I saw this video in which Tony Robbins claims practicing mentally can be more effective than practicing physically.
He refers to a study where basketball players struggling with free throws were split into three groups. One group practiced throwing directly, one group spent the time visualising the perfect shot, and a third group did not practice.
His goes on to claim that the group who mentally practiced showed the most improvement. Are there any studies to back up or refute this claim?
"[I]f an experienced individual has already learned the component motor skills of a physical task, then mental practice may be sufficient to enhance performance without additional physical practice and feedback."
This is pretty much what is being said in the video (starting at 15:00).
More from the study quoted above:
A meta-analysis of the literature on mental practice was conducted to determine the effect of mental practice on performance and to identify conditions under which mental practice is most effective. Results indicated that mental practice has a positive and significant effect on performance, and the effectiveness of mental practice was moderated by the type of task, the retention interval between practice and performance, and the length or duration of the mental practice intervention.
...snip...
Novice subjects benefited more from mental practice on cognitive tasks than on physical tasks. This result is consistent with Ryan and Simons's (1983) argument that if an experienced individual has already learned the component motor skills of a physical task, then mental practice may be sufficient to enhance performance without additional physical practice and feedback. For novices, who have not formed an approximation of the skill, the symbolic rehearsal provided by mental practice may not be sufficient to guide performance. This suggests that mental practice may be more effective, everything else held constant, if novice subjects are given schematic knowledge before mental practice of a physical task.
...snip...
In summary, the results of this study indicate that mental practice is an effective means for enhancing performance, although less effective than physical practice. Thus, for tasks that are dangerous to train for physically, for tasks in which there are seldom opportunities for physical practice, or as a means of supplementing normal training, mental practice should be considered as an effective training alternative.
Source:
Possibly the study mentioned in the video:
