Can you practice and improve physical activities only by thinking?
Yes. In one famous experiment,a college basketball team was divided into three groups.

Group 1 was supposed to show up to practice shooting baskets for a week on a daily basis.

Group 2 was asked to "think about" practicing shooting baskets during the alloted time, without showing up.

Group 3 was asked to "forget about" basketball for the week.

After the one week period, Group 3 showed no improvement in shooting baskets. 

Group 1 improved meaningfully.

Group 2 improved almost as much as group 1, and way more than group 3.