A modern pentathlon is a competition joined by a person, who competes in five games, such as fencing, swimming, horse riding, shooting, and running in one day and the person receiving the highest score after each record from the five competitions is converted into the score of the modern pentathlon is the winner. Since the 5th Stockholm Olympic Games of 1912, the modern pentathlon has been adopted as the basic official sport of 21 Olympic games and has been conducted every time. In line with this, the Union Internationale de Pentathlon Moderne was founded during the London Olympic Games of 1948. However, after the Union Internationale de Pentathlon Moderne introduced the provisions of (combine) combined competitions, the order of the modern pentathlon was changed to fencing, swimming, horse riding, and combined competitions (shooting and running). Thus, the modern pentathlon now consists of five different sports and requires the equable development of physical strength for competition power improvement, such as technique, muscle strength, speed, endurance, etc.

The modern pentathlon can cause idiopathic injuries because it requires a high degree of physical fitness and the technique required by each sport is very complex and differs in each sport, and this is necessary to perform static and dynamic games. According to the sports game, sports injury shows diversity based on the injury type and environment. However, ankle injury is reported to have the highest occurrence rate in the sports field (Klement et al., 2005). Also, sports injury is generally accompanied with functional degradation on the peripheral of the injury and when the consideration of this functional degradation is insufficient during rehabilitation, redamage or a decrease in athletic performance can be caused (Geraci and Brown, 2005; Hertel, 2000). In particular, Bishop and Fallon (1999) who studied the tendency of injury during long-term running training reported that ankle injury was the most frequent with 36% of the total injury and the knee was second with 22%. They also reported that the type of injury was mostly tendinitis. When we look on the basis of the preceding studies, ankle injury, which is mostly experienced by modern pentathlon athletes, is predicted to have close relation with track and field events.

Related to this, Simoneau et al. (2006) who studied the change of muscle strengthening targeted on adults around their ankles for 6 weeks, reported that the stimulation through the muscle strengthening program resulted in the increase of hamstring muscular strength on the plantar and dorsal side and the stability of the ankle joint was improved through this. The sports injury of the ankle is known to have the closest relation with the weakening of the peripheral muscle group and it is reported that the injury mostly occurs during running for athletes who experienced functional degradation on the peripheral muscle groups of the ankle before the injury (Borland and Rogers, 1997; Hufner et al., 2006). Along with this, for the cause of sports injury of the ankle, anatomical alignment of the bone, weight, degradation of parallel ability, inadequacies of the agonist, and the antagonist rate are being reported (Halasi et al., 2005; Hrysomallis et al., 2005; Hubbard et al., 2006; Kaminski et al., 2003; Tyler et al., 2006;).

In particular, introversion sprain of the ligament of the ankle side, which is known as the most general among ankle injury, the main cause of the ankle sprain, is caused by the difference in the anatomical support structure. Recently, studies of the proprioception of the ankle and the studies related to the sports ability progressed and proprioception is the conscious and unconscious awareness of the joint position. It is a type of feedback of the nervous system in the arms and the leg, which is an ability to check the position of the arms and the leg (Lephart et al., 1998). The sensation of proprioception, which tells the proprioceptive information of the muscle movement sensation greatly affects the ability to control the body and when this function is weakened, it is known to increase the possibility for an injury to occur (Lephart et al., 1997; Xu et al., 2004). Proprioceptive sensation can be improved through various methods and Xu et al. (2004) who studied the tai chi program on elders effecting the improvement of their pelvic limp function, reported the improvement effect of proprioceptive sensation compared to the comparative group having a sedentary posture in their lives.

Generally, repeated injury or incomplete recovery of the ankle necessarily causes instability to the ankle and degradation of valgus muscular strength is distinctively observed for ankles with instability (van Cingel et al., 2006). Beumer et al. (2005) reported that ankle injury affects the sports ability of the entire body and especially causes kinetic change in the pelvic limb. Also, Ross et al. (2005) who investigated among the 10 patients and healthy people on the effect of balance recovery ability during landing after the functional instability of the ankle jumped, reported that an injured ankle had low coordination compared to a healthy ankle.

In this way, the cause of sports injury related to ankle sprain or the method to control recurrence are mostly reported consistently but for the effect of ankle injury on the sports ability, there are still different opinions. Moreover, reports on the injury of modern pentathlon athletes are very insufficient and require an urgent study. The purpose of this study is to conduct a survey among male modern pentathlon athletes, who had an experience of ankle injury and male university students with similar characteristics on age, weight, and height to determine how an ankle injury influences the muscle strength of the modern pentathlon athlete’s ankle and the proprioceptive sensation function to increase athletic performance in the future and to provide basic data for the rehabilitation program development.

In the results of the analysis of the differences of the flexor power of the plantar and dorsal sides between an ordinary person and athletes of the modern pentathlon, athletes of the modern pentathlon were significantly higher than general college students for the flexor power of the plantar side at an angular velocity of 120°/sec. Athletes of the modern pentathlon were also higher than general college students for the flexor power of the plantar side at an angular velocity 60°/sec but it had no statistical significance.

In addition, athletes of the modern pentathlon were higher than general college students for the flexor power of the dorsal side at all angular velocities but it had no statistical significance. These results are similar to the results that the irritation of the surrounding muscles of the ankle had caused an increase in the flexor power of the plantar and dorsal sides as reported by Simoneau et al. (2006) and it is considered that it results from the characteristics of the modern pentathlon where there are heavy simulations on the ankle from fencing or running for the advancement of the body.

Related to this, in this study, the exercise group showed a considerably high level compared to the general group for the extroversion muscular strength and this is considered to be the adaptive effect of the defensive mechanism for introversion injury because modern pentathlon athletes have more frequent stress to their ankle from exercise and the strength is higher compared to normal people. Also, for the extroversion muscular strength of the injury group, it showed a considerable decrease compared to the exercise group and a similar level to the general group. This result is considered to have resulted in the repeated ankle injury weakening on the function of the extroversion muscular strength as reported by van Cingel et al. (2006). Opposite to this, for introversion muscular strength, it is considered to have resulted from the low contribution level of the introversion muscular strength for the relative extroversion injury suppression because of the anatomical stability of the ankle ligament mentioned earlier. This result is contrary to the Bressel and McNair (2001) report, studying the instability of the ankle affecting the functional change for gymnasts and the difference of their results to the result of this study is because of the difference in the study subject. For gymnasts, the ankle is required to be mobilized in various directions but for modern pentathlon athletes, the ankle is mobilized in a single direction only for track and field and fencing and it is considered that for modern pentathlon athletes, the characteristics according to the event can be examined as such in this study result. Among the kinetic change of the ankle on ankle injury, one of the generally accepted is the proprioceptive sense (Refshauge et al., 2000). Therefore, to measure this, various methods are introduced, such as standing in one foot with eyes closed or measurement of the body shake when standing in one foot (Isakov and Mizrahi, 1997: Perrin et al., 1997). But to measure the individual proprioceptive sense of the ankle from ankle injury, neurological control must be enabled and the method of suppressing the effect of the central nervous system is required. Therefore, in this study, to exclude visual effect, parts above the calves were fixed to be executed (Willems et al., 2002). Also, according to the report of Gross (1987), there were no difference in the proprioceptive sense of the affected side and constraint side on extroversion and introversion for 14 patients with ankle strain. It is then considered that the change of ankle proprioceptive sense is limited to flexion of the plantar and the dorsal side. As an analysis result of the proprioceptive sense, there were no statistical similarity of the exercise group compared to the general group but not only did it show a higher level of tendency because for the injury group and a similar lowness in the level compared to the exercise group but it also showed low level tendency compared to the general group. These results are similar to many other reported studies and showed to be considered as the important cause of prolonging and increasing the risk of reinjury after ankle injury (Hertel, 2000: Holme et al., 1999; Nilsson et al., 2006). Therefore, not only for the rehabilitation process of these injuries but also for the prevention of ankle injuries, it is considered that an effort is required to increase the ability of proprioception of the ankle.

After measuring the muscular strength on the peripheral ankle and proprioceptive sensation function of the general university students and the modern pentathlon athletes with ankle injury experience, the following result was acquired.

In conclusion, long-term participation to modern pentathlon sports resulted in an increase in plantar hamstring muscular strength and extroversion muscular strength on the ankle compared to general university students and the exercise injury of the ankle resulted in weakening plantar hamstring muscular strength and extroversion muscular strength and degradation of proprioceptive sensation.