H-reflex changes under spinal loading and unloading conditions in normal subjects

Objective: The soleus H- reflex is usually tested clinically in patients ly ing prone, with the H-latency always the criterion of choice; for detecting abnormality. However, stresses on the spine vary during lying, standing, l oading (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 signifi cant low back pain or radiculopathy participated in the study. A Cadwell Ex cel 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 w eight, and standing while unloaded by 25% of his/or her body weight by a ZU NI II unloading system. For each subject, the peak-to-peak amplitudes of th e maximum obtained H-reflex and the onset latencies of 8 separate traces we re averaged for both lower extremities. Two-factor, repeated-measures ANOVA s were used to test the effect of the condition and side on the H-reflex am plitude and latency with (proportional to=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-r eflex latency under the 4 different conditions. Both lower extremities show ed 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 i n turn suggests that testing of the H-reflex amplitude and latency under fu nctional conditions, such as standing may be useful in detecting subtle cha nges in root impingement. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.