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Hi’s and Lo’s of cycling

Our Perspective on Human Performance

Hi’s and Lo’s of cycling

Hi’s and Lo’s of cycling

As the last of the Northern classics are finished, and the Giro is looming, now is the time that many of you who are in store for some Continental cycling, or a late Spring training camp further afield will be anticipating some long awaited back-to-back days of ascending and descending some legendary pro-tour climbs!

As many of my clients know, I’m quite partial to a few Italian mountains having lived in the Veneto for a while. Making the most of such mountainous terrain is every cyclists dream, but there are still sound physiological principles at work, apart from the gradients themselves which will help you get the most from your time on the summits. Altitude training has long been known to benefit athletes in the form of Intermittent Hypoxic Training or Exposure (IHT/IHE). These training modalities are considered performance enhancing as they force physiological adaptations albeit with varying results. As some of the science behind it has been confusing, I will try and simplify this for you in what could become quite a long post, apologies.

The Giro del Trentino started today, and finishes at the top of Monte Bondone, 1,653m above sea level, and is a 1,447m continuous climb made famous by the Swiss pure climber Charly Gaul cruising to victory in harsh snow-bound conditions.  At this elevation (around 1,500m) the partial pressure of atmospheric oxygen (PO2) is  lower than at sea level (159mmHg) even though the percentage of oxygen present in the air remains constant as the total pressure of air is reduced (hypobaric). Therefore, the  gradient force which drives oxygen into the lungs is greatly reduced, as  haemoglobin (see illustration) in the red blood blood cells passing through the alveoli (small membraneous sac structures) of the lungs struggles to absorb the sparse oxygen molecules and deliver this life-giving gas under high tension to the brain, muscles and other tissues, resulting in multiple acute and chronic cardio-respiratory and metabolic compensatory mechanisms. A more in depth explanation of these hypobaric/ hypoxic mechanisms can be read on this dedicated sports physiology information resource.

To summarise briefly, for every 1,000m above 1,500m elevation, VO2max may decrease by 8-11% as the maximal stroke volume (SV) and heart rate (HR) are lowered (resulting in a lower cardiac output, CO = SV x HR), although at rest and during sub-maximal exercise, cardiac output is greater, suggesting a smaller fraction of functional aerobic capacity and a compromised performance as expected. Respiratory rates are elevated as the body tries to maintain a critical blood oxygen saturation level to deliver oxygen to the muscles and tissues. This may be as low as 88-92% blood oxygen saturation (SpO2) at 2,490m. Blood plasma volume is initially reduced to increase the haemaotcrit percentage (ie the relative numbers of red blood cells) which will attempt to compensate for fewer competing molecules of oxygen with haemoglobin. The now ‘infamously’ known cellular mediator,  Erythropoetin (serum EPO) is endogenously released from the kidneys after 3 hours at altitudes greater than 1,500m as to induce further red blood cell production (polycythaemia), with peak levels seen between 24 to 48hrs after hypoxic exposure. EPO levels can remain elevated for two week and longer in responders. The oxygen tension gradient between the blood and the tissues is reduced considerably and what is thought to be the trigger mechanism for longer term metabolic adaptations seen in altitude acclimatisation.


Anaerobic metabolism is more heavily relied upon under hypoxic conditions in a similar way as that of sprinting and hill climbing, and is thought to be improved during IHT/IHE. Lactate concentrations at sub-maximal efforts are increased and peak lactate values are suppressed at maximal work rates. Although a ‘Lactate Paradox’ exists at extreme altitudes, such as at the top of Everest where resting lactate levels are greatly reduced.

Initial acute effects of high-altitude exposure include:

  • Increased respiratory rate and heart rate at rest and sub-maximal exercise.
  • Inability to achieve VO2max.
  • Change in Acid-Base balance  ( H2O + CO2 <-> H2CO3 <-> H+ + HCO3-) Le Chateliers Principle

A low atmospheric pressure of oxygen stimulates increased ventilation, expelling CO2 from the circulation resulting in reduced arterial pressure of CO2 and an increased level of Bicarbonate (HCO3-) ion, increasing the pH (termed respiratory alkalosis). This is compensated for quickly by shifting the balance as HCO3- is excreted through the kidneys.

Longer term effects associated with acclimatisation:

  • Decrease in maximum cardiac output and maximum heart rate.
  • Increase in the number of Red Blood Cells (through the action of erythropoietin in the Kidneys).
  • Excretion of HCO3- in the kidneys to restore acid-base balance.
  • Reduced tolerance to acidosis associated with  Lactate production.
  • RBCs increase efficiency at unloading oxygen to the tissues.
  • Increase in number of mitochondrial and oxidative enzymes.


Acclimatisation to a hypoxic or hypobaric environment can take over 2 weeks for chronic adaptations to stabilise, haematocrit levels at higher altitudes may take even longer to stabilise  to a higher percentage. But, and importantly, no matter how long an individual lives at altitude, they never fully compensate for the lack of oxygen and never regain the level of aerobic power or endurance performance they could at sea level. However, the physiological adaptations induced at altitude are known to translate to performance gains at sea-level in many cases.

Perhaps short lived visits to these altitudes do not result in immediate or drastic performance deterioration for well-trained and elite cyclists with well developed aerobic capacities. Stage 16 of the Giro will attempt a re-visit to Val Martello, which was cancelled due to snow on the Stelvio. The Passo Gavia (2,618m), Passo Stelvio (2,758m) and Val Martello (2,059m) account for the biggest climbing stage of the tour. The rest of us however could use these longer term adaptations to our favour and improve endurance performance at sea level.


A recent study has highlighted that intermittent hypoxic training at lactate threshold intensity and medium duration (30-40min) is an effective training strategy for improving aerobic capacity. The 3 week training programme, of 3 IHT sessions per week (90-120 min at a simulated 2500-2600m normobaric/ hypoxic environment) in 20 well –trained male cyclists saw an improvement in the power at 95% lactate threshold (WRLT) by 11% versus the control group. (The effects of intermittent hypoxic training on aerobic capacity and endurance performance in cyclists– Czuba et al. J Sports Sci and Medicine (2011) 10, 175-183. (www.jssm.org).


Since the benefits of hypoxic training have been known, several strategies have been defined, like Live High-Train High (LH-TH) or Live High- Train Low (LH-TL) and more recently Live Low- Train High (LL-TH).

The results published by the investigators of some of these protocols are inconsistent or ambiguous even, possibly due to methodological differences, including type, volume and intensity of exercise performed under hypoxic environment, as well as the ability level of the research subjects. Few studies have shown enhanced endurance performance at sea-level following IHT and limited data exist with high intensity interval training or lactate threshold intensities in a hypoxic environment.

Inconclusive evidence maybe due to  poor study design or timings looking for metabolic adaptations correlated with a significant performance benefit. This maybe due to short training duration, as well as the low overall volume of interval work for well trained athletes. Efficiency of the oxygen transport system is most often evaluated by maximal oxygen uptake (VO2max) but changes in haematological adaptive mechanisms due hypoxia; haematocrit, haemoglobin concentrations, serum iron and transferrin following IHT were not always observed alongside any performance gain. (Gore et al, 2007, Roels et al, 2005, Hahn et al, 2001.)

Some of the authors conclusions suggest that a continuous exposure of 90 minutes represents the minimal stimulus to trigger an acute secretion of erythropoietin, although lack of control groups or significance invalidate these findings. It is considered that the performance differences are due to changes in aerobic enzyme levels and non-haematological adaptive mechanisms; increased skeletal muscle mitochondrial density, capillary-to-fiber ratio, and fiber cross-sectional area. These changes are associated with an increased hypoxia inducible factor-1a (HIF-1a), which is the global regulator of oxygen homeostasis and plays a critical role in the cardiovascular and respiratory responses to hypoxia. Further, significant changes in lactate concentrations at maximal and sub-maximal work-rates have been observed in many positive studies for improved performance after altitude exposure. Two to three weeks of altitude exposure above 2000 meters results in enhanced muscle buffering in trained individuals. In addition, ability of skeletal muscle to buffer H+ and modulate pH balance and changes in acid-base status (limiting acidosis) have been proposed as potential mechanisms for improved performance after altitude exposure. Reductions in submaximal oxygen requirements of 3 to 10 percent have been reported in a number of independent studies, which may be related to adaptations in the metabolic processes in muscles.

The advent of portable and relatively inexpensive altitude tents or rooms which allow athletes to control oxygen levels during both training and recovery without the hassle of attending training camps, has made IHT/IHE much more available, even to the recreationally competitive cyclist.

Individual variability in response to particular protocols should be taken into consideration regardless of any proposed mechanisms for adaptation. Although choosing a convenient approach and optimising the exposure duration and training intensity and volume would maximise the potential for significant performance gains. The effect of participating in a training camp as opposed to solely training at altitude may confound any performance gain carried over after a period of LH-TH. Further, only a small number of controlled LL-TH studies on trained or elite athletes demonstrated significant improvements in subjects blood parameters, aerobic capacity or work rate performance. Practically, IHT performed in a LL-TH format is difficult to achieve and large volumes of training are carried out on an indoor stationary bike. Although substituting a proportion of outdoor training under hypoxic conditions has had varying results.

Practical recommendations for cyclists to manage altitude acclimatisation:

  1. DietA high carbohydrate, low salt diet allows for better adaptation. A reduced appetite may result in loss of muscle and decline in performance.

  2. Iron – Due to the greater demands on the body to make more Red Blood Cells and haemaglobin, iron supplementation may assist this process  especially in women and vegetarians. Over supplementation of vitamins and minerals are not helpful and are may be potentially dangerous.

  3. Fluids – Air at higher altitude has less water content and is dehydrating. Adequate hydration is key to performance. Therefore, for this reason it is also better to avoid alcohol at altitude.
  4. Performance– will be compromised until adaptation can occur. Even afterwards, peak performances are less probable due to the restrictions on physiology. Pushing your workouts too hard may increase your risk of over-training or injury. It is best to keep a log for rating fatigue during workout and at rest, morning resting heart rate, weight, and mood.



From the literature it is clear that the LH-TL model provides the most adaptation. Athletes can experience passive hypoxia at rest and sleep (IHE), while regular training is performed at sea level or thereabouts. Elevated serum EPO and VO2max coupled with improved performance times have been recorded in well designed studies. Training intensity at a lactate threshold work-rate would be considered the most beneficial as part of a LL-TH format, as described above.

So, to implement what would be the most effective and practical method for any one athlete would still rely on whether that individual is a responder or non-responder to hypoxic/hypobaric training. Although it seems there are more responders in the LH-TL modality. This would suggest that any opportunity to spend time at high altitude, basing yourself in a hotel at a ski-station or resort in the Summer would not only afford great views and hypoxic exposure, but would make sure the legs get that last climb in at the end of the day.

One way of finding out about your response to hypoxia is to design your own personal experiment and training plan before embarking on that Haute route or extended Marmotte week. Measuring a baseline performance parameter prior to undertaking any hypoxic training or exposure is critical to allow for a fair comparison at follow-up, and assess the efficacy of the design. Once this has been done, you can then optimise your hypoxic training even further to get enhanced performance gains. Then any mountain stage or road-race at sea level will feel like a breeze!

Call me if you are interested in setting up your own hypoxic experiment. The Altitude Centre, London offers a range of IHT/IHE services, including fully portable hypoxic training equipment and tents.


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