When a muscle contracts, it develops tension and usually shortens, pulling on the bones or tissues it is attached to and creating movement or force. Inside the muscle cell, tiny protein filaments slide past each other so the whole fiber becomes shorter and thicker.
What “contracting” means
- Contraction means the muscle fibers generate force; they may shorten (like lifting a weight) or stay the same length (like holding a weight still).
- In most everyday movements, contraction causes the muscle to shorten and change the angle at a joint, such as bending the elbow when the biceps contracts.
What happens inside the muscle
- Within each muscle fiber, actin (thin) and myosin (thick) filaments slide past one another, making the basic unit (the sarcomere) shorter.
- This sliding is powered by ATP and controlled by calcium ions, which allow myosin to grab and pull on actin in repeated cycles.
