Named Muscles, Movement and Fibre Types

The muscles that move you

Bones cannot move themselves; muscles pull on them. Skeletal (voluntary) muscles work across joints to create every movement in sport. This module covers the named muscles, how they work in pairs, and the fibre types that suit different activities.

Named muscles

Learn the main muscles by where they are. Front of the body first, then the back:

Label the muscle map

Drag each muscle name onto the shaded muscle. The left figure is seen from the FRONT, the right figure from the BACK.

Straighten the arm

Which muscle contracts to straighten (extend) the elbow?

• Triceps
• Biceps
• Deltoid
• Quadriceps

Antagonistic pairs

A muscle can only pull, never push. That single fact is why muscles must come in antagonistic pairs: something has to pull the joint back the other way. - The muscle that contracts to cause the movement is the agonist (prime mover). - The muscle that relaxes to allow it is the antagonist. To bend the elbow, the biceps is the agonist and the triceps is the antagonist. Straighten it again and the two swap roles: which is which depends on the movement, not on the muscle.

Who relaxes?

When you bend your elbow, the biceps contracts as the agonist. What is the triceps doing?

• Relaxing, as the antagonist
• Also contracting hard
• It is not involved at all
• Acting as the agonist

Match each muscle to its antagonistic partner

Types of movement

Joints allow named movements, and almost all of them come in opposite pairs. Abduction takes a limb away from the midline of the body and adduction brings it back in; rotation turns a limb around its own axis. The pair you will meet most often is flexion and extension:

Name the movements

A netball player jumps to intercept. Raising both arms sideways away from the body is _____ at the shoulder; lowering them back to her sides afterwards is _____. As she bends her knees to absorb the landing, the knee is in _____, and as she straightens up again the knee is in _____.

Point the toes

Pointing your toes downward, like a diver or ballet dancer, is which movement?

• Plantar-flexion
• Dorsi-flexion
• Abduction
• Rotation

Muscle fibre types

Not all muscle fibres are the same. There are three types: - Type I (slow-twitch): contract slowly with low force, but resist fatigue for a long time. Great for endurance. - Type IIa (fast-twitch): faster and more powerful, with some endurance. Good for middle-distance. - Type IIx (fast-twitch): fastest and most powerful, but tire quickly. Built for sprints and power. Everyone has all three. What differs between athletes is the proportion of each, and training can shift Type IIx fibres towards Type IIa but cannot turn fast-twitch into slow-twitch.

Match each fibre type to the event it suits

Analyse the jump shot

A basketball player rises for a jump shot. Work through the analysis the way an exam answer does.

• As she drives upwards, her knee goes from bent to straight. Which movement is that?
• Which muscle is the agonist for that movement, and what is its partner doing?
• She repeats that jump maximally, twenty times, across a game. Which fibre type does most of that work?

Muscle summary

The biceps and triceps work as an _____ pair; the muscle that contracts to cause a movement is the _____. Pointing the toes down is _____-flexion. The fibre type that produces the most force but tires the fastest is Type _____.