Avoiding Exercise Due to Heat Creates a Body Vulnerable to Heatstroke. This Summer, Build Heat Resilience with Indoor Hypoxic Training at 'High Altli'

High Altitude Management Co., Ltd. (Headquarters: Chuo City, Tokyo; CEO: Rena Tsuboi), operator of Japan’s first*1 high-altitude training studio™ 'High Altli,' is promoting the use of indoor hypoxic training as a solution for building heat resilience (heat acclimatization) while avoiding the dangers of exercising under direct sunlight during the peak summer heat season, when heatstroke warnings are frequently issued. Despite being in a cool, air-conditioned indoor environment, the studio simulates a high-altitude environment equivalent to 2,500 meters above sea level, enabling significant increases in heart rate and sweating even with low-intensity, short-duration workouts. This makes it an emerging 'new summer training habit' that helps prevent heatstroke risks while combating summer inactivity and physical decline.

Heatstroke Prevention This Summer: Try High-Altitude Training for Heat Acclimatization

Background: Avoiding Exercise Due to Heat Creates a Body Vulnerable to Heatstroke

The Ministry of the Environment advises that physical activity should be suspended when the heat index (WBGT) reaches 31 or higher (Source: Ministry of the Environment Heatstroke Prevention Information Site https://www.wbgt.env.go.jp/). On days when heatstroke alerts are issued, it is unsafe to conduct outdoor running or sports activities. In reality, during summer, many people say, “It’s too hot to run,” “My training volume has dropped,” or “I’ve stopped exercising altogether.”

On the other hand, experts emphasize that to prevent heatstroke and heat discomfort (a general term for heat-related health issues caused by heat accumulation in the body), it is crucial to regularly exercise and sweat, thereby acclimatizing the body to heat—a process known as “heat acclimatization.” According to a Daikin Industries survey (March 2025), over half of Japanese adults aged 20 and above experienced heat-related health issues during the summer of 2024, and it is known that heat acclimatization requires about two weeks of consistent exercise (Source: Daikin Industries “Everyone Avoid Heat Discomfort This Summer PROJECT” https://www.daikin.co.jp/air/life/heat_project).

In other words, “Exercising in extreme heat is dangerous, but stopping exercise altogether makes the body even more vulnerable to heat.” The solution to this summer dilemma is hypoxic training indoors—building a body capable of sweating, even in a cool environment.

High Altli Benefits: https://high-alti.jp/about/

*Based on internal research (as of July 2026, web survey)

Inside High Altli’s Hypoxic Training Session

What Is Hypoxic Training? Achieving High-Altitude-Level Stress Indoors, Even in a Cool Environment

High Altli’s studio recreates a high-altitude environment equivalent to 2,500 meters by reducing indoor oxygen concentration (using normobaric hypoxia technology).

- Train safely without heatstroke risk in a cool, air-conditioned indoor space - Even low-intensity walking for about 30 minutes in a hypoxic environment increases heart rate, delivering exercise benefits equivalent to several times that of sea level (efficient time-saving training) - Sweating effectively leads to heat acclimatization—building a body resilient to heat - Expect similar benefits to athlete-style high-altitude training, including improved endurance, cardiovascular function (VO2max), and basal metabolic rate

Why Does Sweating Occur in a Cool Room? The Science Behind Hypoxic Training

The air in the hypoxic room is maintained at an oxygen concentration lower than the typical 21% at sea level, reducing the amount of oxygen inhaled per breath. To deliver sufficient oxygen to muscles, the body naturally increases heart and breathing rates, even during light walking at the same pace. In other words, even though physical movement is gentle, the body internally experiences a state similar to “moderately strenuous exercise.”

When heart rate increases and overall metabolism rises, internal heat production increases, raising core body temperature. The body then activates its cooling mechanism—sweating. This explains why participants sweat profusely within minutes, even while simply walking in a cool indoor environment.

What heat acclimatization requires is not “being in a hot environment,” but repeatedly raising core body temperature through exercise and experiencing sweating. Hypoxic training provides the internal physiological stimuli needed for heat acclimatization—increased heart rate and sweating—without exposing the body to external heat stress (and heatstroke risk) like direct sunlight. It allows individuals to safely achieve the Ministry of the Environment’s recommended “slightly strenuous, sweat-inducing exercise for 30 minutes a day,” even during the hottest days of summer.

For runners aiming to build mileage ahead of autumn marathons, this serves as an effective alternative training method during summer months when outdoor running is limited due to extreme heat.

Public Data and Research Supporting This Approach (Evidence)

1. Continuous “sweat-inducing exercise” is effective for heat acclimatization (Ministry of the Environment)

The Ministry of the Environment’s heatstroke prevention website recommends “continuously performing moderately intense exercise that feels slightly strenuous for about 30 minutes a day in a slightly warm environment” as a method for heat acclimatization, noting that the body adapts to heat within several days to two weeks. As heat acclimatization progresses, sweat volume increases, sweat salt concentration decreases, and skin blood flow improves, enhancing the body’s temperature regulation capacity. (Source: Ministry of the Environment Heatstroke Prevention Information Site https://www.wbgt.env.go.jp/)

2. Sweating function declines with aging and lack of exercise (Insights from thermophysiology)

Dr. Yoshimitsu Inoue (Professor Emeritus, Osaka International University; Supervising Expert for Daikin’s “Everyone Avoid Heat Discomfort This Summer PROJECT”), a leading expert in thermophysiology and sweat research, points out that heat dissipation functions such as sweating vary based on age and exercise habits, and that regularly sweating through exercise contributes to building a heat-resilient body. (Source: Daikin Industries “Everyone Avoid Heat Discomfort This Summer PROJECT” https://www.daikin.co.jp/air/life/heat_project)

3. Exercise in hypoxic environments increases physiological load even at low intensity (Japan Sports Association and others)

The Japan Sports Association’s “Sports Medicine and Science Guidelines” categorizes high-altitude training, including the use of hypoxic facilities, as a training method expected to improve oxygen transport capacity and aerobic performance. In normobaric hypoxic environments, heart rate and ventilation increase more easily even at the same pace as sea level, allowing low-intensity, short-duration walking to achieve the necessary load for “sweat-inducing exercise.” (Source: Japan Sports Association “Sports Medicine and Science Guidelines 7: Use of Hypoxic Facilities” https://www.japan-sports.or.jp/Portals/0/data0/publish/pdf/guide7o.pdf)

4. Over Half Experience Heat-Related Health Issues in Summer (Daikin Survey, March 2025)

Over half of Japanese adults aged 20 and above reported experiencing heat-related health issues (heat discomfort) during summer 2024. (Source: Daikin Industries survey, March 2025 https://www.daikin.co.jp/air/life/heat_project)

Member Feedback and Results

According to our member survey, approximately 93% reported experiencing the benefits of hypoxic training.

Actual member testimonials include (from 2025 member survey):

"Thanks to air conditioning, I can train without worrying about heat or cold. I don’t have to worry about excessive sun exposure or dehydration during summer." (Male, 40s)