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Figure 3. (a) Functional hamstring/quadriceps strength ratio developed by the 4 groups. Positive velocity: Hecc/Qcon representative for knee extension. Negative velocity: Hcon/Qecc representative for knee flexion. (b) Conventional hamstring/quadriceps strength ratio developed by the 4 groups. Positive velocity: concentric muscle contraction (Hcon/Qcon). Negative velocity: eccentric muscle contraction (Hccc/Qccc). Values are means (±SD).
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In soccer practice it is normally considered that the quadriceps muscle group plays an important role in jumping and ball kicking while the hamstring group controls running activities and stabilizes the knee during turns or tackles. Moreover, it seems that the contribution of knee flexors to joint stability becomes increasingly important with increasing limb velocity (Hagood et al., 1990). In our study, the four groups of players showed a similar profile at all angular velocities measured (Fig. 2). Expressing the conventional H/Q ratio calculated during concentric and eccentric muscle contractions and also the functional ratio of eccentric hamstrings strength relative to concentric quadriceps strength (Hecc/Qcon) indicate important factors for describing the muscular stabilization of the knee joint during active knee extension (Aagaard et al., 1995). It has been demonstrated that the H/Q ratio was significantly higher for soccer players than for untrained subjects (Öberg et al., 1986), but there was no significant difference between different positions (Figs. 3a, b). This may be due to specific training applied to the players where according to the game demands strength between agonist/antagonist is of great importance.