Effects of Acute Moderate Hypoxia versus Normoxia on Metabolic and Cardiac Function and Skeletal Muscle Oxygenation during Endurance Exercise at the Same Heart Rate Level

Abstract

This study aimed to investigate the effects of acute moderate hypoxia (HYP), compared with those of normoxia (NORM), during endurance exercise with the same HR level on metabolic function, skeletal muscle oxygenation, and cardiac function. Twelve healthy men (aged 25.1 ± 2.3 years) completed 30 min of endurance exercise using a cycle ergometer with the same HR level (136.5 ± 1.5 bpm) corresponding to 70% maximal heart rate (HRmax) under NORM (760 mmHg) and HYP (526 mmHg, simulated 3000 m altitude) after a 30 min exposure in the respective environments on different days, in random order. Exercise load, rating of perceived exertion (RPE), metabolic function (saturation of percutaneous oxygen; SpO2, minute ventilation; oxygen uptake; VO2, carbon dioxide excretion; respiratory exchange ratio; RER, and oxygen pulse), skeletal muscle oxygen profiles (oxyhemoglobin, oxhb, deoxyhemoglobin, dxhb, total hemoglobin, and tissue oxygenation index; StO2), and cardiac function (heart rate, stroke volume, cardiac output, end-diastolic volume, end-systolic volume, and ejection fraction) were measured during endurance exercise. HYP showed a lower exercise load with the same RPE during exercise than did NORM. In addition, HYP showed a lower SpO2, VO2, oxygen pulse, oxhb, and StO2, and a higher RER and dxhb during exercise than NORM. We found that HYP showed lower exercise load and VO2 at the same RPE than NORM and also confirmed a higher anaerobic metabolism and oxygen inflow into skeletal muscle tissue due to the limitation of oxygen delivery capacity.

Simulated Altitude Training and Sport Performance: Protocols and Physiological Effects

“…This type of training is another form of hypoxia training. The study conducted by Park et al [36] investigated the effects of simulated 3000 m hypoxia combined with exercise at 70% of maximal heart rate (HRmax). This condition led to increased anaerobic metabolism and oxygen supply to muscles due to limited oxygen delivery capacity.…”

Effects of Acute Beetroot Juice Supplementation and Exercise on Cardiovascular Function in Healthy Men in Preliminary Study: A Randomized, Double-Blinded, Placebo-Controlled, and Crossover Trial

“…Subsequently, all of the participants underwent a familiarization trial under non-intake conditions using the exercise protocol before the main trial for exercise program adaptation. The exercise protocol consisted of 30 min of endurance exercise on a cycle ergometer (Aero bike 75XLII; Konami Corporation, Tokyo, Japan) at the same HR level equivalent to 70% maximal HR (70% HRmax), calculated using the Miyashita formula (male = 209 − 0.69 × age) [33]. The target HR of the participants, 70% HRmax, was 136.5 ± 1.5 bpm.…”

“…Therefore, a cycle ergometer was selected to obtain accurate data for measuring both blood pressure and cardiac function. The chosen exercise type and duration (30 min) were similar, and 70% of HRmax was used, referring to previous studies that evaluated cardiac function during exercise [33]. In addition, according to the American College of Sports Medicine (ACSM) guidelines, 70% of HRmax is considered a reasonable exercise intensity as it essentially corresponds to the medium-intensity level recommended for improving health [34].…”

Helpful to Live Healthier? Intermittent Hypoxic/Ischemic Training Benefits Vascular Homeostasis and Lipid Metabolism with Activating SIRT1 Pathways in Overweight/Obese Individuals

“…Hence, studies mentioned above imply that hypoxia plus exercise may help with weight loss. With technological advancement, people could exercise in an artificial hypoxic environment (inspired oxygen fraction: 16.5-14.5%, simulated altitude: 2,000-3,000 m) while living in normoxia, widely known as "intermittent hypoxic training (IHT)" [12][13][14]. IHT benefits from hypoxic stimulation without adverse health complications [15].…”