When the hot summer weather makes you feel tired, this feeling is not entirely an illusion: there are real biological reasons behind drowsiness. This month, the temperature soared, setting a record for the hottest on Earth, while also consuming people's physical energy. Exposure to hot environments can trigger a series of physiological processes in the heart, brain, skin, and muscles, leaving you physically and mentally exhausted. Fatigue is a way for the body to tell us it's time to rest. One way to reduce the impact of high temperatures is to reduce physical activity, "said Michael Wasfield, a sports cardiologist at the Massachusetts General Hospital's Baihan Medical Center in Boston, USA. She added that although people can adapt to extreme heat or cold weather to some extent, the body's heat resistance is usually not as good as its cold resistance. Extremely high body temperature can cause significant damage or failure to organs, and when the core body temperature is low, organ function may decrease, but it is easier to recover. The following is an explanation from doctors and scientists for the decrease in physical strength under the scorching sun: The numbers on the thermometer are important, but they cannot completely determine your body's response to heat. Humidity is also important. Sweat evaporates from the skin into the air, cooling you down. In a humid environment, cooling becomes more difficult when the air also becomes wetter. The thermal radiation from electromagnetic waves like sunlight can also have an impact. Even if the air temperature is low, you can still feel the impact of this thermal radiation. Another reason why people feel tired on scorching days is poor sleep. A study in 2022 showed that for every degree of temperature increase, people's sleep time decreases slightly. The main author of the study, Kelton Minner, said that when the outdoor temperature exceeds 10 degrees Celsius at night, for every 1 degree Celsius increase, people's average sleep time decreases by 37 seconds per night. The amount of water consumed can also affect a person's physical strength level. When you feel stuffy, sweating will lose more water, so you need to drink more water to avoid dehydration.