Limb Segment Load Inhibits the Recovery of Soleus H-Reflex After Segmental Vibration in Humans

ABSTRACT

We investigated the effects of vertical vibration and compressive load on soleus H-reflex amplitude and postactivation depression. We hypothesized that, in the presence of a compressive load, limb vibration induces a longer suppression of soleus H-reflex. Eleven healthy adults received vibratory stimulation at a fixed frequency (30 Hz) over two loading conditions (0% and 50% of individual's body weight). H-reflex amplitude was depressed ∼88% in both conditions during vibration. Cyclic application of compression after cessation of the vibration caused a persistent reduction in H-reflex excitability and postactivation depression for > 2.5 min. A combination of limb segment vibration and compression may offer a nonpharmacologic method to modulate spinal reflex excitability in people after CNS injury.

Keywords:

• mechanical oscillation
• compressive load
• postactivation depression
• spinal cord injury

Acknowledgments

This study was supported in part by awards to RKS from the National Institutes of Health (R01HD062507). We thank engineers Jason Wu, MS and Colleen L. McHenry, MS for technical assistance with the feedback controlled vibration and loading systems, and engineer Zhijun Cai, PhD for controller software implementation.