Our results indicate that consistent use of WBV is associated with an increase in walking function, as defined by walking speed, in individuals with SCI who have some ability to maintain voluntary standing. While the lack of a control group, the inclusion of individuals with varying degrees of walking ability, and the fact that it was not possible to blind subjects to the intervention limits the conclusions that can be drawn from these findings, the fact remains that the observed changes in walking speed associated with WBV were equivalent to those reported for studies of locomotor training.16
In individuals with SCI who participated in a 3-month 5-day/week locomotor training intervention, walking speed changes of 0.023 m/s, 0.05 m/s, 0.05 m/s, and -0.005 m/s were associated with manually assisted treadmill training, stimulation-assisted treadmill training, overground training, and robotic-assisted treadmill training, respectively. It is possible that participation in a study made the subjects more conscientious of their walking performance or that the pre-, post-test design increased familiarity with the test, resulting in an improvement. However, we feel these explanations are unlikely, especially in light of comparisons to the locomotor training literature.16
In healthy elders, a change in walking speed of 0.05 m/s (with a similar effect size [d= 0.2]) has been judged to be a clinically meaningful change.25
As illustrated in , 10 out of 17 of the subjects exceeded a change of 0.05 m/s after the 12-session intervention of WBV. Subject 13 was unable to take a single step in the initial test. After the 12-session intervention of WBV, the subject was able to take 4 steps. It could be argued that this magnitude of change may be even more meaningful in individuals with SCI than it is in healthy elders. Our findings are consistent with improvements in walking function observed in elderly individuals8
and in individuals with Parkinson’s disease who received a WBV intervention,11
and therefore provide preliminary evidence that regular use of WBV may be a potent intervention for improving walking function in individuals with SCI.
In the single subject who performed a follow-up test session 5 weeks after the WBV intervention, the effects on walking speed not only persisted, but increased 5 weeks after the WBV intervention. These are similar to findings in individuals with Parkinson’s disease who had a persistent change in walking speed 4 weeks after receiving a 3-week WBV intervention.11
The use of afferent input to induce positive plastic effects in the nervous system has received considerable attention in the recent research literature.26-28
These plastic changes are most meaningful when they are associated with a lasting improvement in function.11, 26
Future studies should assess the persistence of effects of WBV through follow-up testing performed some time after the final intervention.
We observed improvements in cadence, step length of the strong and weak legs, and consistency of hip angle-to-knee angle intralimb coordination after a 12-session intervention of WBV. Furthermore, changes in walking speed and cadence were moderately correlated suggesting the increase in walking speed associated with the WBV intervention is related to an increase in the number of steps taken per minute. In addition to an increase in cadence, changes in walking speed also had a fair relationship with changes in the stronger step length, suggesting that increased stronger leg step lengths may also contributed to the improvements in walking speed. The improvements in walking speed and step length are consistent with increases in stride length reported in individuals with Parkinson’s disease during vibration.6
However, this is contrary to evidence in ND individuals wherein no change in stride length during walking was observed with vibration applied to tibialis anterior, triceps surae, biceps femoris, rectus femoris, or quadriceps femoris.29
Changes in stride length may not be evident in ND individuals because their strides are relatively longer compared to individuals with a neuropathology. For this reason, individuals with neuropathology may have a larger margin for vibration-induced improvement of spatial walking characteristics compared to ND individuals.
The degree of consistency of the hip-knee intralimb coordination of both legs improved, and the improvement was comparable to those observed in a 3-month locomotor training wherein the ACC values improved from 0.56 before to 0.65 after locomotor training.19
However, unlike that prior study wherein the change in intralimb coordination was associated with the change in walking speed, in the present study the change walking speed was only weakly correlated with the change intralimb coordination. Contrary to our findings, in ND individuals, bilateral Achilles tendon vibration did not change walking speed or leg inter-segmentalcoordination30
Also in ND individuals, changes in intralimb ankle-knee coordination were not found with vibration applied to tibialis anterior, triceps surae, biceps femoris, rectus femoris, or quadriceps femoris.29
Our findings and other evidence in individuals with SCI19
suggest that the consistent use of afferent input improves the motor output of the control mechanisms that have been impaired after a SCI.