Effects of inter-effort recovery intermittent hypoxia on nitrate and nitrite bioavailability, endothelial function, muscle oxygenation, and exercise tolerance during sprint interval training

• Grant number: 24/08116-2
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: May 01, 2025
• End date: March 31, 2027
• Field of knowledge: Health Sciences - Physical Education
• Principal Investigator: Marcelo Papoti
• Grantee: Felipe Alves Ribeiro
• Host Institution: Faculdade de Medicina de Ribeirão Preto (FMRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil

Abstract

During high-intensity exercise and systemic hypoxia, the reduction of nitrate ions (NO3-) and nitrite ions (NO2-) into nitric oxide (NO) may contribute to vasodilation, as endothelial nitric oxide synthase exhibits reduced enzymatic activity under lower inspired oxygen fraction, as oxygen is a product. However, the relationships between NO3- and NO2- bioavailability and endothelial function and muscle oxygenation during high-intensity exercise and systemic hypoxia have not yet been experimentally tested. The aim of this doctoral project is to investigate the acute effects of hypoxia on NO3- and NO2- concentrations and their relationships with endothelial function, muscle oxygenation, metabolic involvement, and exercise tolerance during a sprint interval training (SIT) session. To achieve this, a randomized, controlled, double-blind trial will be conducted with 15 healthy, physically active adults undergoing three SIT sessions on a cycle ergometer, characterized by 10 maximal efforts of 30 s with 4.5-min intervals, and performed under normoxia (NOR), continuous hypoxia (HC), and inter-effort recovery intermittent hypoxia (HR) conditions. Before (PRE) and after (POST) the SIT sessions, NO3- and NO2- concentrations will be determined through blood and saliva samples, and blood flow and arterial caliber of the brachial and femoral arteries will be assessed using ultrasound. During the sessions, metabolic involvement and concentrations of oxyhemoglobin and deoxyhemoglobin will be continuously evaluated using a gas analyzer and a near-infrared spectroscopy device, respectively. Data will be analyzed using a mixed-effects generalized linear model, considering fixed effects (group [SIT × CON], condition [NOR × HC × HR], time [PRE × POST]) and random effects (participants).