Does Moderate Altitude Affect VO 2 max in Acclimatized Mountain Guides? Reinhard Pu ¨ hringer, 1,2 Hannes Gatterer, 3 Martin Berger, 4 Michael Said, 4 Martin Faulhaber, 1,2 and Martin Burtscher 1,2 Abstract Pu ¨hringer, Reinhard, Hannes Gatterer, Martin Berger, Michael Said, Martin Faulhaber, and Martin Burt- scher. Does moderate altitude affect VO 2 max in acclimatized mountain guides? High Alt Med Biol. 23:37– 42, 2022. Background: Altitude exposure reduces maximal oxygen uptake (VO 2 max). Usually, the reduction is not restored with acclimatization (at least at altitudes above 2,500 m) and is more pronounced in highly trained athletes compared to nonathletes. It still remains to be elucidated whether these also apply for well-acclimatized individuals (i.e., mountain guides) acutely exposed to moderate altitude (i.e., 2,000 m). Methods: A total of 128 acclimatized male mountain guides of the Austrian armed forces (42.2 – 7.0 years, 177.8 – 5.6 cm, 77.2 – 7.0 kg) of different fitness levels performed 2 incremental cycle ergometer tests 1 week apart, one at low (600 m) and one at moderate altitude (2,000 m). Oxygen uptake, heart rate (HR), and lactate concentration were measured during the tests. Results: In acclimatized mountain guides, lower baseline VO 2 max levels were associated with better preser- vation of VO 2 max at moderate altitude compared to higher levels. At moderate altitude, physiological responses (HR and blood lactate at 100 W) at a submaximal exercise intensity of 100 W remained unchanged or were even slightly reduced in both groups. Conclusions: Long-term acclimatization to moderate altitude may prevent the VO 2 max decline at a moderate altitude of 2,000 m particularly in subjects with lower VO 2 max levels, that is, below the 80th percentile (for age and sex). In people with higher fitness levels, VO 2 max may still be negatively affected. These results are of practical relevance, for example, for workers, athletes, ski and mountain guides, military staff, or rescue staff who regularly or continuously have to perform at moderate altitude. Keywords: acclimatization; aerobic capacity; exercise; hypoxia Introduction A scent to terrestrial altitude is accompanied by re- duced oxygen (O 2 ) availability and an associated drop of arterial partial pressure of O 2 (PaO 2 ) and arterial blood O 2 saturation (SaO 2 ) (Ba ¨rtsch and Swenson, 2013; Burtscher et al., 2019). Consequently, a series of physiological responses are triggered, aimed to restore oxygen delivery to the tissues, for example, immediate increases in minute ventilation (VE), cardiac output (CO), and after several hours hemoconcentra- tion (Wagner, 2000; Mazzeo, 2008; Burtscher et al., 2012; Siebenmann and Lundby, 2015; Schlittler et al., 2021). During exercise at altitude, these compensatory mecha- nisms do not fully compensate for the reduced O 2, resulting in reduced maximal, as well as submaximal, ex- ercise performance (e.g., time trial performance) (Fulco et al., 1998; Wagner, 2000; Bartsch and Gibbs, 2007; Mazzeo, 2008; Faulhaber et al., 2010; Gatterer et al., 2013; Kossler et al., 2021). The impairment is greatest upon acute exposure (Fulco et al., 1998), and the magnitude of the decrement depends on various conditions, especially on the degree of hypoxia and the individual fitness level (Ferretti et al., 1997; Burtscher et al., 2006; Wehrlin and Hallen, 2006). 1 Department of Sport Science, University of Innsbruck, Innsbruck, Austria. 2 Austrian Society for Alpine and Mountain Medicine, Innsbruck, Austria. 3 Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy. 4 Department of Medicine, Military Hospital Innsbruck, Innsbruck, Austria. HIGH ALTITUDE MEDICINE & BIOLOGY Volume 23, Number 1, 2022 ª Mary Ann Liebert, Inc. DOI: 10.1089/ham.2021.0081 37 Downloaded by 52.202.246.201 from www.liebertpub.com at 08/11/22. For personal use only.