Evolution of stiffness index with fatigue.

<p>The relationship between the head-neck segment musculo-tendinous stiffness (S) and the isometric cervical flexion torque developed before the QR (T) for all subjects before and after the fatigue procedure (No fatigue and Fatigue, respectively). Linear regression showed a significant and linear increase of S according to T in the two conditions (P < 0.0001). There was no significant difference for the slopes of the linear regressions, providing the stiffness index of the head-neck segment in flexion, between the two conditions.