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J Neurophysiol (January 25, 2006). doi:10.1152/jn.00149.2005
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Submitted on February 14, 2005
Accepted on January 22, 2006

Quadriceps H-reflex modulation during pedalling

Birgit Larsen1* and Michael Voigt1

1 Dept. of Health Science and Technology, Aalborg University, Center for Sensory-Motor Interaction, 9220 Aalborg, Denmark

* To whom correspondence should be addressed. E-mail: bl{at}neurodan.dk.

The main aims of the present study were 1) to investigate possible phase, speed and task dependent changes in the quadriceps H-reflex during pedalling and to achieve this 2) to develop an optimized H-reflex recording and processing procedure for recording of quadriceps H-reflexes during movement. It was hypothesized that the behavior of the quadriceps H-reflex concerning phase-, speed- and task dependency corresponds to the behavior of the soleus H-reflex during rhythmical leg movements. The applied H-reflex procedure appeared to be reliable for obtaining the quadriceps H-reflex modulation during leg movement. The vastus lateralis (VL) and rectus femoris (RF) H-reflexes demonstrated a phase dependent modulation during pedalling at a frequency of 80 rotations pr. minute (rpm) with almost parallel changes in the reflex amplitude and motor recruitment level. However, when the speed of movement was reduced from 80 to 40 rpm and crank load simultaneously increased (i.e. a halving of the movement speed with a constant motor recruitment level) the quadriceps H-reflex modulation pattern changed significantly in relation to the pattern of motor recruitment, i.e. at 40 rpm the reflex excitability remained high during a gradual derecruitment during power generation in down stroke. Comparison of the operationally defined H-reflex gain function obtained during a) pedalling at 80 rpm and b) isometric quadriceps contractions in sitting position, demonstrated no significant task-dependent changes in the quadriceps H-reflex. Consequently, the hypothesis was only partly corroborated and the findings indicate differences in the neural control of the soleus and the quadriceps muscle during rhythmical movements.







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