Heat acclimation measures in spotlight as summer weather approaches Japan

The Mainichi

12-05-2025

TOKYO -- "Summer days," with high temperatures reaching 25 degrees Celsius or above are forecast over a wide area of Japan from May 13, drawing attention to acclimation measures such as exercise and bathing to help the body sweat and prevent heatstroke.
The Japan Meteorological Agency forecasts cloudy or rainy weather from northeast Japan's Tohoku region to the Kinki region in the west on May 12. From May 13 onward, however, clear skies are expected nationwide, with maximum temperatures reaching around 25 C in many areas excluding Hokkaido. In some regions, highs may even approach 30 C.
Heatstroke occurs when the body fails to regulate its temperature effectively and retains heat, leading to symptoms such as dizziness, lightheadedness, nausea and cramps in the limbs. In severe cases, it can cause impaired consciousness or even death. Since 2010, there have been years in which Japan's annual heatstroke death toll exceeded 1,500. Preventive measures include spending time in cool places, hydrating and taking in salts.
In recent years, heat acclimation measures have garnered attention for heatstroke prevention. Before the full onset of summer, engaging in manageable levels of exercise or bathing to induce sweating can help the body adapt to the heat.
According to the Japan Weather Association, successful heat acclimation makes it easier to sweat and reduces the likelihood of heat retention in the body. As it can take anywhere from a few days to about two weeks to get used to the heat, it is recommended to start this practice by around late May.
Specific activities include 15 minutes of jogging or 30 minutes of walking (five times a week); 30 minutes of moderate exercise such as muscle training or stretching (five times a week); 30 minutes of cycling (three times a week); and bathing in a tub rather than just showering (about three times a week).
However, it is crucial not to overdo it. If efforts to acclimate to the heat result in heatstroke, it defeats the purpose. The Tokyo Metropolitan Government urges individuals to "engage in these activities within a comfortable range, considering personal physical conditions and the day's temperature and environment."