Flexor carpi radialis H-reflex modulation during spinal loading and unloading with varied forearm postures

Flexor carpi radialis (FCR) H-reflex is usually recorded with the patient in lying or sitting postures while the forearm is positioned in supination or pronation to detect C7 radiculopathy. Its amplitude is smaller during forearm supination compared with pronation for unclear reasons and its recordings during postural loading conditions (i.e., sitting or lying) have not been previously reported. The purpose of this study was to examine FCR H-reflex recordings during varied cervical spine loadings and forearm positions. The FCR maximum H-reflex amplitude was recorded from 15 healthy participants during lying, free-sitting and sitting-with-load while the forearm was positioned in either supination or pronation. Four traces were averaged for each combination of conditions. Two-way repeated-measure analysis of variances (2 x 3) was used to examine the statistical differences. The average FCR H-reflex amplitude was significantly greater during free-sitting and sitting-with-load compared with the lying body position. The average FCR H-reflex amplitude was significantly greater when the forearm was positioned in pronation compared with supination. The increase in FCR H-reflex amplitude (augmentation) during forearm pronation and sitting postures compared with supination and lying may have been the result of combined neural and mechanical effects. These results encourage FCR H-reflex recordings during sitting with the forearm in pronation.