Numerous studies conducted around the world have shown that imagery also has an enormous effect on physical and athletic performance.

In an experiment, psychologist Shlomo Breznitz at Hebrew University, Jerusalem, had several groups of Israeli soldiers march 40 kilometers (about 25 miles), but told each group different distances. He had some groups march thirty kilometers, and then told them to go another 10. He told others they were going to march 60 K, but in reality only marched them 40. He allowed some to see distance markers, and provided no clues to others as to how far they had walked. At the end of the study, Breznitz found that the stress hormone levels in the soldiers' blood always reflected their estimates and not the actual distance they had marched. In other words, their bodies responded not to reality, but to what they were imaging as reality.
(Bernie S. Siegel, Love p. 29)

Australian psychologist Alan Richardson has obtained similar results with Basketball players and tested their abilities to make free throws. He took 3 groups of players. The 1st group was to spend 20 minutes a day practicing free throws. He told the 2nd group not to practice, and had the 3rd group spend 20 minutes a day visualizing that they were shooting perfect baskets. As might be expected, the group that did nothing showed no improvement. The first group improved 24 %, but through the power of imagery alone, the 3rd group improved an astonishing 23%, almost as high as the group that practiced.
(Mary Orser and Richard Zarro, Changing Your Destiny (New York: Harper & Row, 1989, p.60)