The relation between foot arch morphology (flat foot and pes cavus) and lower extremity injuries is controversial.^1–9 Some authors have determined a relation between foot morphology and the incidence of lower extremity injury in army recruits,^1–4 whereas others were unable to obtain conclusive evidence in athletes.^5–9 The reason for the discrepancy remains unresolved, but a possibility is the sport specific foot morphology of athletes engaged in various types of sport.

Nowadays, performance athletes begin intense training at a very young age. Such training undertaken when the musculoskeletal system is immature may result in specific changes in the body. It is well known that, when there is a unilateral overload—for example, in tennis players—an athlete may exhibit an obvious discrepancy, such as increased external rotation and decreased internal rotation compared with the opposite side.¹⁰ Although it is not clear, there are some data showing that sport specific training and repeated movements may have an effect on the arch index (AI) of the sole. An increased incidence of flat foot in runners^11,12 and alpine skiers,¹¹ and subnormal transverse foot arch in soccer and tennis players¹¹ have been reported. As there are very few published reports comparing sole AIs of participants of different sports, we conducted this study. Gymnasts were included in view of their participation in sports training at a very early age, weightlifters, because they lift tremendous weights in training sessions, handball players, as representatives of indoor sports, and soccer players and wrestlers, as these are two of the most popular sports.

The purpose of this cross sectional study was to determine the effects of various sports on the AI. We evaluated the foot arch types and AI of a total of 116 high level athletes and 30 non-athletic men using images obtained from a podoscope.

METHODS

Subjects

AIs of 124 male elite athletes (27 soccer players, 24 wrestlers, 19 weightlifters, 32 handball players, and 22 gymnasts) and 30 non-athletic men as a control group were evaluated. Age, age at onset of training, and history of bone/soft tissue injuries in the foot and ankle were recorded.

Sole AI

Subjects were asked to stand still on the podoscope. Digital still camera images of both soles were transferred from the podoscope to a computer. From the stored images, AI was calculated by division of the narrowest part of the sole by the widest part of the heel, then multiplication of the ratio by 100.¹³ All calculations were performed by the same clinician (STA). The clinician calculated another 30 AIs twice, with a one week interval between measurements, to determine intraobserver reliability. The intraclass correlation coefficient was 0.975; the same investigator evaluated all findings.

Statistical analysis

Because the AIs did not show a normal distribution, we applied non-parametric tests: the Kruskal-Wallis test for intergroup differences and the Mann-Whitney U test for the significant intergroup differences. Correlations between left and right sole AI were calculated by Spearman’s rank correlation test in the athletes and non-athletic controls. The significance level was accepted as p<0.05.

RESULTS

The mean (SD) age was 23.4 (3.6) years (range 18–30) for the athletes and 23.2 (3.2) years (range 18–28) for the non-athletes. The mean age at which sports training was initiated was 11.6 (2.8) years. There was no significant difference in age between the athletes, but gymnasts started training at a significantly younger age than the other athletes (7.3 (1.4) years; p  =  0.0004). Eight athletes (three soccer players, two handball players, one wrestler, and two gymnasts) who had been treated for foot and ankle fractures or dislocations were excluded from the study. Table 1 gives details of the subjects.

Table 2 presents the AIs of the athletes and non-athletic controls. The AI of the right foot in the gymnasts was significantly lower than that of the soccer players, wrestlers, and non-athletes (p<0.01). The AI of the right foot in the wrestlers was significantly higher than that of the soccer players, handball players, weightlifters, gymnasts, and non-athletes (p<0.03). For the left foot, the AI in the gymnasts was significantly lower than in the wrestlers and non-athletes (p<0.001), and the AI in the wrestlers was significantly higher than in the soccer players, handball players, and gymnasts (p<0.005). The AIs of both soles in handball players were significantly lower than in the non-athletic controls (p  =  0.049).

Correlation between the AIs of the right and left foot was low in soccer players, handball players, and wrestlers (r  =  0.31, 0.69, and 0.56 respectively), but high in gymnasts, weightlifters, and the non-athletic controls (r  =  0.96, 0.88, and 0.80 respectively).

DISCUSSION

This study was designed to evaluate sole AIs in different sports. The AIs of gymnasts and wrestlers were found to be significantly different from those of the other sportsmen tested, and those of gymnasts and handball players were significantly different from those of the non-athletic controls. The AI was lowest in gymnasts and highest in wrestlers. Correlation between the right and left foot was lower in handball and soccer players (where there is leg dominance) and wrestlers (where there is no leg dominance), and higher in athletes in sports with no dominance and in the non-athletic controls.

There are controversial data in the literature on the relation between foot arch morphology (flat foot and pes cavus) and lower extremity injuries.^1–9 Pes cavus and pes planus may be a causative factor in stress fractures of the femur, tibia, metatarsals, and different parts of the lower extremities in army recruits, but no such relation was found between pes planus and the incidence of lower extremity injury in athletes.^1–9 The reason for these differences has not been elucidated. Differences in evaluation criteria, such as foot arches as mentioned in the longitudinal study of Volkov¹² and arch indices as in the study of Klingele et al¹¹ and the present study, may partially explain the different results between army recruits and athletes. Future prospective studies should thus be undertaken and carefully designed, bearing in mind the effect of foot morphology and possible predisposition to lower extremity injuries in soldiers.

Certain muscles in the foot and ankle either depress or support the arch, and their insufficiency may result in changes in the sole. For example, posterior tibial tendon ruptures and tenosynovitis result in flat foot.¹⁵ The posterior tibial, peroneus brevis/longus, flexor hallucis longus, flexor digitorum longus, and abductor hallucis longus muscles, for example, support the formation of the medial longitudinal arch, whereas the extensor hallucis longus and tibialis anterior muscles have a depressing effect on this arch.^14,16 Exercise treatment for flat foot and pes cavus, with the exception of bony problems (rigid pes planus) such as talocalcaneal fusion, includes stretching and strengthening of the intrinsic and extrinsic muscle groups. Generally, these exercises are accepted as symptomatic therapeutic modalities.^17,18

The AI is highest in childhood and lowest between the ages of 12 and 14. It increases slowly after the teenage years.¹³ The mean age of our study group was about 23 years, and the normal AI for people aged 20–30 is about 60 (32).¹³ We found that the AI for gymnasts was lower than seen in the other sports disciplines and in the non-athletic subjects. Another special feature of gymnasts was the lower age at which training was initiated. In other words, gymnasts start intense training, involving the stretching and strengthening of foot muscles, when the musculoskeletal system is immature. Wrestlers, on the other hand, perform isometric exercises for the foot muscles. We could not find any study in the literature documenting changes in AI or foot arch types in relation to particular sports. Klingele et al¹¹ showed that endurance runners and alpine skiers have a higher prevalence of longitudinal foot arch insufficiency. The reason for the differences in gymnasts and wrestlers may be a coincidental finding, a sports related adaptation, or that a low or high AI favours gymnastics or wrestling. More prospective studies, which are time consuming and expensive, are needed to clarify whether these results are sports related. Studies such as this cross sectional one could provide preliminary information for prospective studies.

The correlation between the right and left sole AIs was lower in handball and soccer (where there is leg dominance) and wrestling (where there is no leg dominance), and higher in sports with no leg dominance and in non-athletic controls. These differences support the idea of sport specific adaptation of sole AIs, but further studies are required.

In conclusion, we found that the foot AIs of gymnasts and wrestlers were significantly different from those of athletes in other sports, and those of gymnasts and handball players were different from those of non-athletic men.