Affiliations: [a] Institute of Movement and Neuroscience, German Sport University, Cologne, Germany | [b] SPRINZ Sport Performance Research Institute of New Zealand, Auckland University of Technology, New Zealand
Correspondence:
[*]
Corresponding author: Tobias Alt, Institute of Movement and Neuroscience, German Sport University, Am Sportpark Müngersdorf 6, 50933 Cologne, North Rhine-Westphalia, Germany. Tel.: +49 221 4982 3322; Fax: +49 221 4973454; E-mail:t.alt@dshs-koeln.de
Abstract: BACKGROUND: Isokinetic tests are used to measure muscular
performance, especially strength. A proper axis alignment ensures high
measuring accuracy. OBJECTIVE: The effects of fixation (minimal vs. maximal),
contraction mode (concentric vs. eccentric) and angular velocity (30 vs.
150°/s) on the kinetics and 3D kinematics of supine knee extensions need
further investigation. METHODS: Eighteen healthy male participants (22.1 y, 1.83 m, 76.0
kg) performed maximal unilateral contractions with minimal (hand grips only)
and maximal (grips, knee, hip and trunk straps) fixation. RESULTS: Peak moments (+5%) and contractional work (+4%)
significantly increased at minimal fixation. Maximal fixation improved sagittal
axis alignment in terms of the trajectory length of the lateral femoral
epicondyle (-34%) and the mean distance to trajectory centre (-19%).
Both kinematic parameters showed highly significant interactions of
fixation, contraction mode and angular velocity (p< 0.01). Initial
axis alignment in relaxed muscular state caused an antero-cranial shift (0.8
and 2.4 cm) of the lateral femoral epicondyle as well as mean roll and yaw
angle tilts of each 2.3° each. CONCLUSIONS: For supine isokinetic knee extensions, hand grips
suffice as fixation to obtain accurate kinematic and kinetic results. If
fixation is tight, the force output will decrease. To minimise misalignment,
lining up should be executed when muscles are contracting isometrically.
