An item of footwear for increasing leg-muscle and/or lower-abdominal-/back-muscle tone comprising: a strap arrangement for securing the item of footwear to a foot of a user; and a sole comprising at least an upper layer, for engaging a foot of a user in use or a further upper layer, and a lower layer, for engaging the ground in use, wherein the upper layer comprises two or more materials of different compressive resistances, or densities, arranged as a frontal/toe region, an arch region and a heel region, the sole is arranged such that application of a user's weight, during use, causes instability in at least one portion of the upper layer, which requires balance correction by a user.