CHANGES OF PLANTAR ARCH AFTER GLOBAL PHYSICAL EXERCISES IN HIGH SCHOOL STUDENTS

. The bipedal position acquired by mankind through evolution comes with a heavy price, such as overburdening of the spinal column and lower limbs, comparable difficulties in both breathing and blood transport to the brain. The loads imposed on musculoskeletal tissues during daily activities are modified by variations in joint mechanics, which increases the risk of orthopaedic dysfunctions. The purpose of this study is to investigate the effects of a 3-month global physical exercise programme using the Pilates method on the plantar arch. The participants were 18 high school students (11 female and 7 male) aged between 14 and 16 years. Methodology: To evaluate the plantar arch under static and dynamic conditions, the barosensitive BTS P-Walk platform (BTS, Italy) was used. The participants performed a group exercise programme over three months under the close supervision of the therapist; it consisted of 20 sessions carried out twice a week on average, with each session lasting 50 minutes. Initial and final results were compared and statistically interpreted (using the Paired Samples t Test and multiple statistical indicators). Conclusion: The study found numerical improvements in all four parameters, and for three of them, the change was statistically significant (P < 0.05 in the Paired Samples t Test). Statistically significant improvements were recorded for the left foot arch when evaluated in the standing position and for both feet during walking.


Introduction
The bipedal position acquired by mankind through evolution comes with a heavy price, such as overburdening of the spinal column and lower limbs, comparable difficulties in both breathing and blood transport to the brain (Dos Santos et al., 2006).
The loads imposed on musculoskeletal tissues during daily activities are modified by variations in joint mechanics, increasing the risk of orthopaedic dysfunctions (Borges et al., 2013).
In both its static and dynamic roles, the foot serves as the structural foundation of body posture (Hillstrom et al., 2013).Correct gait is ensured by optimal foot stabilisation and physiological arches (Müller et al., 2012).
According to Ghasemi et al. (2016), the presence of bilateral foot pronation showed an increase in sacral angle, pelvic inclination, lumbar lordosis and thoracic kyphosis.This indicates that the foot arch has great relevance for the whole body alignment.Woźniacka et al. (2013) have found that high-arched foot is the most common foot defect among children aged 3-13 years, and flat foot is least frequently observed in children aged 3-13 years.
The study by Borges et al. (2013) highlighted that not only structure but also function was altered by improper foot posture; the authors concluded that high arch was correlated with more intense pain syndrome.
A certain amount of physical activity is essential for a child's development (Truszczyńska-Baszak et al., 2017).In general, postural deviations are becoming more and more prevalent, and for adolescents going through a growth spurt, the musculoskeletal system is exposed to factors that could hamper natural growth (Afanasieva et al., 2020).
In addition to the physiological changes experienced by adolescents during the growth period, there are other factors that affect posture and can impair normal growth, such as spending extended periods of time in one position, engaging in little or no physical activity every day, carrying a heavy load unevenly or performing activities that cause the body to move in an asymmetrical manner (Sedrez et al., 2015).
Knowing the importance of proper foot alignment, a variety of intervention methods have been studied with the purpose of correcting foot structure and function.Pabón-Carrasco et al. (2020) state that short foot exercise could be considered a useful tool to deal with plantar pathologies, given that the biomechanics of the lower limb improves through the daily practice of such exercises, which seems to increase stability and stress absorption (Sulowska et al., 2016).These specific exercises target the intrinsic foot muscle that has a major impact on both standing and walking, and along with the rest of its anatomical features, is thought to play a crucial role in preserving the plantar arch and regulating foot posture.
Taking into consideration that specific exercises improve foot posture and function and that a plantar arch outside the physiological range can affect the whole body posture, the authors considered using global physical exercises (such as those specific to the Pilates method), which are confirmed to improve not only posture (Gou et al., 2021) but also static and dynamic balance (Lim et al., 2016) and gait (Roh et al., 2016), in order to see if they can have a positive impact on correcting foot misalignments.
Knowing that maintaining balance and vertical alignment largely depends on postural control and stability (Neculăeș & Lucaci, 2021), and their correlation with the effects of global exercises described by the Pilates method is very likely, practising this form of physical activity will bring a change at plantar level.
The purpose of this study was to investigate the effects of a 3-month global physical exercise programme using the Pilates method on the plantar arch of high school students.

Participants
The participants were 18 high school students (11 female and 7 male) aged between 14 and 16 years (Table 1).None of them showed visible alignment deviations or postural adaptation problems.The students (and their legal guardians) gave written informed consent to participate in the study, and all procedures were performed in compliance with the 1964 Declaration of Helsinki.
The inclusion criteria used were:  Adolescents aged 14-16 years;  No medical history related to structural deviations of the posture.The exclusion criteria used were:  Age under 14 or over 16 years;  Visible structural deviations of the posture;  Previous involvement in corrective programmes or posture exercises.

Instruments
To evaluate the plantar arch under static and dynamic conditions, the barosensitive BTS P-Walk platform (BTS, Italy) was used.This platform, which contains more than 3000 sensors, can evaluate and interpret (using G-Studio software) plantar pressure distribution, whether the plantar arch is physiological or whether there is a flat foot/hollow foot (pes cavus), and can also perform stabilometric analysis.Under dynamic conditions, besides the evaluation of plantar pressure and plantar arch, force, surface area and speed are also recorded while rolling the foot on the equipment.
When the static analysis is performed, the participant's feet are placed over the markings drawn in the middle of the platform.The patient is instructed to maintain a relaxed position, look straight at a fixed point and not to move for 30 seconds (acquisition time is 20 seconds).The raw data are processed by the G-Walk software, which generates a report (Figure 1).The report in Figure 1 shows how the software evaluates the contact surface calculated as a percentage in three areas: forefoot, midfoot and hindfoot.In the lower part of the report, a Plantar Arch Index is presented, which uses normative data allowing the result to be integrated into one of seven possible categories (normal foot, three variations of hollow foot and three variations of flat foot).
The G-Studio software uses a scale ranging from 0% to 100% to place the foot typology into one of seven possible categories, depending on the contact surface found in the midfoot, which is called the Arch Index.
Thus, the arch types have been classified as follows: between 0% and 7% -Heavy High Arch Foot (grade 3 hollow foot, where there is a break in the contact between the forefoot and hindfoot); between 7% and 14% -High Arch Foot (grade 2 hollow foot); between 14% and 21% -Light High Arch Foot (grade 1 hollow foot); between 21% and 28% -Normal Foot; over 28% -the types of flat foot differ from the standard classification (in functional and structural terms) or the one found in the paediatric literature where the flat foot is described as flexible, semi-flexible and rigid.The G-Studio software makes the following classification: between 28% and 35% -Light Flat Foot, when its width is wider than normal in the midfoot portion but the plantar arch is partially preserved; between 35% and 42% -Flat Foot; between 42% and 100% -Heavy Flat Foot (collapsed plantar arch).
For dynamic analysis, the patient is asked to walk from one end of the room to the other and back, with the P-Walk pressure plate positioned in the middle of the distance so that the participant can step on it during natural movement.The walk is repeated until a minimum of 4-5 correct steps performed with each lower limb are recorded on the board.The software makes a comparative analysis of all steps and chooses one of them as the characteristic step (Figure 2).Using the characteristic step of each lower limb, different reports are generated.

Figure 1. G-Studio report -Static plantar analysis
The upper part of the report (Figure 3) shows data for each characteristic step (step time, area, average and maximum pressure).In the central and lower parts of the report, a diagram is presented, which contains the calculation of the plantar surface that makes contact with the platform during dynamic movement and the classification of the type of plantar arch according to the percentage found in the midfoot area (similar to the static analysis).

Procedure
Post-evaluation, the participants performed a group exercise programme under the close supervision of the therapist.The exercises were verbally "guided" by the physiotherapist to establish the initial positions and exercise sequence, setting the dosage through the counting speed and the number of repetitions.The therapist also intervened directly by giving verbal or tactile indications whenever a deviation from the movement plane was noticed or to correct possible wrong executions.
The exercise plan was built based on the Pilates method but respected the therapeutic principles with the aim of reducing clinically unexpressed postural deviations.The patients included in this group participated in a 3-month programme consisting of 20 sessions carried out twice a week on average, with each session lasting 50 minutes.
The principle of progression was also observed, in the sense that the number of repetitions and series was gradually increased, depending on the patients' exercise tolerance.Each session consisted of a warm-up part and the main programme (Table 2).After completing the final evaluation, the results were compared and statistically interpreted.The Paired Samples t Test was used to check whether there were values with statistically significant difference for each selected parameter, and the following statistical indicators were calculated: Mean, 95% Confidence Interval for Mean, 5% Trimmed Mean, Median, Variance, Standard Deviation, Minimum, Maximum, Range, Interquartile Range, Skewness, Kurtosis.

Results
The parameters selected for this study were:  Left Foot Arch Index (static analysis);  Right Foot Arch Index (static analysis);  Left Foot Arch Index (dynamic analysis);  Right Foot Arch Index (dynamic analysis).The results of the initial and final evaluations were compiled in tabular format (Table 3) and statistically processed.The static analysis parameters show how the Arch Index was recorded for the left and right feet in the standing position.For dynamic analysis, the results are based on the foot contact with the device during walking.The percentile value shows how much the midfoot is in contact with the pressure plate.In order to interpret the effects of the intervention plan using physical exercises "guided" by the physiotherapist on the "Left Foot Arch Index (static analysis)" parameter, reference should be made to the ideal value provided by the G-Studio software, which ranges between 21% and 28%.
Table 4 shows an average increase of 4.716, from 6.088 in the initial evaluation to 10.804 in the final evaluation, which is graphically represented in Figure 4.The standard deviation recorded a slight decrease, from 7.58 to 7.45.The increased value of the arithmetic mean and its approach to 21% reveals the presence of a numerically positive effect generated by the physical exercise programme.When applying the Paired Samples t Test (Table 5) to check whether statistically significant changes occurred, a P value of 0.002 was identified.Given that this value is less than 0.05, the mean difference can be regarded as statistically significant.Considering the significant improvement, the effect size was calculated using Cohen's d value, and the result was 0.877, which indicates a large effect size.For the "Right Foot Arch Index (static analysis)" parameter (Table 6), the results show a mean of 14.7978 in the initial evaluation and 16.5061 in the final evaluation, which indicates that the value has increased by 1.708 (Figure 5).The standard deviation recorded a slight decrease, from 8.72 to 7.23.As for the "Left Foot Arch Index (static analysis)" parameter, there is an increase in the arithmetic mean value, which shows a numerically positive effect.For the t Test (Table 7), P = 0.052, which is marginally significant, given that the value is close to 0.05 and the investigated sample is small.According to Table 8, the mean value increased by 2.99, from 12.69 in the initial evaluation to 15.68 in the final evaluation.The standard deviation recorded a decrease, from 9.15 to 7.83.Both the increase in the arithmetic mean value and the P value = 0.024, as revealed by the Paired Samples t Test (Table 9), show not only a numerically positive effect of the programme but also a statistically significant mean difference.For this parameter, Cohen's d value is 0.583, which indicates a medium effect size.As shown in Table 10, the mean value increased by 4.49, from 14.16 in the initial evaluation to 18.65 in the final evaluation.The standard deviation recorded a decrease, from 8.68 to 6.89.The increased value of the arithmetic mean and its approach to 21% reveals the presence of a numerically positive effect generated by the physical exercise programme.When applying the Paired Samples t Test (Table 11) to check whether statistically significant changes occurred, a P value of 0.006 was identified, indicating that the difference was statistically significant.Cohen's d value is 0.744, which can be interpreted as a mediumto-large effect size for the Right Foot Arch Index evaluated during walking.

Discussion
Analysing the results and comparing them with the Arch Index foot typology classification presented by the G-Studio software, an important fact is highlighted.Thus, in the initial evaluation, 16 out of 18 participants showed different types of high arch for the left foot (88.88%) and 11 out of 18 for the right foot (61.11%).At the same time, the way the foot arch worked during walking was different, in the sense that 13 participants presented one of the high arch types for the left foot (72.22%) and 14 for the right foot (77.77%).These data reveal that the group aged 14-16 tends to have high-arched feet, especially for the left foot (which was non-dominant in the investigated adolescents).
Similar results were found by Szczepanowska-Wołowiec et al. (2021) in a cross-sectional study on children with ages between 10 and 15 years; the authors concluded that flat footedness was not considered to be a common deformity among children and adolescents.
Another important element that we can notice after the initial evaluation is the different way in which the foot arch works during walking compared to standing (Figure 6).In the above figure, it can be seen that the Arch Index is very small for the left foot in the standing position and more than doubles during walking (static value is 6.088, but it increases by 108.4% in dynamic conditions, reaching 12.688).For the right foot, the changes from static to dynamic evaluation act the opposite way (while standing, the Arch Index is 14.798, but it decreases by 4.34% during walking, with the Arch Index reaching 14.154).
Comparing the results from the initial evaluation with the final ones, an overall improvement of the Arch Index is observed after the intervention programme, with small particularities.The degree of improvement is consistent with the results found in a recent study by Sánchez-Rodríguez et al. (2020), where the experimental group showed significant improvement after 9 weeks.As seen in Figure 7, the average Plantar Index for the left foot while standing reveals a big improvement, increasing by 4.716% in the final evaluation; at the same time, the t Test indicates a P value less than 0.05, which shows that the mean difference is statistically significant.For the right foot, the improvement is smaller (1.708%), which can be explained by the fact that the initial value was closer to the Normal Foot value compared to the left foot.Even in this case, the difference generated by the intervention programme is marginally significant (p = 0.052).

Figure 8. Dynamic evaluation -Comparison of means
The graphical representation in Figure 8 shows the comparison of Arch Index values resulting from the dynamic evaluation, where both the left foot and the right foot recorded a statistically significant P value < 0.05.It is noted that the initial value for the left foot is lower than for the right foot; however, in the final evaluation, the right foot recorded a greater increase in the Arch Index (4.49% for the right foot vs. 2.99% for the left foot).
The study reveals a set of limitations that need to be considered, such as the small number of participants, which is why it can only provide a vague picture of the specific pattern on how the plantar arch works in the standing position and during walking for high school students aged 14-16 years, and a wider range of participants would be more useful to draw definitive conclusions.The participants' age and gender can also be taken into account.Using homogeneous groups where all participants are in the same category to compare data (such as adding gender-separated pre-adolescent and senior groups) can bring more conclusive results.

Conclusion
Considering all the evaluation results, we can conclude that global physical exercise improves foot posture at the level of foot arch.The study found numerical improvements in all four parameters, and for three of them (namely, the left foot arch evaluated while standing and both feet evaluated during walking), the change was statistically significant (for the fourth parameter, the improvement was marginally significant).
The initial evaluation clearly shows that a high-arched foot is more common in high school students than the Normal Foot typology.The way the foot arch works is different in the standing position compared to walking.At the same time, there are obvious differences between the left foot arch and the right foot arch.
Another conclusion that can be drawn from this study is that global physical exercise has the greatest impact on the most important postural imbalance, in this case, the left foot arch evaluated under static conditions, for which the initial Arch Index was 6.09 but improved by 108% (to 12.69) in the final evaluation.
Given the study results and limitations, further research is needed to assess the short-and long-term effects of different approaches.
Authors' Contribution: Both authors have equally contributed to this study and should be considered as main authors.
Funding: This research received no external funding.

Institutional Review Board Statement:
The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of the National University of Physical Education and Sports in Bucharest, Romania (ID: 1024).

Informed Consent Statement:
The patients/participants provided their written informed consent to participate in this study.

Figure 2 .
Figure 2. Dynamic plantar analysis -Identifying the characteristic step

Figure 5 .
Figure 5. Graphical representation of the values for the "Right Foot Arch Index (static analysis)" parameter

Figure 6 .
Figure 6.Initial evaluation -Comparison of means

Figure 7 .
Figure 7. Static evaluation -Comparison of means

Table 1 .
Data about study participants

Table 2 .
Warm-up and main programme exercises

Table 3 .
Evaluation resultsThe above table indicates that most of the values are below 21-28%, which represents the Normal Foot, especially the results for the "Left Foot Arch Index" parameter, where only two participants (11.11%) out of 18 have a Normal Arch Index.

Table 4 .
Statistical indicators for the "Left Foot Arch Index (static analysis)" parameter

Table 5 .
Paired Samples t Test for the "Left Foot Arch Index (static analysis)" parameter

Table 6 .
Statistical indicators for the "Right Foot Arch Index (static analysis)" parameter

Table 7 .
Paired Samples t Test for the "Right Foot Arch Index (static analysis)" parameter

Table 8 .
Statistical indicators for the "Left Foot Arch Index (dynamic analysis)" parameter

Table 9 .
Paired Samples t Test for the "Left Foot Arch Index (dynamic analysis)" parameter

Table 10 .
Statistical indicators for the "Right Foot Arch Index (dynamic analysis)" parameter

Table 11 .
Paired Samples t Test for the "Right Foot Arch Index (dynamic analysis)" parameter