The processes of balance that configure the joints of the lower limbs originate in the feet in what is referred to as a bottom-up process.
The following text is excerpted from my US Patent No. 5,265,350 which was published in the major developed countries of the world on or about February 3, 1993. I have added emphasis with bold text to highlight key statements
The foot articulates in order to facilitate muscle function. Muscles respond in opposition to loads imposed upon the foot. A process ensues wherein the chain of articulations, initiated at the foot, are continuously mobilized so as to maintain a state of dynamic balance across the plantar-ground interface.
COMMENT: Structures of a ski boot that interfere with or otherwise impede the articulation of a joint or joints will reduce or even prevent a muscle or muscles from effectively contracting and shortening.
Bipedal function or bipedal stance, in the context of the invention disclosed, is defined as being a weight-bearing state wherein the feet are neither supinated (rolled outward) or pronated (rolled inward). This is described as a “neutral” state of the foot. It is usually associated with weight-bearing on two feet wherein each foot bears an equal proportion of the weight of the body.
Monopedal function or monopedal stance is defined as being the state achieved at the conclusion of a progressive weight transfer from two feet to the medial aspect of the plantar surface of one foot. As the weight transfer occurs, the foot to which the weight is being transferred undergoes pronation until a physiologic state of balance is achieved on one foot. Monopedal function distinguishes itself from other possible states of balance on one foot in that the ability to mobilize the joints of the body required to re-orient the centre of mass relative to the foot is possible while simultaneously maintaining a state of balance in relation to the forces acting on the user.
As an example, one can bear weight on one foot without having that foot pronate and, thus, not assume the position required for monopedal function, thus there is no significant inward movement of the ankle bone. This is done by shifting the weight to bear on the lateral aspect of the foot, and using the extrinsic leg and intrinsic foot musculature to support its medial arch. However, this form of balance produces a relatively static position in terms of ability to re-orient the centre of mass of the body relative to the supporting limb. This static quality is typical of states of balance on one foot achieved by other than monopedal function. With monopedal function, medial movement of the inside ankle bone is involved.
Monopedal function is a physiologic state wherein balance is achieved with the weight of the body borne on the medial plantar aspect of one foot. It has been recognized that the ability to balance on one foot (usually the one to the outside during a skiing or skating turn) is superior, in terms of balance and control, to balance on two feet, in sports such as skiing and skating wherein an instrument such as a ski or ice blade is affixed to the sole of the footwear. Monopedal function is extremely relevant in such applications for the following reasons:
(i) Balance on one foot, achieved through pronation, provides superior control of the articulations over balance on two feet. This translates to superior control of the ski or skate blade. It also translates into superior dynamic or kinetic balance. The mechanics of monopedal function permit the centre of mass of the body to be accurately placed and its relative position maintained, if necessary, with regard to the ski or skate blade affixed to the sole of the footwear.
(ii) A dominant position on the outside foot in the arc of a turn affords more efficient and precise control of the instrument since the inner limb, being relatively passive, is utilized primarily for the purpose of assisting balance.
(iii) The most important source of rotational power with which to apply torque to the footwear is the adductor/rotator muscle groups of the hip joint. In order to optimally link this capability to the footwear, there must be a mechanically stable and competent connection originating in the plantar processes of the foot and extending to the hip joint. Further, the balanced position of the skier’s centre of mass, relative to the ski edge, must be maintained during the application of both turning and edging forces applied to the ski. Monopedal function accommodates both these processes.
(iv) In skiing, the mechanics of monopedal function provide a down force acting predominantly through the ball of the foot (which is normally almost centred directly over the ski edge). In concert with transverse torque (pronation) arising from weight bearing on the medial aspect of the foot which torque is stabilized by the obligatory internal rotation of the tibia, the combination of these forces results in control of the edge angle of the ski purely as a result of achieving a position of monopedal stance on the outside foot of the turn.
(v) The edge angle can be either increased or decreased in monopedal function by increasing or decreasing the pressure made to bear on the medial aspect of the foot through the main contact points at the heel and ball of the foot via the mechanism of pronation. As medial pressure increases, horizontal torque (relative to the ski) increases through an obligatory increase in the intensity of internal rotation of the tibia. Thus, increasing medial pressure on the plantar aspect of the foot tends to render the edge-set more stable. The ski edge-set will not be lost until either the state of balance is broken or the skier relinquishes the state of monopedal function on the outside ski.