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Changing shoes

When should one buy new sports shoes?
Q: A question about shoes: I know you say the importance of shoes is the flexibility, so is it important to change shoes if they are old, even if the sole is in good condition?
They lose their support with wearing, but if the support is not necessary, does one only change shoe if the sole is worn down? Providing the insole is changed, when should the insole be changed and why?
Male tennis coach, 24, UK
A: Modern sports shoes lose shock absorption capacity with time, even when not worn at all. With use, the midsole and the outer sole will get worn down. When the outer sole is worn away in any part, it's time to change the shoe, as the foot mechanics will be altered by the change of contour.

Shock absorption is best provided by an insole, and you change the insole when it feels thin, hardened, damaged or worn down.
Many modern sports shoes claim to "support" the foot, both underneath in terms of shock absorption, and from the sides by preventing "unwanted" movements in the foot or ankle. This is a mistaken principle. A shoe which offers such so-called support will inevitably impede the foot, creating the risk of damaging pressure and unnatural movement from the foot up through the leg to the hip.

Shock absorption is important for repetitive impact sports like road running. It is not a big necessity for most tennis surfaces, whereas the traction provided by the sole is crucial, and should be taken into account for each surface played on.  Tennis players should have several pairs to choose from if they play on different surfaces. They should always test the amount of traction needed by putting the shoe on and sliding the shoe over the playing surface: if the shoe skids, there's too little grip, whereas if it judders and jars, there's too much. It's just right if the shoe can move comfortably across the surface.

The question of traction is essential when playing on the carpet (acrylic) surfaces, which were used mainly for indoor courts, but are now also used outdoors. For these courts, the sole of the shoes should be absolutely smooth, otherwise there is a big risk of injuries, especially to the lower leg. Sadly any shoe which provides even minor grip can cause dangerous jarring in the player's leg bones and joints. Among more serious injuries seen through wearing shoes with grip on these surfaces are fractures in the foot and meniscal (soft cartilage) and cruciate ligament damage in the knee.

When these carpet courts were first introduced, most major manufacturers produced smooth soled shoes specifically for them, but now these shoes are very hard to find. Court owners insist on "non-marking" shoes to prevent spoiling the surface, but the injury risk posed by playing in the wrong shoes seems to be ignored at the present time - swept under the carpet perhaps?