Shahrzad Masoumi, postgraduate
Mohammad Mattagitalab, postgraduate
Russian state university of physical culture, sport, youth and tourism, Moscow

Key words: motor asymmetry, shock loads, shock actions, standing vertical jumps, jumping kick.

Introduction. Landing badly from a jump during sports activities is one of the common injury mechanisms leading to lower limb injuries. For example, inadequate knee flexion angles when landing was nominated by former studies as a likely knee injury risk factor when landing [17, 22,]. Anterior cruciate ligament (ACL) is among the most commonly encountered and costly injuries experienced by athletes. It has been shown that over 70% of ACL ruptures occur in a non-contact situation, specifically during closed chain movements requiring rapid decelerations of the body’s center of mass such as; cutting, pivoting, stopping, or landing.

On the other hand, taekwondo as a dynamic form of unarmed self-defense that utilized the entire body can be distinguished from other martial arts by the focus on kicking techniques. There are many kinds of kicking, such as front kick, roundhouse kick, back kick, side kick, etc. Mostly, during performance of these kicks, athletes have to cutting, pivoting and jumping so, the risk of ACL injury come in to existence. Lower limb injury in taekwondo accounts for 37-65% of all injury [24]. There are a few biomechanical studies on taekwondo kicks [1, 2]. Although there are many types of taekwondo kicks, only a handful are frequently used in sparring, with the roundhouse kick being the most popular. But these kicks with jumping that commonly used have not been studied. So, the main goal of this study was to investigate biomechanical characteristics of support leg as a segment that suffer excessive force by impact with ground in tio dolleyo chagi kick. The second objective was to compare these characteristics for dominant and non-dominant leg.

Materials and methods. 6 elite welterweight taekwondokas (age 20.67±2.21 years, weight 51.67±3.77 kg, height 166.3±4.58 cm, and experience10.83±3.8 years) without lower extremity problems in the past were the subjects of the study. According to the results of the laboratory studies, female athletes may get ready for jump landings in the ways that put them at the increased risk for noncontact anterior cruciate ligament injury compared with male athletes [11, 13], so in this study only female athletes were studied and because of the effect of sex hormones on neuromuscular control patterns during drop jump in females. Luteal phase was selected to carry out the experiment. In order to investigate the effect of landing situation on biomechanical characteristics, volunteers performed drop landing as a simple landing that required them to hop from 2 legs and land on a single leg. Both landings were performed with dominant and non-dominant leg.

A three-dimensional motion analysis system (Model 460 Vicon, Made in England); which includes six high-speed cameras (McamVicon) at 120 Hz, one processor (460 vicon) and Workstation software was used to collect the kinematic data. For the purpose of this study 16 highly visible markers were placed on the toe, heel, lateral malleoli, lateral femoral condyle, shank, thigh, greater trochanter, posterior superior iliac spine.

The Ground Reaction Force data was collected using a portable force platform (Model 9286A Kistler, Size 400.600.35 mm, Made in Switzerland) with one cable (Model 1757A) and one control unit (Model 5233A2).

Data analyses

Landing phase was defined as initial contact to max knee flexion. Minimum and maximum flexion and angular velocity at hip, knee and ankle joints as kinematical characteristics and vGRF Peak, vGRF impulse and vGRF Max loading rate as kinetically characteristics were assessed.

Hip angle (the angle between the thigh and the pelvis) increased in the positive direction with hip flexion and increased in the negative direction with hip extension. A hip angle of 0° indicated that the pelvis and thigh were collinear. Knee angle (the angle between the thigh and the shank) increased with knee flexion. A knee angle of 0° represented full extension. Ankle angle (the angle between the shank and the foot) increased in the positive direction with dorsiflexion and in the negative direction with plantarflexion. A neutral ankle angle (0°) was defined as the angle at which the foot was flat on the floor and the shank aligned vertically.

Statistical analysis

The data was analyzed using the statistical software STATISTICA. Statistical analyses were performed by the level of significance at p-value less than 0.05 and T-tests for dependent samples to compare the difference between two types of landing and between dominant and non-dominant leg in each type of landing.

Results and discussion. The descriptive statistics (mean and standard deviation) and t coefficients are presented in Tables 1 and 2.

Table 1. Significant results between drop landing and landing from tio dolleyo chagi

The difference was detected in hip flexion at impact between drop landing and landing from tio dolleyo chagi. This magnitude of difference for the dominant leg was more than for the non-dominant leg but none of them were significant. Hip flexion at maximum in drop landing was more than landing from tio dolleyo chagi. This difference was significant for the dominant leg ( 23.24 ± 10.07 degree in drop landing versus 4.75 ± 13.46 degree in landing from tio dolleyo chagi, T=3.02, P=0.02). The results showed drop landing performed with higher flexion in hip joint than landing from tio dolleyo chagi. No significant difference was found between drop landing and landing from tio dolleyo chagi in angular velocity for both legs.

Knee joint, like the hip, had higher flexion in drop landing than landing from tio dolleyo chagi. This difference was significant at maximum flexion in both dominant ( 51.62 ± 9.38 degree in drop landing versus 36.89 ± 11.54 degree in landing from tio dolleyo chagi, T=5.1, P=0.003) and non-dominant ( 52.39 ±7.34 degree in drop landing versus 36.28 ±17.36 degree in landing from tio dolleyo chagi, T=3.58, P=0.01) legs. Angular velocity of knee in both legs was lower in drop landing compared with landing from tio dolleyo chagi, although the differences were not significant.

Ankle flexion at impact in drop landing was higher than landing from tio dolleyo chagi for the dominant leg but was vice versa for the non-dominant leg it. But these differences were not significant. Ankle flexion at maximum in drop landing was higher than landing from tio dolleyo chagi for both legs. This difference was significant for the non-dominant leg (25.74 ± 6.59 degree in drop landing versus 16.65 ± 6.28 degree in landing from tio dolleyo chagi, T=3.97, P=0.01). No significant difference was found between landings and between legs in angular velocity of ankle.

Regardless of landing’s type, there was a same model for angular velocity for the dominant leg. Angular velocity in ankle joint was higher than knee joint and it had the lowest magnitude in hip joint. No dominance-related differences in kinematical characteristics were present between legs. 

There was a significant difference in vGRF peak between two landings for the non-dominant leg (3.8 ± 1.61 BW in drop landing versus 2.5 ± 0.9 BW in landing from tio dolleyo chagi, T=2.83, P=0.03). This difference was not significant for the dominant leg. vGRF impulse for the dominant leg was significantly different between two landings ( 198.9 ± 96.46 in drop landing versus 109.6 ± 68.15 in landing from tio dolleyo chagi, T=4.4, P=0.007). Significant difference in vGRF max loading rate was noted between two landings in the non-dominant leg ( 92.3 ± 36.04 in drop landing versus 60.17 ± 37 in landing from tio dolleyo chagi, T=2.91, P=0.04). Based on these results, measured kinetic variables in landings performed didn’t show significant differences between the dominant and non-dominant leg (p ˃ 0.05).

Table 2. Significant results between dominant and non-dominant legs

The purpose of the study was to compare the biomechanical characteristics between two types of landing in female taekwondo athletes. Results indicated that the two types of landing performed in this study are different in some kinetic and kinematic characteristics (Tab. 1).

According to previous studies [26], the peak of the vertical ground reaction force, increased with landing height which agrees with the results of this study. Drop landing performed from higher height compared with landing from tio dolleyo chagi kick, therefore peak of vGRF was greater in drop landing. This result is the opposite of the study of Hong-wen wu (2010), who demonstrated that there was no significant difference in peak vertical ground reaction force between two types of landings. The example of dynamometer in different landing after jumping exercises is presented in Figure 1.

Hong-wen wu (2010) stated that there is significant difference on the loading rate between two types of landings. In our study, in line with Hong-wen wu (2010), statistical analyzes also showed that there is a significant difference on the loading rate between drop landing and landing from tio dolleyo chagi kick in non-dominant legs. The vGRF impulse was significantly different in the two landings like that reported by Hong-wen wu (2010).

Former studies stated that landing with the knee in a more extended position (less than 45°) results in the reduced energy absorption and may cause injury [17]. As regards subjects in this study landed with the knee extended position, can be considered landing from tio dolleyo chagi as a cause of ACL injury.

Other studies have reported the biomechanical characteristics differences between landings [26, 27]. These studies involve different landings (counter movement jump and the vertical jump with run-up…), different sport (volleyball, basketball…) and different subjects in age and gender. These differences may elicit different biomechanical effects. Therefore, it may be incorrect to compare results of these studies.

In contrast with other studies, the absence of dominance differences exhibited in our study might be due to the technique under study.

Fig. The example of dynamometer in different landing after jumping exercises

Conclusion. The obtained results indicate to significant differences in kinematic and dynamic characteristics between the analyzed types of landings. Despite asymmetry of the style of taekwondo in many aspects, performance of most kicks is associated with involvement of dominant or nondominant lower limbs. Therefore, regardless of the lack of significant differences between biomechanics of landing on a dominant or nondominant limbs, such studies are useful to analyze the characteristics of asymmetry when performing motor actions to improve sports results and prevent injuries. More studies are needed to confirm this comparing the variables by level and gender as well as using other techniques within the same groups.

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