Altitude training: turn up the heat for enduring benefits

Conversely, the relative lack of oxygen at altitude is something of a double-edged sword, resulting in increased ventilation (breathing rate), increased heart rate, decreased stroke volume (blood pumped per heartbeat), reduced blood plasma volume, all of which limit training intensity and oxygen transport capacity by around15% to 20%. This means that athletes who are already well conditioned can actually undergo some relative deconditioning unless the training is tailored correctly.

The implication of the above is athletes’ training sessions should include adequate short-duration (approximately 1 to 2-minute), high-intensity efforts with long recoveries to avoid a reduction in race-specific fitness⁽²⁾. There’s also some debate about just how relevant the increase in red blood cells/haemoglobin is for superior sea-level performance. That’s because some of the best endurance athletes in the world living and training in inland Ethiopia (approximately 2000-3000 metres elevation), have only marginally elevated hemoglobin concentrations compared to elite athletes living at sea level!

Altitude detraining

One of the most fundamental tenets of training for fitness is reversibility. The good news is that when exposed to a training stimulus, fitness adaptations will take place. Remove that training stimulus however, and those fitness adaptations inevitably start to reverse. It won’t surprise you therefore to learn that the same is true of altitude training. While training at altitude can stimulate additional training adaptations, once an athlete returns to sea level, those gains start to dissipate. But how quick is this process?

It turns out that this question is not straightforward. You might imagine that detraining after altitude training occurs as a simple reversal of the well-documented altitude adaptation response – ie once fitness is enhanced following 2-3 weeks of training at altitude, the decline begins immediately upon return to sea level, with the benefits largely dissipated after 3 weeks to a month. However, elite coaches and athlete practitioners with many years or even decades of experience do not report this; instead they find that many altitude-trained endurance athletes perform best after 10 days of returning to sea level⁽³⁾. This is also the official stance of the International Association of Athletics Federations (the international governing body for track and field), which states that for peak sea level racing performance ‘an altitude training camp should only be planned if there is enough time available for a 3-week stay, plus 12–14 days for re-acclimatization to sea level’⁽⁴⁾

Role of red blood cells

Why is it that performance tends to peak around 10 days after returning from altitude to sea level? One reason is that the blood responses – specifically red blood cell changes – experience a lag in response when departing from altitude. A study on Kenyan runners descending from moderate altitude (2,090m) to near sea level (340m), found that elevated blood haemoglobin levels as a result of training at altitude remained high for two weeks before starting to decline (see figure 2)⁽⁵⁾.

Figure 2: Haemoglobin responses following a return to sea level from 2090m

This extended elevation of haemoglobin explains why athletes can still turn in excellent performances ten days after returning to sea level but it doesn’t explain why athletes tend to actually perform worse for the first seven days upon return. To understand this, we must consider data showing that upon return to sea level from an altitude training camp, many endurance athletes report that they feel like they have lost turnover, that is, the sensation of feeling uncoordinated at fast running speeds^(6,7). Scientists are unclear what causes this sensation – ie whether it is psychological in origin or due to an adaptation in motor control as a result of regular training at slower speeds at altitude. However, a major reason given by coaches and athletes for planning a post-altitude sea level training period is to help re-establish the neuromuscular coordination at the kind of speeds needed during competition⁽⁸⁾.

Extending the window of altitude benefits

Unless you have a relative or mate who lives up high in the mountains within easy driving distance and has a spare room you can have for 2-3 weeks, undertaking a stint of altitude training will require a significant logistics, time and cash investment, especially if it means travelling abroad. For this reason, it’s understandable that athletes want to ensure the timing of any visit to an altitude training camp prior to competition is such that the peak performance benefits coincide with that competition. This is all the more important because many endurance competitions, like a marathon or multistage cycling race, are in essence one-shot events, where the athlete can only effectively attempt one or perhaps two races of this nature within a calendar year.

As we’ve seen above, while athletes returning from three weeks at altitude have undergone key training adaptations (eg enhanced haemoglobin levels), 10 days or so of sea-level training is required to re-establish the neuromuscular coordination, which eats into the 14 days of elevated blood haemoglobin and only leaves a very narrow window of opportunity or ‘sweet spot’ for competition. Given the time and effort needed for altitude training, scientists have wondered if it’s possible to widen this sweet spot by extending the window of opportunity, therefore giving athletes more flexibility with competition timing.

New research

The encouraging news is that new research by a team of Norwegian scientists suggests that there could be a very easy and simple method of achieving this. Published last month in the journal ‘Medicine & Science in Sport & Exercise’, this study investigated the effect of carrying out ‘heat-training’ sessions over a three and a half week period following a 3-week altitude camp on the maintenance of haemoglobin mass in elite cyclists⁽⁹⁾.

Before discussing the study further, why did the researchers investigate heat training sessions as a possible way of extending the benefits of altitude? Well, as contributor Richard Lovett explained in a previous SPB article, hot training environments (over 35C/95F) seem to produce additional training adaptations in aerobic capacity over and above the same session performed in cooler environments^(10,11).

Why heat training might work in this way is something of a mystery. One theory is that it mimics the type of stresses being put on the muscles during altitude training. When you run at altitude, there’s a relative lack enough oxygen and the body makes a variety of adaptations to increase its ability to deliver oxygen to the tissues that need it. In an analogous manner, when you exercise in a very hot environment, oxygen-carrying blood is diverted away from the working muscles to the skin surface in order to lose heat. This could also create a relative oxygen deficiency.

What they did

In this study, 18 highly trained and very fit male cyclists (average maximal oxygen consumption of 76 5mls/kg/min) underwent a 3-week altitude training camp at 2,100m (6,900ft) above sea level. After the camp was finished the participants returned to sea level where they were then divided into two groups (see figure 3):

·        Heat group – this group resumed training sessions at sea level but replaced three of their normal sessions with equivalent sessions performed in a simulated heat environment .

·        Control group - this group resumed their training sessions at sea level with no sessions performed in the heat.

Figure 3: Heat training for altitude study design

All the cyclists rode in the lab on their own bikes mounted to a power trainer. The temperate of the lab was around 20C/68F and the control group simply wore their normal cycling clothing. However, the heat group wore readily-available clothing that limited heat loss, consisting of a thin wool thermal layer on both the upper and lower body, a wool hat, a fleece jacket and a nylon rain jacket, together with leggings that had poor evaporative capacity! The purpose of this multi-layering was to raise the core temperature of the cyclists to the equivalent produced when cycling in a very hot (over 35C/95F) environment⁽¹²⁾.

Training characteristics were recorded during the intervention, while haematological measurements were recorded before the camp as well as two days and three and a half weeks after the altitude camp. In particular, the researchers were keen to ensure that exercise intensities and training loads were not different between heat and control groups during the post-altitude maintenance period.

What they found

The first finding was that (as expected) training for three weeks at the altitude camp led to an average and very significant gain of 4.1% in total haemoglobin levels. The really interesting finding however was what happened when the cyclists returned to sea level. After the 3.5-week sea level training program, the control cyclists (again, as expected) lost 3.3% of their total haemoglobin – ie they had only retained around 20% of the altitude training gains. This was in stark contrast to the heat-training cyclists; they lost just 0.2% of haemoglobin mass, which meant they had retained almost 95% of their altitude camp gains! In addition, the heat-trained cyclists enjoyed an 11.6% gain in blood plasma (fluid) volume compared to the 5.5 gain in the control cyclists. That matters because high blood plasma volume allows a greater cardiac output (stroke volume), which means more blood and oxygen pumped to muscles per minute.

Implications for athletes

If altitude training is something you do from time to time, these findings make for great reading. Basically, they suggest that by performing just three heat sessions per week, you can ameliorate much of the decline in benefits that happen between weeks two and four when returning to seal level. This in turn allows you much greater flexibility when planning your altitude training and dovetailing it into your competition schedule. Could continued heat training prevent or slow the decline in haemoglobin mass for longer than 3.5 weeks? The answer is probably, although more research needs to be carried out.

Another implication of these findings is that this study provides further evidence that heat training is able to (at least partially) simulate altitude training. This means that where altitude training is impractical or unaffordable, athletes could implement a 3-week period of thrice-weekly heat training sessions instead. The benefits might not be quite as dramatic as training at altitude, but this strategy could be a useful tool in the box.

A word of caution however; performing heat sessions such as those described above is quite demanding. Not only does it require a lot more psychological efforts, dehydration due to sweating becomes a real issue. This means that athletes performing heat session should ensure they remain well hydrated with fluid and electrolytes. And like training at altitude, the quality of training in the heat remains important. Therefore, training sessions should not be too long and include high-intensity bursts, and periods spent at race pace!

References

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