This is the age of the trainer. Those chunky shoes gracing the feet of every child in the land (not to mention sporty and sporty-wannabe adults) have to look just right - so much so that manufacturers employ teams of "cool-hunters" to prowl the neighbourhoods to check out what has street-cred. World-class designers, who in a different age would have been creating great public works like Tower Bridge or steam-engine trains now devote their lives to an article of personal apparel.
But this is one reason training shoes offer such potential as a classroom theme. Teachers can tap into children's natural interest in sport and fashion to examine questions of design, technology, science and even art.
How a trainer works
The main purpose of a training shoe used for sport is protection of the foot and legs. During a marathon, a runner's foot hits the ground more than 25,000 times with a force two to three times their body weight. This repeated force could injure the runner and so companies design protective shoes - fitness giant Nike spends more than Pounds 5 million a year developing their range of air-cushioned shoes to reduce the number of injuries.
A runner's heel hits the ground first. The foot sags down to the ground as the body passes over it. The knee bends slightly, cushioning the blow. The other foot reaches forward and the weight transfers to it. The foot on the ground rotates until only the toe is on the ground. The runner pushes off from the toe for the next stride.
Design and technology projects may be criticised for lacking relevance to the "real world". Does designing a pizza compare with designing a railway engine? Yet some of our most innovative and creative designers are working in fields that might be regarded as ephemeral - even frivolous. Peter Fogg, head of design at Nike, takes inspiration from architectural themes, from car parts, from classic shapes like camera shutters and successful designs like the Swatch jelly watch. The Nike Air Terra Humara takes its inspiration from a motorcycle disc brake.
Disassembling familiar products can help pupils understand more about the way they work; but they can also give design ideas for their own technology.
Bones, muscles and trainers
Pupils at Key Stage 2 should be learning that "humans have a skeletal structure for support and muscles for movement". A training shoe topic introduces these areas in a "cool" context. By exploring the way that bones and muscles work together in exercise and sport, children can learn about a topic with links to technology, forces and the use of materials.
WHAT'S INSIDE IT?
The heel counter prevents lateral movement to the foot that could damage the heel or knee. Some newer trainers have this feature built into the sole.
The midsole support cushions the foot. It is made from polyurethane, nylon or EVA (ethyl vinyl acetate) and is thicker at the heel than the toe, since the heel hits the ground first and hardest. In some shoes, there is a gas cushion in the midsole support. A dense large-molecule gas is contained in a flexible plastic skin. It cannot escape through tiny pores in the skin of the gas bag - deflating like a toy balloon. Nike call their gas "Nike air" but the gas is not air; it is a complex large molecule.
The sole of the shoe provides grip, cushioning and resistance to wear. A carbon rubber sole is very hard-wearing. Sole grooves give flexibility and provide grip. They are designed to flex and move with the foot. Two notches on the shoes' uppers have the same purpose. Some shoes have longitudinal slits to provide stability. Some of the slits are actually holes - revealing a steel-like protective interior, while the "bi-directional waffles" - lugs at the toes and heel pointing in opposite directions - are for uphill and downhill traction.
The forefoot cushion eases the foot down to a soft landing. The body has to rely less on muscles to absorb and reduce shock. The forefoot cushion may contain gas, too.
The side panels of a trainer are covered with lightweight nylon. Thousands of tiny holes in "breathing" panels allow air to circulate and moisture to be lost.
Test trainers by dropping a heavy ball-bearing down a clear plastic tube into the cushioned interior. How high does it bounce?
Clamp a shoe to the table by its heel or toe. Carefully apply a force to the other end of the shoe by pulling down with a forcemeter. How much force to bend it?
Try turning a loaded shoe on different surfaces. How easy is it to twist?
Wear tests take manufacturers days of use on mechanical rigs, but you can examine the soles of shoes and look at the wear patterns. Runners and tennis players have different patterns of wear. You can see the "jump-off point" and favoured foot on a well-worn pair of tennis shoes.