## 5 Conclusions  
This article introduces a low-cost system based on a geometrical model and free video analysis software that is capable of measuring angular variations at the sagittal plane in metatarsophalangeal and tibialotalar joints when high heels are used. The information collected in this study for ankle joints is not novel, but allowed the authors to confirm the validity of the followed measuring method and to, thus, support the validity of the angular variations measured at the metatarsophalangeal joints when high heels were used. As far as the authors are aware, these metatarsophalangeal joint angular variations on the sagittal plane when wearing high heels have not been previously published by anyone. The method herein exposed may be especially useful for those new researchers with a limited budget who are looking for a simple gait analysis technique. It also opens new analysis possibilities for walk race trainers that want to improve the technique of newcomers to the discipline, without having to spend a lot of money on expensive gadgets, and even for therapists that want to follow their patient's progression. This study also has several limitations. First, our participants wore shoes that were provided for the experiments, and not their own. This may have influenced their gait characteristics. However, the subjects were allowed enough time to become familiar with the shoes before measures were taken so as to minimize any possible bias. Second, the participants were inexperienced high heel users. According to some authors, such as [PERSON] et al. [16], experience has no effect on heart rate, oxygen consumption or lower limb mechanics. [PERSON] et al. [47] also found that lower limb joint moments or EMG activity remain the same. Others, such as [PERSON] [23], indicated a strong influence on the upper trunk, but a lesser one on knees, and evidence was almost unnoticeable on ankles. [PERSON] et al. [21] studied several variables of the joint angles in the sagittal plane for experienced and non-experienced women, finding that there were no significant differences in any variables of the joint angles in the sagittal plane between the two groups, except that experienced wearers showed a decreased range of motion (ROM) during knee flexion-extension and greater mean ankle plantar flexion during the stance phase. Consequently, although it may initially seem that experience may have an effect on gait, precursory studies indicate no obvious differences in gait kinematics and kinetics on the sagittal plane between experienced and inexperienced high heel users when just the ankle and metatarsophalangeal joints are considered [3; 21]. The use of a low number of subjects in pilot studies, as we have done here, is not ideal, but it is neither unusual. For example, [PERSON] et al. [48] used just one participant, and [PERSON] et al. [2] used three participants to validate their proposals. However, this may potentially introduce undesired biases, and although the results obtained align with those published in previous studies, suggesting that its precision suffices for the intended purpose of studying the angular variations in the joints of the feet, it would be convenient to compare the precision of the methodology with other methods to validate its applicability in fields that usually require more precise approaches, such as the clinical and pathological fields. Future studies of the author's research group intend to follow this line and compare this system with a gold standard one. Conceptualization, J.S.V., A.M.I.-B. and F.C. ; methodology, J.S.V., F.L.S.-G. and A.R.-P.; software, F.L.S.-G. and A.R.-P.; validation, J.S.V., A.M.I.-B. and F.C. ; formal analysis, J.S.V. and F.C. ; investigation, J.S.V. and F.C. ; resources, F.L.S.-G., A.M.I.-B. and A.R.-P.; data curation, A.M.I.-B. and A.R.-P.; writing--original draft preparation, J.S.V., F.L.S.-G., A.M.I.-B., A.R.-P. and F.C. ; writing--review and editing, J.S.V., A.M.I.-B. and F.C. ; visualization, J.S.V. ; supervision, A.M.I.-B. and F.C.