This section is from the book "The Manufacture Of Boots And Shoes: Being A Modern Treatise Of All The Processes Of Making And Manufacturing Footgear", by F. Y. Golding. Also available from Amazon: The Manufacture Of Boots And Shoes.
The active agents in the mechanism of the foot are the muscles, and the passive the bones, ligaments, joints, etc. The bones are the levers, and the muscles the power. Levers are of three kinds, the classification being determined by the relative positions of the power, the fulcrum, or central pivot, and the weight moved.
1. The power - the force that performs the work of lifting or moving, i.e. the muscles.
2. The weight - the resistance offered or weight lifted by the power.
3. The fulcrum - or centre point of the movement of the lever.
There are three orders of levers, the first order being when the fulcrum is in the centre of the lever, the weight and power on either side (X, Fig. 29). A see-saw is a good illustration. The second order is when the fulcrum is at one end of the lever, the weight in the centre, and the power at the other end (Y, Fig. 29). A wheelbarrow illustrates this class - the wheel being the fulcrum, the load carried the weight, and the person wheeling the power. The third order is when the fulcrum is at one end, the weight at the other bearing downwards, and the power in the centre in an upward direction (Z, Fig. 29). A man raising a ladder to a wall illustrates this form of lever.
The foot is said to be a lever of the first order when the toes are pressed to the ground (weight), the heel raised by the power from the tendon Achilles (power), and the ankle joint the movable fulcrum; or, if the toes are off the ground, in the act of raising a ball, it could be classed under a lever of the first order (Fig. 30).
The foot is classified as a lever of the second order when the toes are on the ground as a fulcrum, the weight being that of the body transmitted via the tibia, and the power the muscles of the calf operating through the tendon Achilles (Fig. 31).
The third order is exampled when the heel is placed on the ground, forming the fulcrum, the toes are raised, being the weight, and the muscles of the front of the leg the power (Fig. 32).
The understanding of the mechanism of the foot is not simple, due to the complexity of the joints, the twists and curves of the bones, the transmitted and direct action of the various muscles, and the obliquity of the joints. It is not surprising, therefore, that many opinions are formed respecting the various movements. The difficulty of precisely stating the effects upon the contour and size of the parts of the foot, is the cause of varying theories as to the best form of shoe, advocates of a particular form usually considering the foot in one series of motions only.
Applicable Observations, of practical value in clothing the foot, will be made that will impress the value of the study of the structure of the foot. The non-symmetrical appearance of the foot should be especially noted - the inner edge being practically straight, and the outer one curved. The two sides of the foot are different in construction and function, but the foot is a complement and counterpart of its fellow. When the foot is in a position of rest, the edge of the inner side is hardly straight, but when in activity, it is somewhat concave. Lasts should not be "straights," but rights and lefts. The functions of the toes should be remembered in making or selecting lasts. The great toe, when suddenly called into action, moves outwards, and forms a solid base to propel the body onwards. There are only two phalanges in this toe, giving the impression of strength. This toe is thicker than the others, so that the last should be thicker on the inside. When the heel is raised the great toe moves inwards, as seen by the dotted line in the plantar view (p. 29). By constructing shoes that compel the toe to remain in this position, the space at the end of the phalanx is filled by a growth of bone, etc., and bunions are formed. The smaller toes are flexed when in action, and the joints of the toes present a series of uplifted prominences while gripping the ground. The preservation of these functions should be the consideration of the producer of boots and shoes.
The muscles in exercise promote growth, and when properly developed, they are taut when not actively employed, thereby keeping the bones in place: pressure prevents the development of muscular activity, and the partially formed muscles do not brace up the bones, hence the joints sink. The joint-action of the opposing muscles should be considered, with their variety of movements and alteration in shape.
Free play to the joints is a necessity to the fullest usage of the foot. The "ankle-bone" prominences vary in position on opposite sides of the foot; the outer bone being lower down and further back than the inner. This has an important bearing on the making of shoes. The arches of the foot serve the purpose of affording protection from pressure to the muscles, vessels, and nerves; and the provision for elongation when weighted, must not be overlooked in foot-gear. The transverse arch is not equal at both sides of the foot, the inner side being higher than the outside, and lasts that are equally arched on both sides do not conform to the requirements of the foot (compare Figs. 12 and 13). Fastenings to shoes should not tighten across the instep, but the strain should preferably be from instep to heel. The skin in the arch or waist of the foot is thinner than at the balls of the toes and the heel, giving greater elasticity to the waist, and the thicker skin where pressure is experienced gives protection to the parts that come into contact with the ground. The sole is richly provided with nerves, and projections of badly laid socks, rivets, or other irregularities in the inside of shoes are the cause of much pain to the wearer. The effects of placing heels on boots are many. Some of them are : the prevention of the lowering of the heel of foot to gain the impetus so necessary to exercise the muscles that give the force to spring to tip-toe ; the resting of the foot on an incline plane, and thereby giving it a tendency to go forward towards the toe of the boot; and the production of a more convex instep and the appearance of a shorter foot. It is also supposed to tilt the posterior pillar of the arch of the foot, thus dislocating the bones that give its characteristic; but this should not occur if the heel be placed well under the centre of gravity of the weight transmitted, and the muscles are not otherwise prevented from attaining their proper development. The higher the heel adopted to raise the heel of the foot, the shorter will be length measured as on a size-stick, although the same cannot be said of the actual length of the foot.
To conclude this chapter it is essential to note that exercise increases the circulation of the blood, and that owing to the tendency of the inner sides of the foot to go together (see Fig. 14), the fullest play should be given for the functions of the foot to perform their work, and that any interference with the structure makes it less effective. Cramping the leg and foot with stiff uppers causes the deterioration of the muscles and prevents their proper action. A healthy shoe should give the movements of the foot their action, and should conform to the requirements that are most general, and it should also be borne in mind that alteration in shape takes place during muscular movements, and that foot-gear should vary as the motions of the foot are impeded or increased.