138 1. IntroductIon High altitude is associated with several environmental challenges to natives and sojourners alike. Several environmental stressors such as low temperature, high wind velocity, ionizing radiations and hypobaric hypoxia at high altitude leads to a decrease in physical and mental performance 1-2 . Rapid ascent to altitude without proper acclimatisation in army troops may cause detrimental efects on health and also compromised operational capabilities work performance. Proper acclimatisation can resolve the problems and reduces the severity of illness. Intermittent hypoxic training (IHT) is an approach for faster acclimatisation which can decrease the incidence and severity of high altitude illness. IHT is exposure to normobaric or hypobaric hypoxia at sea level for the purpose of pre-acclimatisation/pre-conditioning to high altitude. Recent studies have reported the use of IHT in sports medicine to enhance physical performance and to induce pre- acclimatisation without any pharmacological interventions 3 . Exposure to a moderate hypoxic episodes have been shown to elicit the benefcial efects by activating the adaptive responses in our body and protects against hypertension, myocardial injuries, heart arrhythmia and bronchial asthma 4, 5 . Our own earlier study reported that IHT have a preconditioning efect for acclimatisation to hypobaric hypoxia prevalent at high altitude 6-8 . Recent study by Kumar et al. 9 demonstrated the better maintenance of redox homeostasis in carotid body by regulating the expression of the HIFα isoforms and modulating the antioxidant enzyme levels in IH trained rats as compared to control. Oxidative stress has been implicated as one of the major reason for high altitude induced illness. It is well known that hypobaric hypoxia at high altitude leads to enhanced ROS generation and several studies have observed increase in oxidative damage markers in response to hypoxia 10-11 . Several physiological processes such as mitochondrial electron transport chain, nitric oxide synthetase and xanthine oxidase get triggered at high altitude that leads to increased oxidative stress 12-14 . Recent studies proposed that enhanced altered hypoxia sensing, rather than hypoxia response mechanism, as the reason for better adaptation in natives 15 . Mammalian cells detect the decrease in oxygen concentrations to activate a variety of responses allowing better adaptation. One such response is stabilisation of the protein hypoxia-inducible factor (HIF-1), which regulates the expression of genes mediating adaptive responses 16 . This includes a prominent role for more than 100 hypoxia-sensitive genes, like erythropoietin (EPO), heme oxygenase-1 (HO-1), inducible nitric oxide synthase (iNOS), glucose transporter (GLUT-1), VEGF, stress proteins and others. Stimulation of these proteins through hypoxic preconditioning has been established to play a part in protecting from tissue damage 17-19 . HO-1 induction represents an important redox sensor and an antioxidant defence. In the presence of HO-1, heme is Received : 03 September 2020, Revised : 22 January 2021 Accepted : 11 February 2021, Online published : 03 June 2021 rapid Acclimatisation to High Altitude by Intermittent Hypoxia training at Sea-Level: role of Biochemical Markers Geetha Suryakumar, Dishari Ghosh, Richa Rathor, Gopinath Bhaumik, Som Nath Singh * and Bhuvnesh Kumar DRDO-Defence Institute of Physiology and Allied Sciences, Delhi - 110 054, India * E-mail: cellbiochemistry@gmail.com ABStrAct Rapid induction of soldiers to high altitude under emergency situation may lead to higher incidence of acute mountain sickness (AMS) and other high altitude illness. Intermittent Hypoxia Training (IHT) at sea level before going to high altitude is an approach for rapid acclimatisation. This approach may be helpful to reduce the occurrence of AMS and leads to better acclimatisation at high altitude in shorter duration. The present study evaluates the role of biochemical markers of acclimatisation after IHT before induction to actual high altitude. The study participants were Indian Army Personnel (n=30) and they were divided into two groups of control (n=16) and IHT exposed (n=14). The intermittent hypoxia training was administered at 12 per cent Oxygen for 4h/day for 4 days at sea level using normobaric hypoxia chamber and within 24 hrs - 48 hrs the subjects were airlifted to Leh, Ladakh, India at 11,700 ft. Preconditioning with IHT may be benefcial in maintaining antioxidant levels and ameliorate oxidative stress at high altitude. The hypoxia responsive proteins like Hemeoxygenase -1 (HO-1) and Vascular endothelial growth factor (VEGF) and the cytoprotective stress proteins, which facilitate the acclimatisation, may also get benefted by IHT exposure. Keywords: High altitude; Acclimatisation; Intermittent Hypoxia training; Oxidative stress. Defence Life Science Journal, Vol. 6, No. 2, April 2021, pp. 138-145, DOI : 10.14429/dlsj.6.16265  2021, DESIDOC