Torque Regularity is not Affected by the Nature of Visual Feedback During Hold Type of Isometric Contractions in Adults

The literature that investigated the influence of visual feedback properties on the magnitude and temporal structure of variability suggests that increases in the precision of visual information of the torque output (through manipulation of visual gain and its intermittency) lead the neuromuscular system to produce torque in a more steady and complex manner. However, less is known about the influence of the nature of visual feedback on torque variability. The present study aimed to investigate the effect of two different feedback natures, one from the angular position and the other from the torque produced, on the magnitude and temporal structure of torque variability during submaximal hold isometric tasks. Twenty healthy and young participants performed a knee extension isometric task, consisting in sustaining an applied resistance equivalent to 40% of their Maximal Voluntary Isometric Contraction for 30 s with visual feedback from angular position (H_angle) and with visual feedback from torque (H_torque). The magnitude of torque variability was calculated through the coefficient of variation. Sample Entropy was used to analyze the temporal structure of torque fluctuations, i.e., torque complexity. We observed no significant differences between conditions (H_angle vs H_torque) in both magnitude (p = 0.117) and the temporal structure of torque fluctuations (p = 0.940). Our results demonstrated that torque regulation seems not to be affected by the nature of the visual feedback during hold submaximal isometric tasks, suggesting a participation of sensorimotor system due to the nature of the task. Researchers should take this into account to take methodological decisions when using hold submaximal isometric tasks to investigate possible changes in motor control.