Altitude Training Uncovered

There are many myths and misconceptions that surround the concept of altitude training within the disciplines of exercise physiology and sports training physiology. Such errors can lead to the misuse of training at altitude, which may lead to disappointment in subsequent performance. This article explores the subject of altitude training, defining what it is, acknowledging potential problems and its ultimate impact upon athletic performance.

Altitude training can be defined as training at heights greater than 2,500m above sea level. At such heights, it is commonly thought that there is a decreased percentage of atmospheric oxygen. However, the percentage of gases in the air we breathe remains unchanged from sea level to high altitude. Instead it is the partial pressure (PO₂) of each gas that is reduced as a drop in atmospheric pressure is seen at altitude. Therefore the air is less dense, consisting of less O₂, CO₂ and N₂ per litre, but the percentage of each gas forming this litre does not change. The fall in PO₂ reduces the driving pressure for gas exchange at the lungs, accordingly arterial O₂ saturations declines and so there is a rapid decline in O₂ availability to the working muscles. From near sea level, to a moderate altitude VO₂ max observes a linear reduction (Wehrlin and Hallen, 2006), on average this equates to -7.7% per 1000m of altitude despite a compensatory cardiorespiratory response.

It is this reduction in air density that can pose problems to training at altitude if an athlete is not fully prepared, one such consequence is a 1°C fall in temperature for each 100m ascent. The combination of a decreased temperature and pressure results in a reduced atmospheric water vapour content, which leads to increased respiration due to a decreased oxygen availability. This lends itself to greater water evaporation from the lungs, thus increasing the likelihood of severe dehydration that will inevitably cause a deterioration in athletic performance. As a result of these factors and a reduced cerebral O₂ saturation, many athletes suffer acute mountain sickness (AMS), the upshot of which leads to a lack of appetite, nausea, excessive weakness, vomiting and increased heart rate. Such symptoms dramatically impact upon the wellbeing of an athlete and in severe cases pulmonary or cerebral oedema can ensue. In order to prevent AMS a gradual introduction to altitude is needed, allowing for acclimation to occur which can take up to two weeks for heights of 2300m. This can be achieved through artificial means such as a hypoxic sleeping chamber or nitrogen generator to lower the atmospheric O₂ content.

An example of a hypoxic sleeping chamber. 

Within the realm of sport and exercise science there has been much debate as to whether the practice of altitude training can improve aerobic performance. It has been hypothesized that the compensatory physiological responses at altitude will result in adaptations that transfer to improved sea-level performance. However, this has been seen to be untrue. 

Altitude training has only been seen to cause performance improvements at altitude, with the majority of studies confirming that altitude endurance training fails to enhance sea-level performance. This outcome relates to the inability to perform at a sufficiently high intensity at altitude, at a height of 4000m exhaustion occurs at just 40% of sea level VO₂ max, thus failing to elicit the relevant aerobic physiological adaptations. However, the live high-train low rationale (Stray-Gundersen and Levine, 2008) provides hope for the significance of the inclusion of altitude for athletes. This theory states that the combined haematological adaptations from altitude and the maintenance of training intensity at sea level results in an improved endurance performance at sea level, giving leave to a 7.8% increase in O₂ carrying capacity. An adaptation such as this is achieved by increases in red blood cell mass, haemoglobin and erythropoietin, therefore increasing the delivery of oxygen to the working muscles.

Overall it has been shown that the combination of living high and training low can enhance sea level performance. This allows for a high training intensity to be maintained whilst also attaining the important haematological alterations that are associated with a high altitude.

References

Stray-Gundersen J., Levine B. D. (2008) Live high, train low at natural altitude. Scandinavian Journal of Medicine & Science in Sports. (1) pp. 21-28.

Wehrlin, J. P. and Hallen, J. (2006) Linear decrease in VO₂ max and performance with increasing altitude in endurance athletes. European Journal of Applied Physiology (96) pp. 404-412

Barefoot running: Factors affecting performance and the implications for injury

Barefoot running and minimalist training shoes have been a hot topic for debate among both amateur and professional runners in recent years. With the emergence of headlines such as ‘Runners without shoes land more gently on the ground, avoiding impact injuries’ (Independent, 2010) there is little wonder as to why the craze has continued to grow. This article looks to explore the practice of barefoot running, deconstructing the myths that surround it whilst also giving some practical advice for performance and injury prevention.

The paper to spark this debate of the benefits to barefoot running was by Lieberman et al. (2010) suggesting that running shoes cause heel striking and that running barefoot would make for a flat/forefoot strike. It was thought that this forefoot strike would negate the impact peak of the heel strike that was frequently linked to running injuries and thus running with this style will not subject the body to the same impact loading. Ultimately, leading to the conclusion that running shoes cause impact shock and accommodate higher injury susceptibility. Perhaps a key result of this study was the introduction of minimalist training shoes such as Nike Free and Vibram Five Fingers, such trainers seek to emulate barefoot running since it was suggested that running shoe cushioning and heel lift were not beneficial. However, running both barefoot and whilst wearing minimalist training shoes result in higher impact force magnitudes and loading rates compared with traditional shod running (Squadrone and Gallozi, 2009). Both variables arguably possess a similar risk of injury as impact shock, thus highlighting flaws in the ‘safe’ and ‘gentle’ nature of running barefoot.

However it has been shown that the impact force acts as an external input to our system, allowing us to detect the nature of the surface and adjust our muscle activation accordingly (Nigg & Wakeling, 2001). Contradicting the notion that impact peak is associated with injury (Zadpoor & Nikooyan, 2011) and instead providing a means for runners to become more efficient in adjusting to different terrains. As opposed to examining ground reaction force data it has been suggested that the study of pressure variables would be more appropriate. This would allow for the identification of the area of the foot that first comes in contact with the ground providing more detail of what foot contact style is being adopted for different conditions (Nunns et al., 2012).

Current empirical evidence is equivocal regarding the potential benefits to barefoot running and running economy. Nevertheless there are a number of factors to consider that may affect oxygen consumption whilst running. The first of which being the affect of added mass, with each 100g shoe mass resulting in a 1% increase in oxygen consumption and with the average training shoe possessing a mass of 300g this could mean an O₂ uptake increase of up to 6%. On the other hand, due to the absence of footwear there is a metabolic cost associated with active cushioning. This takes places via changes in muscular activity in the supporting muscles, all of which is likely to result in a less efficient running performance. Lastly, during barefoot running there is a need for greater sensory feedback. Since the runners feet are coming into direct contact with the ground heightened proprioception is necessary and this may lead to gait alterations making for less efficient strides.
Although barefoot running may allow for the effective use of elastic energy in foot through a forefoot strike one’s strike pattern has not been proven to affect an individual’s running economy. So, forefoot striking offers no economical advantage over heel striking and given that runners naturally adopt their optimal stride type this could reduce their running economy.

 To conclude, barefoot running is not the miracle running practice that sporting professionals originally thought, making athletes more efficient and injury free. Instead it just causes individuals to load the associated joints in a different manner and changing their stride type, the effects of which can be equally as injury inducing. The notion that barefoot running also resulting in greater running economy can also be seen to be a myth as although it rids the exerciser of the added mass effect from trainers it does not account for the need of greater proprioception. Overall leading to gait alterations that would have already been at the optimal measures.