When you ask people how the weather affects their training, they might talk about when it is really hot or really cold or how they don’t like to run when it rains. Those are the obvious changes in the weather. But what about the more subtle forms of atmospheric change? How do factors such as atmospheric pressure, humidity, heat index, and dew point affect how you feel when you train and how your body recovers?
Let’s take a look some of the more overlooked atmospheric metrics and how they can affect how you train:
Atmospheric pressure (also known as barometric pressure) is the pressure exerted by the weight of the air in the atmosphere. Atmospheric pressure decreases proportionally to the increase in altitude – as you go higher, the pressure goes lower. Additionally, changes in weather are often preceded by a sudden change in pressure. Without getting too technical, typically a drop in pressure will bring wind, clouds, and the potential for precipitation; high pressure will bring light winds and sunny days.
So what does this have to do with your training?
Increases in atmospheric pressure also affect your body, not just the weather. As pressure increases, so does the felt pressure on your body. Your body responds to this pressure by sending signals to your brain that tell your brain that something hurts as a result of the increased pressure on your nerves. Joints that are prone to inflammation will now hurt more than usual due to the increased pressure.
Additionally, pressure on your vascular system can result in higher blood pressure and risk of blood vessel ruptures under strenuous exertion.
As a general rule, increased pressure will not make training more difficult. However, you may “feel it” more than other days and old injuries may make themselves known more readily. Also, if you have any issues with your heart or your circulatory system, days of high pressure are days in which you should take it easy.
Humidity is the amount of water vapor that is present in the air at a given time. The higher the humidity, the more “moist” the air feels. Humidity is a pretty well-known phenomenon, especially for those of you who live in the Midwest. However, humidity has a significant effect on your body when you are training.
During exercise you generate heat. As a result, your body cools itself by sweating—but only if sweat can evaporate. In humid weather, sweat evaporates more slowly, causing your body temperature to continue to rise since it is no longer able to cool down like normal. Additionally, dehydration from sweating decreases your blood volume. So while your heart is trying to pump blood to cool you off, it must also work harder to get blood to your working muscles. That’s why it is crucial to drink plenty of fluids before, during, and after exercise.
So how should you train when it is humid? While your training likely won’t need to change, you do need to be aware that you will be more dehydrated and your heart will be working harder. As a result, when the humidity goes up, so does your amount of fluid intake in order to promote heart health as well as proper recovery after the fact.
Extreme temperatures do have their own effects on your body when you’re training. Extreme heat will cause your body (specifically your heart) to work overtime in an attempt to keep your body temperature regulated. Much like with humidity, when the temperature gets too high, your body can no longer keep up. You become dehydrated, fatigued, and are subject to issues like muscle cramps and excessive sweating.
Extreme cold has its own set of problems though. While cold weather will allow the body to stay cool, extreme cold (below freezing) will cause the body to work harder in order to keep your body temperature warm enough. Additionally, when you are wearing layers of clothing for the cold, your body will sweat like normal since your core temp will be regulated by the clothing. This can lead to hypothermia if you are not careful about getting out of the cold immediately following exercise. Also, if you are at risk of heart disease, exercising in extreme cold can increase your risk of heart attack during exercise.
The key to exercising in extreme weather is to dress appropriately, keep hydrated, and get out of the heat or cold as quickly as possible following exercise. Ideally, you should wait until temps are more tolerable (early morning or late evening on hot days and mid-day on cold days) in order to minimize the effects of the extreme weather. Check the temperature before planning your exercise for the day in order to stay healthy and safe.
The heat index is the felt discomfort caused by the combination of heat and humidity. It is not a measurement like temperature or humidity but is instead a tool for measuring the collective effect of heat and humidity together. The higher the heat index, the more felt discomfort you will have while exercising and the greater the risk of heat-related illness and injury.
When the heat index rises over 90, it is best to reschedule your training to a different time of day when the heat index is lower. If this is not an option on some days, then be sure to dress appropriately to allow proper cooling of your body and drink plenty of liquid before, during, and after exercise. If the heat index is over 100, don’t exercise; it isn’t worth the risk. Make time later in the evening or earlier in the morning in order to avoid the potential hazards of exercising during such a high heat index. Obviously, exercising indoors is a great alternative when the heat index is high as well.
The dew point is the temperature at which dew forms. It is the temperature to which air must be cooled at constant pressure and water content to reach saturation. What does this mean for you? Whereas humidity is a relative term that can go up and down throughout the day, dew point is the measurement of how much moisture is actually in the air, therefore it is more consistent. This amount is represented in degrees because the dew point represents the temperature to which air must be cooled for condensation (dew or frost) to occur.
The closer the dew point is to the air temperature, the more saturated the air is and the less perspiration can evaporate and help the body cool itself. This will result in extra stress on the heart and lungs as the body attempts to cool itself… unsuccessfully.
What does this mean for training? Research has shown that for marathon runners, every 10 degree increase in dew point results in a 1.5-3% decrease in performance (more time to complete the same distance). This means that the closer the dew point gets to the actual temperature, the greater effect it will have on your performance in a negative direction.
Check the dew point before exercising outdoors. If it is over 60 degrees, expect training to be more difficult and adjust accordingly if necessary.
All of these factors exist every day. However, some days they will be more pronounced than others. When this is the case, be prepared that it will have a negative effect on your performance and will require you to be more mindful of fluid intake and exertion levels. Be smart, be informed, and make the most of whatever the weather decides to throw your way.
Another thing to keep in mind is that hunting require the same physical exertion as exercise. This means that you need to be mindful of what the atmosphere is doing while you are hunting as well so that you can be mindful of how to dress, eat, and hydrate in order to maintain peak performance in the backcountry.