1. Introduction
hypoxia, FiOAltitude/hypoxic, infections, injuries
HYPOXIC, HYPOXIA, INFECTIONS
The aim of this study was to evaluate the effects of D-aspartic acid (DAA) supplementation during a simulated altitude protocol on the hormonal and hematological responses in athletes. We hypothesized that DAA supplementation would contribute to an increase in the luteinizing hormone (LH), free, and testosterone and a greater increase in hematological variables. Sixteen male boxers participated; they were randomly assigned to an experimental group (DAA) or a control group (C) and underwent 14 days of supplementation, 6 g/day of DAA. Both DAA and C participants were exposed to normobaric hypoxia (FiOAltitude/hypoxic training has been used for many years to improve exercise capacity in athletes. A number of concepts have been developed for using hypoxic conditions to improve performance in various sports. Popular methods include the live high–train low (LH–TL) protocol, where athletes live in hypoxic conditions at moderate altitudes (2000–2500 m above sea level, or a.s.l.) for 10–12 h a day (chiefly in the evening and at night) and train in normoxia, with normal oxygen availability [The improvement in hematological variables expected from the use of LH–TL depends on many factors, including the duration of exposure to hypoxia and the intensity of the hypoxic stimulus, body iron stores in athletes, injuries and infections, and the anabolic–catabolic balance in the body [Testosterone (T) has been proven to stimulate the hematopoietic system by increasing erythropoietin synthesis and secretion, acting on erythroid cells in the bone marrow, improving iron absorption and transport, stimulating iron incorporation into erythrocytes, increasing hemoglobin synthesis, prolonging erythrocyte survival time, and increasing 2,3-diphosphoglycerate (2,3-DPG) levels in red blood cells [One legal substance being considered as an ergogenic aid to support T production is D-aspartic acid (DAA). D-aspartic acid (DAA) is a natural amino acid found in many tissues (including the brain, nervous system, endocrine glands, liver, ovaries, and testes), where it acts as a signaling factor [So far, few human studies have investigated the effects of DAA supplementation on T levels, and their findings have been inconsistent. Some studies showed that ingesting 3 g/day of DAA for a period of 14–28 days had no effect on blood levels of total and/or free testosterone (T and fT) in trained men [To date, the scientific literature lacks sufficient reports on the use of DAA to promote hematological adaptations during altitude/hypoxic training in athletes. Hence, the present study aims to address this specific issue. Based on the above research results and theoretical underpinnings, this study investigated the following hypotheses: (1) DAA supplementation of 6 g/day would contribute to an increase in the blood concentration of LH, free testosterone (fT), and T in the participants; and (2) DAA supplementation during the LH–TL protocol results in a greater increase in the changes in hematological variables induced by hypoxic exposure.