*2.1. Subjects*

The institutional review board at Rey Juan Carlos University approved the study. All subjects signed the informed consent form prior to beginning this study. The following inclusion criteria were required to participate in this study [35]: (1st) to have at least 10◦ dorsiflexion of the ankle after complete knee fully dorsiflexion; (2nd) to have at least 30◦ motion in the functional subtalar joint; (3rd) to have at least 15◦ of motion along the mid-tarsal joint longitudinal axis; (4th) to reach at least 8 mm of non-weight bearing motion of the first ray; (5th) older than 18 years and younger than 38 years; (6th) no lower limb pathology or chronic condition at the time of recruitment and measurement; and (7th) prior experience of the use of shoes with high heel height during at least the prior year [36]. The exclusion criteria included established hallux valgus; prior history of foot and lower limb traumas, fractures, or surgeries; and congenital deformities or existing diagnoses of neurological, inflammatory, metabolic or vascular diseases. Subjects were also excluded if they showed less than 40◦ passive

dorsiflexion of the first MPJ (as a non-weight bearing technique previously described according to Buell et al. [37]). This range has been reported to be the IMPJ dorsiflexion range used during normal propulsion [38,39] and indicates joint structural limitations. In addition, male sex was an exclusion criterion because they rarely wear high-heeled shoes.
