Comparison of electrically and mechanically induced soleus H-reflex depression.
OBJECTIVE
The aim of the present investigation was to compare the responses of mechanically-evoked and electrically-evoked conditioning among three different stimulus intensities and provide possible insight in determining whether these two types of inhibitory conditioning demonstrate the same response across the motor pool.


METHODS
The soleus H-reflex was tested under three different stimulus intensities (25% Hmax, 50% Hmax, and Hmax), and peak to peak amplitudes were recorded after either mechanical or electrical conditioning. For electrical conditioning, the ankle was held at 90 degrees, whereas mechanical conditioning utilized a 10 degree passive dorsiflexion at 15 degrees/sec back to the 90 degree position. All H-reflex measurements were recorded with the ankle at 90 degrees.


RESULTS
A 3 x 2 (stimulus intensity x treatment condition) repeated measures ANOVA indicated significant main effects for stimulus intensity (FGG = 16.23; p = .003) and condition (FGG = 28.48; p < .001), as well as an interaction (F(2,18) = 6.59; p = .008). Simple main effects identified significantly more H-reflex depression for mechanical conditioning (94%, 91%, and 44%) compared to electrical conditioning (65%, 55%, and 19%) at 25% Hmax, 50% Hmax, and Hmax, respectively.


CONCLUSIONS
There appears to be more mechanically than electrically stimulated H-reflex depression when testing at 25% Hmax, 50% Hmax, and Hmax. These results demonstrate the influence of Ia discharge properties on H-reflex depression and may suggest differences in the affinity of Ia terminals to intrinsic presynaptic inhibition at different stimulus intensities.
Harris
R A
RA
Clinical Exercise Physiology Laboratory, Department of Kinesiology, Indiana University, School of Health, Physical Education, and Recreation, Bloomington 47404, USA. Harrisra@indiana.edu
Koceja
D M
DM
D000328:Adult; D003213:Conditioning, Psychological / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation; D010812:Physical Stimulation; D011930:Reaction Time / Q000502:physiology*