Short-term effects of spinal manipulation on H-reflex amplitude in healthy and symptomatic subjects

The purpose of this study is to assess Hoffman (H) reflex after spinal manipulation (1) as a function of experimental position in healthy subjects and (2) in patients with low back pain.

An intervention study was performed to evaluate the effects of sacroiliac (SI) joint manipulation on motoneuron excitability, as measured by the H-reflex. Manual treatment of the SI joint was performed. Hoffman reflex amplitudes before and after SI joint manipulations were measured with subjects lying on the right side (n = 12 healthy subject) or with subjects lying supine (n = 5 healthy subjects), which required turning of subjects onto their sides for SI joint manipulation. Hoffman reflex amplitudes were also measured in 15 patients with low back pain.

No significant changes in H-reflex amplitude in healthy subjects receiving manipulation to the SI joint were observed, provided that H-reflex testing and treatments were performed in the same position, that is, the subject was not moved during the experimental procedure. However, changes in motoneuron excitability after SI joint manipulation were observed in patients with low back pain.

It appears that H-reflex responses after spinal manipulation are sensitive to movement/repositioning, and that the H-reflex depressions after manipulation documented in previous studies were movement artifacts rather than treatment effects. The relationship between etiology of low back pain and changes in H-reflex amplitude after spinal manipulation is not clear and needs further investigation.