7.3.2 Physical Changes as Youth Transition to Adulthood – Summary

As young people transition to adulthood, they experience major physical changes and become sexually mature, legally recognised as adults, and more independent.

Physical Development

changes to the body and its systems. These can be changes in size (i.e. growth), complexity (for example, the increase in complexity of the nervous system) and motor skills (for example, learning to walk).

Growth

• Females gain an average of 16 cm in height and 16 kg in weight.

• Males gain an average of 20 cm in height and 20 kg in weight.

• Growth (epiphyseal) plates in long bones fuse by early adulthood, stopping further height growth.

• Bones continue to increase in strength and density for several years.

Changes to Body Systems

• The reproductive system becomes fully developed and functional.

• Primary sex characteristics (reproductive organs) mature during puberty and are fully developed by early adulthood.

• Secondary sex characteristics develop, such as:

  • Males: deeper voice, facial/body hair, broader shoulders, increased muscle.

  • Females: breast development, wider hips, increased body fat around the hips and thighs.

Changes in Body Composition

• Males gain more muscle mass and develop broader shoulders, creating a more triangular body shape.

• Females develop wider hips and a higher fat-to-muscle ratio, resulting in an hourglass body shape.

Brain Development

• The brain continues to increase in complexity throughout youth and into adulthood.

• New experiences strengthen brain development, improving thinking, learning, and decision-making.