Manual cervical traction reduces alpha-motoneuron excitability in normal subjects

The excitability of the Flexor Carpi Radialis alpha-motoneuron pool following manual cervical traction was assessed in twenty asymptomatic subjects, and compared to a hands only intervention. The excitability of the alpha-motoneuron pool was measured indirectly using the Hoffmann (H) reflex. H-reflex recruitment curves were taken to assess the number of alpha-motoneurons (alpha-motoneurons) firing in response to a given incremental increase in stimulation intensity. The rate of rise of the slope of the H-reflex recruitment curve (Hslp) was assessed using linear regression. Following manual cervical traction Hslp was significantly lower than pre-intervention trials. Manual cervical traction, therefore, reduced the excitability of the Flexor Carpi Radialis alpha-motoneuron pool. This effect was mediated by the central nervous system. There was no significant decrease in alpha-motoneuron excitability following the hands only intervention. Hslp was shown to be a more sensitive measure of changes in the H-reflex than the more traditional parameter of Hmax/Mmax ratio and should be used in future studies of this nature.