J Royal Naval Medical Service 2014, Vol 100.1 67

Special Focus: Sports & Exercise Medicine Athletic training protocols and their application in preparation for mountainous operations

Surg Sub Lt K M Heil, Maj A C M Keenan

Abstract

In recent years, small scale counter-insurgency and expeditionary operations have frequently taken place in mountainous, high- altitude areas. Preparation of soldiers for these environments has typically focussed on extended stays at altitude to ensure physiological acclimatisation. However, with the likelihood that future UK deployments may be unpredictable and thus with little time for preparation, is there a means by which the same acclimatisation may be achieved? The field of athletics has been researching such adaptations since the rise of the elite North African long-distance runners in the 1960s. These athletes all lived high above sea level and had become accustomed to performing in the relatively hypoxic environment found at high . The research has focussed on eliciting physiological acclimatisation in as short a time as possible, while maintaining the ability to train at the correct intensity. In the following review of altitude training we highlight areas for future investigation and assess whether protocols developed for athletes can be applied to military personnel.

Introduction Sports medicine has been challenged by this problem In 2002, 23 of the 27 ongoing armed conflicts were occurring since the 1968 Olympic Games, held in Mexico City at an in mountainous environments (1). More recently, Operation altitude of 2,280m above sea level (6). The performance of HERRICK in Afghanistan has seen ISAF troops working at several endurance athletes was impaired due to increased altitudes in excess of 2,000m (2). The difficulties associated physiological demands of competing at altitude. However, with moving troops and supplies in these environments, during these games many African runners, born and raised together with the tactical benefits of occupying an elevated high above sea level, emerged to dominate long-distance position, have been shown throughout history (3). As UK running (7). This paradigm stimulated research into the Armed Forces further transition to a posture prepared benefits of altitude acclimatisation for elite endurance for smaller scale, expeditionary and counter-insurgency athletes. Currently, altitude training camps are routine, but operations, high-altitude mountainous areas of operations is there a means by which we can employ similar techniques may be encountered more frequently. As with all aspects of to improve the preparation of troops for operations? warfare, preparation for battle is essential, and encompasses physiological preparation for the environment to be Physiological effects of altitude encountered. Altitude can be classified as high altitude (1,500-3,500m), very high altitude (3,500-5,500m) and extremely high Training for high altitude has become of increasing interest altitude (>5,500m) (8). to various military forces. The Indian and Pakistani armies, who have been fighting in the mountains of Kashmir since Figure 1 demonstrates that increasing altitude causes a the 1960s, continue to use 6-7 week altitude acclimatisation constant decline in the atmospheric density resulting in an periods before troops deploy (4). Such significant training exponential decline in the partial pressure of (PO2). burden would benefit from more rapid adaptation that For example, at sea level there is an average air pressure of does not require extended periods at high altitude. The US 760 mmHg, while at the summit of Mount Everest (8,848m)

Army is currently exploring the use of Intermittent Hypoxic this decreases to 253 mmHg. From Dalton’s Law, since O2 Training (IHT) to rapidly prepare troops for operations in constitutes approximately 21% of ,

hypoxic environments after their experiences during the the partial pressure of O2 at sea level is 160 mmHg, but less early battles in the Afghan mountains (5). than 50 mmHg at the summit of Mount Everest. Reduced 68 Special Focus

atmospheric O2 availability results in a decrease in the Altitude acclimatisation inspired PO2 and disturbance in the pressure gradients Haemoglobin (Hb) is the iron-containing O2-transporting required for oxygenation of tissues. metalloprotein in erythrocytes. It is composed of four Figure 1. Changes in PO2 with altitude for global polypeptide chains (two α and two β) each attached to a non-protein haem group. A molecule of O may bind to each locations 2 of the four haem binding sites of an Hb molecule.

Increasing the Hb concentration of the blood increases

O2-carrying capacity, which is the adaptation sought by athletes from training at altitude. This occurs by increasing production of the (Epo) by the kidneys, which may occur as soon as one hour after exposure to hypoxic stimulus. However, maximum circulating concentration is reached ~48 hours after exposure (10). Epo has a number of functions, but the most relevant is the stimulation of the red to synthesise and release more erythrocytes (Figure 3) (7). Increased erythropoiesis raises the haematocrit, the red cell volume (RCV), the red cell mass and the Hb mass. VO2 Max is a reflection of aerobic

fitness and is defined as the volume of2 O consumed while exercising at maximum capacity, expressed as ml/kg/min.

The overall effect of increased O2-carrying capacity of the As the PO2 of inhaled air decreases, the driving pressure of blood results in increased tissue oxygenation and elevated VO2 Max for the acclimatised individual (11). diffusion of O2 across the alveolar-capillary boundary falls, causing a reduction in the arterial partial pressure of oxygen Additional mechanisms related to altitude acclimatisation (PaO2) and O2 saturation (SaO2). The effect of altitude on the oxyhaemoglobin dissociation curve is illustrated include muscular mitochondrial efficiency, which may also in Figure 2. The subsequent decline in the PO2 of the improve aerobic performance (12). blood entering the tissue’s capillaries leads to an overall Figure 3. Hypoxic stimulation of Erythropoiesis by decrease in tissue oxygenation (DO2). A decrease in DO2 up-regulation of Epo. to muscle during athletic training or competition will impair performance (9).

In the short term, at high altitudes, a decrease in tissue oxygenation may be compensated by increasing heart rate. However, prolonged exposure prompts a physiological response (acclimatisation) to enable survival (7).

Figure 2. The oxyhaemaglobin dissociation curve which demonstrates the right shift with increased altitude.

Other medical factors There are a number of other medical factors of relevance when training at altitude. Acute mountain sickness (AMS) presents with headache, , nausea, loss of appetite, weakness and sleep deprivation, and typically occurs at altitudes of 2,400m, although there are no known predictors of risk (13). While not life-threatening in itself, for professional athletes the symptoms of AMS may cause problems with training and should be avoided. J Royal Naval Medical Service 2014, Vol 100.1 69

Life-threatening conditions such as high altitude pulmonary adaptation. As mentioned earlier, this would not be suitable oedema (HAPE) and high altitude cerebral oedema (HACE) for units tasked with rapid deployment, due to the time may develop in susceptible individuals. Unfortunately, it required for extended stays at altitude. For this reason it is is currently not always possible to identify those at risk or unsuitable for operational purposes. the speed of ascent that is dangerous, which is relevant if ascent is too rapid for a given individual or the altitude is Live Low, Train High (LLTH) above 2,500m (13). To avoid these conditions the maximum The LLTH protocol emerged as more athletes embraced altitude used for training purposes rarely exceeds 3,000m. high-altitude training, seeking to take advantage of the Interestingly, attenuation of immune responses has been benefits of higher altitude whilst still living in lower- reported, making those training at altitude more susceptible lying areas. While there have been few studies assessing to developing infections, and increasing their recovery time this protocol, it has been established that it is ineffective from injury (14). in conferring the benefits of altitude sought by athletes. Truijens et al challenged a cohort of high-level swimmers These factors must be considered in relation to the to a five-week training programme involving sessions in a amount of time athletes spend at altitude, and therefore hypoxic flume to mimic either an altitude of 2,500m or a training programmes must be specially tailored to best take normoxic control (19). The conditions failed to demonstrate advantage of the physiological effects of altitude camps, any difference in VO2 Max or performance between the without detriment to their training. hypoxic training and the control groups. The lack of ongoing research into this training protocol means it will be Altitude training protocols discounted from future training programmes, particularly Several different training protocols emerged following the those looking at rapidly acclimatising troops for operations. introduction of high altitude training among athletes familiar with training at sea level. Over time, research has identified Intermittent Hypoxic Training (IHT) those that are most effective, and numerous protocols As previously mentioned, peak levels of circulating Epo occur have emerged (15). Whilst many studies have examined approximately 48hrs post-exposure, with initial increases these methods, no double-blind, placebo-controlled trials in Epo demonstrable as early as one hour. Much effort has have been conducted. For this reason, we will attempt to focussed on taking advantage of such a rapid response with highlight the advantages and disadvantages associated with Intermittent Hypoxic Training (IHT). IHT consists of each protocol as evidence of current best practice. brief exposure to a severe artificial (hypobaric chamber or hypoxic tent) or natural hypoxic environment to stimulate Live High, Train High (LHTH) Epo production. IHT protocols involve periods as short as LHTH was the original high altitude training adopted by 30 seconds but may last up to 90 minutes, conducted during many athletes after the 1968 Olympics. It was the simplest exercise or at rest. of all the training protocols and involved athletes moving to both live and train at altitudes, usually in excess of 2,000m. This protocol has been the subject of intense research over the last few years. This may be due to the increased Early research using a six-week build up and then four- marketing of these training methods to sub-elite and week altitude phase showed improvement in both 3,000m amateur athletes in gymnasiums and sports clubs (20). running performance and participants’ VO2 Max (16). Other studies showed an improvement in two-mile running Dufour et al showed a 5% VO2 Max increase after a time only (14). However, Vallier et al found no improvement twice-weekly hypoxic exposure of between 24-40 minutes: in erythropoiesis or VO2 Max in tri-athletes after spending however, there was no corresponding haematological change three weeks at 4,000m (17). A decrease in running velocity to support these findings (21). Gore et al also showed no was noted by Bailey et al, who also showed a 50% increase change in RCV or Hb mass in their four-week study, but did in gastrointestinal infections for the altitude group after note an increase in participant’s Epo levels after exposures returning to sea level (14). lasting three hours at an altitude equivalent to 4,000-5,500m (12). A meta-analysis of LHTH studies concluded that using an enhanced protocol (optimal height and duration) results Julian et al exposed 14 national level runners to alternating in a positive performance outcome for the LHTH method five-minute periods of with normal 2O levels for for both elite and sub-elite athletes (18). Currently, LHTH 70 minutes (22). This was repeated once daily over five is used predominantly by athletes living at altitude due to days per week for a total of five weeks but was not able to geographical origin, such as those from Kenya or Ethiopia. demonstrate a change in VO2 Max, Epo or 3,000m running performance. Explanations for these results have centred This protocol is the basis for most mountaineering on exposure times, which are too short, as 12-18 hours expeditions, which involve long base camp stays to ensure per day are thought necessary to elicit a response. Though 70 Special Focus

there is very little evidence to support any performance (24). enhancement or physiological change from this type of training, the potential benefits suggest that studies will The evidence for altitude training as a tool for performance continue. If a protocol is developed which can harness this improvement is not conclusive: however, the widespread effect reliably it would be an ideal training tool for preparing use of LHTL protocols and continued support in the troops rapidly for operations at high altitude. community will likely ensure its continued practice (27). It would seem that a LHTL protocol using hypoxic tents Live High, Train Low (LHTL) would be the best means of preparing troops, as it would LHTL has now established itself as the preferred high cause the least disturbance to the training programme of altitude training protocol. Athletes live at high altitude a unit preparing to deploy. The benefits appear to exceed (physically or artificially) for the majority of the day, while the potential difficulties, and a large-scale controlled study training at a lower altitude. It is believed to meet the optimal is required for future research. balance between the advantages of Epo-stimulating hypoxic exposure and the ability to train at full capacity at low Conclusions altitudes. Although research is still in progress, we conclude that a physiological adaption benefit may be gained through Levine and Stray-Gundersen compared LHTL with LHTH acclimatisation using some of the aforementioned protocols, and a Live Low Train Low (LLTL) control group (23). The and in particular the Live High, Train Low approach. The test subjects spent a two-week phase establishing a base level optimal mechanism for achieving this benefit among troops before being randomly assigned to one of three groups for the during pre-deployment training is yet to be determined, and four-week study. The results showed a VO2 Max increase for this will likely continue to be a research area of great interest both the LHTH and LHTL groups, with no change in the to the military community, warranting further investigation. control group who remained at 150m throughout. However, only the LHTL group showed significant improvement in performance (assessed by a 5,000m run). Bruginaux et al References also observed an increase in VO2 Max of ~5% although no 1. Rodway GW, Muza SR. Fighting in thin air: operational significant increase in RCV or Epo levels (24). This research wilderness medicine in high Asia. Wilderness Environ Med established the recommendations which have subsequently 2011;22:297–303. 2. Pierce, Scott W. Mountain and Cold Weather Warfighting: been used in other studies for acclimatisation to avoid AMS Critical Capability for the 21st Century. (SAMS Monograph). and attenuation of immune responses. Exposure should Fort Leavenworth, Kans.: School of Advanced Military Studies, be for over 12 hours a day for longer than 18 days with an United States Army Command and General Staff College, 2008. 3. Stone, J. Military Strategy: The Politics and Technique of War. altitude not exceeding 3,000m. London: Continuum, 2011: 18-36. 4. Truesdell AG, Wilson RL. Training for medical support of Hypoxic tents and houses mountain operations. Mil Med 2006;171:463–7. 5. Muza SR. Military applications of hypoxic training for high- In order to minimise disruption to sea-level training, other altitude operations. Med Sci Sports Exerc 2007;39:1625–31. means of exploiting the benefits of high altitude, low oxygen 6. Peiser B, Reilly T. Environmental factors in the summer Olympics (hypoxic) training, have been developed. These include the in historical perspective. J Sports Sci 2004;10:981–1001. 7. Mooren FC (ed.) Encyclopedia of Exercise Medicine in Health design of hypoxic houses and tents which enable athletes and Disease [Online]. Berlin: Springer; 2012. to simulate living in hypoxic environments while remaining 8. Explorers web: medical. http://www.basecampmd.com/expguide/ in their chosen training location. The method of achieving highalt.shtml (accessed 28 Mar 2014). 9. Terrodos N, Melicha J. Sylven G et al. Effects of training at hypoxia in these protocols is either by use of a hypobaric simulated altitude on performance and muscle metabolic hypoxic chamber or a normobaric hypoxic tent. The hypoxic capacity in competitive road cyclists. Eur J Appl Physiol Occup tents achieve a lower PO2 by replacing the O2 with nitrogen Physiol 1988;57(2):203-9. 10. Human performance resource centre website. www.hprc.online. which reduces the percentage of O2 from approximately org (accessed 23 Mar 2014). 21% to as low as 10%. 11. Guyton AC, Hall JE. Textbook of Medical Physiology.10th ed. Philadelphia, PA: W.B. Saunders, 2000. 12. Gore CJ, Rodríguez FA, Truijens MJ, et al. Increased serum The number of studies assessing these protocols is erythropoietin but not red cell production after 4 wk of increasing but results to date are controversial. A meta- intermittent hypobaric hypoxia (4,000-5,500 m). J Appl Physiol analysis by Hahn et al of six studies (2,650-3,000m for 11- 2006 Nov;101:1386–93. 13. Forgey WW (ed.) Wilderness Medical Society Practice Guidelines 23 nights) showed an overall increase in VO2 Max of 1% For Wilderness Emergency Care. 2nd ed. Guilford, CT: Globe (25). Such a lack of improvement was also shown by Neya Pequot; 2001. et al who observed no improvement in VO2 Max in their 14. Bailey DM, Davis B, Romer L, et al. Implications of moderate altitude training for sea-level endurance in elite distance elite runners after spending 29 nights at 3,000m (26). runners. Eur J Appl Physiol 1998;78:360–8. Limitations with both of these studies have been noted and 15. Heinicke K, Heinicke I, Schmidt W, et al. A three-week traditional neither conformed to the protocols proposed by Bruglinaux altitude training increases mass and red cell volume in elite biathlon athletes. Int J Sports Med 2005;26:350-5. et al, which may have caused the poor responses observed J Royal Naval Medical Service 2014, Vol 100.1 71

16. Mellerowicz H, Meller W, Woweries J, et al. Vergleichende hypoxia does not alter performance or erythropoietic markers in untersuchungen über wirkungen von höhentraining auf die highly trained distance runners. J Appl Physiol 2004;96:1800–7. dauerleistung in meereshöhe. Sportarzt und Sportmedizin 23. Levine B, Stray-Gundersen J. “Living high - training low”: effect 1970;21:207–40. of moderate-altitude acclimatization with low-altitude training 17. Vallier JM, Chateau P, Guezennec CY. Effects of physical on performance. J Appl Physiol 1997;102–12. training in a hypobaric chamber on the physical performance 24. Brugniaux JV, Schmitt L, Robach P, et al. Eighteen days of ‘living of competitive triathletes. Eur J Appl Physiol Occup Physiol high, training low’ stimulate erythropoiesis and enhance aerobic 1996;73:471–8. performance in elite middle-distance runners. J Appl Physiol 18. Bonetti DL, Hopkins WG. Sea-level exercise performance 2006;100:203–11. following adaptation to hypoxia: a meta-analysis. Sports Med 25. Hahn G, Gore CJ, Martin DT, et al. An evaluation of the concept 2009;39(2):107–27. of living at moderate altitude and training at sea level. Comp 19. Truijens MJ, Toussaint HM, Dow J, et al. Effect of high-intensity Biochem Physiol A Mol Integr Physiol 2001;128(4):777–89. hypoxic training on sea-level swimming performances. J Appl 26. Neya M, Enoki T, Kumai Y, et al. The effects of nightly Physiol 2003;94:733–43. normobaric hypoxia and high intensity training under 20. Murphy, S. Ten ways to train like an elite athlete. Guardian intermittent normobaric hypoxia on and Online, 20 Jun 2012. http://www.theguardian.com/ hemoglobin mass. J Appl Physiol 2007;103:828–34. lifeandstyle/2012/jun/20/ten-ways-to-train-like-elite-athlete 27. Elliott S. Erythropoiesis-stimulating agents and other methods to (accessed 10 Mar 2014). enhance oxygen transport. Br J Pharmacol 2008;154:529–41. 21. Dufour SP, Ponsot E, Zoll J, et al. Exercise training in normobaric hypoxia in endurance runners. I. Improvement in aerobic performance capacity. J Appl Physiol 2006;100:1238–48. 22. Julian CG, Gore CJ, Wilber RL, et al. Intermittent normobaric

Authors

Surgeon Sub Lieutenant K M Heil, BEng, Royal Navy Medical Cadet, Glasgow University RN [email protected]

Major ACM Keenan, MRCS, BSc(Hons), Orthopaedic Registrar, RAMC (V), Glasgow University, Wolfson Medical School, University Avenue, Glasgow