In a boot

Boot

A boot is a type of footwear but they are not shoes. Most boots mainly cover the foot and the ankle and extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is clearly distinguishable from the rest of the sole, even if the two are made of one piece....

 or shoe

Shoe

A shoe is an item of footwear intended to protect and comfort the human foot while doing various activities. Shoes are also used as an item of decoration. The design of shoes has varied enormously through time and from culture to culture, with appearance originally being tied to function...

, the shank is a part of the supportive structure between the insole and outsole. The presence of a shank is crucial to the functionality of mountaineering boots

Mountaineering boots

Mountaineering boots are a type of footwear used in the sport of mountain climbing. They are designed specifically for moving over harsh terrain.-Design:Not to be confused with hiking boots, mountaineering boots are usually taller, stiffer, and insulated...

 as they diminish the load incurred by the wearer’s feet

Foot

The foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws...

 and calves

Calf (anatomy)

In human anatomy the calf is the back portion of the lower leg . In terms of muscle systems, the calf corresponds to the posterior compartment of the leg. Within the posterior compartment, the two largest muscles are known together as the calf muscle and attach to the heel via the Achilles tendon...

 over the course of an ascent. Traditionally constructed of steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

, contemporary shanks are more commonly made up of less heat conductive but equally rigid options such as fiberglass

Fiberglass

Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...

 and Kevlar

Kevlar

Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...

. The rigid nature of these materials contributes a protective element to the footwear into which they are integrated, helping shield the wearer’s feet from puncture wounds and stone bruises.