Normobaric intermittent hypoxia (NIH) training is a form of training that involves the individual breathing air with reduced oxygen levels for short periods of time, followed by normal air. This is typically done through a mask or in a hypoxia chamber.The term "normobaric" refers to the fact that the individual is breathing air at a normal atmospheric pressure, unlike in hypobaric hypoxia where the individual is exposed to low pressure at high altitude. NIH training is thought to mimic the physiological effects of high altitude training, such as increased production of red blood cells and improved oxygen delivery to the muscles. It has been studied as a potential therapy for conditions such as sleep apnea, chronic obstructive pulmonary disease (COPD), and even cognitive decline.

However, more research is needed to fully understand the benefits and potential risks of NIH training, as well as the optimal protocol for administering it. It should only be performed under the guidance of a trained professional.

Intermittent hypoxic training (IHT) involves alternating periods of hypoxia (reduced oxygen levels) with periods of normoxia (normal oxygen levels), hypercapnia (elevated carbon dioxide levels), or hyperoxia (increased oxygen levels). The specific IHT protocols used in research studies vary in terms of the duration of the cycles, the number of hypoxic episodes, and the number of training days. Some protocols involve short episodes of hypoxia (1-10 minutes) interspersed with brief periods of normoxia (1-20 minutes) in a single day, while others entail longer daily exposures (1-12 hours) for periods ranging from 2 to 90 days. Some researchers differentiate between periodic and intermittent hypoxia based on the duration of the hypoxic episodes. Periodic hypoxia involves longer sessions (20-30 minutes to several hours) that occur daily or every other day, whereas intermittent hypoxia involves shorter episodes (5-10 minutes) but with a higher frequency of sessions (5-30 cycles). An example of periodic hypoxia is hypoxic pre- and post-conditioning, where severe episodes of hypoxia are repeated 3-6 times spaced at 24-hour intervals, and such periodic hypoxia precedes (preconditioning) or follows (postconditioning) severe injurious exposure. In contrast, IHT with short but more frequent episodes of hypoxia results in progressive adaptation of major functional systems in the body to hypoxia. In a well-established model, pre- and postconditioning involve three trials of hypobaric hypoxia (equivalent to 5 km altitude) lasting 2 hours each, spaced at 24-hour intervals, which effectively protects the brain from post-hypoxic or stress-related injury by mobilizing pro-adaptive gene-dependent responses.

There are various statistics related to Normobaric Intermittent hypoxia (NIH) training that have been reported in research studies, including:

1. NIH training has been shown to increase the production of red blood cells, which can improve oxygen delivery to the muscles. For example, one study found that 21 days of NIH training resulted in a 6.6% increase in red blood cell count in healthy young men (Boutellier et al., 1992).
2. NIH training has also been studied as a potential therapy for conditions such as sleep apnea and chronic obstructive pulmonary disease (COPD). For example, a systematic review of 10 randomized controlled trials found that NIH training improved various sleep-related outcomes in patients with obstructive sleep apnea (Zhang et al., 2019).
3. Some studies have investigated the optimal protocol for NIH training. For example, one study found that a protocol involving 10 cycles of 5 minutes of hypoxia followed by 5 minutes of normoxia, repeated twice daily for 10 days, resulted in significant improvements in exercise performance in healthy young men (Kon et al., 2017).
4. NIH training has also been studied for its potential cognitive benefits. For example, a randomized controlled trial found that 12 weeks of NIH training resulted in significant improvements in cognitive function in older adults with mild cognitive impairment (Liu et al., 2016).

The history of hypoxic training can be traced back to the 1940s and 1950s, when Soviet researchers began experimenting with hypoxic environments to improve athletic performance. In the 1960s, the Soviets introduced intermittent hypoxic training (IHT), which involved exposing athletes to short periods of low-oxygen conditions interspersed with periods of normal oxygen levels.

The use of IHT quickly spread beyond the Soviet Union, with athletes in other countries adopting the technique in the hopes of improving their own performance. Over time, IHT became increasingly popular as a training tool for athletes across a variety of sports.

In the 1990s, scientists began exploring the potential health benefits of IHT, leading to the development of the normobaric intermittent hypoxia (NIH) protocol. NIH involves exposing individuals to short periods of low-oxygen conditions while maintaining normal atmospheric pressure. This makes the technique more accessible and safer than other hypoxic training methods that involve exposure to high altitudes or the use of hypobaric chambers.

Research into the effects of NIH training on health is ongoing, but early studies suggest that it may have a range of potential benefits. These include improving cardiovascular and metabolic function, enhancing exercise performance, and even potentially reducing the risk of certain chronic diseases.

While the use of NIH training remains controversial in some circles due to concerns about safety and efficacy, the growing body of research suggests that it may hold promise as a therapeutic tool for a variety of health conditions.