Soleus motor neuron excitability before and after standing.

H-reflexes have been used to assess the effect of various postures on the excitability of the soleus motor neuronal pool. The purpose of this study was to determine if the excitability of the motor neuron pool, measured via H-reflexes in a seated position, change after a standing protocol in able-bodied individuals. We hypothesized that the excitability of the motor neuronal pool is minimally affected by the standing protocol leading to a reproducible H-reflex. Ten healthy individuals (height = 69.05+/-2.27 inches, weight = 161.7+/-22.44 lbs, age = 27.7+/-7.0 years) participated in the study. Soleus H-reflex recruitment curves were established before and after a standing protocol in a seated position. The standing protocol involved 12 minutes of active upright standing interspersed with 10 minutes of relaxed passive standing in a standing frame, similar to a protocol currently used for spinal cord injured subjects. The maximum M-waves and H-reflex amplitudes were not systematically changed before and after standing. There was also a strong agreement between the H-reflexes and M-waves measured before and after standing (ICC = 0. 99 and .96, respectively). We conclude that the H-reflexes measured in this study were reproducible, indicating that standing had no long lasting effect on the motor neuronal pool excitability. The findings support that the method discussed in this report is appropriate to assess the effects of electrically induced standing on motor neuron pool excitability in individuals with spasticity from spinal cord injury.