Muscle fibers use two important proteins called actin and myosin to help our muscles move. This process is explained by something called the sliding filament theory. Let’s break it down!

1. What Are Actin and Myosin?

• Actin: These are tiny threads that are about 7 nanometers wide.
• Myosin: These are thicker threads, about 15 nanometers wide.

2. How Do Muscles Contract?

• When a muscle gets a signal to move, calcium ions attach to a protein called troponin.
• This makes another protein, tropomyosin, shift and show where the actin can connect.
• The heads of myosin grab onto the actin, create what’s called a “cross-bridge,” and pull the actin threads toward the middle of the muscle section, known as the sarcomere.
• Each time this pulling happens, it can shorten the sarcomere by about 1% to 3%.

3. How Do Muscles Get Energy?

• Muscles need a special kind of energy called ATP to contract.
• About 70% of the energy from nutrients goes into making more ATP using a process called oxidative phosphorylation.
• There are two types of muscle fibers:
  • Fast-twitch fibers: They make ATP quickly but get tired fast.
  • Slow-twitch fibers: They create ATP more slowly but can keep working for a longer time.

All these parts work together to help our muscles contract, which is very important for moving around and staying stable!