When a Muscle Contraction Happens Why Does the Bone Move

When we think about movement in our body, we often focus on our muscles. After all, they are the primary movers of our body. But have you ever wondered why our bones move when our muscles contract? In this article, we’ll explore the science behind muscle contractions and bone movement.

Muscle Contractions

To understand why bones move when muscles contract, we first need to understand how muscle contractions work. A muscle contraction occurs when the muscle fibers in our body shorten and generate tension. This tension is what creates movement in our body.

Muscle contractions are initiated by signals from our nervous system. When our brain sends a signal to a particular muscle, it triggers an electrical impulse that travels along the nerve fibers to the muscle fibers. The electrical impulse causes the muscle fibers to contract, and as a result, the muscle shortens and generates tension.

Types of Muscle Contractions

There are three types of muscle contractions: isotonic, isometric, and eccentric.

Isotonic Contractions: These are the most common type of muscle contraction. During an isotonic contraction, the tension in the muscle stays the same, but the length of the muscle changes. For example, when you lift a weight, your bicep muscle shortens as it contracts to lift the weight.

Isometric Contractions: During an isometric contraction, the length of the muscle does not change, but the tension in the muscle increases. For example, when you hold a weight in a stationary position, your bicep muscle is in an isometric contraction.

Eccentric Contractions: During an eccentric contraction, the muscle lengthens as it contracts. For example, when you lower a weight, your bicep muscle lengthens as it contracts to control the weight’s descent.

Bone Movement

Now that we understand how muscle contractions work let’s explore why bones move when muscles contract.

Our bones are not passive structures in our body. Instead, they are dynamic and constantly adapting to the forces placed upon them. When a muscle contracts, it generates tension that pulls on the bone to which it is attached. This tension creates a force that causes the bone to move.

In some cases, the movement of the bone is straightforward. For example, when you lift a weight, your bicep muscle contracts and pulls on the bone in your forearm. This force causes your forearm to move towards your shoulder.

In other cases, the movement of the bone is more complex. For example, when you walk, the muscles in your leg contract to generate the force needed to move your leg forward. This force is transmitted through your bones, causing your thigh bone to rotate and move your leg forward.


In conclusion, bones move when muscles contract because of the tension generated by the muscle contraction. This tension creates a force that pulls on the bone, causing it to move. Understanding the relationship between muscle contractions and bone movement is essential for athletes, physical therapists, and anyone interested in maximizing their body’s potential. By understanding how our body works, we can develop more effective training programs, prevent injuries, and improve our overall health and well-being.

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