Isokinetic evaluation of knee muscles in soccer players: discriminant analysis

Abstract

Introduction: Muscle activity in soccer players can be measured by isokinetic dynamometer, which is a reliable tool for assessing human performance. Objectives: To perform isokinetic analyses and to determine which variables differentiate the under-17 (U17) soccer category from the professional (PRO). Methods: Thirty four players were assessed (n=17 for each category). The isokinetic variables used for the knee extension-flexion analysis were: peak torque (Nm), total work (J), average power (W), angle of peak torque (deg.), agonist/ antagonist ratio (%), measured for three velocities (60°/s, 120°/s and 300°/s), with each series containing five repetitions. Three Wilks' Lambda discriminant analyses were performed, to identify which variables were more significant for the definition of each of the categories. Results: The discriminative variables at 60°/s in the PRO category were: extension peak torque, flexion total work, extension average power and agonist/antagonist ratio; and for the U17s were: extension total work, flexion peak torque and flexion average power. At 120°/s for the PRO category the discriminant variables were: flexion peak torque and extension average power; for the U17s they were: extension total work and flexion average power. Finally at 300°/s, the variables found in the PRO and U17 categories respectively were: extension average power and extension total work. Conclusion: Isokinetic variables for flexion and extension knee muscles were able to significantly discriminate between PRO and U17 soccer players.

Are There Differences in Concentric Isokinetic Strength Perfor-Mance Profiles between International and Non-International Elite Soccer Players?

“…These relations, however, were not confirmed in another study, which found no significant differences in the PT of the quadriceps and hamstrings, nor the H/Q ratio, across four divisions of soccer players [6], nor between international and national soccer players [3]. In relation to the total work variable, the only study in this area known to us [2] found statistically significant differences with regard to both quadriceps and hamstrings-between professional and U-17 soccer players for all the studied angular velocities. Unfortunately, wider comparisons of TW with other elite players is not available in the current literature.…”

“…Previous research has identified the isokinetic strength of knee extensor and flexor muscles as differentiating factors between soccer players of playing levels [1][2][3][4][5][6][7] and positional differences [8][9][10][11]. Some prior research indicates that soccer playing leads to a significant increase in strength in the muscles surrounding the knee [12].…”

Função muscular de membros inferiores e massa muscular em jogadores de futebol

“…Neste estudo, foi proposto a análise de componentes da função muscular de forma isolada e conjuntamente de modo a perceber se o valor alcançado em um determinado parâmetro poderia ou não alterar a relação existente com a variável dependente. Neste contexto, Mazuquin et al 19 , destaca, por exemplo, que o pico de torque e a potência podem estar relacionados com a capacidade do quadríceps gerar força em ações como chutes, saltos verticais e corridas. Em oposição a essas ações, a atividade antagonista do quadríceps é essencial para a desaceleração do movimento, podendo ser avaliada por meio do trabalho total, que combinado ao torque demonstra o comportamento do músculo ao longo das alterações na amplitude do movimento 19 .…”

“…Neste contexto, Mazuquin et al 19 , destaca, por exemplo, que o pico de torque e a potência podem estar relacionados com a capacidade do quadríceps gerar força em ações como chutes, saltos verticais e corridas. Em oposição a essas ações, a atividade antagonista do quadríceps é essencial para a desaceleração do movimento, podendo ser avaliada por meio do trabalho total, que combinado ao torque demonstra o comportamento do músculo ao longo das alterações na amplitude do movimento 19 . Ou seja, estes aspectos apontam para uma possível assimetria na sinergia em relação ao equilíbrio muscular exigido em cada tipo ou forma de execução de uma tarefa motora.…”

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“…Although the beginning of the lifting is an explosive movement, the subsequent movements are performed at slower speed, which, consequently, requires greater PT at slow speeds (Fry et al, 2003;Chiu & Schilling, 2005), whilst in the majority of sports the muscle demands occur at faster speeds. According to Mazuquin et al (2015), at slower speeds the muscle activation is greater: both for fast and slow twitch muscle fibers, different from faster speeds that have a shorter period for recruiting slow twitch muscle fibers.…”