407Fit Perf J. 2009 Nov-Dec;8(6):407-11.

ISSN 1519-9088

compaRative study of isokinetic vaRiables of the knee in taekwondo and kickboxing athletes

Susane Moreira Machado1 susanetkd@hotmail.com

Renato Aparecido de Souza1,2 tatosouza2004@yahoo.com.br

Adriano Prado Simão2 adrianopsimao@ig.com.br

Diego Pereira Jerônimo1 diego-jeronimo@hotmail.com

Newton Soares da Silva1 nsoares@univap.br

Rodrigo Aléxis Lazo Osorio1 ralo@univap.br

Marcio Magini3 mmagini@hotmail.com

doi:10.3900/fpj.8.6.407.e

Machado SM, Souza RA, Simão AP, Jerônimo DP, Silva NS, Osório RAL, Magini M. Comparative study of isokinetic variables of the knee in taekwondo and kickboxing athletes. Fit Perf J. 2009 Nov-Dec;8(6):407-11.

ABSTRACTIntroduction: The aim of this study was to compare isokinetic variables of the knee such as peak torque

and relative balance of agonist/antagonist of knee flexors and extensors between athletes of kickboxing (KB) and taekwondo (TKD). Materials and Methods: Ten male athletes from martial arts were included in this study (18±3 years old, 1.75±9cm and 65±10kg): five TKD athletes and five KB athletes. The assessment of peak torque and relative muscle balance was performed using the Biodex Multi-joint System 3 dynamometer. Data analysis was performed by means of non-parametric statistics (Mann-Whitney test) with statistical significance at p<0.05. Results: This study showed no differences in peak torque and relative balance of agonist/antagonist of the sports examined. Furthermore, it was found in all assessed athletes a difference of less than 10% when compared the peak torque between the right and the left lowers limbs and a difference of less than 50 to 80% in the ipsilateral quadriceps, harmstrings ratio. Discussion: This information suggests that athletes of TKD and KB have similar conditions of strength and low risk of musculoskeletal injury associated with the knee joint.

KEYWORDSMartial Arts; Muscle Strenght Dynamometer; Musculoskeletal System.

1 Universidade do Vale do Paraíba – UNIVAP – Instituto de Pesquisa e Desenvolvimento – IP&D – São José dos Campos/SP – Brazil2 Universidade Federal dos Vales do Jequitinhonha e Mucuri – UFVJM – Diamantina/MG – Brazil3 Universidade Camilo Castelo Branco – UNICASTELO – São José dos Campos/SP – Brazil

Copyright© 2009 by Colégio Brasileiro de Atividade Física, Saúde e Esporte

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EISSN 1676-5133

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estudo compaRativo de vaRiáveis isocinéticas do joelho em atletas de taekwondo e kickboxing

RESUMO

Introdução: O objetivo deste estudo foi comparar variáveis isocinéticas do joelho, tais como pico de torque e relação de equilíbrio agonista/antagonista, entre atletas de taekwondo (TKD) e kickboxing (KB). Materiais e Métodos: Foram incluídos dez atletas de artes marciais do sexo masculino (18±3 anos, 1,75±9cm e 65±10kg): cinco atletas de taekwondo e cinco atletas de kickboxing. Foi realizada avaliação do pico de torque e relação de equilíbrio agonista/antagonista de flexores e extensores de joelho bilateralmente (dinamômetro Biodex Multi-joint System 3). A análise dos dados foi realizada por meio de estatística não paramétrica (teste Mann-Whitney), adotando-se significância estatística de p<0,05. Resultados: Os resultados não indicaram diferenças no pico de torque e relação de equilíbrio agonista/antagonista entre as modalidades esportivas analisadas. Além disso, verificou-se em todos os atletas uma diferença menor que 10% quando comparados os picos de torque entre membro inferior direito e esquerdo e uma diferença de isquiotibiais menor que 50 a 80% em relação ao quadríceps ipsilateral. Discussão: Essas informações sugerem que os atletas de TKD e KB da amostra analisada apresentaram condições de força semelhantes e baixo risco de lesão musculoesquelética associada à articulação de joelho.

PALAVRAS-CHAVEArtes Marciais; Dinamômetro de Força Muscular; Sistema Musculosquelético.

estudio compaRativo de las vaRiables isocinéticas de la Rodilla en los depoRtistas de taekwondo y kickboxing

RESUMEN

Introducción: El objetivo de este estudio fue comparar las variables isocinética de la rodilla, como el par máximo y relativo equilibrio de agonistas/antagonistas de los flexores y extensores de la rodilla, entre los deportistas de taekwondo (TKD) y kickboxing (KB). Materiales y Métodos: Se incluye diez atletas de las artes marciales de lo sexo masculino (18±3 años, 1,75±9 cm y 65±10 kg): 5 atletas de TKD y 5 KB de los atletas. El evaluación de par máximo y la relación de equilibrio agonista/antagonista de los músculos flexores y extensores de la rodilla bilateral se realizo utilizando dinamómetro Biodex Multi-joint System 3. El análisis de los datos se realizó mediante estadísticas no paramétricas (Mann-Whitney), con significación estadística de p<0.05. Resultados: Este estudio no mostró diferencias en el pico de torsión y equilibrio relativo de agonista/antagonista de los deportes examinados. Además, se ha constatado en todos los atletas a prueba una diferencia inferior al 10%, si se compara el pico de torsión entre la derecha y la izquierda reduce extremidades y una diferencia de menos de 50 a 80% en el cuádriceps ipsilateral, harmstrings relación. Discusión: Esta información sugiere que los atletas de TKD y KB en este estudio tienen la misma condición de la fuerza y bajo riesgo de lesiones musculoesqueléticas relacionadas con la articulación de la rodilla.

PALABRAS CLAVEArtes Marciales; Dinamómetro de Fuerza Muscular; Sistema Musculoesquelético.

INTRODUCTIONThe assessment through isokinetic dynamometry has

been used for the past decades as a method for deter-mining the functional pattern of strength and muscle bal-ance mainly through the ‘peak torque’ and ‘agonist/an-tagonist relative balance’ isokinetic variables1. The peak torque represents the point of highest torque in a given amplitude of the analyzed articular movement2. For a better study of this isokinetic variable, normally a velocity of 60º/s is used, since the lowest the angular velocity, the highest the torque3. The agonist/antagonist relative balance represents an adequate form of identifying the proportion and, consequently, the muscle balance1. Re-garding the relation between the flexors/extensors peak torque on the healthy articulation of the knee, normally a difference of 50 to 80% is verified4.

The use of results of an isokinetic assessment renders possible a new tool and strategy for the restructuring of the sports training plan, as it allows an accurate iden-tification of the muscular function5. Furthermore, refer-ence values for the muscular function can be determined, particularly predicting the risk of injuries6,7. However, the sport activity and the level of physical conditioning may constitute determining factors on the adequate interpre-tation of isokinetic results, that is, the functional demand imposed to the muscle tissue properties on athletes of distinct modalities lead to different expressions of these results. In this sense, the isokinetic studies which verify the muscular function between the various sports modalities are justified.

Few attention has been paid to the muscle perfor-mance of martial arts athletes. Two modalities are of

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special interest to this study and should be highlighted: taekwondo (TKD) and kickboxing (KB).

TKD, whose meaning translates into “the path of feet and hands through the mind”, is of Korean origin and became an official Olympic sport in 2000, at the Sidney Games8. TKD competition athletes use mainly fast and high-amplitude kicks in the opponent’s torso and head, demanding intense use of extensor and flexor muscles of the knee. This way, the specific literature has been in-dicating a relative frequency of muscle injuries in active athletes9. On the other hand, KB is of North American origin and allows full contact between opponents dur-ing the competition. Currently, it is considered a highly popular sport, with an estimate of 1 million practitioners worldwide10. During this sport practice, athletes execute and undergo several blows, such as kicks and hand, elbow and knee punches. Although these two modali-ties intensely demand the recruitment of the muscles in-volved in the kicking, up to now, it has not been found any information in the specific literature regarding the use of isokinetic dynamometry to the muscle assessment of these athletes.

Taking into account the aforementioned and the lack of scientific works involving martial arts athletes, this study’s proposal was to compare isokinetic variables of the knee, such as torque peak and the agonist/antago-nist relative balance among TKD and KB athletes.

MATERIALS AND METHODS

SampleFor convenience, ten male martial arts athletes were

selected, with an average age of 18±3 years, height of 1.75±9 cm, total body mass of 65±10 kg and body mass index (BMI) of 21±3. In order to analyze the data, the sample was divided into two experimental groups, regarding the practiced modality: TKD (n=5) and KB (n=5). The average of previous training time of these athletes was 5±1 years for TKD and 2±1 years for the KB group. For the sample selection, the inclusion criteria adopted were the inexistence of any musculoskeletal in-jury, the capacity to perform the experimental tests, and to practice TKD or KB from two to three times a week in order to participate in State competitions. Volunteers who had shown any kind of muscle injury in the past six months and who practiced TKD or KB as a recreational activity were excluded from the sample.

After being explained about the purpose of the study and the procedures to which they would be submitted, the volunteers signed the Informed Consent Form. This study complied with the rules of realization of experi-ments involving human beings, according to the spe-

cific resolution of the National Health Counsel (number 196/96) and had the approval of the Ethics and Re-search Committee of the Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), under the protocol number H307/2007.

InstrumentationThe Biodex Multi-joint System 3 isokinetic dynamom-

eter (Biodex Medical Systems, Inc., New York, USA) was used to measure the knee muscular function (torque peak and the agonist/antagonist relative balance) at the angular velocity of 60º/s.

Isokinetic dynamometryBefore the tests, the athletes performed an ergomet-

ric bicycle warm-up for ten minutes. After warm-up, the athletes were duly placed on the isokinetic chair in the seating position, with an 85º torso inclination and both thighs accommodated on the seat. The dynamometer’s torque arm was positioned parallel to the athletes’ leg, the resistor was distally fixed and the device’s axis was aligned with the knee axis. In the dynamometer chair, athletes were secured through the use of seat belts on the thorax and pelvis, as well as on the thigh of the limb to be tested. The other limb remained steady due to a belt which was adapted to the chair. Gravity force was then corrected, once the athlete’s performance on the test implies motion against strength gravity11. Each ath-lete performed 15 repetitions at 60º/s for the concentric flexo-extension of the knee, in order to obtain the ‘peak torque’ and the agonist/antagonist relative balance’ vari-ables. Only the five first repetitions were analyzed, taking into account the fact that the other repetitions were used on the fatigue analysis. The 60o/s angular velocity was chosen due to the fact that greater torque generation can be obtained through low velocities, therefore obtaining a performance that is closer to the athlete’s maximum muscular performance11. The amplitude of the test was limited to 100o, starting at 110o for flexion and finish-ing at 10º for knee flexion. The amplitude of complete extension was limited to avoid the ischiotibials’ passive insufficiency effect. All tests were carried out with a stan-dard verbal stimulus, in order to motivate the athletes’ maximum effort during the process.

Isokinetic variablesThe assessment of the ‘peak torque’ and ‘agonist/

antagonist relative balance of knee flexors and extensors’ isokinetic variables was initially made on the right limb and, once finished, on the left limb. The peak torque is expressed in Newton x meter (N.m) and represents the biggest torque of the athletes’ knee articulation. The agonist/antagonist relative balance represents the ratio

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between the peak torque of the knee flexors/extensors expressed as a percentage (%), that is, the absolute value of ischiotibials peak torque divided by the quadriceps peak torque, multiplied by 100.

Statistical analysisFor the results analysis, the Statistical Package for

Social Science (SPSS), version 11.0 was used. The fol-lowing comparisons between TKD and KB athletes were made: extensor peak torque of the right lower limb, flexor peak torque of the right lower limb, extensor peak torque of the left lower limb, flexor peak torque of the left lower limb, agonist/antagonist relative balance of the right lower limb and agonist/antagonist relative balance of the left lower limb. The Mann-Whitney test was used for the comparison of the independent sam-ples (TKD x KB). The adopted statistical significance was p<0.05.

RESULTSThe mean values and standard deviations (mean±sd)

for the torque peak variable are presented on Table 1.

Table 1 - Mean peak torque of right (extensor peak torque of the right lower limb) and left (extensor peak torque of the left lower limb) knee extensor muscles, and right (flexor peak torque of the right lower limb) and left (flexor peak torque of the left lower limb) knee flexor muscles of taekwondo (TKD) and kickboxing (KB) athletes

Peak torque (N.m) TKD (n=5) KB (n=5)Extensor peak torque of the right lower limb 157.23±25.34 148.49±32.74

Extensor peak torque of the left lower limb 155.53±17.78 146.02±31.67

Flexor peak torque of the right lower limb 89.21±13.03 71.76±13.03

Flexor peak torque of the left lower limb 88.13±12.97 68.94±14.93

70

60

50

40

30

20

10

0Right Left

Lower limb

Ago

nist

/ant

agon

ist

knee

rel

atio

n

TKDKB

Figure 1 - Agonist/antagonist knee relation in taekwondo (TKD) and kickboxing (KB) athletes: values expressed as a mean percentage (%)

Significant differences (p>0.05) were not identified when bilaterally comparing knee flexors and extensors between the two martial arts modalities. Furthermore, the follow-ing observations could be made: a) the mean difference between extensor peak torque of the right lower limb and extensor peak torque of the left lower limb in TKD and KB athletes was of 2N.m (2.0%); b) the mean difference between flexor peak torque of the right lower limb and flexor peak torque of the left lower limb in TKD athletes was of 1N.m (1.2%) and c) the mean difference between flexor peak torque of the right lower limb and flexor peak torque of the left lower limb in KB athletes was of 3N.m (4.3%).

Figure 1 presents the agonist/antagonist relation of the knee, which rendered possible the muscle bal-ance analysis of this articulation among athletes. It was observed that TKD athletes present muscle balance of 57±2.3%, both for the right and left lower limbs. KB athletes presented a balance of 48±2.5% for the right lower limb and 47±1.8% for the left lower limb, between the peak torque of flexors and extensors of both left and right knees, respectively. Significant differences (p>0.05) could not be found when comparing the obtained values of each lower limb among TKD and KB athletes.

DISCUSSIONFacing the scarcity of studies on the physical perfor-

mance of martial arts athletes and the real possibility of determining the reference values for muscular function, particularly predicting the risk of injuries through iso-kinetic assessment6,7, the purpose of the present study was to compare the isokinetic variables ‘peak torque’ and ‘agonist/antagonist relation of flexor and extensor knee muscles’ of two distinct modalities: TKD and KB. It has been established that sports training can cause muscular instability related to flexibility and strength, raising the risk of injuries12,13. In this sense, Devan et al.14 have observed that basketball, soccer and grass hockey female players presented a higher risk of knee injury when the isokinetic assessment detected: a differ-ence of more than 10% when contralaterally compar-ing ischiotibials and/or quadriceps15 and a difference of less than 50 to 80% when ipsilaterally comparing ischiotibials and quadriceps16.

Pieter and Taaffe, cited by Pieter et al.17, have tested the isokinetic torque peak of professional American TKD athletes and found values for agonist/antagonist knee relation that were considered below average, noting that these athletes would have a higher predisposition for knee injuries. Although no isokinetic study involving KB has been found, it must be taken into account that sports modalities involving frequent knee rotations and

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torsional movements are also related to this articulation’s instability and chronic pain18.

Regarding the peak torque, it was observed that TKD athletes presented higher peak torque values for flexors and extensors in comparison to KB athletes (Ta-ble 1). Although these differences have not been signifi-cant, it must be taken into consideration that fact that TKD athletes training time was superior, comparing to KB athletes (5±1 versus 2±1 years, respectively). In a study on athletes of other martial arts, Probst et al.12

have observed karate athletes with a minimum experi-ence of two years, and found mean values of torque peak (60º/s) for quadriceps (190N.m) and ischiotibi-als (115N.m) that were higher than those of the ath-letes of the present study. This fact should be taken into consideration due to the distinct nature of each martial arts modality training. While the karate athletes training imposes significant articulation strength, especially con-cerning the execution of knee extension exercises – such as the frontal kick12 –, KB and TKD athletes attribute to their training certain strategies of blow sequences (punches and kicks)8,10,19, not emphasizing all the pow-er and velocity required by the karate athletes.

Another important aspect of the torque peak variable is the bilateral comparison of knee flexors and extensors among athletes of the same sport modality. The maxi-mum difference was of 4.3% for the flexor peak torque in KB athletes. Considering that this assessment accepts a difference of up to 10%15, it can be suggested that the analyzed athletes present an adequate balance between the right and left ischiotibial muscles and the right and left quadriceps.

As for the agonist/antagonist balance of knee flexors and extensors isokinetic variable, it was observed that the athletes of both modalities presented an adequate muscle balance bilaterally, that is, a difference of less than 50 to 80%4,16 (Figure 1). These data seem to dem-onstrate a low risk of muscle injury by distension in the studied population. In fact, although the muscle injuries are relatively frequent in TKD and KB athletes, the most prevailing injuries in these modalities are the muscle con-tusions10,13,19.

Lastly, considering that the isokinetic assessment al-lows the determining of reference values for the muscular function, the lack of scientific information related to the analyzed sport modalities and the minimum experience of two years of the participant athletes, the small and lim-ited sample has provided pioneer data, guiding not only these athletes’ training but also possible future studies. The results have not indicated differences between the

analyzed sport modalities, regarding the ‘peak torque’ and ‘agonist/antagonist knee relation’ isokinetic vari-ables. Furthermore, the analyzed athletes presented an adequate muscle balance. These information suggest that TKD and KB athletes of the analyzed ample have similar strength conditions and low risk of musculoskel-etal injury associated to knee articulation.

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18. Sekiya JK, Kuhn JE. Instability of the proximal tibularfibular joint. J Am Acad Orthop. Surg. 2003;11(2):120-8.

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Received on: 07/02/09 – Accepted on: 10/17/09

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