One of the challengeable topics in motor learning is how to determine which tasks are more complex than other tasks, and the methods are used for this purpose are not very efficient. The purpose of this research was to study the efficiency regarding the number of practice trials to determine the rate of task complexity. In this study, sixty subjects according to the types of task (A - B) and receiving feedback (100%, omitted, self-control) were randomly divided in to six groups. All of the subjects practiced 200 trials, each task on two days. Retention tests were performed during the second and third day, and reacquisition tests were performed on the third day. All of the subjects improved across practice trials on both days but this improvement in B task was significantly better than A task on the second day. Subjects were significantly better in the second retention test comparing with first one; in addition subjects who practiced B task were significantly better than those who practiced A task in the retention tests, and there was not any significant difference between different feedback groups. Subjects were significantly better in the second requisition test comparing with first one, but there was not any significant difference between different feedback, and task groups (p<0.05). Results indicated that A task was more complex than B task, and by using a number of practice trials, we could determine which task was more complex; finally the optimal practice trials was required to understand which task was more complex
