WO 2011/051887 PCT/IB2010/054855 Title: FOOTWEAR FOR POSTURAL TRAINING Technical Field The present invention relates to footwear for improving the posture of the wearer. 5 Background Art Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field. 10 Problems with abnormalities or irregularities of posture may be treated by providing the patient with footwear insoles which provide a specially shaped surface on which the foot can rest, and which are designed to compensate for postural problems. Although in some cases these insoles provide little relief, in many cases insoles 15 provide considerable relief of posture-related ailments. However, they achieve this by the application of an external force that compensates for postural problems. The base of the foot is forced to conform to the shape of the insole. Subsequent postural changes are transferred from this source through the ankle and up the leg. Insoles do not teach the wearer how to correct their related postural problems; they simply treat 20 the results of those postural problems. In most cases the user is dependent upon the ongoing use of insoles. Disclosure of Invention An object of the present invention is the provision of footwear which assists in 25 improving the posture of the wearer, in the sense of actually training the wearer to adopt a corrected posture. The present invention provides an article of footwear which includes: - a flexible upper designed to give good support to, and conform to the shape of, 30 the wearer's foot; and - a series of fluid-filled sacs aligned along the length of the underside of the article of footwear; wherein each sac extends across the full width of the weight-bearing portion of the underside of the article of footwear; and said sacs are arranged so that no part of any 35 of the sacs lies under the arch of the wearer's foot in use. 1 WO 2011/051887 PCT/IB2010/054855 The article of footwear may be a shoe or a long or a short boot, depending upon the degree of support required by the wearer. The sacs may be filled with any suitable fluid, e.g. air. The pressure of the fluid within 5 the sacs is the ambient barometric pressure. Brief Description of the Drawings By way of example only, the preferred embodiment of the present invention is described in detail with reference to the accompanying drawings in which: 10 Figure 1 is a side view of a preferred embodiment of a shoe in accordance with the present invention, showing the lateral aspect of the shoe before a wearer applies weight to the base of the shoe; Figure 2 is a side view similar to Figure 1, but showing the medial aspect of the shoe; 15 Figure 3 is a side view as in Figure 1 but with the wearer applying weight to the base of the shoe; Figure 4 is a plan view of the underside of a basic form of the shoe; Figure 4a is a plan view of the underside of an advanced form of the shoe. Figure 5a is a sectional view of the shoe through the line A-A in an unloaded 20 state; Figure 5b is a sectional view of the shoe through the line A-A when the sac is evenly and correctly loaded by the wearer; and Figure 5c is a sectional view of the shoe through the line A-A when the sac is incorrectly loaded. 25 Best Mode for Carrying Out the Invention Referring to the drawings, an article of footwear in accordance with the present invention is depicted in the form of a shoe 10 which is provided with an upper 11, and a series of fluid filled sacs 12 to 17 inclusive. 30 The upper 11 must give good support to, and fit tightly around the foot of, the wearer, but must also be sufficiently pliable to remain comfortable while conforming to the shape of the wearer's foot. The upper 11 may be made of any of a large range of suitable materials, for example, lightweight canvas or thin leather, secured by laces or 35 hook and loop fastening strips; or an elasticated material sufficiently tight-fitting to give 2 WO 2011/051887 PCT/IB2010/054855 good support. The sacs may be made of any suitable, robust, flexible material, e.g. rubbers or plastics such as polyvinyl chloride. As shown most clearly in Figures 4 and 4a, the sacs 12 - 17 vary in size and shape, 5 but each sac extends across the full width of the weight-bearing portion of the underside of the shoe. It is believed that the exact number, shape and arrangement of the sacs could be varied over quite a wide range:- probably between 4 and 10. Sacs 12 and 13 lie underneath the heel, sac 14 opposite the arch of the foot, sacs 15 and 16 under the ball of the foot, and sac 17 under the toes. In combination, 10 sacs 15, 16 and 17 lie under the forefoot. Figure 4 represents a basic level of correspondence that would be applicable for an early stage of postural training. Figure 4a represents a more advanced level of correspondence that would be applicable for a later stage of postural training. This 15 more advanced shoe has a more accurate shaping of the sacs. In particular this shaping includes a toe sac that conforms closely to the outline of the toes, in a similar way to that of a regular shoe. This more arcuate shaping more closely prescribes correct toe region weight-bearing and correct toe off for gait. 20 Important features are as follows: 1. the sacs are sealed, and do not leak the fluid contained therein. 2. the sacs are capable of moulding appropriately in relation to loading by the 25 wearer. This may be achieved by providing that the fluid is free to move from one portion of a sac to another portion when the wearer's weight is applied. The sacs may be filled with any suitable fluid, e.g. air at ambient pressure. 3. the sacs in total must provide support only for the weight-bearing part of the 30 foot, and not underlie the arch of the foot when in use. 4. enough separate sacs must be used that each part of the full length of the foot has to be correctly positioned for balance to be achieved by the wearer. This extends from the rear-most curved part of the heel to the front-most curved part of the toes. 35 These curved parts of the heel and toes accommodate heel strike and toe off 3 WO 2011/051887 PCT/IB2010/054855 respectively. The curved surfaces naturally facilitate a gentle heel strike and generally improve the energy efficiency of regular gait. Each sac is permanently secured to the underside of the upper, e.g. by welding or 5 gluing. Figure 5a shows a section through sac 16 in an unloaded state. The top surface of the sac is shaped to correspond to the shape of the relative weight-bearing portion of the underside of the foot and is generally concave, to provide a close fit with the generally 10 convex sole of the foot. The height of the sacs may be varied for the intended use of the footwear:- for a person just starting to use this method of posture correction, relatively thinner sacs would make the footwear easier to use, and as the wearer's posture improved, they would graduate to footwear fitted with higher sacs, which are more difficult to use, but which offer a greater range of postural improvement, as 15 discussed below. Typical heights of the sacs, (unweighted) measured from the tips of the side edges to the peak, are: 20-35mm for children's footwear; 20 35-45mm for adults' footwear. The degree and shape of the generally concave upper surface of each sac varies, depending upon the sac's position relative to the foot. Typically, sacs for children's footwear have a concavity of 0-8mm, sacs for adults' footwear have a concavity of 0 25 16mm. Figure 5b shows the sac evenly, (i.e. correctly) loaded by the wearer. This flattens the ground-contacting portion of the sac and thus provides the wearer with an optimal, (i.e. most stable) foot weight bearing platform. 30 It should be emphasised that the footwear of the present invention is not intended for normal use:- it is specifically for retraining the deportment of the wearer so as to offer a permanent correction for postural problems. The footwear of the present invention is intended to be used for short periods only. The shoe is not recommended for regular 35 wear as the unstable features of the shoe may predispose the wearer to injury including a fall. It is not designed to be durable or provide significant traction with the 4 WO 2011/051887 PCT/IB2010/054855 ground. For the above reasons the shoe should only be worn on non slip and flat indoor surfaces. If the wearer applies his or her weight to any of the sacs unevenly, i.e. over to one side 5 or the other, the sac responds by compressing on the side with increased loading, and expanding on the other side, forming that sac into a wedge shape, as shown in Figure 5c. In this situation the contact area of the sac on the ground is significantly reduced and the associated region of the sac is shaped like a rocker. The resultant unstable weight-bearing surface is readily apparent to the wearer. The degree of 10 rocker curvature is intended to be sufficiently steep to elicit the feeling of instability but sufficiently gentle to facilitate controlled balance reactions and correction movements. Thus, the wearer can sense when he or she is spreading their weight incorrectly because the wedged sacs exaggerate any uneven weighting so that it is immediately 15 apparent and can be easily and quickly corrected. Because the effect of the sacs is to exaggerate any imbalance, it makes it easy for the wearer to detect, and therefore correct, this imbalance. A stable weight-bearing platform can only be provided by the correct loading of the sac. This encourages the wearer to spread their weight correctly and evenly across the sacs, so that the lower surface of the sacs maximally flatten 20 providing the optimal weight-bearing surface, as shown in Figure 3 and Figure 5B; in this configuration, the shoe is comfortable and stable to walk on. The balanced loading of sac 12 for heel strike and sac 17 for toe off instructs the wearer of the correct location on the heel for heel strike and the correct location on the forefoot for toe off, respectively. 25 Effectively, because the sacs lie under the whole of the weight-bearing surface of the foot, they provide a balance platform so that the wearer must constantly adjust his or her posture to search for and maintain a neutral, i.e. correctly balanced, state. The footwear of the present invention essentially provides an awareness training regime in 30 relation to postural defects. This training regime automatically involves all regions of the legs. The footwear of the present invention has been found to be effective in correcting all sideways deviations in foot posture including pronation (rolling inward of the foot with a 35 flattening of the foot arch). Because the correction of foot posture can only be achieved by correction of hip and knee postures it is believed that the present 5 WO 2011/051887 PCT/IB2010/054855 invention will correct postural problems of all regions of the legs. It is believed that the improvements in posture will include the pelvis and spine. Training instruction material must be provided with each pair of shoes, to ensure 5 beneficial usage of the shoes. Incorrect usage, such as prioritising lower leg and foot muscles to lift the arch of the foot and prevent the foot from rolling inward, will result in detrimental lower limb, pelvis and spinal function. The wearer must therefore be fully aware that incorrect usage of the shoes will promote and possibly entrench detrimental posture and widespread body function. 10 The footwear of the present invention has been found effective in retraining a wearer's posture so that, after a course of training using the footwear has been completed, the wearer then has markedly improved leg posture for all activities when wearing any footwear or when barefoot. The improvements extend from physically demanding 15 activities to resting non-weight-bearing states. The transference of posture correction obtained from wearing the article of footwear to not wearing it will to some extent be related to the wearer's determination to acquire new systemic posture skills. 6