A heel – the difference in height between the forefoot and the heel (also known as the heel lift) – is usually integrated into conventional shoes for reasons of style or to cushion the impact of a heel strike when walking.
But the body is inherently self-contained, so artificial cushioning isn’t necessary. (1) (2)
From head to toe, our body is built like a giant spring. Consisting of three forward curves (lordosis) and three backward curves (kyphosis), our skeleton as a whole works much like a shock absorber. (3)
Raising the heel of the foot by adding a heel in the shoe hinders this natural function and reduces the tension of the Achilles tendon. This energy is no longer available when you push off with your foot (think of an elastic band...) and prevents the tendon from rising to the task at hand.
For children, a built-in heel lift has far more serious consequences. (4)
In relation to body height, a 2.5cm heel lift worn by a seven-year-old child is the equivalent of a 5cm heel worn by an adult. That means that in principle, nearly every child is wearing 5cm high heels from the age of seven (in relation to their height).