Muscles move our bodies. To do so, they contract, which then generates movement.
Muscles allow us to consciously move our limbs, jump in the air, and chew our food.
But they are also responsible for many more processes that we cannot actively control, such as keeping our hearts pumping, moving food through our guts, and even making us blush.
Our muscles need signals from our brains and energy from our food to contract and move.
To build new muscles through exercise, we make use of their remarkable ability to repair themselves when damaged.
Contraction gets muscles moving
There are two types of muscle: striated and smooth. The former have regular stripes, or striations, when observed under a microscope. These striations are due to the arrangement of muscle fibers, which form parallel lines.
The muscles that move our body parts are called skeletal muscles, and they are a type of striated muscle. We can actively control these with our brain. Another type of striated muscle are those that keep our hearts pumping, which we are unable to actively control.
Specific molecules within the muscle fibers allow striated muscles to contract rapidly, allowing us to move. The main players in this intricate process are molecules called actin and myosin.
Scientists continue to disagree on what allows actin and myosin work together to make an entire muscle contract. What is known, however, is that this process depends on energy generated from the food that we eat.
The contractions that smooth muscles produce tend to be more gradual than those produced by striated muscle. An example is the slow and controlled movement of food through the digestive system.
Smooth muscles do not have striations and we cannot actively control what they do.
Calcium stimulates contraction
The pathways that regulate contraction in striated and smooth muscles are very different. But they do have one thing in common: calcium is the key molecular messenger in the process.
Striated muscles receive their triggers from the brain via motor neurons. This results in calcium rushing into the muscle, allowing actin and myosin to spring into action.
Smooth muscle cells can be activated by neuronal signaling or by hormones. Both mechanisms lead to a change in calcium levels in the muscle cells. This leads to activation of myosin, and, in turn, muscle contraction.
Some smooth muscles are in a permanent state of contraction, and the muscles that line our blood vessels are in this category. A constant supply of calcium allows these muscles to regulate blood flow. For example, when the muscles that line the blood vessels in our face relax, we blush.
When we exercise, we damage our muscles. Afterward, stem cells repair the damage and the muscles get stronger.
New research led by George Washington University School of Medicine and Health Sciences in Washington, D.C. - published this week in the journal Science Signaling - challenges a common assumption about this process.
Cell generate reactive oxygen species (ROS) as a byproduct, especially when energy consumption is high, such as during exercise. ROS can be very toxic to cells and were, until now, thought to hinder muscle repair.
"It is still a common belief within the fitness community that taking antioxidant supplements after a workout will help your muscles recover better," explains lead study author Adam Horn.
But the team's research showed that muscles tightly control ROS levels after injury, and that ROS are essential for repair.
If you are among those who look to antioxidants to speed up muscle repair after your workout, it might be worth letting your muscles do their own thing.