Physiological Adaptations to Hypoxic vs. Normoxic Training during Intermittent Living High

Abstract

In the setting of “living high,” it is unclear whether high-intensity interval training (HIIT) should be performed “low” or “high” to stimulate muscular and performance adaptations. Therefore, 10 physically active males participated in a 5-week “live high-train low or high” program (TR), whilst eight subjects were not engaged in any altitude or training intervention (CON). Five days per week (~15.5 h per day), TR was exposed to normobaric hypoxia simulating progressively increasing altitude of ~2,000–3,250 m. Three times per week, TR performed HIIT, administered as unilateral knee-extension training, with one leg in normobaric hypoxia (~4,300 m; TRHYP) and with the other leg in normoxia (TRNOR). “Living high” elicited a consistent elevation in serum erythropoietin concentrations which adequately predicted the increase in hemoglobin mass (r = 0.78, P < 0.05; TR: +2.6%, P < 0.05; CON: −0.7%, P > 0.05). Muscle oxygenation during training was lower in TRHYP vs. TRNOR (P < 0.05). Muscle homogenate buffering capacity and pH-regulating protein abundance were similar between pretest and posttest. Oscillations in muscle blood volume during repeated sprints, as estimated by oscillations in NIRS-derived tHb, increased from pretest to posttest in TRHYP (~80%, P < 0.01) but not in TRNOR (~50%, P = 0.08). Muscle capillarity (~15%) as well as repeated-sprint ability (~8%) and 3-min maximal performance (~10–15%) increased similarly in both legs (P < 0.05). Maximal isometric strength increased in TRHYP (~8%, P < 0.05) but not in TRNOR (~4%, P > 0.05). In conclusion, muscular and performance adaptations were largely similar following normoxic vs. hypoxic HIIT. However, hypoxic HIIT stimulated adaptations in isometric strength and muscle perfusion during intermittent sprinting.

Effect of Resistance Training Under Normobaric Hypoxia on Physical Performance, Hematological Parameters, and Body Composition in Young and Older People

“…In contrast, the non-significant changes of the muscle strength of the arms were not higher than the measurement error (elbow flexion: ∼6%, elbow extension: ∼8%; see Törpel et al, 2017) and must therefore considered to be insubstantial. In comparison to previous RTH studies using low to moderate loads, the amount of these improvements are comparable (Manimmanakorn et al, 2013a,b;de Smet et al, 2017) or higher (Friedmann et al, 2003). Regarding muscle strength capacity, the RTH-interventions using a moderate to high load achieved comparable (Mayo et al, 2018), higher (*corrected p-value by using the Bonferroni-Holm method -the correction factor corresponds to the number of the tests [time × group effect] within the parameter groups; maximal respiratory exchange ratio: RER max , peak oxygen uptake: VO2 peak , oxygen uptake at one watt per kilogram: VO2 1W/kg , maximal power output: PO max , power output at the second lactate threshold: PO LT2 , heart rate at one watt per kilogram: HR 1W/kg , maximal muscular strength: F max for the exercises elbow extension and flexion/knee extension and flexion, total hemoglobin mass: tHb, blood volume: BV, fat mass: FM, fat free mass: FFM).…”

“…Additionally, previous studies that have investigated a lowload RTH (e.g., de Smet et al, 2017;5 week intervention period, 3x/week, loads 20 to 25% of the 1RM) found no superior effect in comparison to a similarly designed resistance training under normoxia on the VO2 peak in young people. In contrast, the study by Álvarez-Herms et al (2016) found a significant improvement in anaerobic performance (+ 53.8% for the total number of sets at 90% of the 300-m "all-out" test).…”

“…Regarding the primary analysis, we found no superior effects of RTH in comparison to matched designed RT on physical performance (cardiopulmonary and muscle strength capacity), tHb, BV, and body composition (FFM, FM). Heterogeneous results regarding the effect of this type of RTH are currently available: higher effectiveness of the RTH regarding the improvement of muscle hypertrophy (Nishimura et al, 2010), muscle strength capacity (de Smet et al, 2017;Martínez-Guardado et al, 2019), and anaerobic performance (Álvarez-Herms et al, 2014) vs. no superior effects regarding muscle hypertrophy, muscle strength endurance capacity, maximal muscular strength, muscle fiber type distribution, the vascular endothelial growth factor (VEGF), and various enzymes and muscle specific proteins (Friedmann et al, 2003;Ho et al, 2014b). These incongruent results might be reasoned by the differences regarding the designs of the resistance training as well as the hypoxic doses of these studies (including the current study).…”

“…This assumption is reasoned by higher metabolic stress (Scott et al, 2014(Scott et al, , 2015a(Scott et al, , 2017 triggering functional and structural muscular adaptations (Schoenfeld, 2010(Schoenfeld, , 2013. Even though the exact physiological adaptation processes for RTH are not yet precisely known and understood, it is currently known from 18 international publications on RTH-interventions that this special type of resistance training appears to be partially more effective than resistance training under normoxia regarding the improvement of (i) muscle physiological parameter, (ii) neuromuscular adaptation, (iii) hormonal response, (iv) blood parameter, (v) body composition/body mass, (vi) sprint ability, and (vii) endurance performance/cardiovascular health and fitness (Friedmann et al, 2003;Nishimura et al, 2010;Álvarez-Herms et al, 2012;Manimmanakorn et al, 2013a,b;Álvarez-Herms et al, 2014Álvarez-Herms et al, , 2016Ho et al, 2014b;Kon et al, 2014;Kurobe et al, 2015;Chycki et al, 2016;Inness et al, 2016;Yan et al, 2016;de Smet et al, 2017;Mayo et al, 2018;Morales-Artacho et al, 2018;Ramos-Campo et al, 2018a;Martínez-Guardado et al, 2019).…”

Changes in Muscle and Cerebral Deoxygenation and Perfusion during Repeated Sprints in Hypoxia to Exhaustion

“…Previous reports have examined peripheral and cerebral oxygenation with NIRS during repeated sprint exercise, however, none of these studies have been performed with repeated sprint exercise to exhaustion in hypoxic conditions [series of repeated sprints, (Racinais et al, 2007 ; Smith and Billaut, 2010 , 2012 ; Billaut and Buchheit, 2013 ); or incremental ramp test to exhaustion, (Amann et al, 2007 ; Subudhi et al, 2007 )]. In addition, recent research has eluded that there may be greater blood volume shifts in the muscle during repeated sprint exercise possibly due to greater arteriolar dilation together with increased capillary volume (De Smet et al, 2017 ). Therefore, there are factors contributing to the end of exercise within maximal repeated sprints to exhaustion which remain unknown.…”