SEXUAL DIMORPHISM IN SIGNIFICANT CORRELATIONS FREQUENCY BETWEEN THE CHARACTERISTICS OF BODY TRUNK AND FEET IN CHILDREN AGED 4 TO 6 YEARS

Relatively few publications have concerned characteristics of body trunk and feet. It is generally suggested that correlations exist between the characteristics of the developing foot and the spinal column. The purpose of the study was to show sexual dimorphism in frequency of incidence, as well as significant correlations concerning selected body trunk and feet parameters in the group of 4−6-year-old children. The examinations conducted in a group of children aged 4 to 6 allowed for recording 2,988 observations, including 1,482 girls and 1,506 boys, and values of 87 characteristics that described body trunk and feet. The test stands for the measurement of the selected parameters using the photogrammetric method consisted of a personal computer, software, screen and printer, and a projection-reception device with a camera. The general number of body trunk characteristics having significant correlations with feet parameters in females was slightly higher. The number of relationships in sagittal and frontal planes was the same in both sexes. The characteristics that differentiated males from females were found mainly in transverse and frontal planes. The number of feet characteristics that most often showed significant correlations with body trunk parameters was higher in girls than in boys. These were mainly characteristics concerning width and length, longitudinal arch and disorders in the position of the feet. The characteristics that differentiated boys described only the longitudinal arch of the feet.


Introduction
The issue of sexual dimorphism in the field of somatic traits has occurred in numerous publications and seems to be obvious, well-described and undisputed (Górniak, 2000;Webster-Gandy, Warren, Henry, 2003;Wolański, 2005, Gosh, Choudhary, Chowdhury, Ghosh, 2009Perenc, Radochońska, 2012;Koudelová, Brůžek, Cagáňová, #0# Alicja Kaiser, Mirosław Mrozkowiak, Marek Sokołowski Krajíček, Velemínská, 2015;Wojciechowska-Maszkowska, Wieloch, 2015). However, there have been very few publications regarding the impact and correlations of body trunk and foot parameters. M. Steinmetz (1984) assumes there is interdependence between the type of the forming foot and the shape of the spine. The suggestion that if the spinal traits can be corrected by modifying the foot parameters, the foot parameters can be influenced by changing the spinal characteristics, raises a number of objections. However, the results of the studies presented below, at least theoretically, allow such a possibility. M. Steinmetz (1984) also emphasizes legitimacy of wearing corrective footwear since a correctly positioned foot in a special footwear can cause spinal deformation which is consistent with the views expressed by the authors of this paper. The pilot studies by J. Drzał-Grabiec and S. Snela (2012) in the population of 7−9-year-old girls and boys allowed to find relationships between the longitudinal arch of the right and left foot, measured with Clarke's angle, and length parameters describing body posture. According to the research, there was a significant correlation between the longitudinal arch of both feet, measured using Clarke's angle and the spine height between points C7 and S1. This dependence was confirmed when considering the division into subgroups of boys and girls as well as age subgroups. As far as age groups are concerned, a significant correlation was observed only in the group of 9-year-olds.
The purpose of the study was to show sexual dimorphism in frequency of incidence, as well as significant correlations concerning selected body trunk and feet parameters in the group of 4−6-year-old children.

Material and method
The studies conducted in the Warmińsko-Mazurskie Voivodeship enabled to record 2,988 observations including 1,482 girls and 1,506 boys. Body posture was assessed by means of the photogrammetric method with regard to generally adopted principles (Mrozkowiak, 2015). The statistical analysis covered 87 angular and linear parameters of the spine, pelvis, trunk and feet in the sagittal, frontal and transverse planes, in particular age and environment categories (Table 1, Table 2). The empirical data were the quantitative and qualitative characteristics (gender, domicile, etc.). The conducted calculations covering the values of position statistics (arithmetic mean, quartiles), the dispersion parameter (standard deviation) and symmetry indicators (asymmetry and concentration indicators) provided a full view of the distribution of the studied features considering gender, environment and age ranges. The correlations and their significance were assessed using p-value and frequency expressed in percentage. Due to editorial requirements related to article volume, the authors deliberately did not include the detailed description and a full statistical analysis of the findings, citing only partial results ensuing from the subject of the paper.    The fundamental assumption of the study was to always assess the habitual posture as a relatively constant individual characteristic of a human being. This posture reflected an individual emotional, psychical and social condition of the subject. Moreover, the posture provided the most reliable description of the subject's silhouette at a given time and in a place. The conducted diagnostics did not determine whether an individual's posture was correct or not, it only identified the condition of its ontogenetic development. Objectified and comparable test results were able to ensure that the postural parameters adopted for the analysis were recorded with possible to determine compensations. The combined assessment of the trunk and feet allowed to objectively determine the quality of the postural model applied in a given environment, gender and age category. The measuring instrument used in the study determined several tens of parameters describing body posture (Table 1, Table 2). Obtaining the spatial picture was possible thanks to displaying the line of strictly defined parameters on back and feet. The lines falling on the skin of a child got distorted depending on the configuration of the surface screen. The applied lens ensured that the imaging of a subject could be received with the use of the MORA 4G HD diagnostics set, the picture can be received and transmitted onto a computer by a special optical system with a camera. The distortions of the line imaging recorded in the computer memory were processed through a numerical algorithm on the topographic map of the investigated surface. When conducting the study, one should be aware of the fact that the taken photo records an image of the silhouette displayed on a child's skin (Mrozkowiak, 2015). The acceptance of the Research Ethics Committee at the Kazimierz Wielki University in Bydgoszcz had been obtained before the research were conducted 1 .

Results
The analysis of the findings headed in two directions. The first one was to determine how often and which body trunk parameters most frequently revealed a significant correlation with feet parameters within sexual dimorphism. The second, to explain which feet parameters most often significantly correlated with the body trunk parameters, also within sexual dimorphism.
The analysis of the study results with regard to sexual dimorphism, concerning feet parameters with which body trunk parameters correlated most frequently, showed the following parameters in girls: width of both feet (SZP, SZL), length of the left foot (DLL), valgus angle of the fifth toe in the right foot (BetaPp), and of the Plantar surface of left foot (PSL), height and length of the first arch in the right foot (WP1, DP1), width of the first and fifth longitudinal arch of the left foot (SL1, SL5). As regards boys, these were the values of such parameters as height of the second and third longitudinal arch in the right foot (WP2, WP3), width of the third and fourth arch in the right foot (SP3, SP4), height of the fourth and length of the fifth arch (WL4, DL5) and width of the third arch in the left foot (SL3) ( Table 3). The analysis of the study results in terms of sexual dimorphism of body trunk parameters that most frequently differentiated the relationships with feet parameters revealed that among girls these were the values of the following parameters: the angle, height and depth of lumbar lordosis (KLL, RLL, GLL), angle of body trunk bent to the left side in the frontal plane (KNT−), angle of body bent to side in the sagittal plane (KPT−), asymmetry of waist triangles height with the right triangle up (TT−), asymmetry of the distance of lower angles from the spinous process with the angle of the left scapula being more distanced (OL), maximum inclination of one spinous process to the left (UK−). Among boys, these characteristics included: height of thoracic kyphosis (RKP), angle of body trunk bent to the right side in the frontal plane (KNT), asymmetry of the projection line of lower scapula angles with the left one more convex (UB), angle of pelvis rotated to the right (KSM), number of the vertebrae maximally distanced to the left from the spinous process (NK−) (Table 4).
No research similar to those presented in this study had been found in source literature. Statistical analysis revealed a number of dependencies significant for posture equilibrium disorders. Despite evident results of statistical analysis, the above presented relations should not be approached uncritically, for what logical connection can there occur between depth and height of thoracic kyphosis and varus or valgus angle of the fifth toe? While planning a correction procedure, one should take into consideration the above presented correlations not only between values of feet parameters and spine-pelvis system, but also between spine-pelvis system and feet, as well as weight and height, as presented in other research of the authors. The analysed relations between spine-pelvis and feet characteristics at boys and girls aged 4−18 demonstrate that the most often a significant correlation occurs in spinal sagittal longitudinal features, less often in frontal or transverse ones. These features most often showed dependency between right and left foot width, and valgus angle of the right foot's fifth toe. A significant correlation between feet parameters and spine-pelvis characteristics most often occurred with reference to width of both feet. Another correlation was repeatedly revealed between the height and length of lumbar lordosis and thoracic kyphosis, in the angle of upper thoracic part bent (Mrozkowiak, Jazdończyk, 2015). Among the analysed correlations between selected feet characteristics and trunk features in children and youth aged 4−18 years, those most popular and frequent occurred, as expected, at the age of 7−13 years, less frequent -at the age of 14−18 years, and the least frequent -at the age of 4−6 years. It should also be noted that, though in the first age group no meaningful relations with morphological features of feet (length and width) appear, in the remaining two -they do. Within sexual dimorphism at the age of 4−6 years, more numerous and frequent correlations occur among boys than girls. At the age of 7−13 years this disparity levels out, yet still boys maintain a slight dominance. In the last age group, 14−18-year-olds, girls display more numerous and frequent correlations than boys, which was also expected. No quantitative disparity of features occurred within environmental dimorphism in age group 4−6-year-olds, while frequency of significant correlations is slightly higher among boys. However, in the age group of 7−13-year-olds, individuals from urban environment display greater dominance in both, quantity and frequency of correlations with trunk features. In the last analysed age group, of 14−18-year-olds, mutual quantitative and frequency-related disparities disappear, approaching levels of the age group of 4−6-year-olds (Sokołowski, Mrozkowiak, 2017). The frequency analysis of essential correlations between feet and trunk features in youth aged 14−18 years revealed that values of left foot display more frequent correlation with trunk features than right foot. Feet characteristics display more frequent correlations with trunk features in sagittal plane, less in frontal one, and sporadic in transverse one. The features which feet characteristics most often correlate with are: angle of trunk bent to the left in frontal plane and height of lumbar lordosis, angle of upper thoracic bent, length of lumbar lordosis, height of thoracic kyphosis, scapulas height asymmetry, with the right one placed higher (Mrozkowiak et al., 2018). 1. The general number of body trunk parameters that significantly correlated with feet parameters was slightly higher in females. The number of dependencies regarding sagittal and frontal parameters was the same in both female and male subjects. The traits that differentiated males from females mainly concerned sagittal and frontal planes.
2. The number of feet characteristics that most often showed significant correlations with body trunk parameters was higher in girls than in boys. These were mainly characteristics concerning width and length, longitudinal arch and disorders in the position of toes. The characteristics that differentiated boys described only the longitudinal arch of the feet.