KS 3 Science
Antagonistic muscles
How do muscles work?
Muscles can only pull.
Muscles are attached to bones by tendons.
Muscles pull when they contract.
Muscles get shorter and fatter when they contract.
Muscles usually work as pairs pulling in opposite
directions – these are called antagonistic muscles.
The muscles of the upper arm:
Biceps
muscle
Triceps
muscle
Antagonistic muscle action in the human
arm:
Press a muscle to
make it contract
Raising the arm
Biceps contracts
Triceps relaxes
Lowering the arm
Triceps contracts
Biceps relaxes
More antagonistic muscles – the leg:
What happens if:
B
A
Muscle A contracts?
- Leg bends at knee.
Muscle B contracts?
- Leg straightens at knee.
C
D
Muscle C contracts?
- Ankle straightens, pointing
toes.
Muscle D contracts?
- Ankle bends.
Synovial joint structure
Ligament
Ligament
Synovial
membrane
Cartilage
Synovial
fluid
Femur (thigh
bone)