Effect of weight perception on co-contraction of arm muscle activity during lifting objects using augmented reality
Résumé
When manipulating an object, during assembly/disassembly operation for instance, the brain uses color visual stimuli to estimate the objects weight and scales muscle force by the muscular activity control system accordingly. As we are aware to date, no theoretical framework is available that explains the effects of weight perception on muscle co-contraction of the elbow joint during dynamic movement. In this paper, we aimed to estimate the co-contraction level of the biceps and triceps muscles on the elbow joint during repetitive movement tasks by lifting different colored objects. An augmented reality system was proposed, allowing to virtually change the color of the object by head-mounted display (HMD). In order to estimate the fatigue in the involved muscles and compare the co-contraction level when manipulating the objects with different colors, surface electromyography (EMG) activity of the biceps and triceps, the maximal force data and elbow joint angular displacement and angular velocities were recorded, analyzed and normalized as percentage of maximum isometric values. In order to evaluate the effectiveness of the proposed system and the changes of co-contraction index (CI) for different colored objects, fundamental experiments were conducted that subjects had to lift a dumbbell of 5kg as long as they were able to do and at a tempo of 20 movements per minute. Maximal voluntary isometric contraction (MVC) were tested before and after the experiment. The CI was calculated to evaluate the co-contraction level of muscle activity. Median spectral frequency (MDF) were also calculated to estimate the muscle fatigue.
The results of the performed experiments show that the MDF extracted from normalized EMG decreased when subjects feel exhausted. The number of lifting movement while manipulating the dumbbell with black color was lower than those with white color, which indicted that muscle feel exhausted faster with the black color stimuli for weight perception. The results also show that the visual stimuli based on the color of an object for weight perception, can modify the co-contraction of the muscle activity. Furthermore, the results of these study may be useful to design virtual reality environment allowing doctors to help patients to recover hand movement functions, after the injury, during specific rehabilitation process.