Running at Altitude
Running at altitude might be of interest to athletes for two reasons. Firstly, there has been considerable interest in using altitude as a means of enhancing training, by increasing the efficiency in which oxygen is transported to the working muscles. One mathematical model predicts that, if used effectively, altitude training could reduce someone's sea-level marathon time by about 5%, or 8.5 minutes (1).
Secondly, with growing demands from racers to compete in the most extreme environments on Earth, it ought to be useful to improve our understanding of what to expect if preparing to race at high altitude (i.e. the Everest Marathon or La Ultra/The High ultra-race). For example, VO2 max has been found to decrease from 66 (ml/kg/min) at 300-m down to 55 (ml/kg/min) at 2800-m, with corresponding decreases in time to exhaustion (2).
In addition to the drop in VO2 max at high altitude, marathon speed is reduced too, with a difference in speed between marathons at sea level and 4300-m of around 35% (3). Elite runners are able to run at altitude at a higher percentage of their VO2 max and maximal heart rate, compared to other runners (3). Shorter distance running performance is affected too, with time for a 3-mile run being increased by about 8.5% compared to at sea level, although through acclimatisation this can be reduced over a period of days (to 5.7% by day 29) (4).
As our altitude increases, so atmospheric pressure becomes lower compared with at sea level. Although the percentages of the different gases in the air remain the same, at a lower air pressure they are spread out over a larger area, meaning that for each breath there is less oxygen available to come into our lungs. So, as we reach higher altitudes, so our breathing rate increases, in an attempt to bring sufficient oxygen into our lungs each minute to maintain health.
Endurance performance is reduced when first exposed to high altitude, but gradually recovers over a period of 2-3 weeks due to acclimatisation (5). We acclimatise to an increased elevation, by increasing the efficiency at which the reduced oxygen available can be transported in the blood to where it is needed. This involves increasing the concentration of red blood cells (haematocrit), a process that occurs from first exposure to altitude, and increases over a period of days and weeks. Exposure to very high altitudes without acclimatisation has the potential to be lethal, as the brain and other organs can be starved of oxygen, with an increased breathing rate being insufficient to meet requirements for oxygen-delivery.
Haematocrit, EPO & Blood Doping
Blood doping and erythropoietin (EPO) administration are used in attempts to increase haematocrit. Blood doping requires the removal of blood and separation of the red blood cells (RBCs), which can then be injected back into the body at a later date. The idea is that RBC production increases to compensate for the lost blood, so when the extracted RBCs are reintroduced later on, the total concentration of red blood cells will be extremely high. Thus, the oxygen-carrying capacity of the blood will have been increased, and performance should improve as a consequence.
EPO is a hormone that signals the body to increase red blood cell production directly, and can be injected to increase levels of that hormone, with haematocrit increasing as a consequence. Both blood doping and EPO administration are banned by sports governing bodies, but there is interest in using exposure to high altitudes as a natural means of improving haematocrit.
Haematocrit is constantly monitored by internal control systems, with red blood cells being created or destroyed according to requirements. So, just as blood doping and EPO administration require repeated applications to be of use, altitude training requires a continued exposure to high altitude. How best to use altitude training to improve performance is still debated, and the remainder of this article deals with what researchers have found when investigating this approach to training.
The Aims of Altitude Training
To be of benefit, altitude training needs to elicit benefits in aerobic fitness directly, or via an enhanced training stimulus due to the demands of exercising higher up (6). The adaptations might include generalised cardiovascular and neuromuscular adaptations, as the body strives to be as efficient as possible with the limited oxygen available (6). However, exposure to altitude needs to be for a sufficient duration to stimulate adaptations. For example, high altitude (4500-m) training for only a couple of hours, is insufficient to elicit any training benefits of use, in subsequent high altitude sessions (5).
Some athletes have used intermittent hypoxic training (IHT) to improve performance. This requires time to be spent in a controlled environment - often a climate chamber or tent - in which air pressure is kept normal (normobaric), or below normal (hypobaric), with oxygen levels reduced (hypoxic). Alternatively, actually being in a mountainous region, where it is possible to spend some time at high altitude and some lower down, can also be used. The goal is to spend sufficient time in a hypoxic environment to elicit acclimatisation, with the hope this will improve athletic performance.
Live High, Train Low
Because training at high altitude is more demanding than at sea level, it is thought that IHT will enhance the training effect and improve fitness (7). The benefits of hypoxic training are thought to include increased haematocrit, improved aerobic capacity (VO2 max), and improved aerobic exercise performance (7).
'Live high, train low' is a type of IHT. This involves spending time at an altitude sufficient to elicit acclimatisation, but training lower down so exercise intensity is not affected (7). When exercising at altitude, the reduced oxygen availability places increased demands on the body, as muscles and organs struggle to obtain sufficient oxygen to function, and performance diminishes as a result. Training at this altitude would therefore involve a reduction in training intensity.
Living high and training low is intended to give the best of both worlds: improved aerobic capacity due to acclimatisation, and improved performance, because of using that increased aerobic capacity in demanding exercise lower down. Importantly, training at altitude is unlikely to be beneficial to already highly-trained athletes, who instead suffer from the inability to train at their usual speeds and intensities (7).
One study found improvements in 5-km performance in athletes who lived high and trained low for 4 weeks (2500-m), but not in athletes who lived and trained at that altitude (8). 4 weeks at 2500-m was sufficient to increase EPO levels and red blood cell size (about 10% increases), as well as increase haemoglobin concentration and VO2 max.
The improved aerobic fitness permitted a reduced cardiac output during exercise, as the blood's oxygen carrying capacity had been improved, and more oxygen was travelling in the blood each minute. A consequence of this was that the heart did not have to beat as fast, and the blood moved more slowly past the lungs and working muscles, allowing more time for oxygen to be transferred between the lungs, blood and muscles (8).
So, clear improvements in performance have been reported following a live-high, train-low approach for 4 weeks, but not following live-high, train-high. Further, sleeping for 29 nights at a simulated altitude of 3000-m, for about 11 hours a night of total exposure, has been found to be insufficient to influence haemoglobin and VO2 max (9). This appears to demonstrate an important difference between a month of total exposure to high altitude, and a month of only sleeping at high altitude.
Live High, Train High
Although remaining at high altitude for a prolonged period (months) would allow for an at least partial recovery of performance, compared with at sea level, there are other negative consequences of being at high altitude. Oxidative stress is increased, and that stress will be increased further if exercising at a high intensity at that altitude (10). Protein breakdown occurs due to increased needs for proteins to build new and larger red blood cells.
Because the building of red blood cells is a continual process, there is a constant need for small amounts of protein, and if this is not provided for in the diet, it will have to come from muscle tissue, leading to muscle wasting and impaired immune function (6). Supplementing with proteins, whether as branched-chain amino acids (BCAAs), protein bars or protein shakes, may help to top-up protein supply, and reduce or prevent these negative effects of high altitude.
So, living and training at high altitudes will lead to reduced exercise performance, including reduced speeds, power outputs, and reduced oxygen delivery. Individuals can also expect appetite suppression, reductions in protein synthesis, muscle wasting, increased breathing rate, and alterations in metabolism (i.e. fuel usage and aerobic versus anaerobic energy systems) (6). At more moderate altitudes (2500m) it is possible that there is still a stimulus to adapt and acclimatise, but without such a great demand for protein synthesis and metabolic changes (6).
Energy Systems & Substrate Usage
During prolonged exercise at high altitudes, anaerobic energy systems have been found to be utilised more than for the same exercise at sea level, for any individual (11). That is, because of the shortage of oxygen to be used in aerobic energy production, the body has to switch to anaerobic sources earlier on, or at lower speeds (11).
As might be expected, despite all non-acclimatised athletes suffering with the effects of altitude, a faster runner at sea level ought to be a faster runner at high altitude. So, out of a group of sea-level marathoners, those who finish in the first 10 and last 10, will likely finish in similar positions when transported to high altitude for a race, even though everyone's performance will be reduced compared with their times lower down.
In one study of competitors in a 46-km mountain race (11), the runners with the highest blood lactate levels (indicating increased anaerobic energy system usage) finished the race fastest. The faster half of the runners also had higher blood levels of glucose than the slower half of the field, and lower levels of blood fats too, and this occurred from fairly early into the race (measured at 26-km and at an altitude of 3400-m) (11).
It is unlikely that blood glucose levels would have been depleted so early into the race, which might otherwise have accounted for the raised levels of fats and reduced glucose in the slower runners. This suggests that the faster runners were better at releasing glucose into the blood, and utilising it for fuel, than slower runners (including an improved conversion of lactate into glucose via the liver).
As a training effect, when athletes who had been training at moderate altitude (1500-2000-m) returned to sea level, their submaximal blood lactate levels dropped significantly, compared with those of athletes who had only trained at sea level. This suggests improvements in aerobic fitness, and the effects lasted for 20 days following their return to sea level (12).
Interestingly, their performance actually dropped by 2% during this time, presumably because they could not train as hard at altitude, and their fitness suffered as a result. In effect, they could not train as fast as usual, and so lost the ability to run that fast. Athletes training at moderate altitude also reported a 50% increased incidence of upper respiratory tract, and gastro-intestinal, infections, than others (12).
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