Yes, it does sound too good to be true, but it has scientific backing! When you start a training regime tailored for increased muscle strength, the initial gains you achieve result mainly from changes in the nervous system! With this in mind, researchers set up an experiment to see whether just visualising muscle specific exercises could increase muscle strength.
Thirty healthy adults were split into 3 groups: Imagining exercising their little finger, imagining exercising their biceps and no imaginary exercise for the control group. Results showed that those imagining exercising their little finger increased strength by 53% and those imagining their biceps workout increased strength by 13.4%!
The measurements of brain activity that were recorded during visualisation suggest that the strength gains are a result of the improvement in the brain’s ability to send signals to the muscle and activate the muscle fibres.
Ranganathan VK, Siemionowa V, Liu JZ, Sahgal V, Yue GH, From Mental Power to Muscle Power; gaining Strength by using the Mind, Neuropsychology, 2004, 42, 944-56.