Can muscle vibrations counteract disturbed accuracy of movements in diseases of the cerebellum?

Cerebellar dysfunctions (such as in multiple sclerosis – MS) are often associated with impaired wrist movements (dysmetry), affecting the accuracy of fine movements. The aim of British scientists was to test whether vibrations (125 Hz; 0.75 mm), as a dermal-muscular and proprioceptive stimulation, could improve the accuracy of movement in disturbances of motor precision associated with damage to the cerebellum. The focus was on measuring vibration-induced changes in voluntary wrist movement of patients with cerebellar syndromes (including MS) and, by comparison, of healthy subjects.

• In the study group (patients with cerebellar disorders), movements without the use of vibrations were on average hypermetric (over the target), while in the control group they were exact.
• In both groups, flexor vibrations significantly reduced the amplitude of the extension movement – by about 15%. This allowed the study group to achieve on average approximately the correct amplitude of movement, while in the control group the movements became on average hypometric (not reaching the target).

Prepared on the basis of:

Muscle vibration alters the trajectories of voluntary movements in cerebellar disorders — a method of counteracting impaired movement accuracy? Lövgreen B, Cody F, Schady W. Clinical Rehabilitation. 1993;7(4):327-336.

Study population

The study involved 12 patients with cerebellar syndromes (including MS – 5 patients, mean age: 35.9 years; 6 women; study group) and 12 healthy people (mean age: 32.8 years; 5 women; control group).

Test procedure

Patients from the study group and healthy controls from the control group performed active wrist movements separated from the rest of the arm while sitting, starting with the wrist positioned in line with the forearm axis to a 30 degree flexion in one second (or at their own pace). Initially, the desired movement was practiced. Then the vision of the wrist movement was obscured and the practiced movement had to be recreated during the actual experiment. Each subject made 40 movements, and half of them (randomized order) were subjected to flexor tendon vibration.

Electromyograms from the forearm flexors and extensors were recorded and ranges of motion were measured.

Use of vibration in the study

Vibrations with a frequency of 125 Hz and an amplitude of 0.75 mm were administered transdermally to the tendon of flexor carpi radialis, causing a constant and strong stimulation of surface and deep sensation. A plastic head (1 x 1.5 cm) of the vibrator pressed with a constant force (2.5 N) against the tendon at a distance of 6-8 cm from the wrist flexion. In the placebo (no vibration) trials, the vibrator was set up as above, but was not activated.

Results

Wrist extension movements performed without vibration in the study group were generally much more variable than in healthy subjects. Some were clearly hypermetric and some hypometric. On average, in the study group the movements were hypermetric, while in the control group they were exact.

The vibrations reduced the final range of motion in both groups tested. The movements of the patients in the study group after the vibration were on average approximately in the correct amplitude, while in the control group they were hypometric.

In both groups, flexor vibrations caused a significant (p <0.01) reduction in the amplitude of the extension movement – by about 15%. The magnitude of the limitation of motion caused by vibrations did not differ significantly between the study and control groups (p> 0.3).

Comment

The use of vibration stimulators may counteract the effects of cerebellar dysmetry related with, among others, excessive movements.

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