Endurance exercise performance in acute hypoxia is influenced by expiratory flow limitation

Difference in expiratory flow limitations development in normoxia and hypoxia in healthy individuals

The present study investigated the maintenance/repeatability of expiratory flow limitation (EFL) between normoxia and hypoxia. Fifty-one healthy active individuals (27 men and 24 women) performed a lung function test and a maximal incremental cycling test in both normoxia and hypoxia (inspired oxygen fraction = 0.14) on two separate visits. During exercise in normoxia, 28 participants exhibited EFL (55 %). In hypoxia, another cohort of 28 participants exhibited EFL. The two groups only partly overlapped. Individuals with EFL only in normoxia reported lower maximal ventilation values in hypoxia than in normoxia (n=5; -13.5 ± 7.8 %) compared to their counterparts with EFL only in hypoxia (n=5; +6.7 ± 6.3 %) or without EFL (n=18; +5.1 ± 10.3 %) (p=0.004 and p<0.001, respectively). EFL development may be induced by different mechanisms in hypoxia vs. normoxia since the individuals who exhibited flow limitation were not the same between the two environmental conditions. This change seems influenced by the magnitude of the maximal ventilation change.

Fitness Level- and Sex-Related Differences in Pulmonary Limitations to Maximal Exercise in Normoxia and Hypoxia

PURPOSE

Both maximal-intensity exercise and altitude exposure challenge the pulmonary system that may reach its maximal capacities. Expiratory flow limitation (EFL) and exercise-induced hypoxemia (EIH) are common in endurance-trained athletes. Furthermore, because of their smaller airways and lung size, women, independently of their fitness level, may be more prone to pulmonary limitations during maximal-intensity exercise, particularly when performed in hypoxic conditions. The objective of this study was to investigate the impact of sex and fitness level on pulmonary limitations during maximal exercise in normoxia and their consequences in acute hypoxia.

METHODS

Fifty-one participants were distributed across four different groups according to sex and fitness level. Participants visited the laboratory on three occasions to perform maximal incremental cycling tests in normoxia and hypoxia (inspired oxygen fraction = 0.14) and two hypoxic chemosensitivity tests. Pulmonary function and ventilatory capacities were evaluated at each visit.

RESULTS

EIH was more prevalent (62.5% vs 22.2%, P = 0.004) and EFL less common (37.5% vs 70.4%, P = 0.019) in women than men. EIH prevalence was different ( P = 0.004) between groups of trained men (41.7%), control men (6.7%), trained women (50.0%), and control women (75.0%). All EIH men but only 40% of EIH women exhibited EFL. EFL individuals had higher slope ratio ( P = 0.029), higher ventilation (V̇ E ) ( P < 0.001), larger ΔVO 2max ( P = 0.019), and lower hypoxia-related V̇ E increase ( P < 0.001).

CONCLUSIONS

Women reported a higher EIH prevalence than men, regardless of their fitness level, despite a lower EFL prevalence. EFL seems mainly due to the imbalance between ventilatory demands and capacities. It restricts ventilation, leading to a larger performance impairment during maximal exercise in hypoxic conditions.

The Effects of Sodium Phosphate Supplementation on the Cardiorespiratory System and Gross Efficiency during Exercise under Hypoxia in Male Cyclists: A Randomized, Placebo-Controlled, Cross-Over Study

The main aim of this study was to evaluate the effects of six days of tri-sodium phosphate (SP) supplementation on the cardiorespiratory system and gross efficiency (GE) during exercise under hypoxia in cyclists. Twenty trained male cyclists received SP (50 mg·kg⁻¹ of fat-free mass/day) or placebo for six days in a randomized, cross-over study, with a three-week washout period between supplementation phases. Before and after each supplementation phase, the subjects performed an incremental exercise test to exhaustion under normobaric hypoxia (FiO₂ = 16%, ~2500 m). It was observed that short-term SP supplementation led to a decrease in heart rate, an increase in stroke volume, and an improvement in oxygen pulse (VO₂/HR) during low and moderate-intensity exercise under hypoxia. These changes were accompanied by an increase in the serum inorganic phosphate level by 8.7% (p < 0.05). No significant changes were observed in serum calcium levels. GE at a given workload did not change significantly after SP supplementation. These results indicated that SP promotes improvements in the efficiency of the cardiorespiratory system during exercise in a hypoxic environment. Thus, SP supplementation may be beneficial for endurance exercise in hypoxia.

Effects of Acute High-Intensity Exercise With the Elevation Training Mask or Hypoxicator on Pulmonary Function, Metabolism, and Hormones

ABSTRACT

Ott, T, Joyce, MC, and Hillman, AR. Effects of acute high-intensity exercise with the elevation training mask or hypoxicator on pulmonary function, metabolism, and hormones. J Strength Cond Res 35(9): 2486-2491, 2021-The elevation training mask (ETM) 2.0 is an increasingly popular hands-free respiratory muscle training modality proposing to mimic altitude; however, the degree to which this occurs has been questioned. The purpose of this study was to investigate the efficacy of this modality in comparison with using a hypoxicator (HYP) during acute aerobic exercise. Eight regularly active subjects (age: 25 ± 8 years; height: 166 ± 12 cm; body mass 64 ± 10 kg; and V̇o2max: 46 ± 6 ml·kg-1·min-1) completed 3 trials, each including resting metabolic rate measurement, pulmonary function tests, and 13 sprint intervals at 90% V̇o2max using either the HYP, ETM, or control. There was no significant difference in metabolism or heart rate between conditions. Fraction of expired air in the first second was greater after exercise (p = 0.02), while oxygen saturation was lower during exercise with the HYP (p < 0.001). Human growth hormone increased with exercise, but no differences were found between conditions; however, a trend was observed for higher growth hormone after exercise in HYP vs. ETM (p = 0.08). Elevation training mask does not seem to change acute pulmonary function, metabolism, heart rate, or oxygen saturation, indicating it likely does not create a hypoxic environment or mimic altitude.

Red Blood Cell 2,3-Diphosphoglycerate Decreases in Response to a 30 km Time Trial Under Hypoxia in Cyclists

Red blood cell 2,3-diphosphoglycerate (2,3-DPG) is one of the factors of rightward-shifted oxygen dissociation curves and decrease of Hb-O₂ affinity. The reduction of Hb-O₂ affinity is beneficial to O₂ unloading at the tissue level. In the current literature, there are no studies about the changes in 2,3-DPG level following acute exercise in moderate hypoxia in athletes. For this reason, the aim of this study was to analyze the effect of prolonged intense exercise under normoxic and hypoxic conditions on 2,3-DPG level in cyclists. Fourteen male trained cyclists performed a simulation of a 30 km time trial (TT) in normoxia and normobaric hypoxia (FiO₂ = 16.5%, ~2,000 m). During the TT, the following variables were measured: power, blood oxygen saturation (SpO₂), and heart rate (HR). Before and immediately after exercise, the blood level of 2,3-DPG and acid–base equilibrium were determined. The results showed that the mean SpO₂ during TT in hypoxia was 8% lower than in normoxia. The reduction of SpO₂ in hypoxia resulted in a decrease of average power by 9.6% (p < 0.001) and an increase in the 30 km TT completion time by 3.8% (p < 0.01) compared to normoxia. The exercise in hypoxia caused a significant (p < 0.001) decrease in 2,3-DPG level by 17.6%. After exercise in normoxia, a downward trend of 2,3-DPG level was also observed, but this effect was not statistically significant. The analysis also revealed that changes of acid–base balance were significantly larger (p < 0.05) after exercise in hypoxia than in normoxia. In conclusion, intense exercise in hypoxic conditions leads to a decrease in 2,3-DPG concentration, primarily due to exercise-induced acidosis.

Thoracic gas compression during forced expiration is greater in men than women

Intrapleural pressure during a forced vital capacity (VC) maneuver is often in excess of that required to generate maximal expiratory airflow. This excess pressure compresses alveolar gas (i.e., thoracic gas compression [TGC]), resulting in underestimated forced expiratory flows (FEFs) at a given lung volume. It is unknown if TGC is influenced by sex; however, because men have larger lungs and stronger respiratory muscles, we hypothesized that men would have greater TGC. We examined TGC across the "effort-dependent" region of VC in healthy young men (n = 11) and women (n = 12). Subjects performed VC maneuvers at varying efforts while airflow, volume, and esophageal pressure (POES ) were measured. Quasistatic expiratory deflation curves were used to obtain lung recoil (PLUNG ) and alveolar pressures (i.e., PALV  = POES -PLUNG ). The raw maximal expiratory flow-volume (MEFVraw ) curve was obtained from the "maximum effort" VC maneuver. The TGC-corrected curve was obtained by constructing a "maximal perimeter" curve from all VC efforts (MEFVcorr ). TGC was examined via differences between curves in FEFs (∆FEF), area under the expiratory curves (∆AEX ), and estimated compressed gas volume (∆VGC) across the VC range. Men displayed greater total ∆AEX (5.4 ± 2.0 vs. 2.0 ± 1.5 L2 ·s-1 ; p < .001). ∆FEF was greater in men at 25% of exhaled volume only (p < .05), whereas ∆VGC was systematically greater in men across the entire VC (main effect; p < .05). PALV was also greater in men throughout forced expiration (p < .01). Taken together, these findings demonstrate that men display more TGC, occurring early in forced expiration, likely due to greater expiratory pressures throughout the forced VC maneuver.

The Prevalence of Expiratory Flow Limitation in Youth Elite Male Cyclists

The present investigation tested the hypotheses that there would be greater prevalence of expiratory flow limitation (EFL) in endurance-trained (ET) youth cyclists compared with a recreationally active control (CON) group.

METHODS

Twelve ET youth male cyclists (16.3 ± 1.0 yr (13-18 yr), 176.5 ± 6.2 cm, 64.2 ± 5.9 kg) and 12 CON subjects (17.6 ± 2.2 yr (13-18 yr), 177.9 ± 7.1 cm, 74.8 ± 11.2 kg) completed an incremental exercise test to determine peak oxygen consumption (V˙O2peak) on a cycle ergometer. Maximal flow volume loops (MFVL), forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), FEV1/FVC, forced expiratory flow between 25% and 75% of FVC, and peak expiratory flow were assessed before and after exercise, with inspiratory capacity maneuvers and dyspnea ratings measured in the last 20 s of each stage. EFL was quantified as the percentage of the expiratory tidal volume that overlapped with the maximal flow volume loop.

RESULTS

V˙O2peak, dyspnea ratings at peak, and ventilation were higher in the ET compared with CON group (P < 0.05). The ET group experienced greater EFL prevalence at V˙O2peak, with 11 of 12 subjects exhibiting EFL compared with 5 of 12 subjects in the CON group (P = 0.014). When matched for absolute ventilation of 20, 40, 60, 80, and 100 L·min, there were no differences in EFL severity between the ET and CON groups (P = 0.473).

CONCLUSIONS

Elite youth male cyclists have a greater prevalence of EFL at maximal exercise than do CON subjects who are similar in age, height, and lung size. Future research should determine whether EFL in youth ET male cyclists may limit their exercise performance.

The Effects of Chest Wall Loading on Perceptions of Fatigue, Exercise Performance, Pulmonary Function, and Muscle Perfusion

Background: Load carriage (LC), which directly affects the chest wall and locomotor muscles, has been suggested to alter the ventilatory and circulatory responses to exercise, leading to increased respiratory muscle work and fatigue. However, studies exploring the impact of LC on locomotion increased internal work, complicating their interpretation. To overcome this issue, we sought to determine the effect of chest wall loading with restriction (CWL + R) on cycling performance, cardiopulmonary responses, microvascular responsiveness, and perceptions of fatigue. Methods: In a randomized crossover design, 23 young healthy males (22 ± 4 years) completed a 5 km cycling time trial (TT) in loaded (CWL + R; tightened vest with 10% body weight) and unloaded conditions. After baseline pulmonary function testing (PFT; forced expiratory volume in 1 s, FEV₁; forced vital capacity, FVC), cardiopulmonary indices (HR, heart rate; O₂ uptake, VO₂; ventilation, V_E; tidal volume, V_T; and breathing frequency, B_f), rating of perceived exertion (RPE), lactate (BLa), and microvascular responses (oxy-, deoxy-, total hemoglobin; and tissue saturation; StO₂) of the vastus lateralis using near infrared spectroscopy were collected during the TT; and PFT was repeated post-exercise. Results: Pre-exercise, CWL + R reduced (p < 0.05) FVC (5.6 ± 0.8 versus 5.5 ± 0.7 L), FEV₁ (4.8 ± 0.7 versus 4.7 ± 0.6 L), and FEV₁/FVC (0.9 ± 0.1 versus 0.8 ± 0.1). CWL + R modified power output (PO) over time (interaction, p = 0.02), although the 5 km time (461 ± 24 versus 470 ± 27 s), V_T (3.0 ± 0.3 versus 2.8 ± 0.8 L), B_f, V_E, HR, VO₂, microvascular and perceptual (visual analog scale, or VAS, and RPE) responses were unchanged (p > 0.05). CWL + R increased (p < 0.05) the average BLa (7.6 ± 2.6 versus 8.6 ± 3 mmol/L). Conclusions: Modest CWL + R negatively affects pre-exercise pulmonary function, modifies cycling power output over time, and increases lactate production during a 5 km cycling trial, although the cardiorespiratory, microvascular, and perceptual responses were unaffected.

Comparison between a facemask and mouthpiece on breathing mechanics and gas exchange variables during high-intensity exercise

Gas-collection masks are used as a comfortable alternative to the traditional mouthpiece and noseclip during exercise testing protocols in human performance laboratories. However, these masks may introduce potential problems which could affect metabolic and ventilatory parameters, including gas leaks and added dead space. Therefore, the purpose of this study was to compare breathing mechanics, gas exchange variables and ratings of perceived breathlessness (RPB) during high-intensity exercise between a mouthpiece and face mask. Fourteen men [⩒O₂peak = 55.3 ± 7.3 ml·kg^-1·min^-1] were recruited to perform 6 min of cycle ergometry (Velotron Pro, RacerMate, Inc., Seattle, WA) at a work rate corresponding to 90% of ⩒O₂peak while breathing on either (1) a mouthpiece (Hans Rudolph, KC, KS) with nose clip, or (2) a face mask (7450, Hans Rudolph, KC, KS). The difference in ⩒_E between the mouthpiece (156.8 ± 23.3 L/min) and face mask (153.3 ± 21.8 L/min) was not significant (p = 0.534). Similarly, there were no significant differences in breathing mechanics, gas exchange variables or RPB. These data suggest that the facemask can continue to be used interchangeably with the mouthpiece and may even be a more comfortable alternative during high-intensity exercise.

Expiratory flow limitation under moderate hypobaric hypoxia does not influence ventilatory responses during incremental running in endurance runners

We tested whether expiratory flow limitation (EFL) occurs in endurance athletes in a moderately hypobaric hypoxic environment equivalent to 2500 m above sea level and, if so, whether EFL inhibits peak ventilation ( V ˙ Epeak ), thereby exacerbating the hypoxia-induced reduction in peak oxygen uptake ( V ˙ O2peak ). Seventeen young male endurance runners performed incremental exhaustive running on separate days under hypobaric hypoxic (560 mmHg) and normobaric normoxic (760 mmHg) conditions. Oxygen uptake ( V ˙ O2 ), minute ventilation ( V ˙ E), arterial O2 saturation (SpO2 ), and operating lung volume were measured throughout the incremental exercise. Among the runners tested, 35% exhibited EFL (EFL group, n = 6) in the hypobaric hypoxic condition, whereas the rest did not (Non-EFL group, n = 11). There were no differences between the EFL and Non-EFL groups for V ˙ Epeak and V ˙ O2peak under either condition. Percent changes in V ˙ Epeak (4 ± 4 vs. 2 ± 4%) and V ˙ O2peak (-18 ± 6 vs. -16 ± 6%) from normobaric normoxia to hypobaric hypoxia also did not differ between the EFL and Non-EFL groups (all P > 0.05). No differences in maximal running velocity, SpO2 , or operating lung volume were detected between the two groups under either condition. These results suggest that under the moderate hypobaric hypoxia (2500 m above sea level) frequently used for high-attitude training, ~35% of endurance athletes may exhibit EFL, but their ventilatory and metabolic responses during maximal exercise are similar to those who do not exhibit EFL.

Premature birth affects the degree of airway dysanapsis and mechanical ventilatory constraints

NEW FINDINGS

What is the central question of this study? Adult survivors of preterm birth without (PRE) and with bronchopulmonary dysplasia (BPD) have airflow obstruction at rest and significant mechanical ventilatory constraints during exercise compared with those born at full term (CON). Do PRE/BPD have smaller airways, indexed via the dysanapsis ratio, than CON? What is the main finding and its importance? The dysanapsis ratio was significantly smaller in BPD and PRE compared with CON, with BPD having the smallest dysanapsis ratio. These data suggest that airflow obstruction in PRE and BPD might be because of smaller airways than CON. Adult survivors of very preterm birth (≤32 weeks gestational age) without (PRE) and with bronchopulmonary dysplasia (BPD) have obstructive lung disease as evidenced by reduced expiratory airflow at rest and have significant mechanical ventilatory constraints during exercise. Airflow obstruction, in any conditions, could be attributable to several factors, including small airways. PRE and/or BPD could have smaller airways than their counterparts born at full term (CON) owing to a greater degree of dysanaptic airway development during the pre- and/or postnatal period. Thus, the purpose of the present study was to compare the dysanapsis ratio (DR), as an index of airway size, between PRE, BPD and CON. To do so, we calculated DR in PRE (n = 21), BPD (n = 14) and CON (n = 34) individuals and examined flow-volume loops at rest and during submaximal exercise. The DR, using multiple estimates of static recoil pressure, was significantly smaller in PRE and BPD (0.16 ± 0.05 and 0.10 ± 0.03 a.u.) compared with CON (0.22 ± 0.04 a.u.; both P < 0.001) and smallest in BPD (P < 0.001). The DR was significantly correlated with peak expiratory airflow at rest (r = 0.42; P < 0.001) and the extent of expiratory flow limitation during exercise (r = 0.60; P < 0.001). Our findings suggest that PRE/BPD might have anatomically smaller airways than CON, which might help to explain their lower expiratory airflow rate at rest and during exercise and further our understanding of the consequences of preterm birth and neonatal O₂ therapy.

Respiratory Effects of Thoracic Load Carriage Exercise and Inspiratory Muscle Training as a Strategy to Optimize Respiratory Muscle Performance with Load Carriage

Many occupational and recreational settings require the use of protective and/or load-bearing apparatuses worn over the thoracic cavity, known as thoracic load carriage (LC). Compared to normal, unloaded exercise, thoracic LC exercise places an additional demand on the respiratory and limb locomotor systems by altering ventilatory mechanics as well as circulatory responses to exercise, thus accelerating the development of fatigue in the diaphragm and accessory respiratory muscles compared to unloaded exercise. This may be a consequence of the unique demands of thoracic LC, which places an additional mass load on the thoracic cavity and can restrict chest wall expansion. Therefore it is important to find effective strategies to ameliorate the detrimental effects of thoracic LC. Inspiratory muscle training is an intervention that aims to increase the strength and endurance of the diaphragm and accessory inspiratory muscle and may therefore be a useful strategy to optimize performance with thoracic LC.

Quantifying the effects of acute hypoxic exposure on exercise performance and capacity: A systematic review and meta-regression

OBJECTIVE

To quantify the effects of acute hypoxic exposure on exercise capacity and performance, which includes continuous and intermittent forms of exercise.

DESIGN

A systematic review was conducted with a three-level mixed effects meta-regression. The ratio of means method was used to evaluate main effects and moderators providing practical interpretations with percentage change.

DATA SOURCES

A systemic search was performed using three databases (Google scholar, PubMed and SPORTDiscus). Eligibility criteria for selecting studies: Inclusion was restricted to investigations that assessed exercise performance (time trials (TTs), sprint and intermittent exercise tests) and capacity (time to exhaustion test, TTE) with acute hypoxic (<24 h) exposure and a normoxic comparator.

RESULTS

Eighty-two outcomes from 53 studies (N = 798) were included in this review. The results show an overall reduction in exercise performance/capacity -17.8 ± 3.9% (95% CI -22.8% to -11.0%), which was significantly moderated by -6.5 ± 0.9% per 1000 m altitude elevation (95% CI -8.2% to -4.8%) and oxygen saturation (-2.0 ± 0.4%; 95% CI -2.9% to -1.2%). TT (-16.2 ± 4.3%; 95% CI -22.9% to -9%) and TTE (-44.5 ± 6.9%; 95% CI -51.3% to -36.7%) elicited a negative effect, whilst indicating a quadratic relationship between hypoxic magnitude and both TTE and TT performance. Furthermore, exercise less than 2 min exhibited no ergolytic effect from acute hypoxia. Summary/Conclusion: This review highlights the ergolytic effect of acute hypoxic exposure, which is curvilinear for TTE and TT performance with increasing hypoxic levels, but short duration intermittent and sprint exercise seem to be unaffected.

The role of inspiratory muscle training in the management of asthma and exercise-induced bronchoconstriction

Asthma is a pathological condition comprising of a variety of symptoms which affect the ability to function in daily life. Due to the high prevalence of asthma and associated healthcare costs, it is important to identify low-cost alternatives to traditional pharmacotherapy. One of these low cost alternatives is the use of inspiratory muscle training (IMT), which is a technique aimed at increasing the strength and endurance of the diaphragm and accessory muscles of respiration. IMT typically consists of taking voluntary inspirations against a resistive load across the entire range of vital capacity while at rest. In healthy individuals, the most notable benefits of IMT are an increase in diaphragm thickness and strength, a decrease in exertional dyspnea, and a decrease in the oxygen cost of breathing. Due to the presence of expiratory flow limitation in asthma and exercise-induced bronchoconstriction, dynamic lung hyperinflation is common. As a result of varying operational lung volumes, due in part to hyperinflation, the respiratory muscles may operate far from the optimal portion of the length-tension curve, and thus may be forced to operate against a low pulmonary compliance. Therefore, the ability of these muscles to generate tension is reduced, and for any given level of ventilation, the work of breathing is increased as compared to non-asthmatics. Evidence that IMT is an effective treatment for asthma is inconclusive, due to limited data and a wide variation in study methodologies. However, IMT has been shown to decrease dyspnea, increase inspiratory muscle strength, and improve exercise capacity in asthmatic individuals. In order to develop more concrete recommendations regarding IMT as an effective low-cost adjunct in addition to traditional asthma treatments, we recommend that a standard treatment protocol be developed and tested in a placebo-controlled clinical trial with a large representative sample.