Traditional theories consider the forefoot to be a constantly loaded structure, either with the metatarsal load formulas I-V (Lelièvre, Kapandji, etc.), or 2+1+1+1+1 (D. Morton, Martorell Martorell, Viladot, etc.). The reasons for arriving at such a definition reside in misunderstandings both anatomical and structural, in the failure to differentiate load (static and dynamic) and support, in the lack of reference to the diverse global functions of the foot either in one-fooled or two-footed positions, in imprecise functional correlations of the forefoot with regard to the global biomechanics and biodynamics of the foot, and finally in the difficulties of biomechanical research. Anatomical studies (FarabeufT, Lenoir, MafTei, Sanchez, Lues, Viladot, Del Torto e Perugia, etc.) of forefoot structures are significant only for a specific investigation and do not explain the functional biomechanics of the forefoot. During tests with classic Baropodometers (D. Morton, Martorell Martorell, Steinfort) the foot behaves like a cavus foot and is studied in this way, because both hindfoot and forefoot take load, or because the forefoot assumes a contractural pronation to compensate the load. Static loading is constant through its intensity and line of action, and if variable in time, the forces of inertia are non-existent or not worthy of consideration. By contrast, loading is dynamic when the intensity or the line of action, or both these elements, change so rapidly that supporting structures must absorb forces derived from the dynamics of the impact. In human biomechanics the fact that the skeletal structures, undergoing a dynamic load must absorb force, in this case the bones of the foot, the dynamics of impact of foot-to-ground is variable. The support is the surface area by which load is conveyed to the ground in various ways for distribution: this is the meaning of constant support and variable load. The function of the foot is to transfer the load of body-weight to the ground, by the supporting surface of either one or two feet. Under static load the foot is in equilibrium, although this may be stable or unstable dependent on whether the centre of gravity lies medially or otherwise to the area of support. Equilibrium is stable in two-footed and one-footed positions when the body's centre of gravity falls through the medial part of the area of support on two feet or one; it becomes unstable on walking because the centre of gravity tends to fall forward instead of through the area of support. Stable equilibrium in the two-footed position is passive as it is maintained by supporting structures without dynamic muscular action (electromyographic phase zero with only postural activity). By contrast, stable equilibrium in the single-footed standing position is active, for being limited to the supporting area of the single foot, it is only established by dynamic muscular action which carry the load of the forefoot more medially (electromyographic activity). The stable or unstable phases of static load are reversible, as are the phases of stable equilibrium typical of one or two-footed standing positions. The phase of unstable equilibrium whilst walking (static load) is reversible with the phase of dynamic load that intervenes on running or jumping. One-footed or two-footed positions, or the action of walking, concern biomechanics: walking creates loads which produce an intensity or a line of action of which the forces of inertia are practically non-existent or of no importance. To jump or to run concern biodynamics. With a view to define the study of loads simply and in order to consider a large number of subjects, I set up Podostatigraphic and Pressopodostatigraphic systems in 1969, and proved that for the single foot, in bipedal support, the gradient of load moved progressively towards the axis of the IVth ray, with the final load on the heel, cuboid and IVth metatarsal; by contrast in a monopedal position all metatarsals took load, except the Vth, with a final preponderance of load on the 1st. These are the results of isobaric plantar curves (fig. 3) from the same foot in bipedal or monopedal support. Biomechanical studies of the foot define, on the one hand, a constantly loaded structure represented by the heel, cuboid and IVth metatarsal, the so called « calcaneal foot », and on the other hand, a variably loaded structure represented by the talus, the navicular, the cuneiforms and the Ist-IInd-IIIrd metatarsals, being the « Talar foot ». The talar foot and the calcaneal foot (fig. 4) are functionally correlated (eversion and inversion movements) by means of the « axial joint » of the foot which arises at the subtalar joint and runs between the IIIrd and the IVth rays. The mechanics of the foot supported bipedally or monopedally result in a distribution of load corresponding to the formula: metatarsal load 4>3>2 for the single foot in the two-footed position, and metatarsal load 1>2=3=3 in the single footed position. The surface support is constant in the two functional attitudes because the forefoot always supports totally and constantly, moreover between the above mentioned extreme formulas of metatarsal load, there is an infinity of load moments correlated with the innumerable functional moments of the forefoot itself. Also, from an anatomic-architectural point of view, we recognise an axial differentation from a talar foot to a calcaneal foot (the metatarsal proximal structures, the placement and morphology of the plantar fascia, the disposition and morphology of joints) related to precise biomechanical functions. The calcaneal foot and the talar foot are functionally connected by a line of joints, the subtalar joint, the cuboid-navicular-cuneiform joint, the intermetatarsal IIIrd-IVth joint. This « axial joint » and its pivot is represented by the interosseus ligament of the subtalar joint. Furthermore, from an anatomic-functional point of view, we recognise a longitudinal differentiation of the foot into a talar foot and a calcaneal foot, the former constantly loaded (constant load structure) unvarying in its load function, and the latter variably loaded (variable load structure) needing stabilising muscular action to control bone structures and sustain different functional moments. We can define the load variability at forefoot level as a variable of the stabilisation of metatarsals at Lisfranc's joint; this stabilisation is assured by passive supportive structures for the IVth metatarsal, and for medial metatarsals, particularly the 1st, by the dynamic action of the majority of the intrinsic and extrinsic muscles of the foot. In conclusion, the data deduced from biomechanics, biodynamics, anatomo-architecture and functional anatomy of the foot result in tre definition of the forefoot as a « variable load structure ». The classic formulas of constant metatarsal load have lost their importance and this must be realised during the interpretation and treatment of forefoot disorders.