Effect of acute altitude exposure on ventilatory thresholds in recreational athletes

https://doi.org/10.1016/j.resp.2021.103723Get rights and content

Highlights

  • The effect of hypobaric hypoxic exposure on ventilatory thresholds is insufficiently explored so far in recreational athletes.

  • Anaerobic threshold and ventilatory compensation point show a clear left shift during hypobaric hypoxic exercise.

  • VT-guided training has thus to be adapted when training an altitude.

Abstract

Purpose

High altitude (HA) training is frequently used in endurance sports and recreational athletes increasingly participate in cross mountain competitions. At high altitude aerobic physiology changes profoundly. Ventilatory thresholds (VTs) are measures for endurance performance but the impact of exposure to acute altitude (AA) on VTs in recreational athletes has been insufficiently explored to date and most studies investigated effects under normobaric hypoxia.

Methods

In this cross-sectional study we investigated the effects of AA exposure at 2650 m/715 mbar on anerobic threshold (VT1) and respiratory compensation point (VT2) in a graded cycling test in 14 recreational athletes (4 female, 10 male) compared to baseline levels (521 m, 949 mbar).

Results

At VT1, a decline in power output (PO) from median 115.5 W to 105.0 W (median -12.3 %, p = 0.032; Wilcoxon test) during exposure to HA was observed. VO2/body weight and VO2/heart rate decreased markedly (- 9.5 %, p = 0.016; -10.5 %, p = 0.012). At VT2 we found a significant decline of PO from 184.5–170.5 W (-13.1 %, p = 0.0014), of VO2/body weight and of VO2/heart rate (-10.1 %, p = 0.0015; -8.7 %, p = 0.002) compared to baseline values. Absolute VO2 decreased (-9.5 %, p = 0.0014 and -10.1 %, p = 0.0002) while minute ventilation and heart rates remained unchanged at both thresholds.

Conclusion

Our data allows a quantification of performance loss at HA in recreational athletes and demonstrates that VT-guided training intensities and workloads need to be adapted for training at HA.

Introduction

Acute exposure to high altitude (HA) has a substantial impact on pulmonary and cardiovascular physiology in humans with profound physiological changes (Cogo, 2011; Grocott et al., 2007).

The responses to acute hypobaric hypoxia particularly affect the cardiorespiratory and vascular system: An acute decline in arterial partial oxygen pressure stimulates both central and peripheral chemoreceptors and increases breathing rates and ventilation causing respiratory alkalosis (Bartsch and Saltin, 2008; Grocott et al., 2007). Acute altitude exposure elevates heart rate, reduces stroke volumes, stimulates diuresis and can lead to pathological conditions including acute mountain sickness, sleep disorders and adverse neurological effects (Bartsch and Saltin, 2008; Grimminger et al., 2017; Hamm et al., 2020; Pun et al., 2018). Hypobaric hypoxemia further triggers disturbances of autonomic function and activates the sympathetic nervous system (Hamm et al., 2020, 2018).

Of note, individual performance ability is markedly attenuated under acute hypoxic conditions (Ulrich et al., 2017). At HA especially individual aerobic exercise capacity declines while anaerobic performances usually show no deterioriation (Fulco et al., 1998). However, this acute loss of aerobic performance seems to be partly compensated by acclimatization: Both short-term (i.e. after very few days) (Burtscher et al., 2006) and long-term acclimatization (Fulco et al., 1998; Horstman et al., 1980) periods have demonstrated improved aerobic exercise capacity at submaximal workloads.

In order to sufficiently quantify sustainable submaximal workload and consequently values of aerobic fitness, measurement of lactate (LT) and ventilatory thresholds (VT) is frequently performed (Gaskill et al., 2001; Kayser, 1996). In cardiopulmonary exercise testing (CPET) ventilatory thresholds and can be assessed while VT1 marks the anaerobic threshold and VT2 the respiratory compensation point (Wasserman et al., 2005). The concept of VT assessment has been established decades ago by the pioneering work of Wasserman et al. and has since then been broadly implemented in training physiology for both recreational as well as elite athletes. In sports research VT-guided training can be used to evaluate individual performance, andto recommend appropriate training intensity (Esteve-Lanao et al., 2007; Wolpern et al., 2015). VT-based exercise training was demonstrated to significantly outperform overall oxygen capacity in recreational athletes compared to conventional training methods (Wolpern et al., 2015).

Despite its frequent use in training control, there is still little knowledge about the behavior of VTs under acute HA exposure. Exercise at HA decreases paO2 as well as SaO2 levels as pulmonary diffusion capacity is limited due to lower alveolar pO2 and increased pulmonary blood flow during exercise (Bartsch and Saltin, 2008). Additionally, LT and VT change upon hypoxic conditions: Recent studies showed, despite different definitions, a significant reduction of LTs upon acute HA exposure, possibly proportional to the reduction of peripheral oxygen supply (Valli et al., 2011; Weckbach et al., 2019). Azevedo et al. quantified the decline in the respiratory compensation point (equivalent to VT2) upon exposure to hypoxia (Azevedo et al., 2020). Nevertheless this, and many other studies have investigated the effect of normobaric hypoxic conditions on maximal and submaximal parameters of aerobic and anaerobic function (Azevedo et al., 2020; Bebout et al., 1989; Gallagher et al., 2014; Hammond et al., 1986; La Monica et al., 2018). A thorough understanding of VT alterations might be of importance as a rising number of recreational athletes participate in mountain sports at high altitude. Up to date, there is still insufficient knowledge about the behavior of VTs at hypobaric hypoxic conditions especially in average-trained athletes. The aim of our current short study was thus to investigate the effects of an acute altitude exposure (hypobaric hypoxia) on parameters of exercise capacity including ventilatory thresholds (VT1, VT2), oxygen consumption, minute ventilation, workload and heart rate in a cohort of recreational athletes as changes compared to ground level might have an impact on training at HA in this cohort.

Section snippets

Materials and methods

14 healthy recreational athletes (4 women, 10 men, age: 32 yr (29.3–39.5); height: 178.5 cm (171.5–182.8), body mass: 73.5 kg (64.3–82.8); values represent median with interquartile ranges) were included in the present study and underwent a cardiopulmonary exercise test (CPET): Participants performed a graded exercise test (GXT) using a cycle ergometer starting at 40 W (women) or 60 W (men), respectively (cadence revolution between 60 and 70 rpm). Step changes took place every 3 min with

Results

We investigated physiological parameters of performance during CPETs at baseline levels (521 m) and under hypobaric hypoxic conditions at high altitude (2650 m) for anaerobic threshold (VT1), respiratory compensation point (VT2) and for VO2max. Fig. 2 and Table 1 show those values with medians [interquartile ranges] and statistical differences at VT1, VT2 and during maximum oxygen consumption comparing baseline and altitude levels. For VO2max we found significantly decreased (-8.5 %, p = 0.032)

Discussion

In our study we investigated the effect of exposure to acute altitude exposure (2650 m, hypobaric hypoxia) without prior acclimatization on functional parameters at the anaerobic threshold, the ventilatory compensation point and maximum oxygen consumption in a GXT and compared these parameters to baseline levels (521 m). We detected a clear left shift of those parameters with a decline in relative and absolute oxygen consumption as well as power output at VT1 and VT2 in recreational athletes.

Conclusion

Our findings provide evidence that VTs show a distinct left shift under acute hypobaric hypoxic conditions. Our data allows quantification of performance loss at high altitude in recreational athletes. VT-guided training at higher altitudes thus needs to adapt training loads and intensities. Improvement of aerobic capacity due to short-term and long-term acclimatization processes at HA still have to be taken into account.

Funding

DS is supported by the Clinician Scientist Program In Vascular Medicine (PRIME, MA 2186/14−1). KL is supported by the young investigator grant of Ludwig Maximilians University—“LMUexcellent.’’ Funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Availability of data and material

All data sets can be reveived upon request.

Ethics approval

Research was approved by the Ethikkommission der Medizinischen Fakultät der LMU München.

Data availability

All data can be obtained upon request

Author contributions

Dominik Schüttler: Investigation, Writing: Review&Editing, Formal Analysis, Writing – Original Draft.

Ludwig T. Weckbach: Methodology, Investigation, Writing: Review&Editing, Validation, Formal Analysis, Data Curation.

Wolfgang Hamm: Investigation, Writing: Review&Editing.

Florian Maier: Investigation, Resources.

Sari Kassem: Investigation, Resources.

Johannes Schier: Investigation, Resources.

Korbinian Lackermair: Conzeptualization, Methodology, Validation, Writing: Review&Editing, Supervision,

Declaration of Competing Interest

The authors report no declarations of interest.

References (30)

  • M.B. La Monica et al.

    Effects of normobaric hypoxia on upper body critical power and anaerobic working capacity

    Respir. Physiol. Neurobiol.

    (2018)
  • G. Valli et al.

    Exercise intolerance at high altitude (5050m): critical power and W′

    Respir. Physiol. Neurobiol.

    (2011)
  • R.D.A. Azevedo et al.

    Hypoxia equally reduces the respiratory compensation point and the NIRS-derived [HHb] breakpoint during a ramp-incremental test in young active males

    Physiol. Rep.

    (2020)
  • P. Bartsch et al.

    General introduction to altitude adaptation and mountain sickness

    Scand. J. Med. Sci. Sports

    (2008)
  • D.E. Bebout et al.

    Effects of altitude acclimatization on pulmonary gas exchange during exercise

    J. Appl. Physiol.

    (1989)
  • C.J. Boos et al.

    A four-way comparison of cardiac function with Normobaric Normoxia, normobaric hypoxia, hypobaric hypoxia and genuine high altitude

    PLoS One

    (2016)
  • M. Burtscher et al.

    Effects of short-term acclimatization to altitude (3200 m) on aerobic and anaerobic exercise performance

    Int. J. Sports Med.

    (2006)
  • E.R. Buskirk et al.

    Maximal performance at altitude and on return from altitude in conditioned runners

    J. Appl. Physiol.

    (1967)
  • E.R. Buskirk et al.

    . Physiology and performance of track runners at various altitudes in theUnited States and Peru

  • A. Cogo

    The lung at high altitude

    Multidiscip. Respir. Med.

    (2011)
  • J. Esteve-Lanao et al.

    Impact of training intensity distribution on performance in endurance athletes

    J. Strength Cond. Res.

    (2007)
  • C.S. Fulco et al.

    Maximal and submaximal exercise performance at altitude

    Aviat. Space Environ. Med.

    (1998)
  • C.A. Gallagher et al.

    Effect of acute normobaric hypoxia on the ventilatory threshold

    Eur. J. Appl. Physiol.

    (2014)
  • S.E. Gaskill et al.

    Validity and reliability of combining three methods to determine ventilatory threshold

    Med. Sci. Sports Exerc.

    (2001)
  • J. Grimminger et al.

    Thin air resulting in high pressure: mountain sickness and hypoxia-induced pulmonary hypertension

    Can. Respir. J.

    (2017)
  • 1

    These authors contributed equally to this study.

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