Your Heart Pumps an Entire Swimming Pool of Blood Every Week

Your heart is one of the hardest-working muscles in your body, and it never takes a break.

Even while you sleep, it continues pumping blood to deliver oxygen, nutrients, and perhaps most importantly during exercise, move heat away from your working muscles.

The numbers are remarkable.

An average adult heart beats roughly 100,000 times every day and pumps around 2,000 gallons (7,500 liters) of blood daily.¹ Over the course of a week, that is enough blood to fill a small backyard swimming pool.

As soon as you begin exercising, your heart works even harder. Not just to supply your muscles with oxygen, but to help keep your body from overheating.

Heart Tissue and Vascular System

Why Your Heart Has to Work So Hard

Most people think the heart's primary job during exercise is delivering oxygen.

That is certainly important, but there is another job happening at the same time.

As your muscles contract, they become surprisingly inefficient. Roughly 75 to 80% of the energy they use is converted into heat rather than movement.²

If that heat stayed trapped inside your body, your core temperature would climb rapidly.

Instead, your cardiovascular system acts like a cooling network.

Blood absorbs heat from your working muscles and transports it toward your skin, where that heat can escape into the surrounding air. As sweating begins, evaporation removes even more heat from your body.³

Without this constant circulation, your body's natural cooling system simply would not work.

Exercise Changes Everything

At rest, your heart pumps about 5 liters of blood every minute.⁴

During intense exercise, that number can increase to 20 to 25 liters per minute in healthy adults and over 35 liters per minute in elite endurance athletes.⁴

That means your heart may pump five to seven times more blood every minute than it does while sitting on the couch.

A large portion of this increased blood flow is directed toward the skin to help remove heat while the rest continues supplying your muscles with oxygen and nutrients.⁵

Your heart is constantly balancing these competing demands to keep you performing safely.

What Happens When You Become Dehydrated?

Sweating is incredibly effective for cooling, but every drop of sweat comes from your blood.

As you lose fluid, your blood volume begins to decrease.⁶

With less circulating blood available, your heart has to beat faster to deliver the same amount of oxygen and maintain blood pressure.⁶ At the same time, less blood can be sent to the skin, making it harder to remove heat.

The result is a chain reaction:

• Heart rate increases.

• Core temperature rises more quickly.

• Exercise feels harder.

• Performance begins to decline.

Even relatively small levels of dehydration can reduce endurance performance and increase cardiovascular strain, particularly in hot environments.⁷

Keeping Your Internal Cooling System Running

Your heart, blood vessels, and sweat glands work together as one highly efficient cooling system.

To keep that system functioning at its best, you need enough fluid to maintain blood volume and enough electrolytes, especially sodium, to replace what is lost through sweat.

Proper hydration helps support:

• Blood volume

• Skin blood flow

• Sweat production

• Heat removal

• Cardiovascular performance

Your heart is already doing an incredible amount of work every day. Giving it the fluid and electrolytes it needs allows your body's cooling system to keep doing its job when temperatures and intensity rise.

Sources

1. Hall JE. Guyton and Hall Textbook of Medical Physiology. 15th ed. Elsevier; 2024.

2. Powers SK, Howley ET. Exercise Physiology: Theory and Application to Fitness and Performance. 11th ed. McGraw Hill; 2023.

3. Sawka MN, Leon LR, Montain SJ, Sonna LA. Integrated physiological mechanisms of exercise performance, adaptation, and maladaptation to heat stress. Comprehensive Physiology. 2011;1(4):1883-1928.

4. Joyner MJ, Coyle EF. Endurance exercise performance: the physiology of champions. Journal of Physiology. 2008;586(1):35-44.

5. Charkoudian N. Skin blood flow in adult human thermoregulation. Comprehensive Physiology. 2016;6(3):1301-1340.

6. Cheuvront SN, Kenefick RW. Dehydration: physiology, assessment, and performance effects. Comprehensive Physiology. 2014;4(1):257-285.

7. American College of Sports Medicine. Exercise and Fluid Replacement. Medicine & Science in Sports & Exercise. 2007;39(2):377-390.