Aseel Samaro

Examining interacting muscles

There are commonly three things judges look for:1. Symmetry of the muscles (how similar they are)2. Muscularity (how big they are)3. Level of conditioning (how toned they are) (How firm they are)

Muscles works in pairs by relaxing and contracting

To gain symmetry marks the judges look for how similar the muscle pairs look in terms of

ShapeSizecomparing left to right.

Examining interacting muscles

The majority of the 600 muscles of the human body work as pairs.

As one muscle of the pair contracts, the other muscle relaxes and vice versa.

Without muscles working together in this way we would not be able to move our joints freely.

Examining interacting muscles

When muscles contract they pull on both a tendon and bone.

If the bone is at a joint, the bone will move.

Muscles can only pull, they cannot push.

If muscles just worked singly, the bone would simply stay in that position.

Pairs of muscles

To solve this problem, muscles work in pairs called antagonistic muscles

In the arm, the bicep and tricep muscles work as an antagonistic pair to control movement at the elbow.

To move the forearm up the bicep contracts and the tricep relaxes.

To move the forearm down the tricep contracts and the bicep relaxes.

Pairs of muscles

Other examples of antagonistic muscles include:

the quadricep and hamstring muscle in the thigh, which allow bending at the knee

the shin and calf muscles, which allow movement at the ankle

Pairs of muscles

Explain why some muscles need to work in pairs.

We need antagonistic muscles to move bones back to their original position

Scientists use models to explain their ideas.

Models can be extremely useful to help us to visualise something that we cannot actually see.

Models are not usually a perfect representation of the real situation.

Scientists must evaluate any model to decide how well it represents the real world.

A muscles model

A simple model of antagonistic muscles in the arm

In the card and rubber band model of the arm: the forearm moves up as the top rubber band is pulled and moves down as the bottom rubber band is pulled.

This represents what happens in the body.

However, the shoulder joint is fixed in the card model. This is a poor feature of the model because the shoulder joint is not

fixed in the body.

Antagonistic muscles are at work in our eyes.

Pairs of muscles in the coloured part of the eye, the iris, control how big the pupil is.

This prevents the eye from being damaged by too much light entering it.

Did you know?