Muscles and skeleton
The skeleton has about 206 bones in an adult. It holds the body up, protects soft parts (the skull guards the brain, the ribs guard the heart and lungs) and gives muscles something to pull on.
A joint is where two bones meet. Two types you must know:
- Hinge joint (elbow, knee, fingers): moves like a door, back and forth in one plane.
- Ball-and-socket joint (shoulder, hip): a round end fits in a cup, so it can swing and turn in many directions.
A skeletal muscle is joined to bones by strong cords called tendons. When a muscle contracts (gets shorter) it pulls a bone. Muscles can only pull, so they work in antagonistic pairs: biceps bends the elbow, triceps straightens it. Bones are joined to each other at the joint by ligaments.
Structural analysis of dance movement
To analyse a movement, ask four questions: Which joints move? Which way do they move? Which muscles work? Where is the weight?
Example, the plié (a knee bend). The hip, knee and ankle all bend (flexion). The thigh muscles (quadriceps) work hard as the dancer goes down, slowing the fall; the same muscles push the body back up. The knees should point in the same direction as the toes, and the hips stay above the feet, so the weight stays over the feet. If the knees fall in, the knee joint is stressed.
Moving a joint to bend it more is flexion; straightening is extension. A good habit: name the joint and the action, like "knee flexion".
Posture and proprioception
Posture is how you hold your body. Good standing posture: a straight line from ear through shoulder, hip and knee to the ankle, with the spine in its natural gentle curves. Then the bones carry the weight and the muscles do not tire.
Proprioception is your body's sense of where its parts are and how they move, even with your eyes closed. Tiny sensors in muscles, tendons and joints send messages to the brain all the time. Close your eyes and touch your nose with one finger: you can do it because of proprioception.
Practice makes this sense sharper. Dancers, gymnasts and cricketers repeat slow movements to train it.
- Slouching moves the head forward and tires the neck and back muscles.
- Check your line against a wall: heels, hips, shoulders and head just touch it.
Breathing
The main breathing muscle is the diaphragm, a dome-shaped sheet under the lungs. When you breathe in, it contracts and flattens (moves down) and the rib muscles lift the ribs up and out. The chest space gets bigger, so air flows into the lungs. When you breathe out, the diaphragm relaxes and moves back up; the ribs go down and air flows out.
In deep "belly" breathing the belly moves out as the diaphragm goes down, because the organs below are gently pushed. Slow, deep breaths help movers keep calm, control a long phrase of movement and avoid getting tense.
Try it: feel your own body
- Muscle pair: put one hand on your upper arm. Bend and straighten your elbow slowly. Feel the front bulge when it bends.
- Proprioception: close your eyes, stretch your arms out sideways, then touch your nose with one finger.
- Posture: stand with your back to a wall. Do heels, hips, shoulders and head touch it?
- Breath: put a hand on your belly and one on your chest. Breathe in slowly. Which moves first?
Key formulas and definitions
- Muscle contracts → shorter and fatter → pulls the bone
- Antagonistic pair: biceps (bends elbow) ↔ triceps (straightens elbow)
- Hinge joint: elbow, knee. Ball-and-socket joint: shoulder, hip
- Good posture line: ear – shoulder – hip – knee – ankle
- Breathing in: diaphragm moves down, ribs up and out
Worked examples
1. Name the joint type at the knee and the hip.
The knee is a hinge joint (moves in one plane). The hip is a ball-and-socket joint (moves in many directions).
2. When you lift a book by bending the elbow, which muscle contracts and which relaxes?
The biceps contracts (shorter and thicker) and pulls the forearm up. The triceps relaxes and lengthens.
3. A dancer does a plié. Name the joints that bend and say where the weight should stay.
The hip, knee and ankle all bend (flexion). The weight should stay right above the feet, with the knees pointing the same way as the toes.
Common mistakes
- Thinking muscles can push a bone. Muscles can only pull, so a second muscle is needed to pull back.
- Mixing up tendons and ligaments: tendons join muscle to bone; ligaments join bone to bone.
- Believing the belly fills with air. Air goes only into the lungs; the belly moves because the diaphragm pushes the organs below.
- Thinking posture means standing stiff. Good posture is easy and balanced, with natural curves.