Imagen de destino turístico y proceso de elección

Bottom curve or last bottom centre line curve:

This line represents the intersection between the last centre line plane and the bottom surface of the last, Figure 7. This defines the geometry of the last bottom and thus is a primary factor in the position of the foot inside the shoe. It is often broken up into separate regions including the heel seat, the cuboid region which has the shank curve incorporated into it, as well as the toe spring (shown in Figure 9), which have independently

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been shown to affect pressure and comfort scores [36] and are discussed in more detail below. The bottom curve is used to define the last contact point.

Figure 9: Shoe last side view [38].

Last contact point or last ball break point (Figure 7):

When the last is laid on a flat surface the Last contact point is the location upon which the forefoot of the last will contact the flat surface. In this position the last will rest along a line traversing medial/ laterally at the forefoot. The last contact point is then the bisection between this medial/lateral line and the last centre line plane. It is from this point that the toe spring angle and the last depth originate, these are critical to the position of the foot and toes inside the shoe [77]. Generally the toe spring is changed when either the sole material or heel height is changed. The harder the sole the more toe spring required, whilst higher the heel the less toe spring required [38]. The toe spring can have significant effects on plantar pressure and as a result has been the focus of literature on diabetic participants [77], for whom high plantar pressure can be detrimental to foot health.

- 37 - Last Depth (shank curves):

The last depth is the sagittal plane shape of the underside of the last in the middle to rear section of the last bottom centre line curve. A shallow last has little to no curvature in the sagittal plane of the midsection of the foot, whereas a deep last will describe a deep arch. The last depth can also be called the shank curve and some examples of these shapes were provided by Goonetilleke [38] as shown in Figure 10.

Figure 10: Shoe-Last shank curves

(values shown are an example of those used for shoe size 36, the length of all the individual curves are 155mm), the point to the left represents the last contact point and the right side represents the

plantar heel surface [38]

An increase in Last depth has been shown to decrease the pressure time integral in the forefoot, and increase it in the mid and rear foot regions [28]. The same study has shown that the higher the last depth the lower the peak pressure in the forefoot region in the midstance phase. They also summarised that because there was increased arch support for increased last depth the pressure time integral, the peak pressure, and the peak contact area in the midfoot region all increased, these results can be seen in Figure 12, Figure 13, and Figure 14. Shank curve is a feature that is normally changed when heel height is

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increased; the results shown highlight that shank curve is an important factor in pressure investigations of high heeled shoes.

Figure 11: diagram showing the definition of GL taken from Cong et al 2011 [78]

Figure 12: The peak contact area for a range of foot regions, using varied shank curves. GL represents the distance from the waist of the last to the line joining the heel breast to the ball

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Figure 13: The pressure-time integral in the different regions of the foot under a range of shank curves.

GL represents the distance from the waist of the last to the line joining the heel breast to the ball tread. Taken from Cong et al [28].

Figure 14: Peak Pressure in the different regions of the foot using a range of shank curves. GL represents the distance from the waist of the last to the line joining the heel breast to the ball

tread. Taken from Cong et al [28].

Last flare:

The last flare is the longitudinal curvature of the last viewed in the anatomical transverse plane of the wearer. Often referred to as either a straight or curved last, this feature is principally the transverse plane curvature of the forefoot of the last relative to the rearfoot. Varying significantly between different last manufacturers this can often be the

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key feature that affects both comfort and fit in all shoes, including high heels. The mismatch between the shoe and foot flare is said to be a primary factor for discomfort in the ball region as well as the formation of bunions [73]. Moreover, the same investigator states that if there is not perfect fit between the shoe curvature and the foot, the forefoot will be deformed. If the shoes are only worn for the short term then this deformation will be temporary but if the shoes are worm for a long time this deformation could become permanent [73].

Figure 15: Last Flare

(grey scale is a straight last and in blue is the curved last)

Heel seat length:

The heel seat is the region at the back of the shoe and holds the heel in place, providing a flat platform upon which the sole of the foot heel rests. The sagittal plane length of the heel seat is called the seat length. One end of the seat length is the rear most point of the heel, the other end is the location where this flattened section ends and the curvature of the midfoot section begins to angle down towards the forefoot. The point at which the decent down to the forefoot begins is called the breast point, as shown in Figure 16 and Figure 9. The heel seat length is often defined as the distance between the Ho and the breast

point, however, the breast point is arbitrary and thus solely dependent upon subjective judgement made by the last maker. It has been shown that adjusting the heel seat length

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can effectively reduce the heel pressure and impact force [42] and similarly affects due to the seat length have observed on perceived feeling which can be clearly seen in Figure 17 where the two lines show the difference between the two different seat lengths.

Figure 16: Footbed parameters [38]

Figure 17: The effect of Heel wedge angle on perceived feeling

The mean normalised perceived (overall) ratings against the heel wedge angles at 75 mm heel height [36]. HL = the distance from the pternion to the fifth metatarsal head minus the distance from the

- 42 - Medial forefoot angle:

The medial forefoot angle is the angle between a line originating at the most medial point in the shoe apex region (M1 Figure 18), parallel to the last centre line plane, and a line connecting M1 to the medial aspect of the start of the toe allowance section of the shoe. This angle describes the narrowness of the toe section (toe box) of the shoe. A narrow toe box or in fact a toe box of reduced volume, in high heeled shoes has been blamed for the discomfort and poor health of the toes in regular wearers [44].

Lateral forefoot angle:

The lateral forefoot angle is the angle between a line passing through the point tangent to the most lateral point in the shoe apex region (M2, Figure 18), parallel to the last centre line plane and a line connecting M2 to the lateral aspect of the start of the toe allowance section of the shoe. This is the lateral version of the medial forefoot angle and also has a relationship with the narrowness of the toe box area and the volume of the forefoot area of the shoe. It has been shown that shoes with a rounded toe box produce the least pressure on medial aspect of the toes whilst a pointed toe shoe showed the least pressure on the lateral sides [79].

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Figure 18: Last forefoot angles Last ball girth:

The last ball girth is the circumference of last at the last contact point, which incorporates M1, M2 and the last contact point (Figure 19).

Changing the two forefoot angles and/or the last ball girth could lead to compression of the toes which will increase the recorded value of pressure in the forefoot region [79] (it is impossible to increase the compression without increasing the pressure as one directly affects the other). Morten’s neuroma (thickening of nerve tissue between metatarsals 3 and 4) is associated with compression of the inter-digital nerves and has therefore been linked to compression of the forefoot. Adjusting these forefoot features may have a direct effect on foot health if it was to reduce nerve tissue compression [4, 80].

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Figure 19: Last girth measurements

A: heel high instep girth, B: last medium instep girth, C: last ball girth, D: waist girth Last medium instep girth:

The last medium instep is the circumference of the last at the instep and is the smallest girth in the mid foot section of the last, (Figure 19). This provides us with information that can be linked to the fit of the shoe by comparing the difference between this measurement on the foot and the last.

Heel-high instep girth:

The heel-high instep girth is the shortest perimeter around the back of the foot and includes the rear most point of the last (pternion point) and the top surface of the foot in front of the ankle (Figure 19). This is a common measurement to compare the fit of shoes.

Waist girth:

The waist girth is the circumference around the last at the approximate centre of the metatarsal heads, measured in the last centre line plane (defined previously in this chapter). This is very similar to the last ball girth and thus variation in between these two girths might

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be expected to have similar effects. This measure has also been included here because past researchers have used both waist and last ball girth measures and it is useful to be aware of differences in their definition, even if their effects may be similar.

Figure 20: Features of the shoe

(image adapted from that shown in Chapman et al [77]) Toe spring angle:

This is the sagittal plane angle between the forefoot section of the last and the ground in the last centre line plane. For most shoes this is the same for both the last and the shoe, however when there is wedging under the forefoot it is possible that the sole design can change the amount of toe spring from that originally incorporated into the last. In all shoes this affects the natural gait pattern but for high heels it can be particularly important because when heel height is increased the toe spring angle will subsequently need to be changed, to ensure the toes can remain in contact with the ground. It has been

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stated that the role of the toes is to relieve the metatarsal heads of some of the pressure exerted on them [81] which is only possible if they are able to exert a load onto the ground. The amount of toe spring is however related to both sole material and the heel height. A harder sole will require a greater toe spring, whilst the higher the heel the less toe spring required [38]. This angle varies considerably between footwear and many heel height studies appear not to have controlled for this feature nor reported it and thus their results may be adversely affected.

2.2.2. Key features of the sole and heel of the shoe