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Mekjavic I.B.,Jozef Stefan Institute | Mekjavic I.B.,Simon Fraser University | Amon M.,Jozef Stefan International Postgraduate School | Kolegard R.,KTH Royal Institute of Technology | And 5 more authors.
Frontiers in Physiology | Year: 2016

To assess the effect of normobaric hypoxia on metabolism, gut hormones, and body composition, 11 normal weight, aerobically trained (O2peak: 60.6 ± 9.5 ml·kg-1·min-1) men (73.0 ± 7.7 kg; 23.7 ± 4.0 years, BMI 22.2 ± 2.4 kg·m-2) were confined to a normobaric (altitude ≃ 940 m) normoxic (NORMOXIA; PIO2 ≃ 133.2 mmHg) or normobaric hypoxic (HYPOXIA; PIO was reduced from 105.6 to 97.7 mmHg over 10 days) environment for 10 days in a randomized cross-over design. The wash-out period between confinements was 3 weeks. During each 10-day period, subjects avoided strenuous physical activity and were under continuous nutritional control. Before, and at the end of each exposure, subjects completed a meal tolerance test (MTT), during which blood glucose, insulin, GLP-1, ghrelin, peptide-YY, adrenaline, noradrenaline, leptin, and gastro-intestinal blood flow and appetite sensations were measured. There was no significant change in body weight in either of the confinements (NORMOXIA: -0.7 ± 0.2 kg; HYPOXIA: -0.9 ± 0.2 kg), but a significant increase in fat mass in NORMOXIA (0.23 ± 0.45 kg), but not in HYPOXIA (0.08 ± 0.08 kg). HYPOXIA confinement increased fasting noradrenaline and decreased energy intake, the latter most likely associated with increased fasting leptin. The majority of all other measured variables/responses were similar in NORMOXIA and HYPOXIA. To conclude, normobaric hypoxic confinement without exercise training results in negative energy balance due to primarily reduced energy intake. © 2016 Mekjavic, Amon, Kölegård, Kounalakis, Simpson, Eiken, Keramidas and Macdonald. Source


Keramidas M.E.,National and Kapodistrian University of Athens | Keramidas M.E.,Jozef Stefan Institute | Kounalakis S.N.,Hellenic Military University | Geladas N.D.,National and Kapodistrian University of Athens
Clinical Physiology and Functional Imaging | Year: 2012

The purpose of the study was to investigate the effect of interval training combined with a thigh cuffs pressure of +90mmHg on maximal and submaximal cycling performance. Twenty untrained individuals were assigned either to a control (CON) or to an experimental (CUFF) training group. Both groups trained 3days per week for 6weeks at the same relative intensity; each training session consisted of 2-min work bout at 90% of : 2-min active recovery bout at 50% of An incremental exercise test to exhaustion, a 6-min constant-power test at 80% of (Sub 80) and a maximal constant-power test to exhaustion (TF 150) were performed pre- and post-training. Despite the unchanged , both groups significantly increased peak power output (CON: ~12%, CUFF: ~20%) that was accompanied by higher deoxygenation (ΔStO 2) measured with near-infrared muscle spectroscopy. These changes were more pronounced in the CUFF group. Moreover, both groups reduced during the Sub 80 test without concomitant changes in ΔStO 2. TF 150 was enhanced in both groups. Thus, an interval exercise training protocol under moderate restricted blood flow conditions does not provide any additive effect on maximal and submaximal cycling performance. However, it seems to induce peripheral muscular adaptations, despite the lower absolute training intensity. © 2011 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Source


Mekjavic I.B.,Jozef Stefan Institute | Debevec T.,Jozef Stefan Institute | Debevec T.,Jozef Stefan International Postgraduate School | Amon M.,Jozef Stefan International Postgraduate School | And 3 more authors.
Aviation Space and Environmental Medicine | Year: 2012

Introduction: It has been speculated that short (∼1-h) exposures to intermittent normobaric hypoxia at rest can enhance subsequent exercise performance. Thus, the present study investigated the effect of daily resting intermittent hypoxic exposures (IHE) on peak aerobic capacity and performance under both normoxic and hypoxic conditions. Methods: Eighteen subjects were equally assigned to either a control (CON) or IHE group and performed a 4-wk moderate intensity cycling exercise training (1 h · d-1, 5 d · wk-1 ). The IHE group additionally performed IHE (60 min) prior to exercise training. IHE consisted of seven cycles alternating between breathing a hypoxic gas mixture (5 min; FIO2 = 0.12 - 0.09) and room air (3 min; FIO2 = 0.21). Normoxic and hypoxic peak aerobic capacity (V̇O2peak) and endurance performance were evaluated before (PRE), during (MID), upon completion (POST), and 10 d after (AFTER) the training period. Results: Similar improvements were observed in normoxic .V̇O2peak tests in both groups [IHE: Δ (POST-PRE) = +10%; CON: Δ (POST-PRE) = +14%], with no changes in the hypoxic condition. Both groups increased performance time in the normoxic constant power test only [IHE: Δ (POST-PRE) = +108%; CON: Δ (POST-PRE) = +114%], whereas only the IHE group retained this improvement in the AFTER test. Higher levels of minute ventilation were noted in the IHE compared to the CON group at the POST and AFTER tests. Conclusion: Based on the results of this study, the IHE does not seem to be beneficial for normoxic and hypoxic performance enhancement. Copyright © by the Aerospace Medical Association, Alexandria, VA. Source


Keramidas M.E.,Jozef Stefan Institute | Keramidas M.E.,Jozef Stefan International Postgraduate School | Kounalakis S.N.,Hellenic Military University | Debevec T.,Jozef Stefan Institute | And 5 more authors.
Acta Physiologica | Year: 2011

Aim: The purpose of the present study was to evaluate the 'normobaric oxygen paradox' theory by investigating the effect of a 2-h normobaric O 2 exposure on the concentration of plasma erythropoietin (EPO). Methods: Ten healthy males were studied twice in a single-blinded counterbalanced crossover study protocol. On one occasion they breathed air (NOR) and on the other 100% normobaric O 2 (HYPER). Blood samples were collected Pre, Mid and Post exposure; and thereafter, 3, 5, 8, 24, 32, 48, 72 and 96h, and 1 and 2weeks after the exposure to determine EPO concentration. Results: The concentration of plasma erythropoietin increased markedly 8 and 32h after the NOR exposure (approx. 58% and approx. 52%, respectively, P≤0.05) as a consequence of its natural diurnal variation. Conversely, the O 2 breathing was followed by approx. 36% decrement of EPO 3h after the exposure (P≤0.05). Moreover, EPO concentration was significantly lower in HYPER than in the NOR condition 3, 5 and 8h after the breathing intervention (P≤0.05). Conclusion: In contrast to the 'normobaric oxygen paradox' theory, the present results indicate that a short period of normobaric O 2 breathing does not increase the EPO concentration in aerobically fit healthy males. Increased O 2 tension suppresses the EPO concentration 3 and 5h after the exposure; thereafter EPO seems to change in a manner consistent with natural diurnal variation. © 2011 The Authors. Acta Physiologica © 2011 Scandinavian Physiological Society. Source


Mekjavic I.B.,Jozef Stefan Institute | Kounalakis S.N.,Hellenic Military University | Keramidas M.E.,Jozef Stefan Institute | Biolo G.,University of Trieste | And 2 more authors.
Aviation Space and Environmental Medicine | Year: 2012

Introduction: Bed rest is a terrestrial experimental analogue of unloading experienced during exposure to microgravity. Such unloading causes atrophy predominantly of the postural muscles, especially those of the lower limbs. Methods: We tested the hypothesis that 35 d horizontal bed rest alters thermoregulatory responses of subjects (N = 10) immersed in 15oC water, particularly the heat produced by the shivering tremor of the skeletal muscles. Before and after bed rest we measured the thickness of the gastrocnemius medialis (GM), vastus lateralis (VL), tibialis anterior (TA), and biceps brachii (BB) muscles by ultrasonography. During the immersions, we monitored rectal and skin temperatures, heat fl ux, heart rate, and oxygen uptake. Results: After bed rest, muscle thickness decreased signifi cantly by 12.2 ± 8.8% and 8.0 ± 9.1% in the GM and VL, respectively. No changes were observed in the TA and BB muscles. The 35-d bed rest caused a signifi cant reduction in aerobic power, as refl ected in maximal oxygen uptake. There were no signifi cant differences in any of the observed thermoregulatory responses between the pre- and post-bed rest immersions. Conclusions: Cardiovascular and muscular deconditioning had no effect on the heat production and heat loss responses. Due to the signifi cant reduction in the mass of the muscles in the lower limbs, concomitant with no change in heat production, we conclude that leg muscles do not play a signifi cant role in shivering thermogenesis. Source

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