title: H-reflex excitability is inhibited in soleus, but not gastrocnemius, at the short-latency response of a horizontal jump-landing task.
abstract: Impaired spinal-level neuromuscular control is suggested to contribute to instability and injury during dynamic landing tasks. Despite this suggestion, spinal-level neuromuscular control is yet to be examined during a horizontal jump-landing task. The aim of the current study was to assess changes in H-reflexes and its reliability at the short-latency response of landings from short and long distances. Eight healthy individuals (five male, three female; age, 22±1.2yrs; height, 178±8.1cm; weight, 72±15.7kg) participated in the study. H-reflexes were evoked at the SLR in the soleus and medial gastrocnemius muscles, during two landing conditions: 25% and 50% of maximal broad jump distance. H-reflexes were expressed relative to the background electromyography (EMG) and maximal M-wave responses (M-max). Soleus H-reflexes were inhibited when landing from shorter distance (25%, 13.9±7.6%; 50%, 8.3±6.5%; p<0.01). No change in H-reflex excitability was observed in medial gastrocnemius. Background EMG was unaltered across landing conditions. Inhibition of soleus H-reflex excitability from 25% to 50% landing condition indicates a reduced contribution of Ia-afferent feedback to the alpha-motor neuron during landings from greater distances, which may contribute to stiffness regulation at the ankle joint. Unaltered H-reflex excitability of medial gastrocnemius is most likely attributed to its functional role during the landing task.
authors.affiliation: School of Science in Health, Western Sydney University, Australia. Electronic address: c.thompson2@westernsydney.edu.au.
authors.forename: Cassandra S
authors.initials: CS
authors.lastname: Thompson
authors.affiliation: School of Science in Health, Western Sydney University, Australia.
authors.forename: Siobhan
authors.initials: S
authors.lastname: Schabrun
authors.affiliation: School of Science in Health, Western Sydney University, Australia.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Marshall
mesh_terms: D000843:Ankle Joint / Q000502:physiology; D004576:Electromyography; D015444:Exercise; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011930:Reaction Time; D015203:Reproducibility of Results; D055815:Young Adult
keywords: H-reflexes; Landing; Neuromuscular control; Peripheral nerve stimulation; Reliability