[Reproducibility and Bilateral Symmetry of Maximal Isokinetic Trunk Rotation Strength in Healthy and Active Male...

Movements with axial trunk rotation are associated with spinal disease and back pain and may lead to several bilateral adaptations of the trunk muscles, which are another risk factor for back pain. To avoid injury and pain, a targeted preventative training should be implemented to preserve symmetrical strength/forces. The effect analysis of such an intervention requires reliable strength tests to document training progress and enable a clinical assessment. This study aimed to determine the reproducibility of an isokinetic test protocol for maximal trunk rotation strength and the verification of left/right differences of the maximum strength of trunk rotation muscles and hand grip strength. 30 healthy and active male adults (BH = 180.1 ± 5.6 cm, BM = 78.5 ± 8.9 kg, age = 26.5 ± 3.5 years) with no history of back pain were examined in a test-retest design. The participants completed an isokinetic maximum strength test on two different test days (two sets of three concentric contractions, three min set break, angle velocity = 120 °/s) with the same test leader. Reproducibility was evaluated with an intra-class correlation coefficient (ICC (3.1)), standard error of measurement (SEM) and coefficient of repeatability (CR). ICC values of 0.94 - 0.98 on the left and 0.97 - 0.98 on the right were identified for torque, power and work. Mean torque, power and work showed CR coefficients of ± 5.1 Nm or ± 4.0 Nm, ± 11.0 W or ± 8.2 W and ± 9.5 J or ± 6.5 J for right or left rotation. The right-handed participants dominated the sample and had greater maximal hand grip strength, but no left/right trunk muscle asymmetry was found. The test protocol provides reliable data and can be used to characterise trunk rotation strength before and after training interventions in patients suffering from back pain or athletes engaging in sports with unilateral trunk rotation patterns.