Gains, but for how long?
At present little is known about the nature of any long-term benefits that may be conferred by a ‘live high, train low’ regime. Only a handful of studies have monitored volunteers after the completion of their trial, and those that have were stopped after three weeks. In participants who demonstrated a rise in red cell concentration and VO2 max, it would be reasonable to expect improvements in performance to last for the lifetime of their new red blood cells. This may not be very long, however, because red cells undergo premature destruction over just a few days when they’re no longer needed.
In those athletes who do not increase their red cell production during hypoxic exposure, outcomes are even more unpredictable. In this group, red cells are either produced slowly, with concentrations ‘peaking’ late, or else these subjects simply fail to make any response to the level of hypoxic exposure. The result? Either a lengthy delay in response, or worse, no improvement at all. To further confuse matters, some small improvements in performance are sometimes seen in a few of those who fail to recruit additional red cells.
At present the studies that address this issue are small and conflicting, leaving little for us to go on. However, it is thought that positive changes may be due to subtle improvements in muscle performance triggered by the hypoxic stimulus.
Importantly, this research refers to sea level rather than high-altitude performance. The benefits of altitude training for high altitude events is complex.
Who does not benefit?
The response to hypoxia is complex and varies widely from individual to individual. This was confirmed by a study that examined the 39 athletes who had participated in Levine’s landmark experiment. Among those individuals who had failed to respond to the ‘live high, train low’ regime, the study noted that a much smaller and briefer increase in erythropoietin occurred than in those who responded to hypoxia. These ‘nonresponders’ also failed to show any improvements in red cell production, VO2 max or 5,000m
As yet there is no way to distinguish ‘nonresponders’ from ‘responders’ prior to undergoing altitude training. However, it may be possible to distinguish another group who are also unable to respond to hypoxia. Levine’s long-time co-worker, James Stray-Gunderson, identified iron deficiency in up to 40% (20% men and 60% women) of competitive distance runners. Without this essential element, red cells cannot be formed and no amount of erythropoietin will help. Simple blood tests can identify iron deficiency and it can be easily addressed with iron supplements and changes in diet.
Disadvantages of ‘live high, train low’
*Acute mountain sickness (AMS): This is particularly common on arrival at altitudes above 2,500m and is associated with headache, nausea, loss of appetite, fatigue, weakness and sleep disturbance. AMS is also associated with the development of rare conditions such as high altitude pulmonary oedema (HAPE) and high altitude cerebral oedema (HACE), which can be fatal if left untreated. It is therefore vital for athletes and coaches to be aware of such conditions and seek medical advice quickly should problems arise.
*Weight loss and muscle wasting: Weight loss is common with prolonged stays at high altitude. Although the body often targets fat stores in the first days and weeks at altitude, changes in muscle bulk also occur. This is particularly common at higher altitudes, where muscle volume can fall by between 11% and 13%. Lowlanders spending time at altitude also experience changes in the way their muscles obtain glucose and convert it into energy (adenosine triphosphate or ATP). These changes could be responsible for the falls in VO2max that typically occur at altitude.
*Changes in the heart: Hypoxia triggers a rise in blood pressure in those arteries that connect the right ventricle of the heart to the lungs. Although this is usually harmless, prolonged hypoxia can cause the heart to enlarge and increase the oxygen it requires to function effectively. In obstructive sleep apnoea, a common condition characterised by long periods of hypoxia during sleep, an increased risk of high blood pressure and heart disease are both well documented. These findings would suggest that prolonged periods of hypoxia may be dangerous. We do not yet know what period of hypoxia is safe, or who may be at an increased risk of developing these problems.
*Reduced immunity: Hypoxia and intensive exercise are both known to impair the immune system. This may result in an increased risk of developing infections, ranging from common colds and flu, to urinary and respiratory tract infections. This effect may also contribute to the delays often seen in those recovering at altitude from softtissue injuries such as cuts, blisters and burns.
*Risk in pregnancy: Hypoxia can reduce the birth weight of babies born to lowland mothers exposed to high altitude and predispose children to a number of conditions. It is therefore vital to ensure that athletes are not pregnant before undertaking a ‘live high, train low’ regime.
*Dehydration: Hypoxia causes a sudden redistribution of body water and an increase in micturition. This leads to a reduction in plasma volume and an immediate increase in the concentration of cells in the circulation. This should be managed by increasing fluid intake during periods of hypoxia.
*Psychological considerations: Spending up to 20 hours a day in a hypoxic tent can test the motivation and commitment of even those striving for Olympic medals. Suitable distractions and incentives need to be provided and should be incorporated into any regime.
Although ‘live high, train low’ regimes are commonly used by elite endurance athletes in the lead up to major competitions, the evidence to support such methods has a number of limitations. The results of Levine and his colleagues are impressive and clearly suggest that a prolonged period of hypoxia during rest periods contributes to improvements in sea level performance. However, controversies still exist and further confirmation is required. Many experts are not yet convinced that ‘live high, train low’ really works and others are unclear about the pathways that confer the benefits described in this article.
Future research will need not only to support these landmark results, but also ‘fine tune’ the degree and duration of hypoxia that is both safe and effective. Until then athletes following ‘live high, train low’ regimes may be placing themselves at considerable risk without necessarily enjoying the benefits that intermittent hypoxia may provide.
Various Researches on Hypoxic Training
Hypoxic sprint interval training (thirty-second sprints with four minutes of rest, progressing from four to seven over six sessions) showed no advantage with simulated hypoxia. But this study (six sessions total) seems too short to draw any conclusions.
A six-week study demonstrated that sprint interval training in hypoxia upregulated muscle phosphofructokinase activity and the anaerobic threshold more than sprint interval training in normoxia, but still did not enhance endurance exercise performance. I believe this was also probably too short. I’m not saying a performance benefit with simulated hypoxia is certain, but if it’s showing improved adaptations over normoxia after six weeks, it’s not a huge leap to believe it could happen.
However, a different study showed that hypoxic conditions combined with sprint training has the ability to stimulate glycolyitic enzyme ability, which would obviously impart a training adaptation if the effect were high enough.
Sprint training at hypoxia equivalent to 2,400m (five sets of three-minute work intervals) showed trends towards improving some areas. Rating of perceived exertion was higher and changes in bicarbonate levels and EPO trended towards possible improvement over normoxic conditions, but changes in 20m sprint time trended lower.
And yet another interval training study, this time in cyclists, found no differences with hypoxic training, either by performance or measurement of monocarboxylate lactate transporter expression.
In addition, fat oxidation was shown in one study to be slightly diminished (which can be a good thing, if we’re looking for endurance and increased substrate efficiency), and had no additive effect on maximal measures of oxygen uptake (VO2peak) or time trial performance (measured under normoxia).
Obviously, the results of acute hypoxic exercise are vastly different than what we see with long-term hypoxic living conditions, as we’d have with the United States Olympic teams, and even those studies have been all over the map with results. Still, with studies, the modality isn’t the sole determinant of success.
An Important Study on Hypoxic Training by Japan Institute of Sports Sciences
The study that meets most of my criteria was performed at the Japan Institute of Sports Sciences. This study used a hypoxic room versus a normoxic room, and had subjects perform eight weeks of resistance training on nonconsecutive days for sixteen sessions in total.
The hypoxic group was exposed to hypoxic conditions from ten minutes before and thirty minutes after the exercise session (vastly different than other protocols). (To the d-bags who wear hypoxic masks to the gym and take them off between sets to talk: you’re doing it wrong.) To investigate acute responses, the subjects were exposed to these conditions from thirty minutes prior to sixty minutes after, on the first and last days.
The resistance exercises consisted of two consecutive exercises (free weight bench press and bilateral leg press using weight stack machine), each with ten repetitions for five sets at 70% of the subjects’ one repetition maximum (1RM) with a ninety second rest.
Strength and size gains were equal for both groups. During the training, levels of plasma oxygen were lower in the hypoxic group (obviously, as they were breathing less oxygen when the tests were taken) but growth hormone levels were significantly higher. The capillary-to-fiber ratio increased more in the oxygen-deprived lifters and vascular endothelial growth factor (VEGF) levels were also higher. Meaning, the hypoxic group was producing more blood cells and better able to restore oxygen supply to tissues when blood circulation wasn’t high enough for the body’s demand.
Therefore, it’s not surprising that local muscular endurance was increased more in the hypoxic group as compared to the normoxic one. It also provides insight into another study that suggested a health benefit from regular short-term hypoxic training, namely the reduction of arterial stiffness and prevention of arteriosclerosis compared to training performed at a similar exercise intensity (under regular, non-hypoxic, conditions).
Recent meta-analysis indicates that high-intensity, short-term, and intermittent training is likely the most beneficial way to benefit from hypoxic training.