*2.4. Procedure*

Each of 80 participants began static or dynamic study randomly after choosing a sealed envelope that assigned them to one group or another; there were 40 total in each group. They then selected four sealed envelopes with each of the four conditions of the study (unshod, 3 cm, 6 cm, and 9 cm). These dictated the order of use at random. The 40 participants of the dynamic group did the static test in randomly order with four sealed envelopes and vice versa with the 40 participants in the static test (Figure 5).

Before beginning either angular measurements, position "zero" was achieved to calibrate the assessment and determine a reference position from which to begin the angular record. We asked the participants to remain in a relaxed standing position near the generated field for a few seconds until the software determined the Reference [35].

Participants used a pair of sandals with three different prefabricated high heels (Figure 6). The sandals (Figure 7) provided a strap in the first digital web space, and the rearfoot had a semi-rigid bowl that permitted the heels to be held into the shoes. The participants used the sandals and tested the sensations with the cables before starting the study; they then walked along the walkway at a self-selected speed. When they were comfortable, they began the static or dynamic measurements depending on the order chosen by the random chance.

For the dynamic condition study, participants initiated gait for 1 m at a self-selected speed before entering the 1.5 m calibrated capture volume. They then continued walking for a further 1.5 m (two steps); this capture was repeated for 5 trials with each of 3 different types of prefabricated heel heights (3 cm, 6 cm and 9 cm) and unshod condition. Care was taken when inserting and removing the prefabricated heel height so that the sensor devices was not disturbed or displaced. For the static condition study, subjects were asked to stand on their tiptoe (to reach the maximal range of motion of the joint) for 2 s. There were five trials with each of three different types of prefabricated heel heights (3 cm, 6 cm and 9 cm) and unshod condition. The mean of the five trials was used in the posterior analysis for each static and dynamic test.

**Figure 5.** Randomized flow chart.

**Figure 6.** Prefabricated high-heels. The heels were made on hard silicone. The additional height was added over the top.

**Figure 7.** Sandal model used in the study. A free toe-tip-box is present to allow movement of proximal phalanx of the hallux and first metatarsal bone.

Later, a "cardan system" with three possibilities of rotation (X-Y-Z) in two ways was used to draw angular and linear information from both PPH and IMTT bones movements: mediolateral axis (X), defined dorsiflexion (DF), and plantar flexion (PF) movements on the sagittal plane as well as frontal plane inversion (VR) and eversion (VL) movements through an antero-posterior axis (Y). Movement around a craneocaudal axis (Z) was considered to be abduction (ABD) and adduction (ADD) movements on a transverse plane. The anatomical landmarks and coordinate systems were previously detailed [35,44,45]. All bone movements were recorded after considering the laboratory coordinate system. All assessments used the same heel height in contralateral extremity under the foot to maintain the body balance during these trials [46]. Independent assessment of the bone movements showed that the results were only produced by high heel effects and not by bone interference.
