Why High Temperatures Make Us Feel Tired and Uncomfortable: A Scientific Explanation

  The world has entered a heat wave mode, with many areas approaching or exceeding 40°C at every turn, and this may happen every year in the next few years.
  The serious consequences of high temperature are to induce cardiovascular and cerebrovascular diseases and heat stroke, and cause death. However, the general impact of high temperature is to make people tired, upset, not thinking about food and drink, and reduce work efficiency.
  The core temperature (rectal temperature) of the human body is 36.5°C to 37.7°C. Once the ambient temperature rises and the core temperature of the human body deviates from the normal range, a temperature regulator called the hypothalamus at the bottom of the brain will sense and analyze the skin, muscles and other The organ’s temperature sensor provides temperature information, which then activates the thermostat to either heat up or cool down.
  The domestic definition is that a high temperature is defined as when the daily maximum temperature reaches or exceeds 35°C. When the ambient temperature reaches 35°C, the human body begins to sweat to dissipate heat and lower the body temperature. At 36°C, the body will sound the alarm, sweat a lot, metabolize some sodium, vitamins and other minerals, and the blood volume will also decrease. When heat stroke occurs at 38°C, the heart, lungs, kidneys and other organs will participate in cooling the body, and it is difficult to maintain normal body temperature through perspiration. People will pant rapidly, exhale heat, and the heartbeat will speed up, outputting 60% more blood than usual to the body surface for heat dissipation. , people with weak constitution may suffer from heatstroke. At 39℃, human sweat glands fail; at 40℃, people feel dizzy.
  As the ambient temperature rises step by step, the human body will mobilize all physiological functions to cool down. At this time, a whole-body movement that people are not aware of begins, that is, the resting metabolic rate (RMR) increases. A latest study by a research team from the University of Roehampton in the United Kingdom shows that humans have an environmental upper critical temperature (UCT), which is 40°C to 50°C. At this heat, the resting metabolic rate will increase. Resting metabolic rate is the energy consumed to maintain basic physiological functions such as heartbeat and breathing in a quiet state. It accounts for 60% to 75% of the total energy consumption of the human body, which is the minimum energy consumed in a resting state.

  New research shows that at 40°C and 25% humidity, the body’s metabolic rate increases by an average of 35% compared to baseline (normal levels). At 50°C and 50% humidity, the human body’s core temperature rises by an average of 1°C, metabolic rate increases by 48% compared to baseline, and heart rate increases by 64%. However, when a person’s resting metabolic rate increases, it is difficult to notice it.
  When temperatures rise, the body typically activates two main mechanisms to regulate core temperature, sweating and increasing blood flow from internal organs to the skin. Blood flows to the surface of the skin in order to increase perspiration and heat dissipation. This process of course requires energy, and the heart rate will inevitably increase. This results in two effects. One is feeling uncomfortable, nervous and upset. Arrhythmias are often uncomfortable, but increases and decreases in heart rate can also cause discomfort. Increased heart rate indicates an imbalance of the sympathetic and vagal nerves, that is, increased sympathetic nerve activity and decreased parasympathetic nerve activity. Sympathetic nerve function dominates, causing vasoconstriction, increased blood pressure, bronchiectasis, and slowed gastrointestinal peristalsis (sympathetic nerves mainly inhibit the gastrointestinal tract) effect).
  The second is fatigue. The resting metabolic rate increases in high temperature environments. Even if people are not working, sitting in the shade, on the beach or anywhere, or even lying down, they will feel more tired than when the temperature is comfortable. In other words, the hotter the environment, the harder the human body has to work to maintain basic functions, which naturally makes people feel tired and uncomfortable.
  High temperature will affect the structure of DNA and proteins and the integrity of cell membranes. At the same time, high temperature dehydration will also cause electrolyte imbalance, which will seriously interfere with the transmission of information between brain neurons and between neurons and muscles, causing emotional changes such as anxiety and headaches. , judgment and cognitive impairment, and the longer it lasts, the more serious the consequences may be.
  Discomfort and discomfort during high temperatures may also be caused by hyperventilation of the lungs. One of the ways the brain temperature center cools down is through the respiratory system. Under high temperatures, breathing faster and deeper can lower body temperature. However, due to the increase in the amount of exhaled carbon dioxide, the pH of the blood will also increase, which may cause respiratory alkalosis in severe cases. People may experience numbness or a pinprick-like sensation in their hands, feet, face, especially around the mouth, followed by symptoms such as chest tightness, chest pain, dizziness, fear, and even twitching of limbs.
  Getting through the hot summer days requires a multi-faceted effort. For individuals, the answer is to drink plenty of water, get enough salt and electrolytes, and stay away from the heat. For office workers, managers need to strictly implement labor hygiene regulations and take various health care and protective measures for workers under high temperatures.