You’ve likely experienced a hot day working in the heat. You’re hot, thirsty, tired, and sweaty, and the work that you’re used to doing feels even harder. But why?
Your body wants to maintain a really tight temperature range: ~3-4°F or 2-3°C. But even increasing your body temperature by 1-2°F can have a big impact on your body’s physiological responses. Your body temperature goes up when you are accumulating heat faster than you can get rid of it.
You can accumulate heat from the environment, like when it’s really hot and humid outside, or when you’re exercising or working really hard in the heat. When you’re working or exercising, your muscles produce heat as a byproduct of the movements you’re doing. In response to this increase in heat production, we increase blood flow to the skin (to move heat from the body core to the skin) and start sweating to get rid of body heat.
However, if you’re producing heat faster than you can get rid of it, your body temperature will go up. As your body temperature gets higher, you will sweat more too in order to try to get rid of more heat. The hitch is that the sweat must be evaporating off of you to cool you down and reduce your core body temperature (i.e. dripping sweat doesn’t cool you down). As you’re sweating more, you’re losing more body water.
Your blood is made up of ~50% water, and so when you lose this water through sweating, your blood volume goes down. This is a problem because you need blood to go to the working muscles in your body for energy. Your blood carries oxygen, which is essential for your muscles to create the energy they need to keep working. This also means that you have less blood going to the skin to get rid of heat. As a result, your heart (which pumps the blood) has to work even harder to get the same amount of blood to your working muscles and to the skin. This means that your heart rate will be higher when working in the heat vs. working in a comfortable environment.
The loss of water (and therefore blood volume) through sweating is one of the reasons staying hydrated is so important. By replacing the fluids you’re losing through sweating, you can help your heart rate to stay lower during your work in the heat. In turn, this will allow you to work harder in the heat--simply by staying hydrated.
If you’re not staying hydrated on the job, not only will you have a higher heart rate, but you will feel more fatigued, and are more likely to be in a bad mood (frustrated, angry, etc), and you might also experience some “fogginess” in your thinking. So make sure that you’re taking frequent breaks, drinking plenty of fluids, avoiding alcohol, and eating healthy foods.
Most importantly, if you start to experience any of the signs and symptoms of heat injury or illness, be sure to stop working right away and take a break. These are early warning signs that your temperature is getting too high and you need to slow down and take a break. Remember that heat illness can lead to exertional heat stroke and even death. Take any signs and symptoms seriously.
Monitoring your heart rate with smart PPE or a chest strap can help you to know if you might be dehydrated, because your heart rate will be higher than normal for the same workload. Make sure that you are staying aware of how you’re feeling throughout the day, and have a buddy to check in with and talk to so that you can make sure you are both doing okay on really hot, humid days.
Drink plenty of fluids, stay cool, and pay attention to your body and any warning signs it might be giving you to stay safe in the heat.