Fluid-Regulatory Hormone Responses during Cycling Exercise in Acute Hypobaric Hypoxia

The Methodological Quality of Studies Investigating the Acute Effects of Exercise During Hypoxia Over the Past 40 years: A Systematic Review

Exercise under hypoxia and the physiological impact compared to normoxia or hypoxia has gained attention in the last decades. However, methodological quality assessment of articles in this area is lacking in the literature. Therefore, this article aimed to evaluate the methodologic quality of trials studying exercise under hypoxia. An electronic search was conducted until December 2021. The search was conducted in PubMed, CENTRAL, and PEDro using the PICO model. (P) Participants had to be healthy, (I) exercise under normobaric or hypobaric hypoxia had to be (C) compared to exercise in normoxia or hypoxia on (O) any physiological outcome. The 11-item PEDro scale was used to assess the methodological quality (internal validity) of the studies. A linear regression model was used to evaluate the evolution of trials in this area, using the total PEDro score of the rated trials. A total of n = 81 studies met the inclusion criteria and were processed in this study. With a mean score of 5.1 ± 0.9 between the years 1982 and 2021, the mean methodological quality can be described as "fair." Only one study reached the highest score of 8/10, and n = 2 studies reached the lowest observed value of 3/10. The linear regression showed an increase of the PEDro score of 0.1 points per decade. A positive and small tendency toward increased methodologic quality was observed. The current results demonstrate that a positive and small tendency can be seen for the increase in the methodological quality in the field of exercise science under hypoxia. A "good" methodological quality, reaching a PEDro score of 6 points can be expected in the year 2063, using a linear regression model analysis. To accelerate this process, future research should ensure that methodological quality criteria are already included during the planning phase of a study.

Endocrine responses after a single bout of moderate aerobic exercise in healthy adult humans

Exercise is a stress stimulus for the human organism affecting the homeostatic mechanisms of the body, depending on the type, duration, intensity and frequency of exercise. The aim of this study was to determine the effects of a moderate aerobic exercise bout on the Hypothalamo-Pituitary-Adrenal (HPA) axis acute hormonal responses in healthy adult humans. Twelve healthy male and female volunteers (age: 30.6 ± 4.4 years), performed a single bout of a 30-minute aerobic exercise at 70% of VO2max on a treadmill, following standard diet. Blood samples were collected before (t0), at the end of the exercise bout (t30), and 30 min after the completion of exercise (t60). Serum adrenocorticotropic hormone (ACTH), cortisol (COR), aldosterone (ALDO) and renin (REN) were measured. One-way ANOVA was used for statistics. ACTH and COR decreased after exercise, reaching significance (p < 0.01) 30 min after the completion of the exercise bout. ALDO increased at the end of exercise and remained elevated 30 min after its completion. REN significantly increased at the end of exercise (p < 0.05) and remained elevated. The exercise regimen used in this study had beneficial effects on the stress axis, suggesting that specific exercise protocols can be characterised by mild physiological stress-inducing effects hence be prescribed for special diseased populations.

Effects of normoxic and hypoxic exercise training on the bactericidal capacity and subsequent apoptosis of neutrophils in sedentary men

Phagocytosis and oxidative burst are essential mechanisms of innate immunity by which neutrophils eliminate invading pathogens. Afterwards, phagocytic neutrophils are dissipated by facilitating apoptosis to control inflammation. This study investigates how exercise training with or without hypoxic exposure affects the bactericidal activity and subsequent apoptosis of neutrophils following strenuous exercise. A total of 60 healthy, sedentary men were randomly divided into four groups (n = 15 in each group), who were exposed to 21% O₂ [normoxic control (NC)] or 15% O₂ [hypoxic control (HC)] at rest or were trained at 50% of peak work rate at 21% O₂ [normoxic training (NT)] or 15% O₂ [hypoxic training (HT)] for 30 min/day, 5 days/week for 4 weeks. Before the intervention, acute strenuous exercise (SE) enhanced the phagocytosis of Escherichia coli (E. coli) by neutrophils and the release of neutrophil oxidant products in response to E. coli, accompanied by increases in the expression of adhesion molecules (CD62L, CD11b, and CD11a), an opsonic receptor (FcγIIIBR), and complement receptors (C1qRp and CD5aR) on neutrophils. Subsequently, the SE facilitated caspase-3 activation and phosphatidylserine exposure in E. coli-stimulated neutrophils. Furthermore, 4 weeks of HT promoted the expressions of adhesion molecules and opsonic/complement receptors on neutrophils, and it also augmented the bactericidal and apoptotic activities of neutrophils at rest or after SE. However, NT, HC, and NC did not influence these neutrophil-related immune responses to strenuous exercise. Therefore, we conclude that the HT regimen effectively promotes the bactericidal capacity of neutrophils, and facilitates their subsequent apoptosis both at rest and following SE.

The influence of acute and 23 days of intermittent hypoxic exposures on the exercise-induced forehead sweating response

The effect of acute and 23 days of intermittent exposures to normobaric hypoxia on the forehead sweating response during steady-state exercise was investigated. Eight endurance athletes slept in a normobaric hypoxic room for a minimum of 8 h per day at a simulated altitude equivalent to 2,700 m for 23 days (sleep high-train low regimen). Peak oxygen uptake (VO2(peak)) and peak work rate (WR(peak)) were determined under normoxic (20.9%O(2)) and hypoxic (13.5%O(2)) conditions prior to (pre-IHE), and immediately after (post-IHE) the intermittent hypoxic exposures (IHE). Also, each subject performed three 30-min cycle-ergometry bouts: (1) normoxic exercise at 50% WR(peak) attained in normoxia (control trial; CT); (2) hypoxic exercise at 50% WR(peak) attained in hypoxia (hypoxic relative trial; HRT) and (3) hypoxic exercise at the same absolute work rate as in CT (hypoxic absolute trial; HAT). Exposure to hypoxia induced a 33 and 37% decrease (P < 0.001) in (VO2(peak)) pre-IHE and post-IHE, respectively. Despite similar relative oxygen uptake during HAT pre-IHE and post-IHE, the ratings of perceived whole-body exertion decreased substantially (P < 0.05) post-IHE. Pre-IHE the sweat secretion on the forehead (m(sw)f) was greater (P < 0.01) in the HAT (2.60 (0.80) mg cm(-2) min(-1)) compared to the other two trials (CT = 1.87 (1.09) mg cm(-2) min(-1); HRT = 1.57 (0.82) mg cm(-2) min(-1)) despite a similar exercise-induced elevation in body temperatures, resulting in an augmented (P < 0.01) gain of the sweating response (m(sw)f/Delta T(re)). The augmented (m(sw)f) and m(sw)f/Delta T(re) during the HAT were no longer evident post-IHE. Thus, it appears that exercise sweating on the forehead is potentiated by acute exposure to hypoxia, an effect which can be abolished by 23 days of intermittent hypoxic exposures.

Exercise-induced inhibition of angiotensin II vasoconstriction in human thigh muscle

It is well established that metabolic inhibition of adrenergic vasoconstriction contributes to the maintenance of adequate perfusion to exercising skeletal muscle. However, little is known regarding nonadrenergic vasoconstriction during exercise. We tested the hypothesis that a non-adrenergic vasoconstrictor, angiotensin II (AngII), would be less sensitive to metabolic inhibition than an alpha1-agonist, phenylephrine (PE), in the exercising human thigh. In 11 healthy men, femoral blood flow (FBF, ultrasound Doppler and thermodilution) and blood pressure were evaluated during wide-ranging doses of intra-arterial (femoral) infusions of PE and AngII at rest and during two workloads of steady-state knee-extensor exercise (7 W and 27 W). At rest, the maximal decrease in femoral artery diameter (FAD) during AngII (9.0+/-0.2 to 8.4+/-0.4 mm) was markedly less than during PE (9.0+/-0.3 to 5.7+/-0.5 mm), whereas maximal reductions in FBF and femoral vascular conductance (FVC) were similar during AngII (FBF: -65+/-6 and FVC: -66+/-6%) and PE (-57+/-5 and -59+/-4%). During exercise, FAD was not changed by AngII, but moderately decreased by PE. The maximal reductions in FBF and FVC were blunted during exercise compared to rest for both AngII (7 W: -28+/-5 and -40+/-5%; 27 W: -15+/-4% and -29+/-5%) and PE (7 W: -30+/-4 and -37+/-6%; 27 W: -15+/-2 and -24+/-6%), with no significant differences between drugs. The major new findings are (1) an exercise-induced intensity-dependent metabolic attenuation of non-adrenergic vasoconstriction in the human leg; and (2) functional evidence that AngII-vasoconstriction is predominantly distal, whereas alpha1-vasoconstriction is proximal and distal within the muscle vascular bed of the human thigh.