6.2 Human Movement and Growth

Functions of Joints and Muscles in Movement

• The skeletal and muscular systems enable humans to move.
• Contraction and relaxation of skeletal muscles produce movement.
• Skeletal muscles act in opposing pairs. Each opposing pair is called antagonistic muscles.
• Antagonistic action enables movements such as walking, jumping, running, swimming, crawling and lifting objects.

Antagonistic Movement of the Arm

Movement	Muscle action
Bending the arm	Biceps contracts; triceps relaxes
Straightening the arm	Biceps relaxes; triceps contracts

Joints and Associated Structures

• Joint: the meeting point of two or more bones.
• Movable joint: allows a body part to move; example: the hinge joint at the elbow.
• Immovable joint: does not allow a body part to move; example: joints in the skull.

Structure	Function and characteristics
Ligament	Tough, elastic and strong connective tissue that joins bone to bone; binds bones while allowing movement
Muscle	Tissue made of parallel fibres; its cells contain mitochondria that generate energy for contraction and relaxation
Tendon	Strong, inelastic connective tissue that joins muscle to bone; transfers the force of muscle contraction to the bone
Cartilage	Acts as a cushion, protects the joint and reduces friction
Synovial fluid	Lubricates the joint and supplies nutrients to cartilage

Problems Related to Joints and Muscles in Daily Life

• Problems highlighted in the textbook:
  • injuries to joints and muscles caused by physical activities;
  • knee pain among the elderly.
• Problem-based task:
  1. Gather information from websites and references on medicine and a balanced diet.
  2. Discuss suitable methods to prevent joint and muscle injuries.
  3. Present the findings.

Related Careers

• Orthopaedist:
  • specialist doctor who treats injuries such as bone fractures, spinal defects and bone deterioration such as osteoporosis;
  • helps patients undergo musculoskeletal rehabilitation.
• Chiropractor:
  • complementary-medicine practitioner involved in diagnosing and treating mechanical disorders of the muscular system, skeleton and spine.
• Physiotherapist:
  • medical limb rehabilitator or medical rehabilitation officer;
  • helps patients recover and maintain physical function at a high level.

Human Growth Pattern

• Human growth is a permanent and irreversible process involving changes in:
  • size;
  • total number of cells;
  • weight;
  • body shape;
  • body function.
• Growth occurs because the number of body cells increases.
• It occurs throughout the body and differs according to sex and age.
• Human growth stages: infancy → childhood → adolescence → adulthood → old age.

Human Growth Stages

• Infancy, 0–3 years:
  • male and female infants grow at the same rate;
  • growth is very rapid because cell division occurs rapidly;
  • a balanced diet is important for balanced growth.
• Childhood:
  • growth is slower than during infancy;
  • male children grow faster than female children;
  • a balanced diet is essential for balanced cell growth.
• Early adolescence, 13–15 years:
  • both sexes grow rapidly;
  • males grow more slowly than females;
  • females are usually taller and bigger than males of the same age;
  • secondary sexual characteristics begin to develop.
• Later adolescence:
  • female growth slows at 16–18 years and eventually stops;
  • male growth continues until 18–20 years;
  • males therefore usually become bigger than females.
• Adulthood:
  • adult males are generally taller and bigger because male growth lasts longer;
  • growth becomes constant and almost zero;
  • growth stops except in certain parts such as nails, skin and hair.
• Old age:
  • growth almost stops completely;
  • the body begins to shrink;
  • muscles become smaller and skin begins to dry.

Human Growth Curve

• The curve is S-shaped or sigmoid.
• Infancy: rapid growth.
• Early childhood: growth slows.
• Adolescence: growth becomes rapid again.
• Adulthood: growth slows and stops at maturity.
• Old age: negative growth occurs as body size decreases.
• The graph allows the growth rate at different stages of life to be determined.

Growth Patterns of Males and Females

Age or stage	Comparison
Infancy to early childhood	Males and females grow at the same rate
From 4 years	Males grow slightly faster than females
Puberty, 12–14 years	Females reach puberty earlier and grow faster; they are taller and heavier than males of the same age
After 14 years	Males grow more rapidly than females
Adulthood	Males are generally taller and bigger because their growth continues for longer

• Puberty occurs in early adolescence:
  • secondary sexual characteristics develop and become distinct;
  • reproductive organs mature.
• During health examinations, body mass, height and head circumference are common measurements used to monitor the growth of infants and children.