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

Caffeine intake enhances peak oxygen uptake and performance during high-intensity cycling exercise in moderate hypoxia

PURPOSE

We investigated whether caffeine consumption can enhance peak oxygen uptake ([Formula: see text]) by increasing peak ventilation during an incremental cycling test, and subsequently enhance time to exhaustion (TTE) during high-intensity cycling exercise in moderate normobaric hypoxia.

METHODS

We conducted a double-blind, placebo cross-over design study. Sixteen recreational male endurance athletes (age: 20 ± 2 years, [Formula: see text]: 55.6 ± 3.6 ml/kg/min, peak power output: 318 ± 40 W) underwent an incremental cycling test and a TTE test at 80% [Formula: see text] (derived from the placebo trial) in moderate normobaric hypoxia (fraction of inspired O2: 15.3 ± 0.2% corresponding to a simulated altitude of ~ 2500 m) after consuming either a moderate dose of caffeine (6 mg/kg) or a placebo.

RESULTS

Caffeine consumption resulted in a higher peak ventilation [159 ± 21 vs. 150 ± 26 L/min; P < 0.05; effect size (ES) = 0.31]. [Formula: see text] (3.58 ± 0.44 vs. 3.47 ± 0.47 L/min; P < 0.01; ES = 0.44) and peak power output (308 ± 44 vs. 302 ± 44 W; P = 0.02, ES = 0.14) were higher following caffeine consumption than during the placebo trial. During the TTE test, caffeine consumption enhanced minute ventilation (P = 0.02; ES = 0.28) and extended the TTE (426 ± 74 vs. 358 ± 75 s; P < 0.01, ES = 0.91) compared to the placebo trial. There was a positive correlation between the percent increase of [Formula: see text] following caffeine consumption and the percent increase in TTE (r = 0.49, P < 0.05).

CONCLUSION

Moderate caffeine consumption stimulates breathing and aerobic metabolism, resulting in improved performance during incremental and high-intensity endurance exercises in moderate normobaric hypoxia.

CO2-Enriched Air Inhalation Modulates the Ventilatory and Metabolic Responses of Endurance Runners During Incremental Running in Hypobaric Hypoxia

Cao, Yinhang, Naoto Fujii, Tomomi Fujimoto, Yin-Feng Lai, Takeshi Ogawa, Tsutomu Hiroyama, Yasushi Enomoto, and Takeshi Nishiyasu. CO₂-enriched air inhalation modulates the ventilatory and metabolic responses of endurance runners during incremental running in hypobaric hypoxia. High Alt Med Biol. 23:125-134, 2022. Aim: We measured the effects of breathing CO₂-enriched air on ventilatory and metabolic responses during incremental running exercise under moderately hypobairc hypoxic (HH) conditions. Materials and Methods: Ten young male endurance runners [61.4 ± 6.0 ml/(min·kg)] performed incremental running tests under three conditions: (1) normobaric normoxia (NN), (2) HH (2,500 m), and (3) HH with 5% CO₂ inhalation (HH+CO₂). The test under NN was always performed first, and then, the two remaining tests were completed in random and counterbalanced order. Results: End-tidal CO₂ partial pressure (55 ± 3 vs. 35 ± 1 mmHg), peak ventilation (163 ± 14 vs. 152 ± 12 l/min), and peak oxygen uptake [52.3 ± 5.5 vs. 50.5 ± 4.9 ml/(min·kg)] were all higher in the HH+CO₂ than HH trial (all p < 0.01), respectively. However, the duration of the incremental test did not differ between HH+CO₂ and HH trials. Conclusion: These data suggest that chemoreflex activation by breathing CO₂-enriched air stimulates breathing and aerobic metabolism during maximal intensity exercise without affecting exercise performance in male endurance runners under a moderately hypobaric hypoxic environment.

Expiratory Peak Flow and Minute Ventilation Are Significantly Increased at High Altitude versus Simulated Altitude in Normobaria

Simulated altitude (normobaric hypoxia, NH) is used to study physiologic hypoxia responses of altitude. However, several publications show differences in physiological responses between NH and hypobaric conditions at altitude (hypobaric hypoxia, HH). The causality for these differences is controversially discussed. One theory is that the lower air density and environmental pressure in HH compared to NH lead to lower alveolar pressure and therefore lower oxygen diffusion in the lung. We hypothesized that, if this theory is correct, due to physical laws (Hagen-Poiseuille, Boyle), resistance respectively air compression (Boyle) at expiration should be lower, expiratory flow higher, and therefore peak flow and maximum expiratory flow (MEF) 75–50 increased in hypobaric hypoxia (HH) vs. normobaric hypoxia (NH). To prove the hypothesis of differences in respiratory flow as a result of lower alveolar pressure between HH and NH, we performed spirography in NH at different simulated altitudes and the corresponding altitudes in HH. In a cross over study, 6 healthy subjects (2 f/4 m, 28.3 ± 8.2 years, BMI: 23.2 ± 1.9) performed spirography as part of spiroergometry in a normobaric hypoxic room at a simulated altitude of 2800 m and after a seven-hour hike on a treadmill (average incline 14%, average walking speed 1.6 km/h) to the simulated summit of Mauna Kea at 4200 m. After a two-month washout, we repeated the spirometry in HH on the start and top of the Mauna Kea hiking trail, HI/USA. Comparison of NH (simulated 4200 m) and HH at 4200 m resulted in increased pulmonary ventilation during exercise (VE) (11.5%, p < 0.01), breathing-frequency (7.8%, p < 0.01), peak expiratory flow PEF (13.4%, p = 0.028), and MEF50 (15.9%, p = 0.028) in HH compared to NH, whereas VO2max decreased by 2%. At 2800 m, differences were only trendy, and at no altitude were differences in volume parameters. Spirography expresses higher mid expiratory flows and peak flows in HH vs. NH. This supports the theory of lower alveolar and small airway pressure due to a lower air density resulting in a lower resistance.