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AbstractPurpose: To examine changes to neuromuscular control of leg stiffness following 42-min of soccer-specific exercise. Methods: Ten youth soccer players aged 15.8 0.4 hopped on a force plate at a self selected frequency before and after simulated soccer exercise performed on a non-motorised treadmill. During hopping muscle activity was measured using surface EMG from four lower limb muscles and analysed to determine feedforward and feedback mediated activity, as well as co-contraction. Results: There was no change in stiffness following the soccer-specific exercise (26.6 10.6 versus 24.0 7.0 kN·m -1 , p > 0.05), with half the group increasing and half decreasing their stiffness. Changes in stiffness were significantly related to changes in CoM displacement (r = 0.90, p < 0.01) but not changes in peak GRF (r = 0.58, p > 0.05). A number of significant relationships were observed between changes in stiffness and CoM displacement with changes in feedforward, feedback and eccentric muscle activity of the soleus and vastus lateralis muscles following the soccer exercise (r = 0.64-0.98, p < 0.05), but not with changes in co-contraction around the knee and ankle (r = 0.11-0.55, p > 0.05).
Conclusions:Following soccer-specific exercise individual changes in extensor muscle activity modulate changes in CoM displacement and leg stiffness. Individuals who reduce preactivation, braking activity and consequently leg stiffness with fatigue may be at a greater risk of injury.