Recovery effects of repeated exposures to normobaric hyperoxia on local muscle fatigue

Impact of hydrogen-rich gas mixture inhalation through nasal cannula during post-exercise recovery period on subsequent oxidative stress, muscle damage, and exercise performances in men

Molecular hydrogen has been suggested to have a cytoprotective effect on the whole body and to enhance exercise performances. However, the effect of hydrogen-rich gas mixture (HG) inhalation on physiological responses has been poorly investigated. We examined the impact of acute HG inhalation on subsequent oxidative stress, muscle damage, and exercise performances during the recovery period after a strenuous exercise. This is a two-trial, double-blind, crossover, repeated measures study. Eight physically active male volunteers inhaled HG (estimated fraction of inspired oxygen and hydrogen were 21.57 and 4.08% at most, respectively) or normal gas (placebo, ambient air 400 m above sea level) during a 60-minute recovery phase after oxidative stress-inducing exercise) completion comprising 30-minute treadmill running at an intensity corresponding to 75% of maximal oxygen uptake and squat jumps (5 sets × 10 repetitions). Before oxidative stress-inducing exercise and 10 minutes after the post-exercise gas inhalation, blood and urine samples were obtained and exercise performances (jumping ability; pedaling power output; muscle strength) were evaluated. Post-exercise HG inhalation attenuated the increase in urinary 8-hydroxydeoxyguanosine excretion rate (P < 0.05), a DNA oxidation marker, and the reduction in the countermovement jump height (P < 0.05), compared with Placebo inhalation. Other exercise performances and blood oxidative stress and muscle damage markers did not differ between HG and Placebo inhalation. Moreover, the increase in urinary 8-hydroxydeoxyguanosine excretion rate was significantly associated with countermovement jump performance reduction (r = -0.78, P < 0.01). These findings suggested that HG inhalation during post-exercise recovery period might improve exercise performance via reducing systemic oxidative damage. The study was approved by the Human Research Ethics Committee of the University of Yamanashi (approval No. H29-006) on June 28, 2017.

The Effects of Hyperoxia on Sea-Level Exercise Performance, Training, and Recovery: A Meta-Analysis

BACKGROUND

Acute exercise performance can be limited by arterial hypoxemia, such that hyperoxia may be an ergogenic aid by increasing tissue oxygen availability. Hyperoxia during a single bout of exercise performance has been examined using many test modalities, including time trials (TTs), time to exhaustion (TTE), graded exercise tests (GXTs), and dynamic muscle function tests. Hyperoxia has also been used as a long-term training stimulus or a recovery intervention between bouts of exercise. However, due to the methodological differences in fraction of inspired oxygen (F_iO₂), exercise type, training regime, or recovery protocols, a firm consensus on the effectiveness of hyperoxia as an ergogenic aid for exercise training or recovery remains unclear.

OBJECTIVES

The aims of this study were to (1) determine the efficacy of hyperoxia as an ergogenic aid for exercise performance, training stimulus, and recovery before subsequent exercise; and (2) determine if a dose-response exists between F_iO₂ and exercise performance improvements.

DATA SOURCE

The PubMed, Web of Science, and SPORTDiscus databases were searched for original published articles up to and including 8 September 2017, using appropriate first- and second-order search terms.

STUDY SELECTION

English-language, peer-reviewed, full-text manuscripts using human participants were reviewed using the process identified in the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement.

DATA EXTRACTION

Data for the following variables were obtained by at least two of the authors: F_iO₂, wash-in time for gas, exercise performance modality, heart rate, cardiac output, stroke volume, oxygen saturation, arterial and/or capillary lactate, hemoglobin concentration, hematocrit, arterial pH, arterial oxygen content, arterial partial pressure of oxygen and carbon dioxide, consumption of oxygen and carbon dioxide, minute ventilation, tidal volume, respiratory frequency, ratings of perceived exertion of breathing and exercise, and end-tidal oxygen and carbon dioxide partial pressures.

DATA GROUPING

Data were grouped into type of intervention (acute exercise, recovery, and training), and performance data were grouped into type of exercise (TTs, TTE, GXTs, dynamic muscle function), recovery, and training in hyperoxia.

DATA ANALYSIS

Hedges' g effect sizes and 95% confidence intervals were calculated. Separate Pearson's correlations were performed comparing the effect size of performance versus F_iO₂, along with the effect size of arterial content of oxygen, arterial partial pressure of oxygen, and oxygen saturation.

RESULTS

Fifty-one manuscripts were reviewed. The most common F_iO₂ for acute exercise was 1.00, with GXTs the most investigated exercise modality. Hyperoxia had a large effect improving TTE (g = 0.89), and small-to-moderate effects increasing TTs (g = 0.56), GXTs (g = 0.40), and dynamic muscle function performance (g = 0.28). An F_iO₂ ≥ 0.30 was sufficient to increase general exercise performance to a small effect or higher; a moderate positive correlation (r = 0.47-0.63) existed between performance improvement of TTs, TTE, and dynamic muscle function tests and F_iO₂, but not GXTs (r = 0.06). Exercise training and recovery supplemented with hyperoxia trended towards a large and small ergogenic effect, respectively, but the large variability and limited amount of research on these topics prevented a definitive conclusion.

CONCLUSION

Acute exercise performance is increased with hyperoxia. An F_iO₂ ≥ 0.30 appears to be beneficial for performance, with a higher F_iO₂ being correlated to greater performance improvement in TTs, TTE, and dynamic muscle function tests. Exercise training and recovery supplemented with hyperoxic gas appears to have a beneficial effect on subsequent exercise performance, but small sample size and wide disparity in experimental protocols preclude definitive conclusions.

The Impact of Hyperoxia on Human Performance and Recovery

Hyperoxia results from the inhalation of mixtures of gas containing higher partial pressures of oxygen (O₂) than normal air at sea level. Exercise in hyperoxia affects the cardiorespiratory, neural and hormonal systems, as well as energy metabolism in humans. In contrast to short-term exposure to hypoxia (i.e. a reduced partial pressure of oxygen), acute hyperoxia may enhance endurance and sprint interval performance by accelerating recovery processes. This narrative literature review, covering 89 studies published between 1975 and 2016, identifies the acute ergogenic effects and health concerns associated with hyperoxia during exercise; however, long-term adaptation to hyperoxia and exercise remain inconclusive. The complexity of the biological responses to hyperoxia, as well as the variations in (1) experimental designs (e.g. exercise intensity and modality, level of oxygen, number of participants), (2) muscles involved (arms and legs) and (3) training status of the participants may account for the discrepancies.