Baropodometric parameters variation with body weight loss: a prospective cohort study

Background One of the major public health problems of the 21 st century is obesity. Baropodometry is commonly used to determine specic loads on the plantar surface of the foot and the comportment of the body center of pressure (CoP). To evaluate the redistribution of the baropodometric parameters: static and dynamic plantar pressures and antero – posterior CoP, by decreasing body weight. Methods A sample of 43 subjects (24 male, 19 female) participated in the study. A hypocaloric diet was designed with the aim to reduce their body weight. The baropodometric exam was performed in two occasions: weight 1 – Session 1 and weight 2 – Session 2, when they had lost between 12 and 18 kg. The foot was divided in 9 areas: heel, midfoot, 5 metatarsal heads (MTHs), Hallux, 2-5 toes. The Footwork® pressure platform was used to carry out the evaluation. Results Subjects reduce an 11.59% their mean weight. Foot pressure decrease was statistically signicant between the rst and second measurements (p < 0.05). For the static on the Hallux, 2 nd MTH, 3 rd MTH, 5 th MTH and heel, while for the dynamic the pressure decreases on the whole study areas except on the 2 nd and 5 th toes. For the CoP, a notable posterior displacement was observed. There were no gender differences. Conclusion We can conclude that weight loss affected positively to both plantar pressures and CoP, since statistically signicant changes were observed in the baropodometric parameters between the two times studied.


Introduction:
Obesity is in one of the major public health problems of the 21st century and its prevalence has tripled in many European countries in the last decades (1). It is a strongly problem associated with a lower quality of life, as well as with the development of serious chronic metabolic, cardiac and circulatory pathologies and musculoskeletal disorders (2,3).
Quantitative data showed that excessive body weight negatively effects on standing and walking (4,5).
Plantar pressure measurement is commonly used to determine speci c loads on the plantar surface of the foot. There are many case studies that assess pressures of the normal foot and try to establish patterns of pathological pressures (6). The CoP represents the average of all the weight that is in contact with the surface of the oor and is expressed as the point where the vector of the vertical reaction forces of the soil is located (6,7).
In the literature it can be found how body weight in uences on plantar pressure data and on the position of the CoP (8)(9)(10). Excesses of body weight has shown to have negative structural consequences in the feet and lower limbs (11)(12)(13)(14).
Obesity is also related with an anterior displacement of the CoP (15), since the instability in obese people, associated to weight increasing, seems to be determinant with CoP in an anterior position (16).
Computerized baropodometry is helpful for foot diseases diagnosis, foot function evaluation and to follow-up the treatment. It has been practiced to determine speci c weight parameters in obese adults, among others (10,14).
Nonetheless, there are not in the literature speci c studies that have analyzed by computerized baropodometry how plantar pressures and CoP improve by decreasing body weight in obese adults. Therefore, with this study we aim to evaluate plantar pressures and antero -posterior CoP improvement by decreasing body weight in static and dynamic baropodometry data collection in obese adults.

Methods:
Design and sample Between June 2017 and October 2017, we performed a prospective cohort study. The design of the present research was based on and executed according to the STROBE reporting guideline. The study was approved by the Ethics Committee of Clinical Research of Aragón (CEICA) with number C.P.-C.I. PI17/0203. Participants voluntarily signed an informed consent. The study has been conducted in accordance with the Helsinki Principles.
Participants were recruited at one Endocrinology and Nutrition private clinic in Huesca, Spain. Inclusion criteria included overweight subjects between 18 and 65 years old, medical weight loss indicated, no lower limb or spine pathology that might affect normal gait, nor structural or functional deformities in the feet. Candidates who did not comply inclusion criteria, or reported pain in their feet within the previous 6 months, or had any previous foot surgery were excluded.

Procedure
Participants were rigorously evaluated by the same endocrine doctor and podiatrist at baseline (Session 1) and at the end of the study after weight loss intervention (Session 2), when each participant had lost between 11-12% of its corporal weight. Therefore, we obtained 2 weight related with the two sessions: Session 1 -Weight 1; Session 2 -Weight 2.
In order to achieve the proposed weight loss, lifestyle modi cation was applied (17): A speci c very low-calorie diet (< 800 kcal/day), and 2 daily sessions of 15 minutes of anaerobic physical exercise depending on the capacity of the participants, were designed (18,19).
At Session 1 and Session 2, before and after weight loss intervention, participants were subjected to a baropodometric examination (static and dynamic). It allowed to quantitatively mapping pressures in each segment of the plantar surface (20,21). For the static, participants were asked to stand in the center of the platform for 5 seconds, with their arms on either side of the body in a natural position looking straight ahead (22). To minimize individual´s corporal uctuations in static (as body weight oscillation and imbalance) we applied this procedure 3 times per session (22). For the dynamic, participants were asked to walk barefoot on the platform at their normal pace following the 3-step protocol, which requires landing on the platform on the third step of gait (23). To minimize individual's corporal uctuations in dynamic (as body weight oscillation, imbalance and changes in gait speed) we applied this procedure 3 times per session (22). Both feet were subdivided into 9 areas: heel, midfoot, 5 MTHs, the Hallux, 2-5 toes (Fig. 1). Selection of the areas of the present study is justi ed because it is based on the daily clinic, where the consultations of overweight patients are usually due to discomfort or pain in MTH, reason why these are studied separately and is supported by authors like Hills et al. (11), who performed a complete study of the differences of pressures between obese and non-obese subjects. <Figure 1 goes here> Peak pressures of these areas in kg/cm2 and the position of the CoP, were obtained using the Footwork® software (20).
Peak pressure data were graphically exposed and related with the two weights for each patient.

Statistical Analysis
An initial exploratory analysis of all clinical variables was carried out. Continuous variables were expressed as mean ± standard deviation (SD), whereas qualitative variables were expressed as frequencies and percentages. Continuous data were checked for normality by Kolmogorov-Smirnov Test. Chi-Square Test was applied to show the relationship between qualitative variables. To compare mean weights between two independent groups according to normality, we used Student's-T Test and ANOVA Test to "m" groups. Differences between Session 1 and Session 2, were performed using mean comparison methods, Wilcoxon when the variable did not follow normal distribution, and Student's T for related samples when there was normality. To quantify the difference between weight and plantar pressures and the CoP at Session 1 and Session 2 the "change percentage" was calculated, which was de ned as the relative variation in percentage points between both sessions: Weight-Change % ( The "improve" variable was established in order to analyze the possible relationship between weight loss and the 9 pressure foot areas considered at Session 1 and Session 2 for both: static and dynamic baropodometry. Statistical signi cance level was set at p < 0.05, con dence level set in the comparisons was 95%. The statistical analyses were performed using the SPSS software 22.0 for Windows (SPSS Ibérica, Madrid, Spain).

Results:
The mean comparison of the two weights studied is shown in Table 1. The loss of weights between both times was statistically signi cant (p < 0.05). As well there can be observed the weight differences between genders which had no statistical signi cance.  Table 2 shows the analysis of the relationship between the dependent variable (change CoP %) and the independent variables (gender and change weight %), which aims to nd a predictive equation. Independent variables have a 23.1% explanatory capability about the comportment of the dependent variable. For the plantar pressures, in static, Table 3, a statistically signi cant mean pressure decrease between the rst and the second measurement on the Hallux, 2nd MTH, 3rd MTH, 5th MTH and heel was observed.   Table 5 shows the descriptive analysis, as well as the number of patients (n) considered in each case. The relationship between weight change and pressure change was studied using the Spearman correlation coe cient.  In static, it is observed that the weight variation is statistically signi cant in the Hallux, 1st MTH, 2nd MTH, 3rd MTH and 4th MTH.
In dynamics between Session 1 and Session 2 we found only a signi cant association between pressure changes and weight variation in the 2nd to 5th toes and midfoot.

Discussion:
Changes in long -term posture, such as those produced by weight gain, may induce permanent degenerative changes in the musculoskeletal system (25). Therefore weight loss, will in uence positively body posture, which can be perfectly veri ed by studying plantar pressure and the movement of the CoP (26).
In the present research there have been no signi cant changes between the variation of the CoP and the gender, as evidenced by Rogind et al. (27) and Nordahl et al. (28). But we have observed that the CoP moves backwards when losing weight. These results match with those obtained by DeVita et al. (29), who demonstrated that the CoP displaces forwards when weight increases. Gilleard and Smith in 2007 (16), emphasized this and added the hypothesis of the lack of stability in obese as a determinant of anterior displacement.
Obesity has been associated with greater forward movement of the center of pressures (15). Body mass gain in obese people generates an instability increasing which leads to a major muscular response to maintain the CoP in the center of the support polygon. The location of the fat mass in the body (thorax-abdominal in men; hips in women) contributes to the antero-posterior instability (30).
In the literature we nd opposite opinions about the in uence of the weight in plantar pressure values. Several studies agree that there is a direct correlation between both factors (11)(12)(13), i.e. weight in uences plantar pressures, which has structural consequences in the feet and lower limbs (11).
Our ndings showed that when weight decreased statistically signi cant differences were found on the MTHs in static and on the midfoot in dynamics (31). These ndings are supported by Birtane et al. (32), who demonstrated that weight gain does not increase peak pressures of the forefoot walking, although it was found that the most sensitive anatomical area was 1st MTH where it was observed that weight gain increases peak pressures (13).
In the study of Arnold et al. (33), they observed the correlation between higher plantar pressures when weight increases. There were studied three times: when subjects increase 5, 10 and 15 kg, being found the relation for the two latest weights on the Hallux, every MTHs and heel.
Riddiford-Harland et al. (34), justi es the fact that the middle zone is the most sensitive to pressure change due to the increase in the impact forces that limit the capacity of the medial longitudinal arch to attenuate this change and therefore the adaptation occurs by increase the support of the middle part of the foot (34). Arnold et al. (33) manifests that in his study this area does not appear as statistically signi cant because weight gains only reached up to 15 kg, our study does not support this hypothesis since the weight loss oscillated between 5.5 and 13.2 kg and this was the only statistically signi cant area along with the toes.
In the case of Hills et al. it was noted that the most notable increase in peak pressure among non-obese and obese occurred on the middle region of the foot. Their study coincides with our data but with large differences in the mean of body mass between obese and non-obese subjects, 36.0 kg for women and 43.6 kg for men (11). Arnold bases his foundation on this study, that a greater variance in weight between both groups (obesity and non-obesity) more signi cant the difference on the middle zone (33).
The results of the present study can be related with those of Song et al. (35) and Mueller et al. (13), who defend that when the weight increases the plantar arch descends (more in pronated foot) increasing the load on the medial surface of the foot´s sole, coinciding with our study.
One limitation of the present research should be highlighted, the lateral movement of the CoP as no considered. Anyway, the ndings of this work reveal the important relationship between weight and musculoskeletal system.
We can conclude that weight loss positively affects the static CoP and plantar pressures, both static and dynamic, since there is observed statistically signi cant changes on antero -posterior CoP and plantar pressures between the two times studied. CoP moves backwards which means balance and healthy postural gain, it should be noted that weight reduction affects differently static and dynamic plantar pressures. We can observe that there is no anatomical area of the 9 studied which coincides between static and dynamic studies as statistically signi cant.   Dynamic baropodometry footprint (left), 9 study foot areas (right).