Professional sports teams and other elite athletes often involve scientists to optimise these training camps, and for good reason. Acclimatisation to both altitude and heat can be crucial in prolonged stage races such as the Tour de France, but timing is actually a great challenge – especially given the changes in altitude in the various stages. Before the team presentations and the first week’s flat sprint stages are over, the effects of the acclimatising training probably largely vanish.
High-altitude training camps have a long history in exercise physiology and are now common practice in elite sports and especially in cycling. However, failure to acclimatise to the frequent extremely high temperatures in prolonged cycling stage races can be equally catastrophic for participants. Heat acclimatisation training is therefore an attractive alternative or supplement for the most ambitious athletes. However, the latest research shows that the timing of the training camps is crucial.
“In the prolonged stage races, the important and often decisive mountain stages take place at high altitude, with lower oxygen pressure and often combined with heat stress, and both can hamper performance. However, these stages rarely take place before the second or third week of the races and therefore long after the training camps, where the athletes have acclimated to the oxygen content and temperature. Research shows that high-altitude training – and the resulting acclimatisation – needs to be placed as close as possible to the start of the race. Otherwise, the effect evaporates, whereas the effect of the heat acclimatisation training is somewhat easier to maintain,” explains Lars Nybo, Professor, Movement and Neuroscience, Department of Nutrition, Exercise and Sport, University of Copenhagen.
Live and train at high altitude
New research from sports physiologists Lars Nybo, Bent Rønnestad and Carsten Lundby goes beyond summarising many hours of training and using clipless pedals. In the new article, they both review the past several years of research in the field and give their own practical perspectives on the potential for exploiting acclimatisation to the low oxygen and high heat athletes can encounter in mountainous terrain under extreme temperatures.
“It is important both to minimise the harmful effects on performance associated with the reduced oxygen uptake in the blood in the mountains, partly to reduce the risk of heatstroke and overheating on hot days but also to acclimatise and thus optimise performance of the already top-trained athletes by increasing the blood volume slightly. Only a few percentage points separate the very best athletes, so this may be the last and perhaps decisive factor,” says Lars Nybo.
As researchers, Lars Nybo and his colleagues are primarily interested in understanding the physiological mechanisms involved, such as how haemoglobin increases in the blood through training at high altitude.
“Acclimatising the blood requires weeks of exposure at high altitudes but is also extremely attractive, since increased haemoglobin can significantly improve the oxygen supply and thus prolong the peak mountain performance of athletes such as cyclists,” explains Lars Nybo.
Measurements can be deceptive
The maximal oxygen uptake drops significantly at high altitude, about 5–7% per 1,000 metres climbed. Weeks of training in the mountains can compensate for this by increasing haemoglobin – the oxygen-binding protein molecule in the red blood cells.
“A few years ago, the consensus was that athletes should stay at high altitude but train at a little lower altitude, since they would lose training intensity by training at high altitude because they cannot push themselves as hard. However, new studies suggest that, even though high altitude may reduce the effectiveness, the training will still provide a similar physiological stimulus or perhaps an even better one because the muscles acclimatise better. Especially short intensive intervals at high altitude work well for both power training and increasing oxygen uptake,” says Lars Nybo.
Lars Nybo emphasises that the blood’s reaction to high altitude results from increased production of erythropoietin in the kidneys – a hormone probably better known as EPO. EPO has been a notorious doping agent, because it stimulates the production of red blood cells and haemoglobin and thus the ability to take up oxygen and transport it to the muscles, which compensates for the low-oxygen conditions in the mountains.
“When training at high altitude, however, you must be careful not to be fooled by the apparently very rapid effect of this training. Elevated haemoglobin measurements do not necessarily indicate increased haemoglobin mass, since the first hours of high-altitude exposure already increase the blood volume and the measurements become artificially high. At least 3 weeks of high-altitude exposure is required to be sure that the elevated EPO translates into significantly higher haemoglobin,” explains Lars Nybo.
One hour per day may be enough
Cyclists in the prolonged cycling stage races such as the Tour de France, Giro d’Italia and Vuelta España have many stage finishes several kilometres above sea level and are also often challenged by heat stress on days with intense heat.
“Trials with acute exposure – a 43-km time trial at 36°C without prior acclimatisation – showed a 16% decline in rider performance in a cool environment. After 2 weeks of acclimatisation, this decline was reduced to less than 2%, and there was no difference in time,” says Lars Nybo.
Heat acclimatisation largely increases the body’s thermoregulatory capacity: the ability to sweat. It does this by improving sweat gland function – the sudomotor response – and thereby increasing the maximum sweat rate, lowering the resting core temperature and the threshold for starting to sweat.
“Similar physiological acclimation can be induced with shorter training in climatic chambers 1 hour per day or training with a sweatsuit, but training more in heat also achieved a different and more surprising effect. Heat and endurance training increase the volume of blood plasma and, even more importantly, the amount of haemoglobin and thus also improving maximal oxygen uptake at high altitude,” explains Lars Nybo.
Preseason high-altitude camps have little effect
Training at high altitude to stimulate erythropoiesis and in the heat to increase blood plasma and haemoglobin therefore seems attractive. Nevertheless, the researchers caution athletes to consider this combination carefully before rushing into it.
“High altitude typically acutely reduces plasma volume, whereas the opposite response is a significant part of heat acclimatisation and therefore probably necessary for heat to drive blood cell formation. However, few well-controlled studies have tested whether these stress factors can be advantageously combined or instead counteract each other,” says Lars Nybo.
However, the greatest challenge for training seems to be timing. Half of the increase in haemoglobin is already gone 7 days after returning to normal altitude, and the baseline completely returns 14 days later. If high heat and flatter stages are expected in week 1 of a stage race, focusing on heat acclimatisation rather than high-altitude training may therefore be more relevant.
“In any case, high-altitude training camps should be carried out right before the competition period. High-altitude camps conducted in the winter or preseason will almost certainly have no direct effect on performance several months later unless something is done to maintain the effects achieved,” explains Lars Nybo.
In addition, balancing the stress and anxiety of travelling to a 3- to 5-week camp under different and foreign conditions must also be considered. Some studies suggest that 3–4 weeks of more consistent exposure to heat is sufficient and 1 hour of cycling in a heated room at regular intervals may maintain the effects, but definitive evidence is lacking.
“Last year we were allowed to follow Jumbo-Visma during the Tour de France, but performing consistent experiments on a large group of riders without disrupting the season is incredibly difficult, and the effects certainly varied significantly between riders. So perhaps the most important activity is measuring what happens to the individual rider to find the right balance between stress and acclimatisation for each individual,” concludes Lars Nybo.
