How does muscle bend and straighten a joint?

Muscles work in pairs to bend and straighten joints. When a muscle contracts, it pulls on the bone that it is attached to, causing the joint to bend. When the muscle relaxes, the joint straightens.

For example, when you bend your elbow, the biceps muscle (located on the front of your upper arm) contracts and pulls on the forearm, causing the elbow to bend. When you straighten your elbow, the triceps muscle (located on the back of your upper arm) contracts and pulls on the forearm, causing the elbow to straighten.

Skeletal muscles are attached to bones by tendons, which are tough, fibrous cords of connective tissue. When a muscle contracts, it exerts a force on the tendon, which in turn pulls on the bone. The amount of force that a muscle can exert is determined by its size, the number of muscle fibers it contains, and the frequency of its contractions.

Most skeletal muscles are arranged in antagonistic pairs, with one muscle working to bend a joint and the other muscle working to straighten it. This arrangement allows for precise control of joint movement. For example, when you walk, your muscles must contract and relax in a coordinated fashion to allow you to take each step smoothly.