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Muscles are fascinating, but many people don't know how they work. Muscles move body parts by contracting and relaxing, and they can only pull bones, not push them. So, how do muscles work when we push something? Muscles work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint, and then the extensor contracts to extend or straighten the limb at the same joint. For example, the biceps muscle is a flexor, and the triceps is an extensor. When you bend your elbow, your biceps contract, and when you straighten your arm, your triceps contract.
| Characteristics | Values |
|---|---|
| How muscles move body parts | By contracting and then relaxing |
| How muscles move bones | By pulling them |
| How muscles work | In pairs of flexors and extensors |
| How flexors work | By contracting to bend a limb at a joint |
| How extensors work | By contracting to extend or straighten a limb at a joint |
| Example of a flexor | Biceps muscle |
| Example of an extensor | Triceps muscle |
| What happens when muscles contract | They get shorter and thicker |
| What happens when muscles relax | They get longer and thinner |
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What You'll Learn
Muscles pull or relax to move your body
Muscles move body parts by contracting and then relaxing. They can pull bones, but they can't push them back to their original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint. Then, when the movement is completed, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint. For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor. When you bend at your elbow, the biceps contracts.
Muscles are attached to our bones. When you tighten the muscles in your upper arm, they get shorter. They are attached to your shoulder at one end and to the bones of your lower arm at the other end. The muscle pulls your lower arm bones towards your shoulder, bending your arm.
Chest muscles being called "push" muscles implies the motion you perform. You use your chest muscles to push things away, back muscles to pull things closer. But even when pushing, chest muscles contract and back muscles stretch, and when you pull the opposite happens.
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Muscles work in pairs of flexors and extensors
When a muscle contracts, it gets shorter and thicker. When it relaxes, it is longer and thinner. If the muscle was not attached to anything, this wouldn't have much of an impact. However, muscles are attached to our bones. When you tighten the muscles in your upper arm, for example, they get shorter. They are attached to your shoulder at one end and to the bones of your lower arm at the other end. The muscle pulls your lower arm bones towards your shoulder, bending your arm.
The biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor. When you bend at your elbow, the biceps contracts, and then, when the movement is completed, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint.
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Muscles are attached to bones
For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor. When you bend at your elbow, the biceps contracts, and the triceps relaxes. Then, when you straighten your arm, the triceps contract, and the biceps relax.
Muscles are laid out in long strands, like a rope. You can only move something heavy with a rope by pulling on it, not by pushing. The same thing applies to your muscles. So, even though we talk about 'pushing' with our chest muscles, for example, these muscles are actually contracting, not pushing.
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Muscles contract and relax
Muscles work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint. Then, when the movement is completed, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint. For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor. When you bend at your elbow, the biceps contract and the triceps relax.
It's important to note that muscles cannot push. For example, when you push something away, your chest muscles contract and your back muscles stretch.
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Muscles cannot push
Muscle fibres are laid out in long strands. The only way to get them moving is by pulling on them, you simply can't push. The same thing applies to your muscles. Even when pushing, chest muscles contract and back muscles stretch, and when you pull, the opposite happens.
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Frequently asked questions
Muscles don't push, they pull. When a muscle is relaxed, it is longer and thinner. When you tense the muscle, it contracts, to get shorter and thicker.
Muscles move body parts by contracting and then relaxing. Muscles can pull bones, but they can't push them back to their original position. So they work in pairs of flexors and extensors.
When you tighten the muscles in your upper arm, they get shorter. They are attached to your shoulder at one end and to the bones of your lower arm at the other end. The muscle pulls your lower arm bones towards your shoulder, bending your arm.
