H-reflex changes under spinal loading and unloading conditions in normal subjects.
OBJECTIVE
The soleus H- reflex is usually tested clinically in patients lying prone, with the H-latency always the criterion of choice for detecting abnormality. However, stresses on the spine vary during lying, standing, loading (weight lifting) and unloading. So the objective of this study was to measure changes in the H-reflex under 4 different loading conditions and to investigate whether mechanical loading of the spine would affect the H-reflex parameters.


METHODS
Twenty healthy volunteers (22-46 years) with no history of significant low back pain or radiculopathy participated in the study. A Cadwell Excel electromyography unit was used to elicit and record the soleus H-reflex. The tibial nerve was stimulated at the popliteal fossa using 1 ms pulses at 0.2 pps of H-max. Each subject was tested under 4 different conditions: prone lying, free standing, standing while lifting 20% of his or her body weight, and standing while unloaded by 25% of his/or her body weight by a ZUNI II unloading system. For each subject, the peak-to-peak amplitudes of the maximum obtained H- reflex and the onset latencies of 8 separate traces were averaged for both lower extremities. Two-factor, repeated-measures ANOVAs were used to test the effect of the condition and side on the H-reflex amplitude and latency with ( approximately =0.025).


RESULTS
The H-reflex was inhibited during standing, loading and unloading as compared with prone lying. The H-reflex was recovered during loading as compared with during standing. There were no significant changes in the H-reflex latency under the 4 different conditions. Both lower extremities showed similar pattern of changes in the H-reflexes.


CONCLUSIONS
These results imply a significant interplay between peripheral and central mechanisms and their effects on the spinal motoneurons. This in turn suggests that testing of the H-reflex amplitude and latency under functional conditions, such as standing may be useful in detecting subtle changes in root impingement.
Ali
A A
AA
Texas Woman's University, School of Physical Therapy, 1130 M.D. Anderson Blvd., Houston, TX 77030-2897, USA.
Sabbahi
M A
MA
D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007866:Leg / Q000502:physiology; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011843:Radiculopathy / Q000175:diagnosis / Q000503:physiopathology; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D013979:Tibial Nerve / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*