# Simulated Altitude Training and Sport Performance: Protocols and Physiological Effects
## 3 Discussion
### Training Duration and Athlete Proficiency in HIIT  
Studies investigating high-intensity interval training (HIIT) in a hypoxic environment have shown that oxygen concentrations ranging from 14% to 15.3% can lead to improvements in both aerobic and anaerobic performance. Additionally, intermittent high-intensity hypoxia interval training (HHIT) has demonstrated various internal benefits, including enhanced cardiorespiratory endurance, increased maximal oxygen intake, improved power output, and adaptation of hematological variables to hypoxic conditions commonly experienced during plateau competitions and challenging situations faced by athletes dealing with performance stagnation. However, it is important to note that there exists inconsistency between the performance benefits and factors such as athlete proficiency, duration of hypoxia exposure training, and oxygen concentrations. In a 4-week HIIT program with a reduced oxygen concentration of 14.6% (FiO\({}_{2}\) = 14.6%), trained cyclist athletes showed significant changes in hematological variables. These changes included increased VO\({}_{2}\)max, higher frequency of interval training, molecular adaptations, improved blood perfusion in crucial muscle groups, and notable enhancements in blood perfusion within major muscle groups [19]. Similar findings were observed in a study by [PERSON] et al. [48], which involved long-distance athletes but at lower oxygen concentrations. Their research demonstrated that up to 4 weeks of training led to increased VO\({}_{2}\)max and alterations in hematological variables. However, studies have shown that physiological adaptations and performance changes resulting from intermittent hypoxia training beyond four weeks can vary. Another study conducted by [PERSON] et al. [30] involved a 7-week simulated hypoxia training at an altitude of 3000 m with an oxygen concentration of 14.6% in the HIIT group. Surprisingly, no clear trend of improvement in VO\({}_{2}\)max was observed for triathletes and cyclists. However, significant enhancements in VO\({}_{2}\)max were evident only during intermittent training periods when the recovery intervals were exposed to hypoxic conditions. Moreover, there were no significant differences in VO\({}_{2}\)max between the intermittent training group in the hypoxia chamber and the control group. Therefore, further research is necessary to clarify and establish appropriate hypoxia interval training protocols tailored to dedicated athletes, considering the specific characteristics of the training subjects and the duration of training [29]. In terms of athlete proficiency, several studies have examined the effects of hypoxia high-intensity interval training (HHIT) on different groups of participants. In one study, basketball players training at a 15% hypoxia concentration and a simulated altitude of 2500 m experienced a significant 7.8% increase in VO\({}_{2}\)max and a notable decrease in Delta-lactic acid after 3 weeks of HHIT. However, no significant changes in relevant hematological variables were observed during the intermittent hypoxia intervals [29]. Another study focused on repeated sprint training as part of hypoxia HHIT, involving 50 professionally trained cyclists randomly assigned to different groups. The groups included a normoxia group at sea level (485 m altitude), a hypoxia group at 3000 m altitude, and a control group without interval training but exposed to hypoxia. The results revealed that the hypoxia group showed greater improvements in sports-specific performance, significant molecular adaptations, and increased blood perfusion within the active muscles when compared to the sea level group [19]. In a study involving long-distance athletes with a mean age of 18.9 years, aerobic and anaerobic exercise performance and physiological parameters during HHIT were investigated. Participants were randomly assigned to a normoxia group (FiO\({}_{2}\) = 20%) and a hypoxia group (FiO\({}_{2}\) = 15.4%) to perform three sets of HIIT sessions over a 2-week period.