## 1 Introduction  
The common clinical presentation of plantar fasciopathy (PF) includes pain and discomfort normally in the inferior heel region; however, it can also be associated with the radiation of pain along the entire foot as well. Plantar fasciopathy is a clinical manifestation that is usually accentuated with the first steps in the morning, and with sudden acute painful episodes in daily life [1; 2; 3; 4]. There are no high-quality epidemiological studies that are available on the prevalence of PF in the general population. In the US alone, heel pain is seen in 11-15% of provider visits requiring professional care [5]. The etiopathogenesis of plantar fasciopathy is mostly due to imbalances in the biomechanics of the subject, such as subtalar hyper pronation, medialized subtalar axes, and the flattening of the medial longitudinal arch [2], but another series of associated factors such as osteoarthritis, neurological involvement, direct microtrauma, and systemic conditioning factors can also promote its appearance [1]. During the human gait cycle, the length of the plantar aponeurosis suffers alterations [6]. A significant increase in the length of the plantar aponeurosis occurs in the middle phase of the gait cycle, while a shortening occurs in the Windlass mechanism, when the foot leaves the ground [7]. At the end of the final stance phase of the gait cycle, the foot tries to propel itself off the ground, increasing the dorsiflexion of the metatarasophalangeal joints [6], thus decreasing the traction branch of the plantar aponeurosis from its point of origin to its insertion point. Changes in the length and the traction of the plantar fascia produced during human locomotion increase its mechanical load and tension, and in the case of pathology, these can cause pain and discomfort [8]. With regard to the biomechanical research on gait analysis, [PERSON] et al. presented a three-dimensional (3-D) foot model that was able to simulate the biomechanical behavior of the plantar fascia during the stance phase. They were able to demonstrate an increase in tension and peak stresses in the fascia during the stance phase, and in the phase from midstance to pre-swing. Based on these findings, a reduction in the force of the Achilles tendon and adjustments to the gait pattern, such as walking at a lower speed to reduce heel elevation height, or wearing rocker bottom shoes, may decrease the plantar fascia load [9]. Recent studies have shown interest in the biomechanics of human gait, reaching the conclusion that biomechanics should be considered as a risk factor for PF. Equally, plantar fascia disorders could lead to an alteration in the gait pattern and kinematic changes of the lower extremity, which may help to prevent PF [10; 11]. It is difficult to fully understand the causes and prognosis of pain in PF patients, based only on a few biomechanical human gait parameters. Because of this, several studies have been carried out to identify not only the biomechanics, but also the parameters that can be measured, such as evaluating the geometry, phase, and time of gait with an intelligent gait analysis system [11]. In this regard, previous studies have suggested that minor changes in the angle (sagittal plane) of foot motion might lead to a higher magnitude of facial strain, and they may lead to other injuries of the lower limbs [10; 12]. Foot pronation could be a cause of plantar fascia tension when people walk, which facilitates the center of pressure shifting from the lateral to the medial side of the foot, thus inhibiting the sagittal movement of the foot and inducing the early tension of the plantar fascia [13]. In addition, previous research suggested that being overweight could add stress to the plantar fascia during walking [14]. Most of the plantar fascia research is carried out in subjects with unilateral plantar fascioquh, or in studies that do not specify whether both feet are affected or not [9; 12; 13]. Only [PERSON] et al. reported on this condition in subjects with bilateral plantar fascioquh [11].