How Inactivity Affects Human Body Systems

Instructor: Joanne Abramson

Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.

Physical inactivity affects you inside and out from head to toe. This lesson discusses how a lack of exercise can lead to a variety of physical disorders in many of your body systems.

Activity Is Important!

Are you getting your daily physical activity? The American Heart Association recommends 30 minutes a day five days a week. I'm sure you know that exercise is great for weight loss and keeping your muscles strong, but did you know that is also keeps the rest of your body systems in top shape, too?

A lack of physical activity has a profound effect not just on your external physique, but also on your internal health. All of your organ systems, from your cardiovascular system, to your gastrointestinal system quickly start to falter when you slack off on your exercise. So stop making excuses and lace up your running shoes! Your body can't wait!

Musculo-Skeletal System

As the name suggests, your musculo-skeletal system includes your muscles and bones, which work together to get your body moving. Your body must expend a lot of energy to maintain your muscles, so if you aren't using a particular muscle group enough, your body quickly gets the message that you don't need it, and the muscle group starts to break down. This break down of muscle tissue is referred to as muscle atrophy, and the resulting weakness makes it harder to complete everyday tasks like cleaning or cooking.

A diagram of muscle atrophy.  caption=

Similarly, your bones are constantly being broken down and rebuilt. Your body gets rid of old bone cells, replacing them with new ones so that they can be as strong as possible. If your bones aren't moving around or supporting weight, then they are broken down at faster rate than they are rebuilt. This is called osteoporosis, and it makes your bones weak, brittle and easy to break.

Cardiovascular System

Your cardiovascular system includes your heart, lungs, and blood vessels. This system is responsible for getting blood and oxygen to all parts of your body. Your heart is a muscle, and like other muscles in your body, it starts to atrophy if you don't exercise. A weak heart means that it is harder to get oxygen to your cells and you start to feel more tired overall.

Additionally, without physical activity, your blood vessels become thicker and less flexible, while your blood becomes stickier. This dangerous combination increases your risk for a blood clot, a semi-solid mass of collected blood cells that can block a blood vessel. Blood clots are deadly if they occur in your heart (heart attack) or brain (stroke).

Physical inactivity increases your risk for blood clots. If a blood clot blocks a blood vessel in your heart or brain it can be deadly.
Digram of a blod clot.

Endocrine System

Your endocrine system regulates your body's hormones. One well-known hormone in particular is influenced by exercise. Insulin regulates the amount of sugar in your blood stream, preventing your blood sugar levels from either getting too high or too low. Insulin binds to cells so that the cells can absorb sugar from the blood and use it for energy. A lack of physical activity means that your muscle cells don't use insulin as much, and the binding sites for it start to disappear. As a result, your body becomes less responsive to the hormone. This can lead to type 2 diabetes, when your body stops responding to insulin completely.

Insulin binds to a receptor on a muscle cell so that the cell can use sugar for energy. Physical inactivity causes the muscle cells to loose receptors and the body becomes resistant to insulin.
Diagram of an insulin receptor on a muscle cell.

Have you ever noticed that you sleep better after you exercise? This is partly because working out enhances your body's circadian rhythm, or natural cycle of sleepiness and wakefulness. Part of your circadian rhythm involves body temperature. Inactivity corresponds with a lower daytime body temperature, which interferes with the natural release of hormones that make you sleepy. This in turn disrupts your sleep cycle and can lead to sleep disorders.

Nervous System

Your nervous system includes your brain and spinal cord and is the control center for the rest of your body. Like the other systems we've discussed so far, if you aren't using it, you're losing it. Many studies have shown that if you are not physically active you are at a greater risk for cognitive decline and dementia as you age.

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