Provocative new research suggests mental activity plays an important role in the maintenance of strength.
The finding is significant for all who have worn a cast or have been immobilized for a period of time. Disuse atrophy or the weakening of muscles after inactivity is a common result of immobility, with the restoration of strength and mobility a significant issue.
Now, new findings show that the mind is critical in maintaining muscle strength following a prolonged period of immobilization and that mental imagery may be key in reducing the associated muscle loss.
Researchers at the Ohio Musculoskeletal and Neurological Institute (OMNI) at Ohio University explain that strength is controlled by a number of factors — including skeletal muscle and nerves.
While the skeletal muscle system has received considerable study, the nervous system is also an important, though not fully understood, determinant of strength and weakness.
Brian C. Clark, Ph.D., and colleagues set out to test how the brain’s cortex plays into strength development. They designed an experiment to measure changes in wrist flexor strength in three groups of healthy adults.
Twenty-nine subjects wore a rigid cast that extended from just below the elbow past the fingers, effectively immobilizing the hand and wrist, for four weeks. Fifteen subjects who did not wear casts served as the control group.
Of the group with wrist-hand immobilization, half (14) were asked to regularly perform an imagery exercise, imagining they were intensely contracting their wrist for five seconds and then resting for five seconds.
They were verbally guided through the imagery exercise with the following instructions: “Begin imagining that you are pushing in as hard as you can with your left wrist, push, push, push…and stop. (Five-second rest.) Start imagining that you are pushing in again as hard as you can, keep pushing, keep pushing…and stop. (Five-second rest.)”
This was repeated four times in a row followed by a one-minute break for a total of 13 rounds per session and five sessions per week. The second group performed no imagery exercises.
At the end of the four-week experiment, both groups who wore casts had lost strength in their immobilized limbs when compared to the control group. Remarkably, the group that performed mental imagery exercises lost 50 percent less strength than the non-imaginative group (24 percent vs. 45 percent, respectively).
The nervous system’s ability to fully activate the muscle (called “voluntary activation” or VA) also rebounded more quickly in the imagery group compared to the non-imagery group.
“These findings suggest neurological mechanisms, most likely at the cortical level, contribute significantly to disuse-induced weakness, and that regular activation of the cortical regions via imagery attenuates weakness and VA by maintaining normal levels of inhibition,” the research team wrote.
In other words, imagery appears to have reduced the loss of muscle strength. The study serves as a proof-of-concept for imagery as a therapeutic intervention for muscle weakness and voluntary neural activation.
The article is published in the Journal of Neurophysiology.
Source: American Physiological Society