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.

摘要
引言：足球运动员的肌肉活动可通过等速测力仪（isokinetic dynamometer）进行测量，该设备是评估人体运动表现的可靠工具。
研究目的：开展等速运动分析，并明确哪些变量可区分U17（Under-17）青少年足球组别与职业（PRO）足球组别。
研究方法：共评估34名运动员（每组各17名）。用于膝关节屈伸分析的等速运动变量包括：峰力矩（Nm）、总功（J）、平均功率（W）、峰力矩出现角度（°）、主动肌/拮抗肌比值（%），分别在60°/s、120°/s与300°/s三种速度下进行测量，每一组次包含5次重复动作。本研究开展了3次威尔克斯Λ（Wilks' Lambda）判别分析，以识别对两组类别划分更具显著性的变量。
研究结果：在60°/s速度下，职业组的判别变量为：伸肌峰力矩、屈肌总功、伸肌平均功率以及主动肌/拮抗肌比值；U17组的判别变量则为：伸肌总功、屈肌峰力矩与屈肌平均功率。在120°/s速度下，职业组的判别变量为：屈肌峰力矩与伸肌平均功率；U17组的判别变量为：伸肌总功与屈肌平均功率。最终在300°/s速度下，职业组与U17组对应的判别变量分别为：伸肌平均功率与伸肌总功。
研究结论：膝关节屈伸肌肉的等速运动变量可显著区分职业与U17年龄段足球运动员。