With summer in full swing, it’s essential to recognize that a sweltering heat index can pose unique health challenges, especially during physical activity. Our body’s internal mechanisms strive to maintain equilibrium, but extreme heat and humid weather can complicate this delicate balance. During this time of year, working out in high temperatures can significantly strain the body.

In this blog post, we’re going to talk about:

• body temperature regulation and thermic balance
• cardiovascular changes that take place when training in the heat
• proper hydration during workouts in higher temperatures
• tips for safe summertime training

Regulating Body Temperature

The human body is in a constant state of thermoregulation, meaning it must maintain an internal temperature within a narrow range in order to function properly.

Thermoregulation is a crucial physiological process that ensures an optimal and stable core temperature typically around 98.6°F (37°C), irrespective of external conditions.

Thermic balance refers to the equilibrium that the human body maintains between heat production and heat loss.

During high-temperature workouts, the thermic balance of the body is put under stress. Heat production spikes due to increased muscle activity. At the same time, high ambient temperatures make heat loss more challenging, causing the body’s thermoregulation responses to be insufficient and potentially leading to dangerous overheating.

Cardiovascular Response to Heat Stress

Physical training in hot conditions is taxing on the cardiovascular system. As part of the thermoregulation process, the heart rate increases and blood vessels to the skin dilate in an attempt to dissipate heat into the cooler surrounding environment.

However, this diverts blood flow away from the muscles and internal organs, reducing the amount of oxygen and nutrients they receive. This cardiovascular strain can lead to an increased risk of heat-related illnesses, including heat exhaustion and heat stroke.

In extreme conditions, the body might also experience a decrease in blood volume due to excessive sweating which greatly increases the risk of dehydration.

Cardiac drift is a phenomenon that occurs during prolonged exercise, especially on a hot summer day. It is characterized by a progressive increase in heart rate and a decrease in stroke volume (the amount of blood pumped out of the heart with each beat).

This happens despite maintaining a constant exercise intensity. Essentially, as the exercise continues and the body temperature rises, the heart needs to work extra hard to maintain blood flow to the muscles and cool the core body temperature. 

Understanding this concept is crucial for those who exercise in hot conditions, as it underscores the importance of modifying training intensity and ensuring adequate hydration to prevent excessive cardiovascular strain.

Dehydration

Dehydration poses significant risks, particularly during intense or prolonged exercise in hot and humid conditions. It occurs when the body loses more fluids through sweating than are replenished through drinking, leading to a state of fluid imbalance.

The initial symptoms of dehydration can include:

• thirst
• dry mouth
• fatigue
• dizziness 

If left untreated, severe dehydration can lead to alarming symptoms like severe muscle cramps, a rapid heart rate, sunken eyes, shriveled skin, low blood pressure, and in extreme cases, delirium or unconsciousness.

Dehydration can impair cardiovascular function, as it reduces the volume of blood in the body, forcing the heart to work harder to deliver oxygen and nutrients to the tissues. 

The state of dehydration also negatively impacts the body’s thermoregulation, increasing the risk of overheating.

Heat Exhaustion and Heat Stroke

Heat exhaustion and heat stroke are severe heat-related illnesses that can occur when the body becomes too hot. They represent the failures of thermoregulation and thermic balance to keep the body cool and are potentially life-threatening conditions that require immediate medical attention.

Heat exhaustion manifests through symptoms like:

• Heavy sweating
• Rapid pulse
• Dizziness
• Fatigue
• Nausea or vomiting
• Feeling faint or light-headed
• Cool, clammy, pale skin
• Muscle cramps

It’s very important to recognize these signs early, as heat exhaustion can progress to heat stroke if not promptly addressed.

Heat stroke is a more severe and immediate medical emergency. Symptoms may include:

• Hot, red, dry or damp skin
• Strong, rapid pulse
• Headache
• Dizziness
• Nausea
• Confusion
• Loss of consciousness

It’s critical to seek immediate medical attention if any of these symptoms are present as heat stroke can lead to serious complications such as organ damage or death.

Hydration Guidelines

Proper hydration is crucial to maintain thermic balance and cardiovascular health during hot weather workouts. Start by hydrating even before the exercise begins; aim to drink 16-20 ounces of water at least 4 hours before, and 8-12 ounces of water 10-15 minutes before starting your workout.

During the exercise, it’s recommended to consume 7-10 ounces of water every 10-20 minutes. For a one-hour training session in a hot environment, you would want to consume an entire 32 ounce water bottle.  

A Note About Sports Drinks

If you’re exercising for longer than one hour, especially during the heat of the day, consider a sports drink that contains electrolytes to replenish what is lost through sweating. Electrolytes play a vital role in maintaining homeostasis within the body. They help to regulate heart and neurological function, fluid balance, oxygen delivery, acid-base balance, and much more.

Sodium and potassium, two crucial electrolytes, help maintain fluid balance, nerve function, and muscle contractions. When these electrolytes are depleted, it can lead to muscle cramping, fatigue, nausea, and even more serious conditions like heat stroke (see above).

The sodium in sports drinks helps to promote thirst and encourage fluid intake, which can be beneficial in preventing dehydration. For workouts exceeding an hour, or for workouts in high heat and humidity, sports drinks can be an effective tool for hydration and energy supply, supporting both performance and recovery. 

My personal favorite hydration powder is LMNT. It is the perfect balance of electrolytes, easily mixes with water, no sugar added, and comes in a variety of flavors.

Replenishing electrolytes during prolonged exercise, especially in hot weather, is essential! Don’t leave it out of your regimen.

Practical Advice For Training on Hot Days

• Avoid the hottest part of the day: do your fitness training in the moderate temperatures of the early mornings or evenings. Exercising in the morning can help kickstart your metabolism and keep it elevated for hours. It can also serve as a mood booster, providing an energizing start to the day. On the other hand, evening workouts can be great stress relievers, helping to clear the mind after a busy day. 
• Wear loose-fitting clothes in light colors: Loose, breathable clothing allows for better ventilation, helping the body to cool more efficiently by promoting airflow and enabling sweat to evaporate. Clothing that will block UV rays is ideal.
• Increase the length of your warm-up: Increasing the length of your warm-up helps to prepare your body for additional heat stress. A gradual warm-up increases circulation, raises your heart rate progressively, and gets your muscles accustomed to the heat. It allows your body to start the sweating mechanism, which is crucial for cooling down during the exercise and primes your cardiovascular system for the forthcoming exertion. 
• Hydrate, hydrate, hydrate: before, during, and after your workout. Enough said.
• Take it easy: Decreasing the intensity of your workout during extreme temperatures is a sensible approach. High temperatures increase the body’s need for oxygen, which can make the heart work harder and raise your heart rate. Another thing to keep in mind is that the body’s primary focus in hot conditions is to cool itself down, which can compromise its ability to provide energy for a strenuous workout. So, you might experience early fatigue, decreased strength and speed, and slower reaction times. 

Summer is a wonderful time of year to stay active and enjoy the outdoors. However, awareness and precautions must be taken to ensure our physical exertion in hot conditions doesn’t put us at risk. Remember, the goal is to stay healthy, active, and safe!