6.2 Human Movement and Growth
Human movement is produced by the interaction between the skeletal system and antagonistic muscles acting across joints. Human growth is a permanent, irreversible process that follows an S-shaped (sigmoid) curve with distinct characteristics across different life stages and between genders.
Learning Objectives
- Explain the antagonistic action of skeletal muscles (biceps and triceps) in the bending and straightening of the arm.
- Describe the functions of joints, ligaments, tendons, cartilage, and synovial fluid in movement.
- Recognise careers and daily life problems related to joints and muscles.
- Describe the characteristics of human growth across the five main stages: infancy, childhood, adolescence, adulthood, and old age.
- Interpret the human growth curve (sigmoid curve) and compare the growth patterns between males and females.
Human Arm Movement and Joint Structure
Antagonistic muscles work in pairs across a movable hinge joint to bend and straighten the arm.
Short Explanation
What is human movement?
Movement in the human body relies on antagonistic muscles working in pairs across movable joints. When one muscle contracts, its partner relaxes.
For example, the biceps contracts and the triceps relaxes to bend the arm, while the triceps contracts and the biceps relaxes to straighten it.
Tendons transfer the force of these contractions from muscles to bones, while ligaments hold bones together. Cartilage and synovial fluid protect the bone ends and prevent friction.
Human growth occurs through cell division, exhibiting an S-shaped (sigmoid) curve characterised by rapid infant and adolescent phases, separated by slower childhood growth, reaching a plateau in adulthood, and ending with negative growth in old age.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What happens to the biceps and triceps muscles when the arm is straightened?
What are the two main functions of synovial fluid in a joint?
Why are adult males generally taller and bigger than adult females?
Common Mistakes
- Confusing the roles of tendons and ligaments: assuming tendons join bone to bone, or ligaments join muscle to bone.
- Stating that growth completely stops everywhere in an adult body, forgetting that parts like nails, hair, and skin continue to renew and grow.
- Assuming females grow faster than males at all stages, rather than only during early adolescence (puberty, between 12 and 14 years old).
Concept Misunderstandings
Both opposing muscles contract at the same time to create movement.
Antagonistic muscles work oppositely—one contracts while the other relaxes.
Tendons are elastic like rubber bands.
Tendons must be inelastic to effectively transfer the muscular contraction force directly to the bone.
Movable and immovable joints are the same.
Movable joints allow limb mobility (such as the elbow hinge joint), whereas immovable joints (such as skull sutures) do not allow movement.
Summary
- Human movement is driven by antagonistic pairs of skeletal muscles acting across movable joints.
- Inelastic tendons transfer muscle force to bones, while elastic ligaments hold bones together.
- Cartilage and synovial fluid reduce friction and protect the joint.
- Human growth is an irreversible process represented by a sigmoid ("S-shaped") curve.
- The growth curve consists of rapid infancy, slower childhood, a rapid adolescent growth spurt, stable adulthood, and shrinking in old age.
Short Activity
A. Objective Quiz
1 Which tissue connects a skeletal muscle to a bone and transfers contraction force?
2 During which age period do females typically grow more rapidly and become taller and heavier than males of the same age?
B. Fill in the Blanks
3 The curve showing the stages of human growth forms an S-shape, which is also known as a curve.
4 The tough, flexible tissue that acts as a cushion to reduce friction between bones at a joint is called .
C. Drag and Drop: Match the Component to Its Function
Drag each component to the function or property it matches. On a phone, tap an answer first, then tap a matching box. Tap the Answer Choices area to return a selected item.
C. Match the Component to Its Function
Write the correct component next to each function or property.
| Function / Property | Component |
|---|---|
| 1. Elastic tissue that joins two bones together | |
| 2. Lubricates joint and supplies nutrients to cartilage | |
| 3. Action that bends the arm | |
| 4. Action that straightens the arm |
Answer choices: Ligament • Synovial fluid • Biceps contracts • Triceps contracts
