Pronation and supination are terms often incorrectly applied to eversion and inversion. Pronation refers to the movement of the foot complex as a whole, and consists of a combination of eversion through the subtalar joint, internal rotation of the tibia, and other movements occurring across the transtarsal joints and through the forefoot. This term is most commonly to the motion of the foot in gait, and occurs through the first half of the stance phase, as the centre of pressure moves through the lateral aspect of the heel, to the medial side of the forefoot and the first metatarsal head.
– G. Robert Colborne, Ph.D

Eversion and inversion refer to rotation of the foot about its long axis. When the sole of the foot is rotated towards the transverse centre line of the body the foot is said to be inverted. When the sole of the foot is rotated away from the transverse centre line of the body the foot is said to be everted. What most people refer to as ankle flexion is rotation of the foot about it’s transverse axis as dorsiflexion and plantarflexion. Dorsiflexion is flexion of the ankle that moves the toes of the foot closer to the shin. Plantarflexion is flexion of the ankle that moves the toes of the of the foot farther away from the shin.

The rotation of the foot about its long axis as inversion and eversion is coupled through a joint of the ankle called the subtalar joint to axial vertical rotation of the tibia. Inversion of the foot is accompanied by external rotation (towards the outside of the body) of the tibia. Eversion of the foot is accompanied by internal rotation (towards the transverse centre of the body) of the tibia.

The action of the ankle joint complex is triplanar in nature in that inversion/eversion, medial/lateral vertical axial rotation of the tibia and dorsiflexion/plantarflexion of the ankle occur concurrently and are not mutually exclusive of each other. The subtalar joint of the ankle complex acts as a 1:1 torque converter in translating rotation of the foot about its long axis (inversion/eversion) into vertical axial rotation of the tibia (medial/lateral rotation).

next post…… Pronation and the Biomechanics of Edge Control


If you purchased a pair of ski boots or had work done by a boot-fitter you may have been told that your feet pronate and that this will cause your arch leg to collapse creating a myriad of problems including a lack of control and especially an inability to effectively transfer energy. You may have also been told that your foot functions best in skiing when it is immobilized, preferably in a neutral position, one that completely prevents pronation. All of the preceding are myths. But more than simply being untrue, they are potentially dangerous. ‘Pronation is bad’ is nothing more than a good story; one that most people buy into simply because they have no idea of what pronation is. So they tend to assume that the store clerk or boot-fitter actually knows what they are talking about.

When I first started modifying ski boots in 1973 in an attempt to help my own skiing I bought into the pronation is bad story after reading an article in a running magazine about how over-pronation (an invented term) was causing injuries in runners. The article implied that the human feet, far from being a marvel of complex engineering, are riff with problems like ‘pronation‘  that require corrective devices such as footbeds or prescription orthotics to make feet function properly. This made sense to me at the time, but only because of what I didn’t know. After reading the story in the running magazine, I had what I thought was an epiphany; ‘If foot defects can cause a myriad problems in running, imagine what havoc they must be wreaking in skiing’. Thinking I was on to something, I had prescription orthotics made for my wife and myself by a sports podiatrist. Later, I began making custom footbeds for ski boots. In the 1970s, I was one of the few boot-fitters in world making custom footbeds. And while the response of the majority of skiers I made them for was overwhelmingly positive there was one problem, my own custom footbeds didn’t work for me. In fact, footbeds and prescription orthotics made skiing much more difficult for me than insoles with no arch support. Unfortunately, the pronation is bad story caught on. Soon the evils of over-pronation morphed into the evils of pronation period; any and all pronation was bad and should be stopped or at least greatly restricted.

As Mark Twain quipped, “It ain’t what you know that gets you into trouble. It’s what you know for sure that just ain’t so”. For the past 30 years most of the world has known for sure that pronation is bad. Now a study published this month (1) confirms what I and others have maintained for years, not only is pronation not a predisposition to injury but there are significantly less injuries in those whose feet pronate.

Far from being a bad thing in skiing, pronation is the key to setting up the over-centre mechanism that makes the forces of skiing work for you instead of against you. So what is pronation?

In future posts I will explain what pronation is and why it is essential to sound ski technique and the ability to balance on the outside ski.

1.  British Journal of Sports Medicine (

Sources of the story on the Danish study include:

A Popular Myth About Running Injuries – New York Times

Speciality running shoes may not reduce injuries – Health – CBC