# Simulated Altitude Training and Sport Performance: Protocols and Physiological Effects
## 2 Hypoxia Environment Training Protocols
### Incremental Hypoxia Training  
In addition to the more common high-intensity hypoxia interval training, another protocol of hypoxia training is to gradually decrease oxygen concentration and increase exercise intensity. In a study related to oxygen concentration tapering training, [PERSON] et al. [1] investigated the effect of incremental hypoxia interval training on the aerobic capacity and endurance performance of cycling athletes. This training consisted of 3 weeks of intermittent hypoxia training, three times per week. Each session consisting of four sets of all-out 30 s sprint intervals, accompanied by a 90 s low-intensity recovery state, simulating an altitude of 2500-3000 m. Additionally, the \(\text{FIO}_{2}\) was adjusted as the number of training days decreased, from 17% on day 1 to 14% on day 10; the \(\text{SpO}_{2}\) value was controlled at 88% on days 1-2, 84% on days 3-4, and 82% on days 5-10. The \(\text{VO}_{2}\)max increased by 3.98% in the incremental hypoxia interval training group, and so did the lactate threshold, power output, and average speed, while no differences in hematological variables were found in the trained cyclists during the 3 weeks of incremental hypoxia training.  
In [PERSON] et al. [16]'s study of 10 sub-elite male short-distance sprint light-boat athletes who underwent 3 weeks of incremental hypoxia treatment, while being connected to the system via a face mask, the incremental hypoxia treatment used [PERSON] et al. [33]'s protocol. The incremental hypoxia concentration experiment followed a specific design, starting at 12% in the first week, reducing to 11% in the second week for 6-10 days, and reaching 10.9% in the third week. Pre- and post-tests were conducted, including an incremental step test to assess peak power, \(\text{VO}_{2}\)max, exercise economy, lactate threshold, average burst force over 500 m, and short-distance sprints of 5 \(\times\) 100 m. Throughout the experiment, intravenous blood samples were collected for analysis of hemoglobin concentration, hematocrit, ferritin, erythrocyte sedimentation rate, and white cell count. The findings demonstrated a 6.8% improvement in peak power, an 8.3% enhancement in mean repeat sprint power, and a 3.6% rise in hemoglobin concentration. However, no notable benefits were observed in lactate threshold, mean 500 m power, \(\text{VO}_{2}\)max, or exercise economy.  
In non-athletes, incremental hypoxia training was performed in the non-athletic progressive intensity study by [PERSON] et al. [34]. The first phase consisted of 30 min low-intensity continuous exercise (e.g., walking) at 60-70% of maximum HR; the second phase consisted of eight sets of 2 min high-intensity exercise with 1 min rest between sets at 85-95% of maximum HR. It was observed that in the hypoxia group of women with menopause, the endothelium-dependent vasodilation (FMD) increased from 4.4 \(\pm\) 1.8% to 6.4 \(\pm\) 2.0% after 10 days of hypoxia training, and the vasodilatory reactivity improved. The physiological benefits of hypobaric hypoxia training in postmenopausal women mainly involve improving the physiological parameters of FMD.  
Compared to high-intensity intermittent exercise in a hypoxia environment, progressive hypoxia exposure training can bring about changes and improvements in exercise performance, cardiorespiratory fitness, and anaerobic fitness; however, there are only few studies related to high-intensity intermittent and sub-intensity training. Therefore, if we consider the physiological adaptations associated with exercise, progressive intensity and hypoxia training protocols may provide the time needed to adapt to training, allowing the individual to adapt to physiological changes and bring about better athletic performance; however, more research is needed to further investigate the relevant training protocols.