Quadriceps H-Reflex Modulation During Pedaling

Quadriceps H-reflex modulation during pedaling. J Neurophysiol 96: 197–208, 2006. First published January 25, 2006; doi:10.1152/jn.00149.2005. The main aims of this study were 1) to investigate possible phase-, speed-, and task-depen- dent changes in the quadriceps H-reflex during pedaling, 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 move- ments. 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 showed a phase-dependent modulation during pedaling at a frequency of 80 rpm with almost parallel changes in the reflex amplitude and motor recruitment level. However, when the speed of movement was re- duced from 80 to 40 revolutions per minute (rpm) and crank load simultaneously increased (i.e., a halving of the movement speed with a constant motor recruitment level), the quadriceps H-reflex modula- tion 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 func- tion” obtained during 1) pedaling at 80 rpm and 2) isometric quadri- ceps contractions in sitting position showed 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