What is the effect of imagining doing an exercise on muscle growth?

Question

I recently read a study by Yue, G et al. (1992) which I found incredibly interesting. I have no background in physiology and I was hoping that someone who does can clear things up.

If I understood it right, the study had two groups of people who trained their Hypothenar eminence (pinky) muscles. One of the groups did so by doing the actual exercise and a second did so by imagining themselves doing the same exercise. The group that did the exercise improved by 30% and the group that imagined themselves doing it improved by 22%.

Did those who imagined themselves doing the exercise have a muscle increase in their muscle or did the improvement come from the brain having better control of that muscle? Also, what should I expect if I imagine myself lifting a dumbbell all day?

_{Yue, G., & Cole, K. J. (1992). Strength increases from the motor program: comparison of training with maximal voluntary and imagined muscle contractions. Journal of Neurophysiology, 67(5), 1114-1123.}

Answer 1

The article by Ranganathan et al (2004) provides some relevant information. The authors discuss how it can be increased by two main factors, neural adaptation and muscle growth. They note how the motor skill acquisition literature supports the use of visualisation as an adjunct to actual practice as a means of improving performance:

Research on motor skill acquisition has demonstrated clearly that mental practice leads to improved performance (Corbin, 1972; Feltz & Landers, 1983). Thus, the neural events controlling the muscle parameters for performance (e.g., amplitude, timing) can be improved through mental practice.

They mention studies that have found no effect of visualisation on strength (e.g., Herbert et al 1998).

However, in their study they did find an effect of visualisation on strength. They attribute this gain to neural adaptation rather than muscle growth.

The key findings of this study were that mental training increases voluntary strength of both distal and proximal muscles of human upper extremities and the strength improvements accompanied elevations of time-locked (to MVC trials) cortical potential (MRCP). Based on the MRCP data (Figs. 3–5), we are confident that the primary mechanism underlying the strength increase is a mental training-induced enhancement in the central command to muscle. The data suggest that repetitive mental attempts of maximal muscle activation trained and enabled the brain to generate stronger signals to muscle. ... greater strength is a consequence of stronger brain activity. A stronger central command could recruit the motor units that were otherwise inactive in an untrained state and/or drive the active motor units to higher intensity (higher discharge rate), leading to greater muscle force

References

• Corbin, C. B. (1972). Mental practice. In W. P. Morgan (Ed.), Ergogenic aids and muscular performance (pp. 93–118). New York: Academic Press.
• Feltz, D. L., & Landers, D. M. (1983). The effects of mental practice on motor skill learning and performance: A meta-analysis. Journal of Sports Psychology, 5, 25–27.
• Herbert, R. D., Dean, C., & Gandevia, S. C. (1998). Effects of real and imagined training on voluntary muscle activation during maximal isometric contractions. Acta Physiologica Scandinavica, 163, 361–368.
• Ranganathan, V. K., Siemionow, V., Liu, J. Z., Sahgal, V., & Yue, G. H. (2004). From mental power to muscle power—gaining strength by using the mind. Neuropsychologia, 42(7), 944-956. PDF