A stroke can critically impair motor function, including manipulative abilities in the upper extremities and balance and gait in the lower extremities. There is a well-established relationship between the reduction in voluntary strength in the affected muscles of the lower extremities and the ability to execute activities of daily living. Plus, decrease in voluntary strength of the knee extensors in the affected limb is closely linked to reductions in walking speed, impaired stability and increased postural sway.
There is growing support for the use of resistance training in stroke rehabilitation, but there are several factors that still limit the use in a rehabilitation program. After a stroke many patients have low motivation, attention and tolerance to discomfort, and an increased vulnerability to stress. In addition, activation of muscles is reduced due to changes in motor unit number, recruitment, discharge rates, and in balance between agonist and antagonist muscles. Therefore, exertion of high voluntary force may not be an ideal rehabilitation option for stroke patients.
A study was completed to determine the effect of Whole Body Vibration on isometric and eccentric torque and electromyography (EMG) variables of knee extensors on the affected side of stroke patients. Sixteen patients were enrolled in an inpatient rehabilitation program after a stroke. Eight patients were randomly assigned to the vibration group and received 20 Hz vibration (5mm amplitude) while standing on a vibration platform for 1 minute six times in one session. Patients in the control group also stood on the platform but did not receive vibration.
Isometric and eccentric knee extension torque increased 36.6% and 22.2%, respectively, after vibration and 8.4% and 5.3% in the control group. Vibration increased EMG amplitude 44.9% and the median frequency in the vastus lateralis by 13.1% without changes in the control group (10.6% and 3.9%). Vibration improved the ability to generate mechanical work during eccentric contraction by 17.5%.
These results suggest that one session of whole body vibration can quickly increase voluntary force and muscle activation of the quadriceps muscle affected by a stroke. One session of whole body vibration (20 Hz frequency, 5mm amplitude) was shown to quickly increase isometric and eccentric strength of knee extensors at the affected side. Whole body vibration may help to increase the effectiveness of an additional functional rehabilitation program.
