INTERSESSION RELIABILITY OF THE INTERPOLATED TWITCH TECHNIQUE APPLIED DURING ISOMETRIC, CONCENTRIC, AND ECCENTRIC ACTIONS OF THE HUMAN KNEE EXTENSOR MUSCLES

Introduction: Although it has been shown that voluntary activation (% VA) of the knee extensors during isometric contractions can be reliably assessed with the interpolated twitch technique, little is known about the reliability of % VA during concentric and eccentric muscle actions. Therefore, relative and absolute intersession reliability of quadriceps muscle's % VA during different contraction modes was determined. Methods: After a familiarization session, 21 participants (17 males, 25 +/- 2 yrs) completed two testing sessions. Paired supramaximal electrical stimuli were administered to the femoral nerve during isometric, concentric, eccentric MVCs, and at rest to assess % VA (stimuli were applied at 70 degrees knee flexion). Results and discussion: Data indicate that % VA of the knee extensors can be reliably measured during isometric [intraclass correlation coefficient (ICC) 50.89, coefficient of variation (CV) 54.1%], concentric (ICC50.87, CV56.6%), and eccentric muscle actions (ICC50.86, CV57.0%).