Effects of specific rhythmic arm cycling parameters on the amplitude modulation of the Soleus H-reflex




Loadman, Pamela M.

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Rhythmic locomotor activity involving the arms or the legs results in task and phase specific Hoffmann (H)-reflex modulation between the two arms or between the two legs. As well, specific ipsilateral and contralateral movement effects are observed. Recently it has been found that there is also interlimb (between arms and legs) task modulation of the H-reflex, using a rhythmic arm cycling paradigm. That is, the stationary Soleus H-reflex amplitude during arm cycling was attenuated when compared to a static condition (Frigon et al. 2004). The specific parameters of the arm cycling movement which may contribute to this attenuation however are unknown. The purpose of this research was to examine whether the interlimb Soleus H-reflex suppression is specific to: the phase of the arm movement; the movement of both arms; arm excursion; and, rate of arm cycling. Participants sat in a custom designed chair to prevent leg and trunk movement and performed bilateral arm cycling at frequencies of 1 and 2 Hz and with short and long crank lengths (to alter arm range of motion; ROM). As well. ipsilateral (relative to leg stimulated) and contralateral single arm cycling were performed at 1Hz with a long crank length. The Tibial nerve at the popliteal fossa was stimulated psuedorandomly at four phases of the arm cycle and changes in the Soleus H-reflex were recorded while maintaining a small, but stable motor (M)-wave for all trials. EMG was recorded from the Soleus, Tibialis Anterior. Vastus Lateralis and the Anterior Deltoid muscles. Peak to peak amplitudes of the H-reflex from each participant were determined off line and normalized to the M-max determined from individual M-H recruitment curves. Results indicate comparable suppressive effects in all phases of the arm movement, and with bilateral or unilateral cycling. The large ROM and the 2 Hz frequency of movement resulted in a stronger inhibition than with the small ROM and the 1 Hz arm cycling. This suggests that neural processes associated with generating both the rhythmic arm cycling pattern and the peripheral feedback from the arms, have an effect on the H-reflex modulation in the legs. We conclude that a general, rather than a specific, signal related to rhythmic arm muscle activity mediates the suppression of Soleus H-reflex during arm cycling.



human locomotion, kinesiology