The issue concerning the build and performance of the foot has been debated in numerous scientific publications for many years. Feet are one of the most important elements of the human motor system responsible for amortisation, endurance when maintaining a standing position for a long time and a strong take-off while walking and running [1]. Assessing foot arch is crucial in terms of diagnostics, particularly in the puberty period. Some deviations from proper foot arch are reflected in the pathogenesis of diseases developing in other parts of the body [2].
In contemporary sport, injuries are a common phenomenon and difficult to avoid even in the case of recreational physical activity [3]. Particular attention should be paid to youth, especially football as they are prone to excessive loads of the lower extremity musculoskeletal system. The formation of the foot arch in football players is determined by a wide range of factors such as body mass, type of footwear, the surface on which training sessions are held and training loads [4,5].
Undoubtedly, football is the most popular and most widespread team sport in the world. The Polish Football Association (PFA) has 530000 male players and 8000 female players registered [6]. According to the literature, the number of injuries in this sport is estimated to constitute 50-60% of all sports injuries. The research carried out on football players revealed that as many as 97% of players suffered musculoskeletal system injuries at some point in their career [4].
The demands that football players have to face are of particular significance in the case of young footballers. Initial training in Poland starts at the age of 8-9 [7]. The cumulating microinjuries and excessive training loads in a young growing body may lead to post-injury degenerative changes and to the recurrence of the injury [7,8]. The form and intensity of training should be appropriately adapted to the age and physical capabilities of a child. Many players are not aware of the disorders of foot build and functioning and thus, by training regularly and intensively for competitions, they increase the severity of the pathology or are conducive to the occurrence of injury [9]. A complete examination of all the foot dimensions and arches as well as the influence of significant factors on its shape will make it possible to assess the predisposition for injuries [10,2]. Therefore, the aim of this work was to assess foot arch and the distribution of foot-to-ground contact forces in young football players as well as their influence on the frequency and types of injuries.
The study included 30 male football players aged 13-18 (mean age 14.5 years). The group consisted of 20 boys from the U-15 category from the Progres Sports Academy in Cracow and 10 players from the lower- and upper-secondary schools in Cracow under the patronage of Marcin Gortat. All the participants (N=30, 100%) had training experience of more than 5 years.
Among the examined players, mean length of the left foot was 25.5 cm and of the right foot – 25.3 cm. Moreover, mean width of the forefoot was measured and it was 9.5 cm in the case of the left foot and 9.6 cm in the case of the right foot. Mean width of the hindfoot was 5.8 cm for both feet.
The study involved a podoscopic assessment of both feet, an examination of both feet on a tensometric mat and a survey.
During the podoscopic test, both feet were assessed simultaneously. Each of the players was standing on a podoscope with bare feet placed parallel to each other. A proper body posture was maintained, upper limbs were held freely along the trunk. The selected parameters were assessed with the use of a 2-D podoscan with built-in sensors and a laptop with special software analysing the image obtained from the scanner. Owing to the construction of this equipment, the obtained result was real (1:1 scale) and the software made it possible to record and store images as well as automatically measure and compare potential asymmetries and angles [2]. In order to assess the longitudinal foot arch, the Clarke’s method was applied. The transverse foot arch was evaluated by means of the Wejsflog index.
A computerized platform (tensometric mat) was used to assess the distribution of forces on the plantar side of the foot, which makes it possible to find the location of excessive loads. After the examination on the mat, the following measurements were obtained: centre of gravity location, maximum support point, the plantar side of the right and left foot surface expressed in cm2, the distribution of weight between the two limbs and the distribution of loads between the left and right leg.
The survey included 26 closed-ended questions and personal information questions regarding such data as gender, age, body mass and body height. The questions referred to the frequency of training sessions, types and location of injuries and treatment applied in young footballers. The players responded to the questions independently after being provided the survey instructions.
The statistical analysis was performed with the use of the STATISTICA 13.1 PL software. The quantitative analysis included calculations of the number and percentage of players in particular sports classes. In order to find correlations between the variables, chi-square test (χ2) was applied. In the case of small groups, Yates’s correction or Fisher’s exact test was applied. The results were significant when their probability value (p) was lower than the significance level χ = 0.05 (p < 0.05).
As far as longitudinal foot arch is concerned, the most common type found on the basis of the Clarke’s angle was flat foot (for both legs). The norms for the Clarke’s angle which were accepted for the players aged 13 ranged between 32 and 57° for the left foot and 32-59° for the right foot. In turn, the norms for the study participants aged 18 ranged from 42° to 54°. While analysing the transverse foot arch on the basis of the Wejsflog index, it was noted that the largest group of the examined players had a proper foot arch both in the left and right foot (table 1).
Type of longitudinal and transverse foot arch in the examined footballers
| increased | normal | decreased | flat | |||
|---|---|---|---|---|---|---|
| Longitudinal foot arch | Left foot | N | 0 | 10 | 0 | 20 |
| % | 0 | 33 | 0 | 67 | ||
| Right foot | N | 0 | 12 | 0 | 18 | |
| % | 0 | 40 | 0 | 60 | ||
| Transverse foot arch | Left foot | N | 0 | 26 | 0 | 4 |
| % | 0 | 87 | 0 | 13 | ||
| Right foot | N | 0 | 22 | 0 | 8 | |
| % | 0 | 73 | 0 | 27 |
The analysis of the statistical data revealed that several participants (N=8) had their centre of gravity moved forward. A slightly lower number of subjects (N=5) had it moved to the left or forward to the right (N=4). The remaining study participants had their centre of gravity moved backward to the right (N=3), forward to the left (N=3), backward (N=3) and located in the middle of the support polygon (N=3). The lowest number of people (N=1) had it moved backward to the left.
The next variables to be examined were the middle point of the maximum foot load and the symmetry of foot load. In over a half of the study participants (N=16, 54%) had their middle point of the maximum foot load in the right hindfoot. Considerably fewer individuals had it in the left hindfoot (N=7, 23%) and right forefoot (N=6, 20%). It was least common in the left forefoot (N=1, 3%). In turn, in the case of foot load symmetry, the largest number of players loaded their left limb (N=15, 50%). Bearing loads by the right limb was less common (N=10, 33%). The lowest number of the study participants (N=5, 17%) bore loads symmetrically by the right and left limb.
Another factor investigated in this study was the distribution of foot-to-ground contact forces. In some of the study participants (N=12, 40%), larger loads were borne by the left foot, while a smaller group (N=6, 20%) bore larger loads on the right foot. In the remaining participants (N=12, 40%), foot-to-ground contact forces were distributed similarly.
Finally, the percentage distribution of loads between the forefoot and hindfoot was analysed. In the case of the left foot, the largest loads were noted in the hindfoot (N=17, 57%), while slightly fewer participants bore loads on the forefoot (N=7, 23%). In turn, the remaining players demonstrated equal distribution on both sides (N=6, 20%). The percentage distribution between the forefoot and hindfoot of the right limb indicated that the largest group of individuals (N=19, 63%) bore more load on the forefoot, and less load on the hindfoot (N=8, 27%). A proper equal distribution of loads was observed least frequently (N=3, 10%).
The first survey question concerned the frequency of training sessions per week. The majority of the study participants (N=21, 70%) trained 4 times, a smaller group of players (N=7, 23%) trained 5 times, while the lowest number (N=2, 7%) trained 6 times a week. None of the participants selected answers “once”, “twice”, “3 times” or “7 times”.
In the question concerning the duration of one training session, the majority of the respondents (N=22, 73%) selected the answer “90 minutes” and participants (N=8, 27%) choose “more than 90 minutes”. None of the players selected the answer “45 minutes” or “60 minutes”
The next question regarded warming up before the training. The vast majority of the respondents (N=29, 97%) always did warm-up exercises, while considerably fewer participants (N=1, 3%) did them only sometimes. None of the respondents selected the answer “rarely” or “never” (table 2).
Implementation of warm-up exercises before the training and stretching exercises after the training among the examined players
| N | % | ||
|---|---|---|---|
| Warm-up before the training | Always | 29 | 97 |
| Sometimes | 1 | 3 | |
| Rarely | 0 | 0 | |
| Never | 0 | 0 | |
| Stretching after the training | Always | 12 | 40 |
| Sometimes | 15 | 50 | |
| Rarely | 3 | 10 | |
| Never | 0 | 0 |
Another question concerned applying stretching exercises after the training session. Half of the respondents (N=15, 50%) sometimes did stretching exercises, while slightly fewer participants (N=12, 40%) did them after every training. In turn, the lowest number of the study participants (N=3, 10%) rarely did stretching exercises. Nobody selected the answer “never”.
The next question referred to injuries. The majority of the study participants (N=26, 87%) had incurred a sports injury, while the remaining ones (N=4, 13%) had never experienced that.
In the following question, the respondents were asked about the location of the injury. The most common answers included the muscles of the thigh (N=15, 58 %) and the knee joint (N=11, 43%). The foot and the ankle joint constituted the same percentage of all the injuries (N=10, 39%). The least common injuries were hip joint injuries (N=7, 27%) calf muscle injuries (N=6, 23%).
The next question regarded the type of the injury that the study participants incurred. The most common type of injury included a pulled muscle (N=12, 46%) and muscle strain (N=11, 42%). Sprains (N=10, 39%), overloads (N=9, 35%), abrasions and local hematomas (N=7, 27%) were slightly less common. Fractures (N=4, 15%) and inflammations (N=4, 15%) constituted a scant minority, while the least common injuries included dislocations (N=3, 12%) and tears (N=2, 8%).
The question concerning the recurrence of the same injury received more answers that were positive (N=16, 53%). The remaining respondents (N=14, 47%) did not incur the same injury again.
Finally, the players were asked about the type of injury that they incurred due to football. The most common answers included ankle joint sprains, Achilles tendon damage and knee joint injury (table 3).
Type of injury experienced by the examined players
| Achilles tendon injury | Ankle sprain | Knee joint injury | |||
|---|---|---|---|---|---|
| N | % | N | % | N | |
| Yes | 12 | 46 | 10 | 39 | 11 |
| No | 14 | 54 | 16 | 61 | 15 |
The correlations between the loads borne by lower limbs and selected factors were examined. The correlation between the loads borne by lower limbs and the frequency of injuries among the examined players was the first correlation to be assessed. No statistically significant correlations between the variables were noted either for the left or for the right limb (table 4).
Correlation between loads borne by a lower limb and the frequency of injuries
| Chi-square | df | p | |
|---|---|---|---|
| Loads borne by the left lower limb and the frequency of injuries | 0.099 | df=2 | P=0.95152 |
| Loads borne by the right lower limb and the frequency of injuries | 1.533 | df=2 | P=0.46454 |
The second correlation under examination was the correlation between the loads borne by lower limbs and types of foot arch in the study participants. The analysis did not reveal statistically significant correlations between the variables either for the left or for the right foot (table 5).
Correlations between loads borne by a lower limb and foot arch
| Chi-square | df | p | |
|---|---|---|---|
| Loads borne by the left lower limb and left foot arch | 3.807 | df=2 | P= 0.14907 |
| Loads borne by the right lower limb and right foot arch | 0.988 | df= 2 | P=0.60998 |
The third correlation investigated was the relation between the number of training sessions per week and the frequency of injuries among the study participants. The analysis revealed a statistically significant correlation between the examined variables (table 6).
Correlation between the frequency of training sessions per week and the frequency of injuries
| Chi-square | df | p | |
|---|---|---|---|
| The frequency of training sessions per week and the frequency of injuries | 6.923 | df=2 | P=0.03139 |
Football is the most popular sport in the world. The research conducted by the International Federation of Association Football (FIFA) in 2006 indicated that in that period approximately 265 million people played football in the world [11]. Like in the majority of sports, playing football poses several risks of injuries in players, both during competitions and when played for leisure.
According to Brito et al. [12], the prevalence of injuries among players reaches the level of 1.2 to 4.7 per 1000 hours of exposure during a season. Faude, Robler and Junge [13] indicated that the prevalence of injuries among players aged 13-19 was at the level of 1-5 cases per 1000 hours of training. Leininger, Knox and Comstock [14] reported that the ratio of injuries connected with age was at the level of 0.4% among children aged 2-4, 12.3% among 5-9-year-olds, 49.0% in the age group of 10-14-year-olds and 38.4% among children aged 15 to 18. The study by Żołnikowski et al. [6] revealed that the largest percentage, i.e. 85% of football injuries, were incurred by players below 23 years of age, where under-15-year-olds constituted 45% of them. Our study revealed that injuries related to playing football were common and were incurred by the majority of the examined players.
According to Adamczyk and Luboiński [15], the most common injuries include pulling a muscle (10-47% of the injuries) and ankle joint sprains (28-35%). Similar conclusions were also drawn by Grzybowski and Radzioch [16], who examined 339 cases in the period of 6 years and observed that sprains were the most common injuries (52.6%). Other injuries were muscle and ligament damage (20.7%) and abrasions (17.6%). What is more, injuries usually occurred in the knee joint (35.7%), ankle joint (21.8%) as well as thigh (16.7%) and calf (9.9%). According to other authors, i.e. Hadała et al. [17], the most common types of injuries included abrasions, pulling and sprains, while the least common ones were muscle strains and fractures. The studies also confirmed that the knee joint (33%) and ankle joint (30%) were the most common injury locations. Similar results were obtained in our study. The examined players usually experienced pulling, strains, sprains and overloads. They most often regarded thigh muscles, knee joint, ankle joint and foot.
The lower limb is the most common location of an injury so, undoubtedly, proper foot build is of high significance. Each foot dysfunction can lead to the disorders of the biokinematic chain of the whole body. Therefore, in terms of prevention, getting to know correlations between indicators describing the foot and somatic body features and between foot dysfunctions and motor system disorders and lifestyle diseases is extremely important. Moreover, performance of feet significantly influences gait and run quality and affects the results obtained in numerous sports [18, 2, 19, 20]. Gueen et al. [21] observed that while running, individuals with flat feet had their forefoot and midfoot considerably loaded, due to which they were more prone to injuries.
According to the results obtained by Grabara [22], sports training leads to the lowering of longitudinal and transverse foot arch and toe deformities. Her results are also similar to the results of research by Lautor et al. [23], who observed a frequent occurrence of flat foot and hallux valgus. The correlation between adaptive changes occurring in the foot as a result of training and training experience was also revealed by Farhan et al. [9]. While analysing the longitudinal foot arch with the use of the Clarke’s angle, it was found that in the majority of players, both feet were flat. However, although longitudinal flat foot is a common disorder, transverse flat foot has not been noted very often.
Disorders in foot build exert a considerable influence on the frequency of injuries. According to Williams and McClay [24], players with a lower foot arch are more prone to soft tissue damage and knee joint injuries. In our research, no significant correlations were found between the location of foot loads and the frequency of injuries and between loads borne by limbs and foot arches. In turn, an interesting conclusion can be drawn from the statistically significant correlation between the frequency of training sessions and the frequency of injuries.
The presented results and an attempt at their interpretation constitute the material that is useful in assessing feet among young footballers. They may complete further research directed mainly at assessing the effects of improper foot build on the frequency and types of injuries as well as the influence of load distribution in the area of forefoot and hindfoot on the type of foot arch.
Flat foot was the most common type of longitudinal foot arch among the examined footballers.
Normal foot was the most common type of transverse foot arch among the examined footballers.
No correlations were found between foot load location and the type of longitudinal foot arch.
No correlations were revealed between foot load location and the frequency of injuries.
The frequency of training sessions exerted an influence on the prevalence of injuries in the examined football players.