The growth spurt

Hands and feet grow first at puberty

Regular trips to the shoe shop and trousers that rapidly become too short are common occurrences during puberty.

In their teens, children put on an amazing growth spurt to reach their final adult height. At their fastest, boys can grow taller by as much as 9cm a year and girls at a rate of 8cm a year. It's no wonder teenagers are clumsy. Their body is shooting upwards at a speed their brain simply cannot keep up with.

Outside-in

		teenagers shoot up so fast that their brains can't keep up

This phenomenal growth starts at the outside of the body and works in. Hands and feet are the first to expand. Needing new shoes is the first sign of trouble.

Next, arms and legs grow longer, and even here the 'outside-in' rule applies. The shin bones lengthen before the thigh, and the forearm before the upper arm.

Finally the spine grows. The very last expansion is a broadening of the chest and shoulders in boys, and a widening of the hips and pelvis in girls.

Growing up and tripping over

Many teenagers shoot up so fast that their brains cannot keep up. As their height increases, their centre of gravity lifts. This happens so quickly that the brain does not get a chance to calculate the new rules for balancing. Clumsiness is often unavoidable.

The trigger

Rapidly increasing height is a sign that a teenager is experiencing puberty. Growth is triggered in both boys and girls by increased levels of the sex hormone testosterone. This chemical also triggers the sexual organs to develop. In fact, the relationship between growth of the skeleton and puberty is so strong that a teenager's developmental age can be measured by looking at the maturity of the bones in their hand and wrist.

Watch a child's hand grow into an adult's. You will need Flash Player, download it for free.

Perfect timing?

Timing is everything. No teenager wants to be developing too quickly, or lagging behind. In reality, many of them grow up much earlier or later than the average and this is perfectly normal.

The average boy is growing fastest between 14 and 15. Girls start earlier, growing fastest when 12 and 13. Girls also end their growth spurt earlier at 18, while boys need another two years before they finish growing aged 20.