Intermittent Hypoxic Training and Relevance in Sports Activities
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
performance times.
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.
Gains, but for how long?
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.