Test–retest reliability of the soleus H-reflex is affected by joint positions and muscle force levels

The purpose of this study was to determine the test–retest reliability of the soleus (SOL) H-reflex during rest and isometric contractions at 10%, 30%, and 50% of the maximal voluntary force (MVC) at the ankle joint angles of neutral (0°), plantarflexion (20°), and dorsiflexion (?20°) respectively, in a sitting position. Ten healthy participants, with mean age of 24.9 ± 5.0 (SD) years, height 168.3 ± 8.8 cm, weight 62.7 ± 12.3 kg, were tested for the SOL H-reflex (H_max) on two separate occasions within 7 days. The intraclass correlation coefficient (ICC) for the test–retest of the SOL H-reflex during rest was found to be high at ankle joint angle of neutral (ICC = 0.92) and plantarflexion (0.96), and moderate at dorsiflexion (0.75). Inconsistent ICC values (range from 0.62 to 0.97) were found during the submaximal voluntary contractions at the three ankle joint positions. High ICCs were also found in H_max/M_max ratio at neutral (0.86), plantarflexion (0.96), and dorsiflexion (0.84) positions. It was concluded that the test–retest reliability of the SOL H-reflex was affected by the intensity of voluntary contraction and ankle joint position. The H-reflex demonstrated a higher reliability at the neutral and plantarflexion positions than that at the dorsiflexion position during rest, and a higher reliability at 10% MVC than that at 30% and 50% MVC.