Comparison of Wrist Positions and Assessment Techniques to Evaluate Disynaptic Group I Inhibition

Reciprocal inhibition is one of the most extensively studied neuromuscular reflexes in humans, where an antagonist muscle is inhibited when the agonist is activated. The assessment of reciprocal inhibition, mostly done at the ankle level, has been carried out to analyze plastic changes after neurorehabilitation strategies. At the wrist joint, research has been scarce, with only a few studies assessing the inhibition between flexors and extensors, which is hypothesized to be mediated by disynaptic group I inhibition. The main goal of this study was to investigate the influence of the wrist position on the level of inhibition between flexor carpi radialis (FCR) and extensor carpi radialis (ECR). For this, two different methods were applied: 1) the H-reflex conditioning-test paradigm, and 2) the modulation of the on-going electromyography. FCR H-reflex was conditioned through radial nerve stimulation while the forearm was in supine and neutral positions. Both postures were also compared while participants maintained a submaximal isometric contraction of the FCR, conditioned by the stimulation of the radial nerve. For both techniques, higher levels of inhibition were achieved for the neutral position, for the same conditioning stimulation intensity. We conclude that the position of the wrist highly affects the inhibition between FCR and ECR. These findings have implications for the development of a standard methodology to assess changes in the inhibition between wrist flexors and extensors.