Mitochondria are energy producing structures, which live in the cells of body tissues, organs and muscles. These amazing little structures need carbohydrates and oxygen to work properly. Since mitochondria are required for all bodily functions and movement, you definitely can't live without them. But your mitochondria levels drop when your heart isn't working at its full potential, and your oxygen levels are diminished due to lack of exercise. Fatigue occurs when energy production is slowed down and the body requires the same amount of energy to get work done.
Bones love a workout, almost as much as they love calcium. The lack of weight-bearing exercise causes bones to lose density and the ability to properly store calcium. Less calcium in your bones means more of a mineral build up in organs such as your kidneys, the cause of kidney stones. If the period of inactivity is long enough bones eventually began to weaken. This often times results in osteoporosis, which leads to a much higher risk of painful bone fractures. And ain’t nobody got time for that.
Just like bones, muscles benefit from a good workout. One of the first signs of being out of shape, due to inactivity, is loss of strength and muscle tone. When muscles are idle, blood flow slows down and the exchange of waste products and nutrients decreases. And less mitochondria results in lack of muscle coordination. Without exercise, the "electrical" connection between your nerves and muscles is sporadic - at best. How does this affect you? You'll typically find it more difficult to move around with the agility that you once could. It can also mean decreased strength and an increased risk of muscle injury because of the shrinking muscle mass.
Whatever your age, it's important to keep your heart as healthy as possible. Even though your heart muscle is different from your skeletal muscles, the same health-related principles apply. Without proper exercise, the heart muscle shrinks. This makes it difficult to adequately distribute blood throughout the body and causes the heart to work much harder to get the blood to where it actually needs to go, especially in your hands and feet. Sluggish blood flow can lead to a plaque formation in the blood vessels. This in turn, can causes high blood pressure, dizziness and circulation problems - all of which are potentially dangerous if left untreated.