Spinal cord H-reflex post-activation depression is linked with hand motor control in adults with cerebral palsy

•We explored the post-activation depression of H-reflexes in the upper limbs of adults with cerebral palsy.•In this study, we linked changes in spinal reflex pathways to upper extremity motor function in adults with cerebral palsy.•While the literature focuses on supraspinal pathways, our results identify spinal modulation as a possible locus for motor control in CP. Cerebral palsy (CP) is associated with upper extremity motor impairments that are largely assumed to arise from alterations in the supraspinal networks. The objective of this study was to determine if post-activation depression of the spinal H-reflexes is altered in adults with CP and connected with altered upper extremity function. The post-activation depression of the flexor carpi radialis (FCR) H-reflex of adults with CP and healthy adults (HA) controls were assessed by 1) a 1 Hz continuous single-pulse stimulus train and 2) 0.11 Hz / 1 Hz paired-pulse stimuli. Secondarily, we measured the maximum key grip force and the box and blocks assessment of manual dexterity. Our results revealed that adults with CP had reduced post-activation depression of the FCR H-reflex during the stimulus train and the paired pulse protocol. A greater reduction in H-reflex post-activation depression was connected to lower manual dexterity and weaker grip forces. Our results indicate that the post-activation depression of the upper extremity spinal H-reflex pathways is altered in adults with CP and possibly linked with their uncharacteristic upper extremity motor performance. Alterations in the spinal networks may also play a significant role in the altered motor control of adults with CP. Our results identify spinal H-reflex modulation as a possible locus for hand motor control in CP.