The effect of Speed and direction of isometric Trunk exertion on trunk controllability during target tracking tasks in asymptomatic subjects

The target tracking tests is a known method to quantify the performance of the neuromuscular system. It has been used in several studies for evaluation of neuromuscular control strategies. The purpose of the present study was to examine the effect of direction and speed of isometric trunk exertion on the trunk controllability during the target tracking tests in sagittal versus axial rotation torque plane. Twenty- two healthy subjects (13 female and 9 male) randomly performed target tracking tasks at levels of 0% to 80% Maximum Voluntary Exertions (MVE) and seven different directions (0 ̊، 30 ̊، 60 ̊، …، 180 ̊) in upright standing posture. In this study، the tracking system included a moving target circle، which moved on a straight line in specific direction from 0 to 80% of individual MVE with speed of 5، 6 and 7% MVE/s. The d irection of isometric trunk exertion was presented to participants in the real time visual feedback by a computer monitor positioned in front of them. Trunk controllability was determined by computing the control errors (Absolute Value Error from the Target [AVET]، Error from the Target Path [ETP] and Error from the Target in the Target Path [ETTP]) during each performance. Analysis of variance was used to test the effect of speed and direction of isometric trunk exertion on trunk controllability. The results have shown that the direction of isometric trunk exertion had significant effect on the AVET and ETTP (p= 0. 000) while the effect of speed and interaction between direction and speed were not significant. The error decomposition in to two independent parts showed that the only direction of exertion on ETTP was significant (p= 0. 000) and speed of exertion on any of them (ETP and ETTP) was not significant. On the other hand، Borg scale (a simple method of rating perceived exertion) significantly affected by direction (p= 0. 000) and speed (p= 0. 000) of exertion during the target tracking tests. According to the findings of the current study، the effect of d irection of isometric trunk exertion on the controllability was significant. Trunk controllability was significantly decreased during rotational exertions which may impair trunk neuromuscular coordination، increasing the risk of developing low back pain.