumption (VO2max) of the athlete.
Over time, high altitude training can result in the increase of VO2max, but exercise performance is not completely associated with VO2max. High altitude training can also result in other changes of non-blood factors, such as energy saving, lactic acid threshold, and oxygen utilization of muscle. Upon the stimuli from hypoxia and exercise, the body produces a variety of adaptive responses such as changes to muscle mass and capillaries in skeletal muscle and increased ratio of capillaries to muscle fibers. Previous studies have demonstrated that high intensity training under hypoxic environment can promote the mRNA expression of vascular endothelial growth factor (VEGF) in skeletal muscle, thus improving oxygen transportation and intake in muscle tissues. In addition, hypoxic training can also enlarge the cross-sectional area (CSA) of skeletal muscle.
These changes don’t happen over night. They can take weeks, if not months to occur. 
Keeping in mind the adaptations and changes the body goes through when altitude increases, some athletes find that hypoxia training gives them a competitive edge at lower altitudes.  It is important to be mindful of the dangers of increasing altitude too quickly as well as exercising at a higher altitude than you live at. 
It is recommended to consult your physician prior to starting high altitude training.  When starting high altitude training, start slow, monitor your hydration, your nutrition, heart rate and pulse ox.